49 replies to this topic

[Tech_Nut]

Tamiya version of the BT46.

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The Brabham BT 46 F1 car above was, to my knowledge, the only attempt ever made to utilitise "surface cooling" on a race car. The concept failed, and the car was quickly fitted with radiators.

I was wondering whether or not it would be possible to use a similar arrangement of cooling "units" (radiators, whatever), but with the units installed as part of a wing. For example, on an F1 car, if you made the underside of the rear wing out of an aluminium matrix, and piped a small proportion of the cooling water through that matrix, would the heat being dissipated at the surface of the wing create an increase in downforce? After all, the heat transfer would excite the air flow, make it (the air) run faster and reduce the pressure at the under wing surface, thereby increasing the downforce for that particular wing angle. (I think my physics on this one is sound .... ).

For sure, there are downsides wiith this layout. First there would be the negative effect on the car's C of G by the weight of the pipework and the weight of the water inside the pipwork, both mounted high up on the rear of the chassis. Also, radiators would still be required (tho' slightly smaller) so there would need to be a very clever valve arrangement to divert sufficient water between the wing and the radiators.

Finally, if you again think of one of today's F1 cars, and throw away the wooden plank on the underside of the chassis, you could then mount a single long, thin radiator "unit" in its place. With a similar proportion-valve arrangement described above, you would have another area where the heat being dissipated under the car could excite the airflow, and for the reasons described above, would generate more downforce.

Final thought. If you could mount a radiator in the wing, I would estimate (guesstimate actually) that it would be able to radiate away about 10% of the engines heat. As far as I understand it, the engine oil-cooler is about 10% of the size of the water radiators......

Anyone else want to chip in their 2c on this one?

[Beej]

I wasreading "The Complete F1 Encyclopedia" and it stated that the BT46 only had radiators fitted to make the Fan car principal leagle. The book maybe wrong but it seems right to me

[desmo]

I think the packaging, C of G and mass downsides you cite would kill the wing radiator concept, but the skid block rad I find intriguing. The skid block material is never specified in the regs, only a specific gravity range 1.3 to 1.45. 3.13.1 f) will be harder to get around: "[The skid block must]Have no holes or cut outs other than those necessary to fit the fasteners permitted by 3.13.2 or those holes specifically mentioned in g) below." Would a foam be considered a "homogeneous material? There might be some wiggle room in the regs for a little creative interpretation.

[MRC]

I've had the same idea of running the engine coolant through the wing to increase downforce. Some friends of mine and I have tossed the idea around, and without putting numbers to the idea, figured that the heat transfer would not be great enough to make it feasible.

Convective heat transfer is h*A*(delta T). The big thing here is what are you going to get for h? To increase h, you want to make sure that the flow along your boundary will be in the turbulent regime. I imagine that this should not too much of a problem. The other is issue is what is the Q(dot), or what is the heat transfer rate? (Assume perfect heat exchanger efficiency for now, to make things easy).

If you ran the coolant through the wing, the fluid would likely go through a very thin duct of some sort. The duct must be subdivided that you are assured that the Reynolds number will be high enough that you always have turbulent water flow, again to keep h as high as is feasible.

So, the questions are:

1)What do you estimate the heat transfer rate at? Then you can get the increase in downforce (at least some reasonable estimate)
2)What extra pump power will be required to maintain the neccesary water velocity in all heat transfer sections?
3)You are likely going to be carrying more water. How much more weight are you adding?
4)What is the CG penalty? With the heating of the lower flat bottom section, this would not be a detriment to CG.

One way that you could approach the problem is to just pick how much downforce increase that you want, and see what kind of heat trasfer rate that you would need in order to do this. That would give you a number, and you could at least see if it was in the realm of reasonabilty or not.

This would not be a difficult probelm to do with a CFD package that handles conduction and convetion well.My guess is that they have thought of it already.

That's my $.02.

[desmo]

This Brabham isn't the "fan car" one. This is Gordan Murray's surface radiator car. IMO, one of the most beautiful F1 designs ever penned. Pity it didn't work!

[DOHC]

The surface radiator car and the fan car are the same, BT46 and BT46B, respectively. (The model above is the BT46, without fan.) The fan was added when the surface heat dissipation was found to be insufficient. The fan of course also added downforce, but it was only used once, in the Swedish GP 1978, which the car won with Lauda at the wheel. It's questionable if it was correct to let it race in Sweden and keep the victory, because it was a moving aerodynamic device, and they were in principle banned already. As the fan was illegal, conventional radiators had to be added to make the car work properly.

