93 replies to this topic

[Paolo]

I received a letter from a Forum reader who was lucky enough to be a F4 pilot.
He asked some info about the peculiar air intakes of that plane.
There are many aerodynamicists here, and I think it's an interesting subject.
These intakes have two features that strike the eye at first :

1) no shock cone : something very different from, say , contemporary F104 or Mirage.
Probably they were 2D shock diffusers, the same principle used in F15 Eagle .
Only, F15 air intakes had variable geometry, while it appears F4 ones were fixed.
I found no specific info on the internal working of F4 intakes, so I wonder : had they some movable parts I'm not aware of ? Fixed geometry seems strange for such a sophisticated aircraft. Even Mig 21 had a variable geometry intake, thanks to a sliding nosecone.

2) A big boundary layer control plate. This plate was obviously there to start a new, thin boundary layer at a short distance from the intake, avoiding the ingestion of the thick layer developing from the nosecone. It probably caused a Cd increase in exchange for improved engine efficiency.
I have no info on wether there was also some other form of boundary layer control, such as aspiration. Did not notice any signs of it, though.
On the lower part of the control plate, a triangular extension can be seen. It was not present on the prototype, and it looks extremely similar to the one seen on the unlucky CF105 Arrow.
Of course, a vortex generator to keep the engine well fed at high AOA.

The reader speaks of "splitter vari-ramps" and says that "later F4 had active ramps". I suspect these BL control plates could then move to vary the intake-throath ratio... but have no evidence.

Another interesting point in the letter says " I flew C and Ds and each one had a slightly different config. Obviously there was a problem. Aggressive yaw control by the pilot was the only way to prevent flame out"
This could mean one of the intakes could get in the fuselage's aerodynamic shadow in some situations ? Has anyone heard of similar instances ?

Any other thoughts, or info, from someone here, on these intakes ?

[dosco]

1. The "shock cone" you're looking for is actually a 2 piece ramp that is formed by part of the splitter (flat) and a flat plate inside the intake. By changing the angle of the ramp, the shock wave(s) can be controlled, etc etc etc.

2. The splitter functions only to prevent ingestion of the fuselage boundary layer into the compressor face of the engine....the reason for that is to prevent compressor inlet flow distortions which would have caused compressor stalls (the older F-4s (and older aircraft in general) didn't have effective variable-stator-vane (VSV) and/or main engine controls). Compressor stalls are bad news because if they're bad enough they can break compressor blades, cause flame-outs, etc etc.

"Aggressive yaw" control means that the pilot had to worry about vortex ingestion into the engine air intake. Inlet flow distortions were bad in those days due to lack of effective engine control (see #2 above). Probably less of a problem in pitch than yaw.....

Modern engines have VSVs (each ring is independently controlled) and FADECs (full authority digital engine control) that allow very precise engine control and do wonders to prevent compressor stalls. As the flow distortion travels through the compressor, the FADEC will preferentially close the VSVs and smooth out the flow, thereby precluding stall conditions. Very cool stuff.

[dosco]

http://www.tamiya.co...tom/phantom.htm

Although this is only a model, it's a nice scale version of the real thing. The flat plate-looking things right at the front of the intake form the variable-geometry ramp for supersonic flight.

The idea is to form a couple of angled shock waves, with the final shock wave a weak "normal" (at a right angle to the flow) shock wave which brings the air to high-subsonic speeds for the engine compressor.

If you had 1 shock wave bringing the flow from supersonic to subsonic, the heat/energy losses across the shock would result in the engine have to do more work to create thrust (and there would be more aero drag on the airframe).

[dosco]

Originally posted by Paolo

1) no shock cone : something very different from, say , contemporary F104 or Mirage.
Probably they were 2D shock diffusers, the same principle used in F15 Eagle .

Only, F15 air intakes had variable geometry, while it appears F4 ones were fixed.
I found no specific info on the internal working of F4 intakes, so I wonder : had they some movable parts I'm not aware of ? Fixed geometry seems strange for such a sophisticated aircraft. Even Mig 21 had a variable geometry intake, thanks to a sliding nosecone.

One last thing.... although both the F-4 and F-15 have variable geometry intakes, they work in totally different ways.

The F-15 has a ramp system that is formed by the upper surface of the intake, while the F-4s ramp system is formed by flat plates that are parallel (relatively speaking) to the fuselage.

They both do the same thing.

[BRNDLL]

I love to read this stuff guys... thanks for the Off Topic discussion.

My father was an avionics engineer that worked on F4's during the Vietnam conflict.

bb

[BRIAN GLOVER]

Howdy Paola,

The F15 intake design was greatly influenced by the problems encountered in the F4 vari-ramp. If you take a look down into the intake of the F4, you will see variable inlet doors or ramps. The function of these was to control air flow to engines regardless of whether the aircraft was stationary on the ground or flying at Mach II. Pitot probes were located in each intake on the outer wall (sorry no pictures). Based on the speed of the air, these ramps located opposite the probes on the inside wall were positioned to create shock waves as has mentioned by Dosco.
The shock wave reduced intake air to sub-sonic.

The two piece splitter type thing against the fuselage in front of the intake is what puzzles me. I've seen these mounted in various 'fixed' positions, however, I believe on the F4 E, the front part of this splitter was activated with a push rod. They are hinged in the middle and the rear piece is aligned with the inner wall at the leading edge of the intake and was not adjustable.
Immediately behind this aft piece, is the vari-ramp.
Sometimes it was mounted 4 or 5 inches away from the fuselage at the closest point and sometimes it was just about flush. Sometimes the two plates were in alignment and sometimes they hinged a few degrees. Something was not right in State of Denmark.
Maybe they work in conjunction with the internal vari-ramp.

