26 replies to this topic

[Wuzak]

Hi guys.

I wanted to discuss Franklin's creation last time he was about, but couldn't because, well, he was banned...

Anyway, here it is (as posted in the other thread).

http://people.tribe....a/photos?page=1

From memory the engine and prop come from an air racing category, for convenience. The engine is a VW variant - 1300cc?

The prop is a two blade fixed pitch type.

As I have never designed a racing vehicle in my life, I would like Franklin to explain some of the reasoning behind his design.

For instance, in a low power thrust driven vehicle I would think that rolling resistance is crucial to the performance. The front wheels don't look to be the best option in that regard, from my perspective. But other design considerations may have been at play - such as the need to run on the salt flats.

The next question is the prop. Obviously a fixed pitch prop is designed for a certain speed range, but Franklin intends to (has?) use the Propster in 1/4 mile runs as well as for top speed runs. Have you a selection of different props to use for different requirements?

Also regarding the prop, a significant proportion of the propellor's arc is shrouded by the bodywork. This would seem to be less than desirable. Can this be improved significantly?

Franklin, do you have the specs for the Propster - weight, power, length, wheelbase, track, etc?

The photos seem to b eteh same as from a couple of years ago. Have you made any improvements since then, or are you planning/designing/building a new model?



What other prop driven cars have there been over the years? Any other LSR type cars?

[Franklin Ratliff]

Originally posted by Wuzak
Hi guys.

I wanted to discuss Franklin's creation last time he was about, but couldn't because, well, he was banned...

Anyway, here it is (as posted in the other thread).

http://people.tribe....a/photos?page=1

From memory the engine and prop come from an air racing category, for convenience. The engine is a VW variant - 1300cc?

The prop is a two blade fixed pitch type.

As I have never designed a racing vehicle in my life, I would like Franklin to explain some of the reasoning behind his design.

For instance, in a low power thrust driven vehicle I would think that rolling resistance is crucial to the performance. The front wheels don't look to be the best option in that regard, from my perspective. But other design considerations may have been at play - such as the need to run on the salt flats.

The next question is the prop. Obviously a fixed pitch prop is designed for a certain speed range, but Franklin intends to (has?) use the Propster in 1/4 mile runs as well as for top speed runs. Have you a selection of different props to use for different requirements?

Also regarding the prop, a significant proportion of the propellor's arc is shrouded by the bodywork. This would seem to be less than desirable. Can this be improved significantly?

Franklin, do you have the specs for the Propster - weight, power, length, wheelbase, track, etc?

The photos seem to b eteh same as from a couple of years ago. Have you made any improvements since then, or are you planning/designing/building a new model?



What other prop driven cars have there been over the years? Any other LSR type cars?

Thrust driven cars where the thrust vector isn't through the center of gravity are a good way of committing suicide.

[Powersteer]

This is the fastest 40 mile an hour vehicle ever made.

[Wuzak]

Originally posted by Franklin Ratliff


Thrust driven cars where the thrust vector isn't through the center of gravity are a good way of committing suicide.

And? Why is that Franklin?

Are we to assume then that the Propster's line of thrust is through the centre of gravity?

[Powersteer]

http://images.tribe....ad-5683a171f53c Apparently he knew about tyre load and the anti-ankermann geometry before formula one ever did.

[Franklin Ratliff]

Originally posted by Wuzak


And? Why is that Franklin?

Are we to assume then that the Propster's line of thrust is through the centre of gravity?

The fact the prop is BEHIND the car NOT above it was your first clue.

[Wuzak]

Originally posted by Franklin Ratliff


The fact the prop is BEHIND the car NOT above it was your first clue.

That the thrust is through the CoG?

Still haven't explained why that is desirible in such a car......or what it had to do with anything I said in the first post.


btw, have you got any photos of the engine/prop assembly prior to installation in the car?

[Wuzak]

These things http://www.answers.c...ic/air-boat-jpg woudl appear to have a thrust line which does not go through the CoG.

[Franklin Ratliff]

Originally posted by Wuzak


That the thrust is through the CoG?

Still haven't explained why that is desirible in such a car......or what it had to do with anything I said in the first post.


btw, have you got any photos of the engine/prop assembly prior to installation in the car?

A thrust vector not through the center of gravity steers the car.

That's why on a wheel-driven car when one wheel develops more thrust than the other the car starts yawing.

[Franklin Ratliff]

Originally posted by Wuzak
These things http://www.answers.c...ic/air-boat-jpg woudl appear to have a thrust line which does not go through the CoG.

The major masses in an airboat are the engine and passengers. Notice where they are in relation to the center of the propeller.

[Wuzak]

Originally posted by Franklin Ratliff


The major masses in an airboat are the engine and passengers. Notice where they are in relation to the center of the propeller.

One picture has the driver in front of the prop and the passengers sitting down in the boat...

Imagine a small skinny person steering the boat and two fat tourists for passengers. Where is the CoG then?

[Wuzak]

Originally posted by Franklin Ratliff


A thrust vector not through the center of gravity steers the car.

That's why on a wheel-driven car when one wheel develops more thrust than the other the car starts yawing.

Well that is obvious if the thrust is to one side. But that does not explain why it isn't desirible to have the thrust vector above or below the CoG.

[Franklin Ratliff]

Originally posted by Wuzak


Well that is obvious if the thrust is to one side. But that does not explain why it isn't desirible to have the thrust vector above or below the CoG.

On boats the thrust vector is below the c.g.

Know how to spell B L O W O V E R?

[Wuzak]

Originally posted by Franklin Ratliff


On boats the thrust vector is below the c.g.