[12.9:1]

Perhaps you all are not aware, that a heat exchanger in-duct with properly designed divergent
inlet and convergent outlet, can produce thrust exceeding it's drag.
The first example that I'm aware of was - the P51 Mustang, and I expect some improvements have been made since the 30s

[FNG]

Hmmm considering the last two races MS and Juantoya have lost their front wings, I don't know if I would want cooling on my wings. I guess the rear wing would be ok. If that breaks your race is done anyways. Good idea though

[RDV]

The Brabham BT 46 F1 car above was, to my knowledge, the only attempt ever made to utilitise "surface cooling" on a race car. The concept failed, and the car was quickly fitted with radiators.

Several other teams , to my knowledge, were toying with idea, I myself had layed out a proposal , but on doing deeper into it with some calcs ,quickly discovered that every airstream licked surface of the car including tyres and drivers helmet would be @ 70% of surface required for adequate cooling even if flow was laminar everywhere..... think of Scheider Cup racers where 60% of the wing top & bottom surfaces , fuselage sides and part of float upper surfaces where used for cooling..... in cleaner air, and constant high(ish) speed.

A considerably bigger area/power ratio than achievable on a single seater.
Extra mass of coolant was also a concern ( with an adequately cooled car ), as was back pressure on system , Cosworth water pumps on engines of the period spec were a bit on the ragged edge...
I dont know if Gordon was winging it or misplaced a decimal point...

OT for a moment , does anyone know of a site with photos of these planes?

As far as added downforce from heated/cooled wings , MRC will toss some calcs at it, but first priority is getting lunch, must break this habit of reading this forum on breaks....

[RDV]

...On second thoughs , knowing Chiti and Alfa , they probably gave him duff data as to engine thermal output....

[Tech_Nut]

My suggestion about replacing the plank was really just a conceptual one. I suppose a "hot-floor" is a concept that could be applied to any race car. What I'm asking is would it would have any signifcant effect on the cars aerodynamics in general, and particularly whether it would affect the car's downforce. Air passing a cold surface would obviously behave differently when the surface is heated by a certain amount. But would this difference be significant or not? I remember reading somewhere that when pilots switch on the de-icing heaters in the wings they have to re-trim the plane 'cos of the slight difference in lift, so I guess the principle is proven. (Tried to find some info on this with google but didn't find anything).

I guess the whole concept comes down to this:



The wing here will generate precisely "X" lbs of downforce at 24 degrees C. If the blue area is then heated to 110 degrees C, what will the downforce be now?

Any of you physics/aero wizards know the answer to this one? My own guess would be that the downforce would increase, but only by a very small amount. But to an F1 designer the downforce issue would be secondary to the fact that the conventional side-radiators would be able to be reduced in size by a useful 10% or so.

[Jezztor]

The Gordon Murray BT44B appeared to have radiators or intercoolers embedded in the front wing, as did the Rory Byrne Toleman TG183. Any clarification on the BT44B?

Back onto cooling - last year when I planned a formula ford chassis project (Alfa Twin Turbo V6 from 145, 6 speed porsche g/b & custom everything else), I urged our designers and engineers to be as experimentative as possible. I had designed the underside of the car (parts of it being ground effect), with a full-width diffuser, which had electronically activated cooling gel layers on the top lip (like those seen on www.howstuffworks.com, just very much thinner, but can't find the page) and the inside surface with electronically activated heat strips, heating to about 80*C. We were sponsored by an electronics company who initiated the ultra thin design of the cooling gel. This stuff is pretty amazing, as soon as current passes through it, it becomes ROCK hard, and cold (-45*C). Unfortunately the total sponsorship wasn't able to cover costs - so the project was not finished

Jezz

[DOHC]

I think it's fair to say that neither the BT44B nor the TG183 had "front wings" in the conventional sense. They rather had fronts that were housing the radiators. Of course, that was in some sense just a heritage from the 60s, combined with the front wings of the 70s and early 80s. And there were many other cars that had various versions of "bluff" noses. They did provide downforce, but a clean wing was IMO always superior. In 1970, the Lotus type 72 was the first F1 car to move the radiators away from the front and into side pods (although Lotus had toyed with this idea for quite a while already), and ever since you have had to make a choice where to put the radiators. (Maybe today you have to have them in side pods because of the very strict and conforming tech regs.)