Later F4s had active yaw damping and with that long nose, with any yaw, the boundary separation turbulence or 'shadow', extended beyond the splitter and into the intake





[QUOTE]Originally posted by Paolo

2) A big boundary layer control plate. This plate was obviously there to start a new, thin boundary layer at a short distance from the intake, avoiding the ingestion of the thick layer developing from the nosecone. It probably caused a Cd increase in exchange for improved engine efficiency.
I have no info on wether there was also some other form of boundary layer control, such as aspiration. Did not notice any signs of it, though.
On the lower part of the control plate, a triangular extension can be seen. It was not present on the prototype, and it looks extremely similar to the one seen on the unlucky CF105 Arrow.
Of course, a vortex generator to keep the engine well fed at high AOA.

The reader speaks of "splitter vari-ramps" and says that "later F4 had active ramps". I suspect these BL control plates could then move to vary the intake-throath ratio... but have no evidence.

Another interesting point in the letter says " I flew C and Ds and each one had a slightly different config. Obviously there was a problem. Aggressive yaw control by the pilot was the only way to prevent flame out"
This could mean one of the intakes could get in the fuselage's aerodynamic shadow in some situations ?

[Exar Kun]

I know jack-diddly squat about aerodynamics so sorry if this has been answered in above posts and I've just missed it. I seem to recall there being lots of perforations in the splitter plate just preceding the intake - what were these for?

Despite having similar, wedge-shaped air intakes, the F-14 did not have the 'nodding' intakes of the F-15. What happened with it? I know there is some sort of hole (for lack of a better word) not far behind the intake on top of the aircraft facing aft - did this have anything to do with it. I also know the TF30 engines had terrible problems with flameouts in this aircraft (but I think less-so in the F-111 where they never replaced them during their service life?) - was this to do with the intake geometry or just an inherant problem with the engine.

Thanks.

[dosco]

Originally posted by Exar Kun
I seem to recall there being lots of perforations in the splitter plate just preceding the intake - what were these for?

I dunno exactly (I don't have an "owner's manual," but I'd suspect suction thru the holes draws off the "new" boundary layer formed on the plate.

Originally posted by Exar Kun

Despite having similar, wedge-shaped air intakes, the F-14 did not have the 'nodding' intakes of the F-15. What happened with it? I know there is some sort of hole (for lack of a better word) not far behind the intake on top of the aircraft facing aft - did this have anything to do with it. I also know the TF30 engines had terrible problems with flameouts in this aircraft (but I think less-so in the F-111 where they never replaced them during their service life?) - was this to do with the intake geometry or just an inherant problem with the engine.

The F-14 ramp works in similar fashion (variable geometry internal flat plates), though the intake itself doesn't angle down like the F-15.

The aft-facing "slot" is designed to mitigate inlet flow distortions that could cause compressor stalls - presumably by expelling air from the intake (a professor I had was on the F-14 design team....one day in class we asked him about the "flat spin" scene in the movie "Top Gun".....he got really pissed off and then explained that the inlet was designed specifically to mitigate inlet flow distortions, and the aft-facing slot functioned in that regard....and that the scene in the movie was BS).

Yes the TF30 had compressor surge/stall problems. Twofold problem - the engine didn't have a FADEC, which would help prevent compressor stalls/surges/flameouts. The inlet was also part of the problem, but with everything being a compromise (in terms of design) it's safe to assume the inlet is the "best condition" for all of the design/performance conditions.

The other problem with the engine was the low thrust, even with afterburner. In the older models, full afterburner was required for catapult launch.....in the F-14D "Super Tomcat," the "cat" can be performed with max dry thrust (no afterburner).

Same deal with the F-111....I think it was the "H" model of the aircraft (I dunno exactly). It had uprated engines installed also, which drastically improved takeoff performance (although takeoff was still done with afterburners engaged).

[A3]

Originally posted by Paolo
Only, F15 air intakes had variable geometry, while it appears F4 ones were fixed.
I found no specific info on the internal working of F4 intakes, so I wonder : had they some movable parts I'm not aware of ?

This question has already been answered, but anyway:


(note the pivot for measuring air intake speed).

The splitter plate is divided into two sections. The forward section is fixed (non-moving). the rear sections pivots to limit the amount of air flowing into the intake at high speeds.

[Paolo]

Thanks for the excellent response, guys. I'm no engine specialist and have been learning a few things.
Yes, I suspected there would be some movable parts in the intakes, since fixed geometry is normally used only for speeds up to Mach 1.3, but didn't know about the inner vari-ramps.
I profit from A3's excellent pic to point out the triangular "tooth " on the lower part of the BL control plate.

Originally posted by Paolo

On the lower part of the control plate, a triangular extension can be seen. It was not present on the prototype, and it looks extremely similar to the one seen on the unlucky CF105 Arrow.
Of course, a vortex generator to keep the engine well fed at high AOA.

[BRIAN GLOVER]

F14, F4s,F111s are what we called grapes. A couple of hard turns and all the energy oozes out of it. The F14 in particular. The Tomcat is a lumbering, poor performing, aerial truck. It weighs about 54 000lbs. Add fuel tanks and missiles, it weighs 70 000lbs. This energy cannot be easily regained.

The F4 required energy management of the highest order, but would recover faster than a F14. The variable wing was one of the major aviation engineering blunders of the 20th century.

A3, if you would post a picture of a F4 C or D cockpit and draw numbered arrows to the flight instruments which are directly ahead of the pilots view, Ill explain how to develop a scan and control input for max energy management and maintenance.

Next to and either side of the optical sight unit (early Heads up) directly ahead of the pilot's eyes are angle of attack indexers. Airspeed and mach indicator is found sw of the radar scope as is the angle of attack indicator and accelerometer. Directly below the radar is the attitude director or indicator and SE of that is the emergency attitude indicator. E of that is altitude and fuel quantity (internal). These instruments are monitored extensively in high flight.
Less important things are further out of the scan such as engine instruments and far below are weapons control panels and far sw are missile control panels and other sub panels.

An excellent book on EM is called, "Boyd" by Robert Coram. Boyd was a fighter pilot who designed the F15 and 16. Buy it now. Boyd developed the math for the design of these aircraft and was first applied to F15 and 16 aircraft in the US. The Rooskies were a little further ahead.