Know how to spell B L O W O V E R?

Below or on the CoG?



I can see that you can spell blowover. Bravo!

[Wuzak]

It would be helpful if you would expand your answers to include explanations...

Anyway, I'm sorry I used the airboats as an example of where the thrust line is in comparison to the CoG.

Looking at the Propster it would be my guess that the CoG is lower than the thrust line. But appearences can be deceptive.

Did you do calculations to determine if this was the case?

[Franklin Ratliff]

Originally posted by Wuzak


Below or on the CoG?



I can see that you can spell blowover. Bravo!

If you think it's on the c.g. your grasp of physics is insufficient for any further discussions in this thread.

[Wuzak]

Originally posted by Franklin Ratliff


If you think it's on the c.g. your grasp of physics is insufficient for any further discussions in this thread.

I'm not sure that I said that the thrust line is on the CoG. In fact I think I was suggesting the opposite a couple of posts ago. If anything I was confused as to what you were driving at.....


btw my grasp of physics is just fine, thankyou.

Your response sounds like an arrogant way of closing the discussion without having to explain yourself.

[Franklin Ratliff]

Originally posted by Wuzak



I'm not sure that I said that the thrust line is on the CoG. In fact I think I was suggesting the opposite a couple of posts ago. If anything I was confused as to what you were driving at.....


btw my grasp of physics is just fine, thankyou.

Your response sounds like an arrogant way of closing the discussion without having to explain yourself.

I've explained what happens when thrust vectors are BESIDE, ABOVE, BELOW and THROUGH the c.g.

[Wuzak]

Originally posted by Franklin Ratliff


I've explained what happens when thrust vectors are BESIDE, ABOVE, BELOW and THROUGH the c.g.

You have?

[Stoatspeed]

Originally posted by Franklin Ratliff


On boats the thrust vector is below the c.g.

Know how to spell B L O W O V E R?

This is yet another assinine Franklin rant ... to obtain stable forward motion, thrust vector has to act in opposition to the net drag vector .... on a boat this dominated by the hydrodynamic drag on the hull, (and of course varies with water speed, hence the need for adjustable tilt on the prop. ) so it is below the CG of the boat.
"B L O W O V E R" is an aerodynamic phenomenon, when the hull acts like a kite ....

Stop feeding the troll, or we'll have a re run of the Indy Car/Supermodified thread ... up to 299 pointless posts and counting ... :yawn:

[Franklin Ratliff]

Originally posted by Stoatspeed


This is yet another assinine Franklin rant ... to obtain stable forward motion, thrust vector has to act in opposition to the net drag vector .... on a boat this dominated by the hydrodynamic drag on the hull, (and of course varies with water speed, hence the need for adjustable tilt on the prop. ) so it is below the CG of the boat.
"B L O W O V E R" is an aerodynamic phenomenon, when the hull acts like a kite ....

Stop feeding the troll, or we'll have a re run of the Indy Car/Supermodified thread ... up to 299 pointless posts and counting ... :yawn:

Once a boat is on plane performance is dominated by AEROdynamic drag.

Dynamic stability is obtained by putting the CENTER OF PRESSURE behind the CENTER OF GRAVITY. This is why adding a skeg or enlarging the rudder increases dynamic stability.

Blowovers occur when a critical angle of attack is reached because the CENTER OF LIFT is FORWARD of the CENTER OF GRAVITY and are accelerated by the thrust vector acting BELOW the center of gravity. Making the rudder DEEPER produces a nose down moment that augments PITCH STABILITY.

[AdamLarnachJr]

One might say that the center of gravity would be displaced once the thrust creating device is added, further complicating this Frankorvian Theory of thrust vector movement.

You also might say that since you'd be chasing tail for the rest of your life figuring this out, you might just think and say... what the hell am I doing?

[Wuzak]

Starting again......

Franklin, all I want is for you to discuss your Propster.

What your aims were/are, progress of the project, developments, etc.

And I would like to ask some simple questions...

Have you weighed the vehicle? If so, how much does it weigh?

How much HP does the engine have?

What is the construction of the car?

[Franklin Ratliff]

Originally posted by Wuzak
Starting again......

Franklin, all I want is for you to discuss your Propster.

What your aims were/are, progress of the project, developments, etc.

And I would like to ask some simple questions...

Have you weighed the vehicle? If so, how much does it weigh?

How much HP does the engine have?

What is the construction of the car?

The car weighs about 800 lbs empty.

Construction is monocoque created by embedding a chromemoly tubing spaceframe inside a foamcore sandwich composite.

Engine horsepower is unknown but figures of around 65 horsepower are often quoted for 1,800 cc normally aspirated VW Bug motors with an induction system such as a Weber two barrel.

[Powersteer]

What about design direction, why is it designed the way you wanted it? Why do you have a beetle engine? Are you aiming for a speed catergory? What is going to happen to the Propster? Is it just a testbed for more to come?

[Wuzak]

Originally posted by Franklin Ratliff
Construction is monocoque created by embedding a chromemoly tubing spaceframe inside a foamcore sandwich composite.

Did you feel you needed the extra strength by doing this, or do you think the spaceframe could be sufficient for the purpose?

Originally posted by Franklin Ratliff
Engine horsepower is unknown but figures of around 65 horsepower are often quoted for 1,800 cc normally aspirated VW Bug motors with an induction system such as a Weber two barrel.

Any plans for tuning the engine?

[Franklin Ratliff]

Originally posted by Wuzak


Did you feel you needed the extra strength by doing this, or do you think the spaceframe could be sufficient for the purpose?




Any plans for tuning the engine?

Extra strength.