[desmo]

12.9:1- Did you ever see the Mike McDermott article in the April/May '98 issue of RaceTech on this? I'll quote a little, though I won't attempt to write out the maths referred to in the sidebar.

"Assuming that an engine is a typical one-third efficient in converting the fuel's chemical energy into mechanical energy at the flywheel, then two-thirds of the the fuel energy has to be rejected as heat. A 700BHP engine has to lose 1400BHP as heat either via the the coolant or out of the exhaust pipe. Can any of this energy be recovered and put to good use? Probably with careful attention to detail."

"The crude calculations in the sidebar show up to 1.6% of the heat energy being available as thrust at 135 mph. This is 3.2% of the mechanical power and for a 700BHP car could be as much as 22BHP; at 200 mph it's more than twice as much. You just can't ignore the possibility of more than 40BHP at the top end. A major advantage of this additional power is that it creates a thrust directly on the car, specifically on the radiators and ducting, from the air, not between the tires and the track, so it by-passes grip limitations. To achieve this the duct has to be carefully designed to ensure effective pressure/velocity recovery both before and after the radiator. Not for nothing was the ramjet originally called the 'aero-thermo-dynamic duct'."

"It is not clear to me if, or where, this effect is currently being exploited in racing. In general, great care is taken to coax the right amount of air into the radiator but, provided the exit is in a low pressure region which extracts the air, that seems sufficient. In single-seaters, space to achieve the optimum exit is undoubtedly limited, particularly with the new narrow F1 format. Judging from press photographs, the ducting on most of the 1998 F1 cars is typified by the Williams F20. This terminates inboard of the rear wheel and ahead of the rear axle line and the exit air then has to find its way through the suspension, exhausy and diffuser assemblies. The design probably at least provides effective pressure recovery and so minimises drag. But for maximum thrust the exhaust stream has to exit as a parallel jetand to react on the surrounding air. The airflow in the space immediately behind a race car is famously disturbed. So extending the radiator exit duct to form a nozzle at the extreme rear of the car is unlikely to create a jet effect. A significantly different exit duct is to be seen on the 1998 F1 Arrows A19. The exits on te Arrows are relatively large and they feed into an area directly ahead of the rear tyres."

"Arranging for the exhaust system to heat the air in the duct would help. If the exhaust gasses are cooled in the process, this is no bad thing. The viscocity of a gas falls with temperature, so the cooler the exhaust gasses, the lower the exhaust back pressure- but not much lower. The ramjet effect shouldn't be confused with pointing the exhaust pipe exit backwards to get thrust. That mass flow, being only the air breathed for its combustion needs by the engine, is much smaller, typically no more than 5% of radiator airflow."

"Manufacturers in F1 are already producing engines capable of operating at higher coolant temperatures. This is said to allow car designers to use smaller radiators, which require smaller ducts, creating less drag, to improve the car's aerodynamic performance. By raising the exit air temperature, the same developmentenhances the thrust available from the ramjet effect. Thermodynamicas, as always, tells us that nothing is for nothing. Raising the coolant temperature in an engine reduces the working temperature difference and so, in principle, reduces the thermodynamic efficiency although, in a practical engine, other temperature-dependant effects can reduce or overcome this drawback. At the least, the ramjet effect could be, or maybe already is, for those who know, a way of recovering some of this lost efficiency."

One of the accompanying illustrations shows a radiator duct forcing the airflow upwards 90 degrees to provide downforce. This seems to presage the Mac "chimany" rad exits, at least superficially. Also, the reference to the A19's at the time rather novel rad exits in front of the rear tires seems as well to presage a lot of obvious later aero development in this very area. I wonder if the exhaust airflow- being much a smaller mass flow, but containing comparable heat to the rad outflow might make a more promising heat source for aero energizing. No untidy coolant plumbing and mass either- granted this has been done in the diffusers already certainly.

The use of all the 'wasted' heat energy produced by the IC engine is like gold to the thermodynamic alchemist seeking to turn this into useful work. From the P-51 to the Napier Nomad compound CI aircraft engine, to the turbocharger, it makes a shimmering and elusive target to pursue. The allure of the 'lost' two-thirds is well-nigh irresistable!

[DOHC]

Originally posted by desmo
The use of all the 'wasted' heat energy produced by the IC engine is like gold to the thermodynamic alchemist

That was very well put!

But instead of working on the problem I think I'll wait until I see a stalled F1 car get off the grid even if it can only utilize 40 hp of the lost thermal effect. 40 hp should be sufficient to get it going.