[QUOTE]Originally posted by A3
[B]

This question has already been answered, but anyway:

[dosco]

Originally posted by BRIAN GLOVER

An excellent book on EM is called, "Boyd" by Robert Coram. Boyd was a fighter pilot who designed the F15 and 16. Buy it now. Boyd developed the math for the design of these aircraft and was first applied to F15 and 16 aircraft in the US. The Rooskies were a little further ahead.

My brother-in-law just told me about this book......I HAVE to get a copy!

[kos]

just to share

when I was a student I found two excellent TSAGI's (Russian Central Aero-Hydrodynamics Institute) bulletins about creation and production of F-14 and F-15 in the university's library.

It was simply fascinating - each bulletin consisted of about 200 pages of highly condensed and carefully selected/crosschecked information. Spend half of my lectures reading them

What I've found very interesting is how much McDonnell Douglas and Airforce learnt from F4 - in requirements specification for F-15 almost every performance/technological parameter was given in comparision with Phantom.

[Jack-the-Lad]

This is quite interesting to me, as when I was in Vietnam (1969, USMC) the F4 was a primary ground support aircraft used for bombing and strafing tactical targets. My lasting impression is of the enormous noise the engines generated. More germain to the topic of this thread, would any of the intake characteristics described here contibute to the number of decibels coming out the other end?

Jack

[dosco]

Originally posted by Jack-the-Lad
This is quite interesting to me, as when I was in Vietnam (1969, USMC) the F4 was a primary ground support aircraft used for bombing and strafing tactical targets. My lasting impression is of the enormous noise the engines generated. More germain to the topic of this thread, would any of the intake characteristics described here contibute to the number of decibels coming out the other end?

Jack

Not really.....the noise is mostly a function of the engine pressure ratio and bypass ratio. Also, the F-4 had an afterburner.....which if engaged, creates a shitload of noise.

Of course, the intake has to be properly matched to the engine for the engine to function correctly, so in a roundabout way, I suppose you could say that it contributes to the noise level......

[A3]

Originally posted by BRIAN GLOVER
A3, if you would post a picture of a F4 C or D cockpit and draw numbered arrows to the flight instruments which are directly ahead of the pilots view, Ill explain how to develop a scan and control input for max energy management and maintenance.

Sorry, don't have the time to draw lines at the moment.

Does this show enough?

[Jack-the-Lad]

Coincidentally, I sat in an F4 cockpit at the Air Force Museum at Wright-Patterson AFB just last weekend! Seeing everything that goes on inside that cockpit increases my enormous respect for pilots even more!

Jack

[BRIAN GLOVER]

Thats an early C. The top of the IP is below eye level. Whats missing is the optical sight unit and
a of a indexers and in flight fuel lights above that. Draw horizontal lines from the left stopping on what ever you choose. You can number the lines or we will just count down from the top. Maybe different color lines will work.
Can you see where I'm pointing to with my mouse? I thought not. That would be easy wouldnt it?

Originally posted by A3


Sorry, don't have the time to draw lines at the moment.

Does this show enough?

[BRIAN GLOVER]

Heck, we had it easy compared to you guys. Each thing you see on this IP is a simple device and easy to understand and opperate. It all goes into your subconscience and becomes second nature. Have you seen a F1 car steering wheel, now that's complicated.

Originally posted by Jack-the-Lad
Coincidentally, I sat in an F4 cockpit at the Air Force Museum at Wright-Patterson AFB just last weekend! Seeing everything that goes on inside that cockpit increases my enormous respect for pilots even more!

Jack

[A3]

And here is an F-4 manual:
http://www.simpits.o...hp?file=F-4.pdf

[BRIAN GLOVER]

Where did you get this stuff? This server undergoes more maintenance than an F4.
I'll get to work.

[A3]

Originally posted by BRIAN GLOVER
Where did you get this stuff?

Google.

[ciaoduc]

I was an F-15E crew chief at RAF Lakenheath for four years and have a good deal of experience with those variable ramps. They are generally very reliable, but when something goes wrong they can be a bear to work on...
Anyway, I've always wondered what an F-16 does to combat the whole shockwave problem.

[fattogatto]

Originally posted by Jack-the-Lad
This is quite interesting to me, as when I was in Vietnam (1969, USMC) the F4 was a primary ground support aircraft used for bombing and strafing tactical targets. My lasting impression is of the enormous noise the engines generated. More germain to the topic of this thread, would any of the intake characteristics described here contibute to the number of decibels coming out the other end?

Jack

In a way,

Not necessarily the decibel level, but one of the most memorable sounds is an F4 coming overhead and into the pitch (a 180 degree turn made over the landing runway.) Normally initiated at relatively high speed (300 knots or so) and reducing speed throughout the maneuver and on inside downdwind, the throttle changes and reaction of the inlet guide vanes created a most unique wailing sound. You never had to look up to see it was a Phantom in the break.

[dosco]

Originally posted by ciaoduc
I was an F-15E crew chief at RAF Lakenheath for four years and have a good deal of experience with those variable ramps. They are generally very reliable, but when something goes wrong they can be a bear to work on...
Anyway, I've always wondered what an F-16 does to combat the whole shockwave problem.

I was an aircraft maintenance officer for a while in the USAF. Good times.

The F-16 inlet has a splitter that (to me, anyway) looks like it creates a shock wave over the intake. Less efficient than a "vari-ramp," but easier to operate/maintain (just the inlet, anyway).

[A3]

Interesting article about inlets: http://www.codeonema...vertless_1.html

[dosco]

Originally posted by A3
Interesting article about inlets: http://www.codeonema...vertless_1.html

Very interesting. Thanks for the article, A3.

[BRIAN GLOVER]

This is longer than I had hoped for, but anyway, for the aviators and would be aviators, I hope that you find this interesting.

The object for combat flight apart from destroying the enemy, is to conserve energy in the aircraft. Energy is either altitude or velocity. One can be converted to the other readily. In a turn, even a mild turn or pull back, energy bleeds off.
In high G maneuvers, this bleed off becomes the enemy . Modern fighters have minimized this with vectoring nozzles and canards, and some very clever people.

