Developing new type of VTOL Flying Car

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William Walker

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Oct 11, 2021
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Hi all, my name is William Walker,
I am developing a new type of VTOL flying car. I have just built a full scale unmanned prototype and we have begun to test it. It weighs 150 lbs + batteries, which is about 20% more than we expected. I originally designed the vehicle to have a thrust to weight ratio of 2. The vehicle uses four 10kW motors with 32in x 6.5 in props which generate 64 lbs thrust each, 2 in the front and 2 in the back that are mounted coaxially thrusting through a hole in the wing. We expected 80 lbs thrust out of each motor, so it is 20% less than we expected. Here is a link to see pictures of the vehicle. The cockpit is not mounted yet:

Full Scale Vehicle Final Contruction - Google Drive

I have built a 1/6 scale vehicle that flies very well:
https://drive.google.com/file/d/1q6iPsVydYqC_2YI6IAgRftKsNPcW9C_0/view?usp=sharing

Here is a link to see a flight simulation of the vehicle flying:
https://drive.google.com/file/d/1AAvC3BLvut7xjlhY81S9EqD8OW0Qw-kS/view?usp=sharing

The vehicle can lift the front end with 2 batteries in the vehicle. Unfortunately the motors can not lift the back end, unless we manually lift the back end first. We think this is because, when on the ground, the 6 ft x 2 ft opening in the back under the wing is not big enough to vent the thrust and the pressure is building up. Because one of the props is mounted in the hole, we think the pressure is causing this motor to fail, which then affects the top motor, which is mounted on top of the hole. Pictures attached.

When we place 24 cm high crates under each wheel, motors are able to lift the back end by them selves. We could just cut the bottom of the vehicles side panels so they allow the thrust to vent better. But this is not a solution, since the situation will get worse when we build the manned vehicle, which will be heavier and will require even more thrust. Instead I think that the prop motors need to be placed on top of the hole, so that the motors develop their full thrust before it is directed into the hole. This is how the 1/6 scale model is configured and it works very well. The pressure under the wing from the thrust will then just help lift the vehicle.

I did a simple test with a small hand held coaxial motor setup attached to a stick. As I lowered the prop motor setup into a hole in a box without a bottom (placed on a table top), I noticed the setup getting lighter as it approached the hole and getting heavier when the bottom motor is in the hole. When I lifted the box a little off the table, I observe the same effect but with less changes in weight. If I lifted the box completely in the air, I noticed no change in weight when I repeated the experiment. These results led me to the above mentioned conclusions.

I have been doing a lot of reading and it looks like the coaxial motor loss will be about 25%. If this is true, then this explains why the back end of the vehicle is not lifting. According to our calculations, even if we remount the motors on top of the hole this will not be enough thrust. We could connect the two motors mechanically together, but it would still not generate a enough thrust to be able to maneuver. So we have decided to order another more powerful 40KW back motor with a 3 bade prop with higher pitch 32in x 12in. It is coming from China and will be here in a month. Hopefully this will solve the problem.

What do you think? Do you agree with my thinking about the back motor situation?

Your input would be appreciated, Thank you.
 

BBerson

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The prop (or fan) needs to be inside a proper duct. Not above and not below. Doesn’t matter much where the motor is.
 

henryk

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coaxial motor setup attached to a stick.
=exellent idea,but danger=needs huge shields...


-do You know "CRFLIGHT" syctem ?

=in modyfied ,can genetate 15 kG thrust force with 1.3 m rotor and 1 kW power...

=Hiller Platform +4 (or 3) ducted fans controll system seems not so danger !
 

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jedi

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I admire your computer skills and inventiveness.

Can I assume that the dimensions of the full size are street legal. Width 8 feet or less. length 16 feet or less.?

The 32 inch diameter props are a problem. Downwash velocity will be high and thrust efficiency will be low. Paramotors with a 48 to 52 inch prop put out about 150 pounds thrust maximum. How much thrust do you need per location, front or rear? More to the point, what is the design gross weight? 150 x 3 is only 450 pounds. With a 1.5 thrust to weight ratio that allows 300 pound max gross weight. With a 200 pound pilot that makes a vehicle weight allowance of 100 pounds. I am sure you see the problem here. I would like to review your calculations to support the post #1 claims above.

20% excess weight and 20% loss of thrust is a 40% reduction of lifting ability. It will be very difficult to make up the difference with small fixes. You are not alone. This is the problem all designers face. The solution is out there we just need to find it.
 

D Hillberg

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Duct under wing... Air exiting causes "lift in the wrong direction" Air flowing under the wing static air above.

Look back in history for powered lift and VTOL machines

Why reinvent the wheel
 

rv6ejguy

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Interesting project. With 40Kw of power, what is the endurance with your present battery? Seems like you'd need roughly a 90 lb. battery for even 10 minutes of vertical flight.
 
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Vigilant1

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Due to the low specific energy of existing batteries, a practical VTOL is probably going to require very low disk loading (i.e. a lot of rotor disk area per HP). In many small internal combustion helicopters we see figures of more than 2.5 square feet per HP. In OPs design, it is about 0.4 sq ft per HP. That's going to produce quite a difference in efficiency.
 
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WonderousMountain

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My assessment is aft duct is not pragmatically sized.
Looks great, doesn't lift that well. Fix it before buying
anything unnecissary.
 

Lendo

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I saw a model aircraft some years ago, it wasn't VTOL but a very stable platform.
George
 
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