I would believe that the thrust derived from lost heat and the enormous volumes of hot exhausts (or for that matter, the suction created by the airbox inhaling 450 liters of air per second at 18k RPM) are close to completely negligible. (A rocket engine wouldn't take you very far on 50 kg of gasoline, but an F1 car runs something like 100 km.) What is not negligible, however, is the effect of routing the hot gases through the rear wing assembly, and the effect of turbulence on what would otherwise be a laminar flow.

[desmo]

I knew I'd run into trouble omitting the maths! Of course, we require sufficient mass flow through the rad to remove the heat power. The effect is velocity sensitive, you can only potentially see that 40BHP @ 200mph. Like a ramjet, it won't work from a standing start.

[DOHC]

Oh, desmo, don't worry, I know! (So I was exaggerating by a bit.) But the point is, I think it's quite a difference between being able to make a radiator which has little or no drag penalty at high speed (a la P-51 Mustang) and actually getting some propulsion of any significance.

I've also seen suggestions that the exhausts from an F1 car would assist propulsion, but the mass flow/momentum carried is way too low. Even in turboprop airplanes and helicopters, you typically see the exhaust outlet on the side rather than pointing rearwards. And mind you, we are then talking gas turbines! But their power (and thrust) is of course significantly lower than in the gas turbines used in turbojet and turbofan aero engines. (Fuel consumption is lower too!) And as for turbines used in racing, the 1968 Lotus 56 and the 1971 Lotus 56B had their exhaust outlet pointing up. It must have been because they preferred downforce to propulsion...

[RDV]

as for turbines used in racing, the 1968 Lotus 56 and the 1971 Lotus 56B had their exhaust outlet pointing up. It must have been because they preferred downforce to propulsion

More because the layout of the engine, it was a shaft driven helicopter engine , with a side exhaust on its original instalation . on the 56 & 56B as the engine was in a bathtub shaped monocoque ( non stressed engine) only way was to point exhaust up

I've also seen suggestions that the exhausts from an F1 car would assist propulsion, but the mass flow/momentum carried is way too low.

but enough to usefully re-energize difuser flow on flat bottomed cars, as cars from 87 to not very long ago had them, a bit throttle sensitive but definitely a gain, incidentally because of the mass-flow of hot air very difficult to simulate in wind tunnel. check out its use on aircraft ejector stacks (Lempror type ---familiar to steam engined locomotive fans) to aid cooling on air-cooled engines and used on todays F1`s to help internal flow... as for thrust , not enough to take in account...

[DOHC]

Originally posted by RDV
it was a shaft driven helicopter engine, with a side exhaust ... only way was to point exhaust up

Exactly. And it's still more or less standard to construct helicopter and/or turboprop engines with side exhausts, as there isn't much to gain in reconfiguring the engine with a rear exhaust.

[BRIAN GLOVER]

Talk airplanes and Im there. Love that P51. Some turbo prop airplanes, such as King Airs, use Pratt@ Whitney split shaft turbines. The prop gearbox is driven off the turbine. That means the engine has to be mounted backwards and the intake is mounted below, like the P51 radiator intake. The air and fuel go in the same direction of the plane. This means that the airflow changes direction twice. It flows thru the compressor which is driven by bleed offs from the turbine. The exhaust outlet is just behind the prop and offers little or no thrust augmentation.

The solid shaft turbo-props work like a normal jet engine except that the prop gearbox is driven off the front of the shaft, such as in Garret engine powered turbo props, such as Cesna Conquests and Commanders, etc. All large turbo-props starting with the Vickers Viscount use single shaft engines.
The exhaust outlets provides up to 20% additional thrust augmentation on the Garretts. Turbo-props are much more efficient than pure jets at low altitudes that is why modern jets have 'high bypass'fans, and the cowl is altered at altitude for no bypass.

For engineers, a point of interest is the complex propeller pitch control mechanisms in each application, the solid shaft being the most complex. Those are the ones that make all that racket in ground opperations, which require manual prop pitch changes for taxiing. A reverse pitch can let you back into a parking space, but that is not a good idea. This is refered to as the 'beta' mode as opposed to automatic pitch control(constant pitch) in the flight mode, or 'alpha' mode, which also has feather modes and 'reverse' for the ground roll after landing. After landing, you move thrust levers from reverse to idle, and the condition levers from flight to ground idle(beta mode) for taxi opperations and then the function of the thrust levers change, for ground use.
The turbine and the prop stay at a constant rpm. 1800 for the props and 100 000 for the turbine shaft. The props take forever to stop after shut down. Cruise thrust settings are set with shaft torque indicators same as helicopters. This only describes the Garrett and the Hartzel systems, but there are many different mechanisms and opperational procedures for eachmanufacturer.