The IP depicted in A3s picture is 50s and 60s technology, however some of the ground born technology and the information it transmits, dates to WW II. Modern fighters and even the Falcon 20 that Charlie flies with their fancy 'Glass' displays have exactly the same information as this old F4 panel, it just presented in a nicer package. They still receive WWII information however..
I don't know whether you fly any video games or not, but the HUDs depicted are almost identical to modern fighters on some of the new games...
I have a F22 sim and it quite a lot of fun, but no matter how hard you turn, the airspeed remains constant. I know the F22 is pretty advanced, but not to that degree.

I'll attempt to describe the flight instruments and their function as briefly as I can and the sequence of scan.

Basically, the input varies with the weight and drag of the aircraft , so the following inputs, we assume that we know how much fuel we are carrying and what ordnance. This information changes from minute to minute and the flight dynamics change accordingly. The low profile missions performed toward the end of your tour (experience required) require high G load turns at low levels and the highest level of EM and conservation.

There are a lot of important instruments to monitor not with standing, lock ons by SAMS and other Charlie fire. (No.16)
The HUD or OFI (No.5) is actually is what you monitor the most at a conscience level as well as actual observation outside the cockpit, like a couple of bobble heads. We will concentrate on flight instruments for the aero guys here.(No.12 and 20) is not a HUD but a means to select and display HUD display and data.

The following flight instruments are monitored at a subconscious level including throttle position and flight control input. Stick and rudder.


The big one in the middle, (No. 21) the AI or attitude indicator, is the most important. ( A back up one [no 38] is there for good reason although, even without these two instruments, you can make it home in IF conditions using other instruments.)
The IP shown is not energized and the AI is in a tumbled state, but there is a lot of information here. It is like a little globe with 360' markings on 2 axis plus pitch and roll information. The sphere in the HI stays in the same position relative to earth(Gyros) and the aircraft rotates around it, and attitude is referenced with the cross-hairs. The blu half on top and the black part at the bottom.The 5 little white dots on the LHS is the glide slope indicator and the curser is on the middle dot. A turn and bank indicator is at the bottom just like on your Cessna 150.

All modern aircraft have a similar type of AI. The same as Charlie's Falcon 20, or even a Cessna 150, every performance parameter is initiated by this instrument. For instance, for a given pitch, a given configuration( Ordnance, fuel load, flaps and gear, etc) a given power setting, the aircraft will perform in a specific manor. All performance can be pre determined after this input. If this is not your first lesson when you begin flying, punch your instructor on the nose.


Next is the AOA indicator(No.41).

The aero guys on this forum talk of AOA. As with F1 cars, any deviation of AOA alters performance of the airfoil drastically and it is even more pronounced on a delta wing as apposed to a glider's high aspect ratio wing.
.. Stalling an airfoil means that you have just exceeded it's the critical AOA and created large amounts of drag..

High G turns and approach to landing will deflect this needle the most. Max maneuverability comes between 350 and 450kts at 18 000 to 25 000 feet. The highest rate of acceleration comes with a push over on top with zero G vertical acceleration.
The wing is considered unloaded at this point. You can unload the wing at any attitude. You may argue that you can accelerate straight down at a higher rate, but you will have limited options converting this energy into anything useful.
High AOA will also cause an audio and indexer indications(No.4) to light up in sequence.
A Falcon 20 also has indexers and an AOA meter. ( Google a picture please A3)

In light executive jets, this is a crucial instrument, as they don't really have enough thrust to keep them flying at their service ceilings. The function of the AOA indicator in fighters is for a slightly different purpose but are very much related.
Early Lear Jets flew just about at a stall and couldn't be hand flown at their SC. I know, 'cause I did charters in those SOB things. Ofcourse, these type of aircraft are limited to low G loads. 3.8 g actually @ full gross..

The airspeed indicator is crucial. Without airspeed, you aint flying. There are two (No.9 and 19. The pitot tubes are on the vertical fin.) The indicated airspeed is what you use for flight and true airspeed will indicate atmospheric conditions. Indicated AS, true arspeed and ground speed are all different values

The G meter and vertical speed indicator. (no 47 and 24). The VSI is used in conjunction with the altimeter (no23) and shows what is about to happen vertically. The altimeter lags this instrument. A positive VSI after take off suggests that you retract the gear and referenced mostly in IFR after that. It is actually a leaking altimeter.

The G meter will indicate and record max positive and negative G loads during the flight. At speed, this instrument, the airspeed indicator and AOA indicator become related.

This instrument is found in aerobatic aircraft. Hooking up your G suit was optional. Few used it, save for the heavy drinkers. The back seater always used it. It is far too restrictive at crucial moments of flight.

The altimeter(no.23) is shown with the Coleman window set at 29.92"ag. If this F4 is at the Homestead AFB in Florida and the ambient pressure was 29.92, the elevation of the airport will be 500' as indicated. If there was a one (1) in the window on the left, the elevation would be 10 000'. It will indicate up to 100 000 feet. 100 will appear in the window.
29.92" is set in the Coleman for pressure altitude and is used above transition altitudes approx 18 000ft in the US.
Desert Storm and Operation Iraqi freedom are flown at pressure altitudes as in most of the rest of the world, except for transition to the base. Actual altitude is with radar.( No.15)
Setting the Coleman for a reporting base pressure will give actual elevation.


The HSI Horizontal Situation Indicator (no.40) is a slaved compass gyro with two needle that can point to either a radio beacon (AM radio stations) or a TACAN depending on frequency selection and this with DME, you can situate yourself horizontally.
It is pointed 170'
Once it is energized, it should give the same value as the wet compass on the windshield.(No.3) as found in a Sopworth Camel. 170' The same way a ship can get a bearing and distance from a light house, TACAN does this electronically. This orientates the pilot to the target area.

Check wet compass regularly againts the HSI. The Gyro instruments can fail. The Navy F4s instruments took a beating.


