Our design team wants to add 2-3 duct fans or plain propeller engines to our R/C car. Why you ask? Well we are in a pushing contest where size and weight are limited. In order to produce more force horizontally and vertically we want to use airplane engines.

My question for this board is...how much "thrust/force" will a airplane engine produce? Is a ducted fan better than just a propeller? Thoughts or concerns? Thanks for your help!!

For low speeds props are much better.

I think designing a gearbox to acheive a very high gear ratio would be much better.

FYI- A .46 size engine with the right prop will only yield about 7 pounds of thrust max.

It would be reasonable to do both, if the rules allow for it. Have an engine running an insanely high gear ratio and have an airplane engine with prop pushing down on top of it to give you better traction.

Thanks for the quick info. I never thought we could get 7lbs of thrust out of an airplane motor.

Is there a somewhat easy way to calculate the thrust produced? I'm guessing that its a factor of RPM and prop pitch? Can anyone help here?

Let me further add, we must stay with electric motors. Thanks again for all your help!

Look for Motocalc on the web.
This program predicts performance of electric motor combinations, but if you adjust the parameters to get the correct prop rpm/ motor power output it can be used to predict how much trust a certain prop will produce at a certain rpm...

...put a Wright R-2800 engine on the car...you will win the contest...

Wow! That motocalc program is amazing. I'm not sure I got any valid data out of it, but it will calculate anything!

The problem I'm running into now is if I get a 13" prop I can't find an electric motor big enough to turn the prop at say 10k RPM. Says I need around 1HP. Biggest electrics I've found are like .4HP. There needs to be a website that puts motors with props and gives you all the info you need Oh well,

One other quick question, When I changed the pitch of the prop it didn't seem to affect my static thrust at all? Does this mean I should get the smallest pitch possible?

Take a close look at the brushless motors...there are motors that can be pushed to like 2 HP or even more...
You can also use the option "multiple motors on a gearbox" if I'm not mistaken.

For example: I used the program to predict static thrust of a APC 16-8 prop doing 9000 rpm...no problem.

The thing you are trying to do requires a large, low-pitch prop. To much pitch will result in a stalled prop in a static situation like yours.

Ever thought of putting an E-motor on those cars? If you take a high power brushless, with a very large gear spinning a big prop, you can generate a lot of thrust.
That's the big advantage of electric motors: they can be geared to suitable rpm's.

I've been looking at hobbylobby.com and can't find a 1HP brushless motor let alone a 2HP. They are all like 300W and that is with a gearbox. I think we can accomidate a 12" prop, so we should be able to get enough thrust if we can find a big enough motor. Maybe even two of them.

Is a battery capable of pulling 40 AMPS continuously? That seems like a crapload of current

Can you double the voltage on these motors? If we could do that we could double the RPMs and the Power. I have a feeling they would get to hot, pull way to much current and ruin everything

The gearbox you would reccommend be like 3:1? or even bigger than that.

I'm 100% sure there are motors that will put out at least 1500 watts... Take a look at the Hacker motors, for example the B 50 L series.
The gearbox you should use depends on the motor. There are high and low revving electric motors. A high revving motor should be geared down to something like 1:6.
Sanyo RC2400 cells can take 40 amps easily. Even 60 shouldn't be a problem, at least, if you're not drawing that much current for like 3 minutes continuesly. Take a look on the web what the electric pylon fliers put their cells through...

I found this electric conversion of a Great Planes 46 size Giles using the MaxCim motor system. 35 - 60 amps, a 16 inch prop, and cliamed 8+ lbs of static thrust. Sounds like this could come close to what you are looking for. Also sounds EXPENSIVE!!!!

http://www.greatplanes.com/reviews/g...rcm.html#power

There are r/c or model pulling contests out there, it might help to be a little more specific on what you are going to do and what kind of push is needed, pulling weight can be up to 500 lbs on carpet using foam tires, less on dirt or concrete. What electric motor you need will depend on the number of cells you can use, the amount of speed required if any at all, not to mention the surface used.

A cheap way some found to build pullers is using the motor and gear box out of the little electric go carts kids ride in, very low ratio and quite strong. Ratios for pullers can get as high as 500-1 or more. some electric motors can turn as high as 50,000 rpm . the simple stock motors will turn up to 30,000 with no load on just 7.2 volts.

If it has to be a prop or air power I would speculate the prop is going to be better for static thrust, fans usually need the intake airflow to reach their full potential, which is why they don't always take off so well but fly fine once up to speed.

Doubling the current quadruples the power (P=I x E).
To double the current with an identical load, you must double the voltage. When voltage and current have doubled, power quadruples.