There is such a nice sound when going from ground idle to flight idle before take off. As you move the thrust levers forward on the take off roll, the sound stays constant, yet you feel the thrust increase.

The split shaft requires thrust levers for for both flight and ground opperations. RPM will vary and the props will auto feather at shutdown. Cruise is set with pressure ratios.

Sorry, couldnt help myself. For the aviation enthusiasts, it may interest you to know that when you attend a school for type ratings on a particular aircraft, most of the ground training is for systems on the aircraft. A thorough understanding of aircraft systems may save your ass one day.

Originally posted by DOHC
Oh, desmo, don't worry, I know! (So I was exaggerating by a bit.) But the point is, I think it's quite a difference between being able to make a radiator which has little or no drag penalty at high speed (a la P-51 Mustang) and actually getting some propulsion of any significance.

I've also seen suggestions that the exhausts from an F1 car would assist propulsion, but the mass flow/momentum carried is way too low. Even in turboprop airplanes and helicopters, you typically see the exhaust outlet on the side rather than pointing rearwards. And mind you, we are then talking gas turbines! But their power (and thrust) is of course significantly lower than in the gas turbines used in turbojet and turbofan aero engines. (Fuel consumption is lower too!) And as for turbines used in racing, the 1968 Lotus 56 and the 1971 Lotus 56B had their exhaust outlet pointing up. It must have been because they preferred downforce to propulsion...

[ray b]

about hot wings or ground efx rads
you DONOT WANT TO heat the lower pressure side of the wing
as heat wil raze the pressures
flat or hi side maybe but not the curved lower side!!!
esp not the front of the lower side leading edge of curve part as shown
under the car you want less pressure and heat will raze it there toooo!!!
just like the weather , hi=hot and lows=cold

[DOHC]

There is such a nice sound

Couldn't agree more! Nice post, Brian!

[MRC]

I am not seeing why you would not want the underside of the wing much hotter than the top, if it were easily implemented.

From the ideal gas law, I would think that a temperature rise, would be good.

density = pressure / (Universal Gas Constant * Temperature)

[Jezztor]

I agree MRC, from what I understand, for moving flow hi temp = low pressure, low temp = high pressure - may be wrong though, because simple gas laws state (smaller volume = higher pressure, higher temp = higher pressure, but that is because of collision with particles & the container walls, with moving flow, there are no 'container walls'). Clarification?

Jezz

[ray b]

Originally posted by Jezztor
I agree MRC, from what I understand, for moving flow hi temp = low pressure, low temp = high pressure - may be wrong though, because simple gas laws state (smaller volume = higher pressure, higher temp = higher pressure, but that is because of collision with particles & the container walls, with moving flow, there are no 'container walls'). Clarification?

Jezz

I am a sailor and understand airflow+ airfoils
sure seems to me both roadway and undersides of car form walls
and heating the air will raze pressures under the car REDUCING DOWNFORCES

on a wing curved side is lower pressure[so it is sucked]
hot air is higher in pressure and will hurt lift effects NOT ADD to them
if lower pressure flow is heated it's pressure is razed and suction is less

[Tech_Nut]

Hmmm. Think I'll go with jezz and mrc (and myself! )

Inside a "closed container" a higher temperature means more pressure as per Charles Law etc...

But the underside of a wing in open air is about as un-closed as you can get. The local air pressure around a heated flat surface would be less than ambient as the hotter air molecules become more agitated and therefore less dense. The local pressure would go down. But, in the context of the diag' in my previous post, I'm not sure if this slight reduction would be useful (or even measureable).

[DOHC]

Well, the ideal gas law says that

p*V = k*T,

with p=pressure, V=volume, T= temperature and k=constant. So pV/T = k, and therefore if the temperature of the gas increases, e.g. by heating the gas, there is a corresponding increase in pV. Normally this means p is up, or V is up (expansion of the gas) or both. It appears to me that if you heat the flow as in Tech_Nut's picture, you should get a greater gas volume and/or a pressure increase locally under the wing. Wouldn't that be detrimental to downforce?

This is not the same as routing high velocity hot exhausts through the wing assembly.