Those are the flight instruments, but two others you would want to keep and eye on is the EGT(no. 31.) If it creeps up past 650'f, you have a problem.680'f, you will melt something.
Incidentally, it drops to 600'f when burners are lit.

Fuel quantity(no.26) is very important. You can use the air above you or the air in your tanks.

So how do you put it together?

The F4 has ailerons that only go down. A spoiler deploys on the opposite wing. When a roll to bank is initiated, much drag is induced and short and abrupt roll durations are required. I think the spoiler minimizes adverse yaw. (aero guys???) for smooth flow to the inlets. Anyway, I'm still a stick and rudder guy since the age of 10.
Have you seen energy conservation methods of birds? Sparrows are my favorite. They use less energy by reconfiguring their profiles from short bursts of thrust to lowest drag profiles every second, than if they sustained constant thrust.

The higher the bank, the higher the drag. Even at 5 G load, you will lose 100KTS/ second.

The 'stick'. The round button with the white dot in the center is the trim button. A two axis 2 speed electric trim for aileron and elevator. (Pitch and roll trim.) The red button on the left is the push to talk. The button on the right is the mouse for the HUD. Red button below is bomb release and missile launch and trigger is not seen as it is in the front of the stick.

The following describes the 'Rolling Scissors' avoidance maneuver in case a MiG is trailing you. The MiG does not perform well down low. 18 000' . Panel(no.16) hopefully doesn't light up.

So a quick left roll to 70' and a push down to unload with burners.

Input: Stick forward and left to zero g. ( Use your own internal G meter) Rudder deflection is simultaneous with aileron deflection, same as Douglas Badar did in his Spitfire.

Scan: (AI) 70' roll pitch forward 20'. Airspeed goes to higher value and loss of altitude. ASI and altimeter. Fuel fuel fuel. You gotta have enough to make it to the tanker.

Roll to right 70' pull back and climb to initial altitude.

Input: Pull back and roll to right 70' and pitch up 20' into the blu. Velocity to altitude.

Scan: (AI) AOA indicator, G meter, airspeed, altimeter. Indexer light one(of 3) 3rd light means you are pulling too hard. Remember the swallow ? OK, so a F4 is not exactly a swallow. I'm talking about energy conservation.

Roll left 70' push forward(unload to zero g) Negative g is drag.

Input: Stick left to 70' and forward to 20' nose down. Roll duration is kept to minimum (drag)

Scan: fuel, altimeter. Bottom and top altitude should remain constant. Seat of pants is another way of monitoring these instruments.- Initial Airspeed should be recovered fully after each unload..Fuel.

Repeat till out of range. Rondeveaux with tanker and look for damage on your buddies planes..

I hope you are all still awake. I'm not. Hope it makes sense.




[QUOTE]Originally posted by A3
[B]

[dosco]

Originally posted by BRIAN GLOVER

The object for combat flight apart from destroying the enemy, is to conserve energy in the aircraft. Energy is either altitude or velocity. One can be converted to the other readily. In a turn, even a mild turn or pull back, energy bleeds off.
In high G maneuvers, this bleed off becomes the enemy . Modern fighters have minimized this with vectoring nozzles and canards, and some very clever people.

Those are the flight instruments, but two others you would want to keep and eye on is the EGT(no. 31.) If it creeps up past 650'f, you have a problem.680'f, you will melt something.
Incidentally, it drops to 600'f when burners are lit.

The F4 has ailerons that only go down. A spoiler deploys on the opposite wing. When a roll to bank is initiated, much drag is induced and short and abrupt roll durations are required. I think the spoiler minimizes adverse yaw. (aero guys???) for smooth flow to the inlets. Anyway, I'm still a stick and rudder guy since the age of 10.

Cool post, BRIAN.

A couple of things.....

1. Energy management....things are a bit easier these days with the improvement in engine performance (better control thru improved VSV design and FADEC). But the basics remain the same.

2. Funny that you mention EGT. On the aircraft I worked on (KC-135R and C-5) the KC-135R model (re-engined variant with CFM56 engines) used N1 (because it had a ****-hot FADEC system). The C-5 used EPR and the pilot was supposed to monitor TIT (turbine inlet temp).....the C-5 engines (GE TF-39s) had a piece-of-junk mechanical fuel control which required constant "trimming" (matching the VSV schedule to the fuel schedule). Interesting how different airplanes/manufacturers use different control schemes for the engines.

3. Back then, many fighter aircraft had control reversal problems due to aeroelasticity. At the a particular speed, when the aeileron was deflected, the entire wing deflected in the opposite direction due to insufficient wing strength/rigidity (causing some problems as you can well imagine). The roll spoiler system defeated that problem.....of course you give up some "control crispness" with that system.....or in the case of the B-52, which uses a similar layout, your flight envelope becomes limited in roll. As far as adverse yaw, you pretty much get yaw no matter what.

[dosco]

Originally posted by BRIAN GLOVER

The aero guys on this forum talk of AOA. As with F1 cars, any deviation of AOA alters performance of the airfoil drastically and it is even more pronounced on a delta wing as apposed to a glider's high aspect ratio wing.
.. Stalling an airfoil means that you have just exceeded it's the critical AOA and created large amounts of drag..

Almost forgot, BRIAN.

A pilot buddy of mine once told me:

"Use the stick to control speed, use the throttle to control altitude."

One of my favorite sayings.

[WPT]

For those who would like to read about inlet design, may I suggest ' Modern Combat Aircraft Design' by Klaus Huenecke ( Naval Institute Press). WPT

[BRIAN GLOVER]

Hardly a problem on the F4. I don't know why they chose this method of roll contol. Since roll control was mid wing, roll response was sluggish at low speeds. 270'/second at the best of times.

I'm still not clear why roll causes adverse yaw. Something to do with lift acting perpendicular to the relative wind.
An interesting excercise you can perform in your Cessna 150 or P51, is a series of 'Dutch' rolls.
You fly along straight and level and roll from left to right from 30 to 50' at various rates. A corresponding rudder input will be neccesary to keep the nose rotating at a fixed point on the horizon and the ball must stay in the middle. The greater the aileron deflection, the greater the rudder deflection. Oh yes, if you are new to this, do it on the way back from the practice area. You and your passenger will throw up. In the case of the P51, your gun sight will not align unless you perfect this.