Joe Myers

If you've got the room for power...try this...

Torcman brushless motors

Look for the TM 685 MONSTER.... capable of putting out up to 3500 watts, between 4000 and 8000 rpm direct drive... Swings props up to 26 inch...

Whatever you do, don't look at the price tag....lol

nah! Put a glow engine with some punch on! Use ThrustHp to calculate static thrust.

What size is this car you're working on?

Are you wanting horizontal thrust, down thrust (for traction) or both?

FYI: Chevron (race cars, not the oil company) got outlawed from Can-Am racing in the early 70's for having a car that was BB Chevy powered (510cid) and had like a 4 or 5 foot fan in the center of the car mounted flat to pull air up from the track. Working with hard rubber seals around the outside lower body work it was most effective. They were known as the vacuum cleaner cars. They dominated 'till they got outlawed for throwing debris straight up off the track. That was the official reason anyway .

I don't know if this type design might help or not. I hope it at least amused someone. I am the king of useless information! Just ask my wife...

On your standard size RC car there will be not enough area to create a lot of down force....plus sealing will be a problem in model sized cars...

F1 cars used the system also years ago...except that they didn't use a fan, but a particular shaped duct under the rear of the car to extract air...

It was outlawed in F1 because the rubber sealing strips under the car tended to come loose during the race, flying all over the place and thus presenting a danger to other pilots...

The Le Mans type cars are using those air ducting undertrays now.

I was at a Can-Am / Trans-Am joint race in Riverside Ca. Way back when. Somebody had an "off" and spread gravel and sand all over the track. The "Hoovermobiles" threw this stuff straight up! The dust cloud went up around 30 feet! I can only guess how high the gravel went...

BTW, Mark Donahue won the Trans Am part of it in a Rambler (AMX), followed by Roger Penske's Sunoco Camaro. A non "Hoover" Can-Am car won. They all died of suction fan failure.

F1 cars can create over 1300 pounds of down force when at speed, with just a spoiler front and back...

The advantage of the fan would be constant down force at all speeds...but I tend to think spoilers are more economic on power consumption...

That fan solution sounds like a typical seventies thing...

Back in those days you could see some pretty strange contraptions running around in F1 also... how about 4 wheels at the front end of the car instead of 2...Racing can produce some pretty strange stuff...

The more the FIA outlaws things to reduce speeds, the faster these cars seem to be going....it's a never ending saga...

I remember that 4 steer car! Tyrell Elf. Jackie Stewart drove one for a while.

The fan thing in was a low/high speed thing. If you're not familiar with 'em, laid out like the Audi R-8 Le Mans car. Similar shape. Speed range at the old Mid Ohio, 50 to 200+ MPH.

I have dated myself, 70's thing. I had bellbottoms with cuffs and 4 inch shoes too. It's a miracle I survived.... :stupid:

I got over 8 lbs. static thrust from my TT Pro .46 measured with an electronic fish scale. I think the prop was an APC 11x6.

Interesting thread.

I wonder if you can do better on an APC 12.25x3.75 or a 12x4. That's what the fun fliers are using.

What might help to concentrate and increase static thrust would be a duct around the propeller. It would also help with safety, keeping wandering fingers out of the prop.

Sure, a duct would help.

But don't put the duct to close to the blades, and don't go putting too much of a wire screen front and back of the prop...

A 12/4 or a 12.25/3.75 prop will provide a lot more thrust compared to an 11/6...

I had a friend who put a 40 sized aircraft engine on an old RC10 chassis long ago and it was the fastest thing I'd ever seen in RC. He mounted the engine on a homemade pod and used a three bladed prop for clearance. He could only run it in large mall parking lots because of the speed involved. I'd bet the farm that he was pushing 120 or better flat out. I don't remember the pitch he was using. The car died quickly when he made too sharp a turn one day.

OK and airplane engine on an R/C car. But how about the other way around?

I plan to use a OFNA Force engine .21 (rated at 22,000 RPMs, 2.1 HPs) to use it in a Ducted Fan 3.5 inch diameter. So far manufacturers agree that the specs of the engine will do. But how about the way it is built & the purpose it will serve.

For example:
I think that most of the stress in an airplane engine is made pulling the shaft out of the engine, thus forcing the inner bearing (axial movement), but on a car engine the stress is made perpendicular to the shaft of the engine.

Will my plane loose the engine in the sky? I don't want to risk it...

2.1 hp from a .21 engine at 22000 rpm...? Maybe at 32000 rpm...

But anyway, the pulling force from the tiny prop you are going to use is not going to hurt your engine in any way...
Ball bearings are pretty strong...