[Jezztor]

Originally posted by Tech_Nut
Hmmm. Think I'll go with jezz and mrc (and myself! )

Inside a "closed container" a higher temperature means more pressure as per Charles Law etc...

But the underside of a wing in open air is about as un-closed as you can get. The local air pressure around a heated flat surface would be less than ambient as the hotter air molecules become more agitated and therefore less dense. The local pressure would go down. But, in the context of the diag' in my previous post, I'm not sure if this slight reduction would be useful (or even measureable).

Exactly. My definition of a 'closed container' is where the air is trapped - no mechanical flow whatsoever. Road surface & Diffuser surface are not enclosing items - there is still an 'opening' and a 'closing' to the area. Same with wing elements, there is an upper, a lower, but air flows through (flowing air is what I define as mechanical flow).

Tech_Nut - i do believe that if the heat was sufficient it would help, the thing is it needs to be able to heat the airflow adequately and quickly enough to be useful - higher temperature would ensure quicker 'response' to the heat. Obviously at a certain degree, the soak temperature would melt off the rear wing or provoke structural failures - but nothing a bit of testing can't determine :-)

Back to ray, in sailing, your sails act as a container, because they are 'stopping' the flowing air. Although there is an 'opening' to the area, there is no 'close', thus mechanical flow is hindered upon 'entrance'. A sail that catches air perpendicular to its flow is very close to a 'closed' container, as the 'oncoming' air acts as a 'lid' to the area.

In addition, higher temperature creates a lower density (remember that density, as MRC stated above, is not the same as pressure). In flowing air, a lower density means a lower pressure, thus more 'downforce'.

I hope this is making sense, I'm trying to use terms that one can understand...

Jezz

[DOHC]

Wait, "closed container" in this context means volume V=constant. You absolutely don't have such conditions in sailing. There is a significant mass flow past the sails. So V is not constant there. What is typically constant in sailing is temperature T. So the gas behaves like

pV = constant

On the convex side (suction) of the sail, the air travels a longer distance, implying that a small "packet" of air travelling along the flow lines "expands" so volume increases. Consequently pressure must decrease. On the concave side of the sail the conditions are reversed. Net effect: the pressure on the concave side is higher than on the convex side (you might have guessed from the concave/convex shape ;) ) and there's a net force on the sail.

[Jezztor]

Hm, absolutely true. I meant that it is more of a 'closed' container than a wing profile. I dont think that can be disputed. For enlightenment's sake, could someone explain exactly how a sailing mast & sail work, with relation to wind direction?

Jezz

[DOHC]

I hope that ray b will give it a try. But what I was referring to is sailing windwards; then the sails (of let's say an R12) work just like a wing/flap system (or wing/slat). I think what you referred to, Jezz, might have been sailing free wind. That's a bit different, and the sails then work more like a parachute, i.e., creating a resistance to free wind, and deriving a forward thrust from that (alternatively, for the parachute, decreasing free fall speed). This mode is much less sophisticated from the aerodynamic point of view. But I hope there's some sailing expert around to enlighten us.

[ray b]

end plates try to make a F-1 wing like a closed example by limiting flow from hi to low sides
and in a under car flow sure seems to me the box is made by top-car and road on the bottom.
also the unmodified air flow away from the wing limits and boxes the wings flow some, no not perfectly, or totaly , but air will react to the box effects in a limited way of the outside air.

on a boat bigger sails still work on the same laws as a F-1 cars wing with difference in pressures providing the forces. only real difference is size!!

basic sailing when going directly down wind drag is moving boat without any lift effects at all , BUT
it is much slower then a zig-zag course of say 15% off a strait-line or dead down wind course to get lift back into sails and travel a greater distance MUCH FASTER even if much more distance is covered. allso as boat has a motion and that effects the angle of the apparent wind by moving the winds angle forward to increass the lift and speeds. A fast cat can beat the winds true speeds by sailing over 15 mph in a 10 mph wind as apparent wind on deck will be the sum of boats speed plus winds speed, so it can sail faster than the wind.
And iceboats can take the speeds to 3x or4x winds speeds with their lower drag but never go dead down wind allways tack at a angle off the winds directions, so they are near a upwind sail form, even going nearly down wind very fast some go over 100mph in less than 30mph winds

[Jezztor]

Interesting post, ray b.

Yes, thats exactly what I had in mind, DOHC. Sorry about the confusion - as you can see, topic of 'boats' is out of my depth

Jez

[DOHC]

Hey Jezz, what are you, a landlubber? (Me too!;)) It's called "ships". Calling a ship a boat is like calling a car a --- cart?