Originally posted by dosco



3. Back then, many fighter aircraft had control reversal problems due to aeroelasticity. At the a particular speed, when the aeileron was deflected, the entire wing deflected in the opposite direction due to insufficient wing strength/rigidity (causing some problems as you can well imagine). The roll spoiler system defeated that problem.....of course you give up some "control crispness" with that system.
As far as adverse yaw, you pretty much get yaw no matter what.

[BRIAN GLOVER]

Thanks A3. Ugly seems to be in. Seems to me, there was a time that if a plane looked nice, it flew nice..

Originally posted by A3
Interesting article about inlets: http://www.codeonema...vertless_1.html

[dosco]

Originally posted by BRIAN GLOVER
Hardly a problem on the F4. I don't know why they chose this method of roll contol. Since roll control was mid wing, roll response was sluggish at low speeds. 270'/second at the best of times.

It might not have been a problem in retrospect, but when the aircraft was initially designed in 1954, high-speed aeroelasticity was not well understood throughout the industry (although it may have been at the academic level).

I have no doubt that the wings were upgraded on a periodic basis, but I'm also pretty sure that when each wing mod was made, there wasn't much thought about changing the roll system to all aeileron vs aeileron+spoiler (that would have been a major undertaking and cost big $$).

Originally posted by BRIAN GLOVER

I'm still not clear why roll causes adverse yaw.

Piece of cake. The drag caused by the aeileron itself causes a "torque" force (draw a line from the aircraft CG to the drag force, then multiply forceXdistance and you get a moment) about the aircraft's CG and therefore creates yaw.

As far as dutch roll, it is a "stick fixed" mode of dynamic stability....any/all aircraft, depending on its design, will exhibit dutch roll of different amplitude and frequency. And yes, it'll make you puke. I flew on a KC-135R that lost it's yaw damper inflight.....the 2 hour ride home wasn't fun (although the pilot did a pretty good job of keeping things smooth).....

[kos]

Originally posted by dosco
Piece of cake. The drag caused by the aeileron itself causes a "torque" force (draw a line from the aircraft CG to the drag force, then multiply forceXdistance and you get a moment) about the aircraft's CG and therefore creates yaw.

So if an aircraft uses reversely deflected stabilizers instead of aeileron to control roll, there's no induced yaw and the sight is more stable, right?

[Colin]

Originally posted by A3
Interesting article about inlets: http://www.codeonema...vertless_1.html

Hey, my boss was the program manager of that! I work with the guy with the patent for it.

And the JSF at least looks a lot nicer than the F-16 DSI. But then beauty is in the eye of the beholder.

[dosco]

Originally posted by kos


So if an aircraft uses reversely deflected stabilizers instead of aeileron to control roll, there's no induced yaw and the sight is more stable, right?

Yes.

F-14, F-15 use it (that I know of).

[BRIAN GLOVER]

OK, so splain me how a Mitsubishi MU2 has adverse yaw to the right when the spoiler is deflected on the left for a left roll. (No Aeilerons) IE: as the left wing goes down, the nose moves to the right. When it rolls counter clockwise about it's longitudinal axis, it also rotates clockwise on it's vertical axis. The wing going up has more drag????
How about the wing going down has a higher AOA and moves forawd because of the lift moment moving forward???

[QUOTE]Originally posted by dosco
[B]



Piece of cake. The drag caused by the aeileron itself causes a "torque" force (draw a line from the aircraft CG to the drag force, then multiply forceXdistance and you get a moment) about the aircraft's CG and therefore creates yaw.

[dosco]

Originally posted by BRIAN GLOVER
OK, so splain me how a Mitsubishi MU2 has adverse yaw to the right when the spoiler is deflected on the left for a left roll. (No Aeilerons) IE: as the left wing goes down, the nose moves to the right.

Interesting. I Googled "Mitsubishi MU-2 adverse yaw" and what I found says that the Mitsu will yaw more to the left if a left roll is initiated ("proverse yaw"?? heheh).

Which makes me think I might have the idea of "adverse yaw" confused with something else.....I'll have to dig around now and find the answer.

[Paolo]

"Proverse" yaw (you should patent this, Dosco) is what I would expect too, from a spoiler controlled aircraft.

Adverse yaw is caused , on an aileron equipped plane, by the difference in drag between the internal and external wing. Deflecting an aileron , say, 10 degrees up or down will not cause the same drag increment ; usually, deflecting it downwards will cause a greater increment than deflecting it upwards.
Therefore, the falling wing has less drag than the wing going up, and adverse drag ensues.

It must be noted that the falling wing will have the local air incidence angle linearly increased
from the root to the tip ; while the "climbing "wing will meet air at a linearly decreasing incidence angle from root to tip.
This effect diminishes the adverse yaw, but normally it's a lot weaker than the moment caused by drag differential between opposite ailerons.

Of course, i can imagine wing profiles whoose drag would be lessened by the opening of a spoiler (causing therefore adverse yaw); yet I doubt they would be practical or flyable.

On the other hand, maybe Brian speaks out of personal experience.

Discussion worth continuing, I guess.

[A3]

Originally posted by BRIAN GLOVER
Thanks A3. Ugly seems to be in. Seems to me, there was a time that if a plane looked nice, it flew nice..

True...

[dosco]

Originally posted by BRIAN GLOVER
I'm still not clear why roll causes adverse yaw.

Duh.....I'm a knucklehead.

Adverse yaw....when rolling to the right, the aircraft yaws to the left (or vice-versa).

OK - I was confused about the subject.

Virtually all fixed-wing aircraft (that I can think of, anyway) have roll-yaw coupling....in other words, when yaw is induced, roll also occurs; and vice-versa.