[desmo]

Just to be pedantic, I thought ships were by definition three-masted square rigged sailing vessals. And do square rigged sails work on the same aerodynamic principle as a fore and aft rig?

[DOHC]

Originally posted by desmo
do square rigged sails work on the same aerodynamic principle as a fore and aft rig?

Basically yes, but square riggers are more tailored to down wind sailing (and have reached some of the highest speeds in that mode, can't recall off the top of my head, but in the vicinity of 20 knots average during 24 hours). But fore+aft rig is more flexible, and requires much less manpower.

[Jezztor]

Landlubbers ahoy! Yes I'd have to say i am - but today spoke to a guy who sails, asked him to explain stuff to me. And this weekend I've booked several books on the topic, so hopefully I'll be a bit more of a pirate in a few weeks hey, at least I'm willing to learn..! heh.

Jezz

[ray b]

Originally posted by desmo
Just to be pedantic, I thought ships were by definition three-masted square rigged sailing vessals. And do square rigged sails work on the same aerodynamic principle as a fore and aft rig?

well sort of, a square rig will not point very high at all, and most cannot tack [change directions thru the winds eye] but go down wind and back up wind in the new direction [whair ship] or jibe but hi/low pressure drives sails, the same way and are faster at a small angle off dead down wind too .also because that way they donot block sails with other sails dead air!!
they get some drive from jibs [triangle sails] in front of and between masts and can pull the yardarms allmost to a fore and aft setting but just donot work very well but can get to windward
slowly and with alot of work and time. in a storm most square sails are furled and only jibs are used to claw off a lee shore and in no wind men in boats row/tow them up wind.

a boat is a vessel that can be carried on a ship as in ship's boat!!!! both can be sail powered!!

[DOHC]

Originally posted by desmo
the thermodynamic alchemist

Desmo, I'd like to get your permission to use this brilliant formulation of yours ad lib when I lecture at my university. I don't teach thermodynamics per se, but it does enter in some of my advanced math modelling classes.

It's funny, sometimes, how some people think they can beat thermodynamics. And there's a number of surprising and simple examples that people hardly believe in spite of having spent years at the university. Here's one of my favorites that I'd like to share with you, for the fun of it and for education too.

A body of mass m moves to the right with velocity v. It has a "weightless" string with a hook attached. At time t=0 the hook catches another, similar, body of mass m, and after that the two connected bodies move with

1) velocity v/2

2) velocity v/sqrt(2)

Take your choice! The first alternative is based on the principle of conservation of momentum (which before t=0 equals m*v), the second on the principle of conservation of energy (which before t=0 equals m*v^2/2).

Just think of this for the fun of it. Try to work out exactly why and find a decent motivation. People do get it right after a while of thought, but they are often surprised. Some have a hard time accepting the answer, even though it's their own answer. And after this they are usually not "thermodynamic alchemists" anymore.

[desmo]

By all means DOHC feel free. As for your conundrum, I am stumped (in my defense, my father was a physics professor. ) The second alternative sounds more probable but it's just a gut feeling.

[Wolf]

Tech Nut, though idea seems tempting, how would You insulate the upper side of the wing ? Heat dissipation would otherwise make the temperature of the both upper and lower surface equal and would heat both sides of the airflow, presumably resulting in marginal increse of the downforce (convection of the heyat to the underside of the wing would be increased because of lower Reynolds number on the underside of the wing)... I stll think that making a small winglets above exhausts would increase engine performance (reducing exhaust pressure, and hence creating reduced 'environment' pressure) would outweigh possible advantages of increased downforce.

[testarosa]

I'd like to put in one vote for (1). Kinetic Energy isn't conserved in collisions.

[DOHC]

Testarosa, that's right. Here momentum is conserved, not energy, so alternative 1) is correct. Alternative 2) can't be correct, because if the velocity afterwards was v/sqsrt(2), then the momentum would be 2*m*v/sqrt(2) = m*v*srqt(2), which is greater than the original momentum, m*v.

But here's the hard part: as the velovity afterwards is v/2, the energy is total mass * velocity^2 / 2, or 2*m*v^2/8 = m*v^2/4. This is only half of the original energy! Where did the other half go?

[Jezztor]

Ah, yes. Interesting... I was on the right track, but never really got around to double-checking with useful text book info...

Kinetic energy is conserved in collisions, but only elastic ones. Obviously this is not elastic - that was my line of thought too.