I won't go into details about adverse yaw, but here is an excellent explanation of the phenomena: http://www.aerospace...ics/q0045.shtml

Check it out.

The Mitsubishi aircraft that Brian Glover mentioned has the opposite problem (at least from what I could find on the web).......the aircraft has a tendency to yaw in the same direction as the applied roll, requiring opposite rudder input (when rolling) to prevent a roll-induced dive.

[dosco]

Originally posted by Paolo
"Proverse" yaw (you should patent this, Dosco) is what I would expect too, from a spoiler controlled aircraft.

I can't I got it from http://archives.glas...8/msg00089.html

Heh heh heh.

[dosco]

Originally posted by BRIAN GLOVER
Ugly seems to be in. Seems to me, there was a time that if a plane looked nice, it flew nice..

Yeah, Kelly Johnson's philosophy.

Computerized flight controls have changed all that (in fighter aircraft, anyway).

Some of the more modern aircraft aren't bad looking.....the single-seat Sukhoi Su-27 (and it's single-seat derivatives) are sweet looking, IMO.

[BRIAN GLOVER]

It is a very interesting phenomenon. Another long post, sorry, but here are some thoughts that seem to be the only ones that I have these days that I wish to express..
I believe your explanation is the most valid, Paola. The chord of the ascending wing alters sufficiently to create more lift which comes with added drag with downward aileron deflection. I would assume that spoilers are used to appose this yaw. In the case of the MU 2, they chose this method of roll control to prevent adverse yaw. I really like this aircraft, although I have not flown it. On final, you dare not use roll control as it may stall the wing and cause a spin. You only use the rudder especially in IFR conditions. I knew someone who owned one.
Unfortunately, many pilots have died flying this plane. It has short stubby little wings that need lots of speed. I forget which navy aircraft it's gear comes from, but you can slam that thing onto the ground and you can lower the gear at 200 kts, so why bring it in below that speed even on short final. What ever I fly, I come in hot. You just have so many options if things go wrong.
Even if you fly a little piper with a cruise speed of 120KTS, hold that speed to the threshhold. Your instructor will freak out. You hold it off the ground till it stops flying' thats all.

The F4 may also use a spoiler to minimize adverse yaw for inlet considerations.
I have flown many different types of aircraft and I have rolled just about every one. I can't help it. It's like jumping into a car and seeing what it can do.

Adverse yaw is something you live with when flying a plane and appropriate rudder deflection becomes instinctual.
Like a car, if the engine doesn't blip, I cant change down. I get this mental block.

AOI must not be confused with AOA. Incidence is the fixed angle of the wing to the fuselage.

Maj. Stanford Tuck's autobiography,"Fly For Your Life" explains the use of the rudder while flying a Spitfire. Read it, you will really really enjoy it..


Now each wing feels completely different and you can actually recognize the engineer. For instance, if any of you have the opportunity to fly any Ted Smith designed airplane: Mooney, Aero Commander, all the Commanders from 690 to 1000. Jet Commander, Aerostar, now owned by Piper, seize it. How does Ted do it? There is a relationship between the Little Mooney Mite and the Aerostar. Some planes just feel right.

Bob Hoover and Chuck Yeager were asked which plane they like best and without hesitation, they said the F86 Sabre. Did the engineer know it felt so good? These two guys have flown more aircraft than any other. Yeager flew a F16 when he was 70.


How the hell can you arrange the same components that any aircraft has, and make them feel so good and balanced yet some feel so awful? . Ofcourse, Teds designs have one thing in common, the wings are all high laminar flow and highly loaded, so payload is forfeited for performance. It feels so good.
I don't want to get Ben too excited about feelings, you know how those liberals are? But these feelings are designed into the machines on purpose, so what ever machine I operate, I am always aware of the engineer responsible for it..

If any of you have the inclination to build your own airplane, try Dick Van Grunsven's RV 4. eaa.org. A friend of mine took 7 years to build his. It is an aerobatic approved cruiser. Really really nice.

I recently drove a new 5 series BMW. How can those Germans make a car feel so nice? I drove a Peugeot 206 in S Africa recently and I just wonder how engineers can build in so much fun. A truly wonderful little car.
And then there is a 911 Porsche. Whether it is an old SWB car are a new 996, it is a sheer delight. How can you arrange Mc Pherson struts, semi trailing A arms and a rear engine to work that well and feel so good. A Ferrari 360 is a wonderful car and the Italians incorporate this fun factor into every car they design, but it aint no 911. 18 entries into this years LeMAns alone and no 360 will be close to those beloved 911s at the end of the race.
I've owned 10 Corvettes and they feel, well American. That's not bad, because Id rather drive my wife's Olds 4.0 cross country than the BMW. But if I lived in Asheville N Carolina, I'd take the BMW. The Olds will do better in the Snow though.
The Vette can take loads of extra HP without altering its dynamics, but add 200hp to the 206 and you will need Marcos Grunholm's advice.. You can take a Z06 way past it's limit in complete confidence. Try that with a F360. The nicest car I have ever driven is the 96 Corvette GS coupe. I have an affinity toward SWB cars and close coupled aircraft.
If you guys want to get to really feel a wing, take some glider lessons. It is a fraction of the cost of powered flight and 20 times more fun at a novice level. The WW II Luftwaffe pilots all started on gliders. I was taught by a FW 190 pilot in the Blue Ridge Mountains in Canada. The fist time you solo in a glider, you will experience flight for the first time. I learned to fly gliders in my late 20's after flying since I was 10 years old with powered flight. Add power and flight dynamics change. The more power you add, the more you are dependent on that power. Not a bad thing, just differnt

A glider also has adverse yaw and in unstable high thermal conditions, the one wing can get a lot more lift than the other. The nose still points toward the wing that is ascending. How the ****? I live with it, but I don't understand it.

I prefer a aerobatic glider. Its glide ratio is less, but much more fun. You can experience 4 to 6 thousand feet per minute climb without an engine. When you soar with an eagle, literally, you will have just seen the face of God. Do it fellahs. I urge you. Do it.