Just a flyer, could that other half "lost" be matter energy/

Jezz

[DOHC]

The lost half is just lost, typically to heat. What the example shows is that there is no way you could catch that other mass and pull it along without losing half of the original energy. What's worse, you cannot recover this lost energy in terms of kinetic energy, because then you would violate the conservation of momentum principle.

This is rather disturbing -- there is always an energy loss at least that big. It's sort of akin to the fact that a thermodynamic machine (like an ICE) cannot have 100% efficiency. There must always be an energy loss, and that energy is irrevocably lost. This is where desmo's "thermodynamic alchemy" comes in -- you often see or hear about people who believe that they have a new smart principle to extract just a little bit more...

Of course, real engines usually don't reach the theoretical max efficiency, so then you might be able to squeeze out a wee bit more, by improving the engine. But in the end, there is, on theoretical grounds, an energy loss that one just can't get around. And that energy loss is often surprisingly big.

There's also en electrical analogue of that example, with two capacitors, one with an initial charge Q and the other with zero initial charge. At t=0 you connect them in parallel, and in doing so you must necessarily lose half the energy.

Physics is sometimes quite irritating!

[Wolf]

Speaking of ships and boats, one must observe that with bermuda rigged vessels one utilizes the jib (or genoa) to increas sail efficiency (and, IIRC, some spinnakers can be used to that effect- reacher, I belive)... By trimming the sails properly, one gets the airflow between sails to accelerate along the leeward side of the mainsail by narrowing the 'channel' between sails. And what Ray b said about exceeding true windspeed is correct only for non-displacement ships on a broad reach, sorry I'm just being pedantic about it...

[RDV]

read Feynman, desmo, he had a very good " out of the box" but spotting the relevant physics view of things, i`ll plump for alt 1 as if 2 total momentum after "hook " would be bigger


link= http://www.scs-intl.com/online/

[RDV]

...ah , see that I was only looking at page one of thread and adequately answered on page two, easier way to live in the real thermodynamic world is to postulate " there is no free lunch " every time you have a too bright idea , and try to find the flaws in it ... I know it contravenes Godel but very good at restoring sanity....

[12.9:1]

Earlier in this thred, one of the discussions dealt with the amount of thrust (if any) from the exhaust of reciprocating and turbine engines.

While doing research on some other stuff, I came upon an article in the Smithsonian magazine
Air & Space (dec 1997-Jan 1998) "Monster Engines" - regarding reciprocating engines under
development in the mid 40s - all stillborn, wen the jet engine became the only game.

In a typical reciprocating engine, a significant amount of energy escapes through the exhaust, and in some cases, the exhaust even produces a modest amount of thrust. The propulsion effect resulting from the hot gas blasting out the stub exhaust ports on an engine such as a Merlin, for example, could typically add 10 percent to the thrust of the engine-propeller combination. The Crecy derived a full third of it's thrust from it's memorably explosive exhaust.

The Crecy enjoys a mystique among aircraft aficionados, partly because the engine--a 1,593-cubic-inch supercharged two-stroke-cycle V-12--was so radical. According to people who knew the Crecy well, the most distinctive feature of the engine was its sound. Being a two-stroke, the Crecy's exhaust valves opened while there was still significant pressure in the cylinder. The effect was akin to a rifle shot--or, when the engine was running at full power at 2,750 rpm, 33,000 rifle shots per minute. "The soud of it was enormous"

Rolls-Royce worked on the Crecy from 1937 to 1942

It seems to me that Ferrari has all but eliminated the tail-pipe from their exhaust system, perhaps
going for maximum velocity-- and THRUST ? ?

.

[DOHC]

Well, I doubt that there's a lot of thrust to gain in F1. Even at 18,000 rpm, a 3-liter engine breathes at most 450 liters of air per second. That's a lot actually, but as standard sea level 15 C air has a density of about 1.23 kg/m^3, the mass flow is about 0.5 kg/s. Neglecting the mass of the fuel, the exhaust weight produced is also 0.5 kg/s. Now, if you can send the exhausts rearwards at a speed of 100 m/s (that's a lot but in the ballpark of exhaust gas transport in the headers), you still don't produce more thrust from the gas than 0.5 kg/s * 100 m/s = 50 N.

If the car is at a standstill on the grid, and you're not in gear, release the brakes and step on the gas pedal, the car just won't move...

Well, in theory, if we can neglect friction ;) , then those 50 N thrust will produce an acceleration of almost 0.01 g.