By the same token, a friend of mine, the same one who built the RV 4, and ex RAF, has a 80 hp Aronca Champ with a high wing and tandem seating. On a hot Florida day, with two up,you have to coax this lovely flying machine off the ground. You are lucky to achieve 50ft/min climb, but the sense of achievement and pleasure is as great as pointing a F4 nose skyward to a stall in 10 miles vertical.
What is the envelope of that wing, you must ask yourself. Then find it.

Dan Gurney was asked on a recent interview what form of racing he likes. He has raced stock cars, sprint cars, F1, Le Mans etc. He said it doesn't matter, as long as he is racing. It took Hans Stuck two years to learn how to drive the AWD Audi. Get the video from Audi. It took me two years to transition from a Pitts Special S2B to a German Extra 300. I'll never go back. They have symmetrical wings that create no lift. The flight characteristics are the same inverted as they are upright. If the engine quits, you have twice your altitude in distance to look for a place to crash and not much time either, but aaah, how it feels when that prop keeps spinning.

Do you remember when Jean Alesi drove the Benneton after Michael Schumacher set it up, Alesi couldn't drive it. All stability was dialed out of it, because stability robs performance. As it is does with an airplane.

The interesting thing about flight for car guys, is that it makes you more sensitive to chassis set up in your car.
To experience and exploit each wing design is a pleasure to behold.
I assume that you are sitting down right now. Push down on the floor with your left foot. Can you feel the weight transfer to your right cheek on your ass? That's right, you ass is a sensitive instrument in Chassis set up and essential for coordinated flight. Hans Stuck does not use seat padding, because he wants to feel the chassis.

I was taken around Kyalami in S Africa in a F40 for 5 laps. It would have been longer, but I had to tell the diver to stop before I threw up.. I have never been in a downforce car before and it seems to defy physics. The owner says it is the best road car ever. He should know because he also owns a 288 GTO, F50 and an Enzo. Says a lot about the old 308 steel chassis.
The question is; Can Michael Schumacher actually recognized the aero tweaks that Rory Byrnes performs on his Ferrari? Can you feel it like you can on an aircraft wing? What went trought the minds of Jim Hall, Phill Hill and Jo Bonnier, when they operated that wing on the Chaparral for the first time? What an incredible experience that must have been.
Adrian Newey and Rory Byrnes could not drive but Jim Hall and Bruce McLaren could. At what level must the engineer or the aerodynamicist comprehend his work? Some need this symbiotic relationship with a driver.
I understand Byrnes is closer to Barrachello than Schumacher in this symbiosis.

Does this belong on a Tech Forum? I actually think it is very technical, sides, who else can I talk to besides you guys about these type of feelings. Ben???

Originally posted by Paolo
"Proverse" yaw (you should patent this, Dosco) is what I would expect too, from a spoiler controlled aircraft.

Adverse yaw is caused , on an aileron equipped plane, by the difference in drag between the internal and external wing. Deflecting an aileron , say, 10 degrees up or down will not cause the same drag increment ; usually, deflecting it downwards will cause a greater increment than deflecting it upwards.
Therefore, the falling wing has less drag than the wing going up, and adverse drag ensues.

It must be noted that the falling wing will have the local air incidence angle linearly increased
from the root to the tip ; while the "climbing "wing will meet air at a linearly decreasing incidence angle from root to tip.
This effect diminishes the adverse yaw, but normally it's a lot weaker than the moment caused by drag differential between opposite ailerons.

Of course, i can imagine wing profiles whoose drag would be lessened by the opening of a spoiler (causing therefore adverse yaw); yet I doubt they would be practical or flyable.

On the other hand, maybe Brian speaks out of personal experience.

Discussion worth continuing, I guess.

[dosco]

Originally posted by BRIAN GLOVER
It is a very interesting phenomenon. Another long post, sorry, but here are some thoughts that seem to be the only ones that I have these days that I wish to express..

I believe your explanation is the most valid, Paola. The chord of the ascending wing alters sufficiently to create more lift which comes with added drag with downward aileron deflection.

Does this belong on a Tech Forum? I actually think it is very technical, sides, who else can I talk to besides you guys about these type of feelings. Ben???

Brian, excellent post, my man.

The link I provided pretty much says the same thing as Paolo 'splained. If you're rolling left, the right wing has more induced drag (more lift from the aeileron) and therefore the aircraft yaws to the right while simultaneously banking to the left.

You were instructed by a Fw-190 pilot? Cool.....that aircraft is one of my faves (along with the Merlin engined P-51).....my favorite version of the Focke was the Ta-152. BTW I was a volunteer at the Champlin Fighter Museum in Mesa, AZ.....quite an interesting collection....and frequent visits by WW2 fighter pilots made things really interesting. My fave at the Champlin museum was the Fw-190 D9 "Dora." Very very cool.....one of 3 airworthy in the world, valued (at the time) at $5 million. Gave me goosebumps every time I walked by it.

Keep the posts coming....

[BRIAN GLOVER]

I can hear that Merlin. That is the greatest sound in the history of this planet.

[QUOTE]Originally posted by A3
[B]

True...

[dosco]

Originally posted by BRIAN GLOVER


Now each wing feels completely different and you can actually recognize the engineer.

The question is; Can Michael Schumacher actually recognized the aero tweaks that Rory Byrnes performs on his Ferrari? Can you feel it like you can on an aircraft wing?

The devil is in the details, man. And some engineers are better than others, if you hadn't already figured that one out Don't get me started ;)

[A3]

Originally posted by BRIAN GLOVER
I can hear that Merlin. That is the greatest sound in the history of this planet.

Then you've got to see this.

Btw, I love your stories. Flying has always been my dream, just can't afford it.

[Exar Kun]

Originally posted by A3


Then you've got to see this.

Hehe - I knew what that was before I even clicked on it.

The FW-190D9 and Sptifire Mk IX are my favourite aircraft of WW2. I have to reserve a space for the B-17F which my grandpa was flight engineer on during the war but it will always be the fighters that truely capture the imagination.