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Mar 24, 2015, 01:06 AM
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Curtiss-Wright model 2500 air car


so i have wanted to build a model of the air car for the longest time. the one in these pictures is just the small test build to get an idea of a few possible problems.
mostly, how much are counter rotating props needed, what effects balance and rpm have, and what surfaces work.
so far its very clear that counter rotating props are needed, as small changes in rpm do make the model turn as well as bank fore/aft. also balance is fairly crucial as a small shift of the battery also makes the model slide left/right.

i have not played with the vent controls yet as this version only has a differential thrust receiver, thats what my next model will feature

so any information on previous models (if there are any) is much appreciated. also thoughts on the next version are most welcome
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Mar 24, 2015, 01:48 AM
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pictures of the controls i have in mind. white arrows are open vent flows, red is the resulting directions.
the next model will be larger by quite a bit so i can carry normal micro servos and brushless motors. controls should be simple, throttle for lift fans, an aileron rudder mix, and elevator for forward and reverse.
i have a good supply of depron in 2,3 & 6mm and various other materials for construction. initially it will not be pretty (oh wait neither was the real one haha) but function is the aim.
I'm not sure if i will need an internal deck to force air around the perimeter or not, the little one does good without one. maybe i should add one and see what difference it has.
Mar 26, 2015, 03:26 PM
Registered User
Interesting project alright

I built up a skirtless hovercraft that is sort of similar to what you're doing. Originally I had tall sidewalls the same as you but I found it was too unstable in hover. I ended up making a perimeter wall from hardwood beams, they are very hard wearing and provide a lot of strength/rigidity to the model. It hovers infinitely better with those than than tall, thin sidewalls so you might think about trying that out if you have problems.

I used an EDF on a servo for thrust vectoring control, very effective but probably overkill. My gut says the vent controls probably aren't going to work very well for you as there isn't enough pressure under these things to make an effective 'jet' for propulsion, but you might drop the pressure enough near the vent for the model to collapse toward that side, raising up the other side and making it go the opposite way than you wanted. Try it out and prove me wrong though, I'd be keen to see if it works as I pondered the same thing.

What you found with the uneven balance leading to it moving could be exploited for propulsion. I'm picturing having the battery on a sliding mount controlled by servos, when the battery is centered it hovers evenly and doesn't move, if you want to go forward shift the battery forward etc. Quite neat as it could give you full forward/back/left/right control without any further props needed. Yaw might be a problem though.
Mar 26, 2015, 06:47 PM
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i have made a number of small hovercraft and GE models before, one fairly similar to yours, and while those work well, thats not what i'm after.

i'm trying to build a model that looks and functions similarly to the real ground effect vehicle built in the 50s, the Curtiss-Wright model 2500 air car in the pictures


AIRCAR CURTIS WRIGHT HOVERCRAFT 1960.mpg (3 min 52 sec)

its more of a semi-scale model than best performance kind
Last edited by derk; Mar 26, 2015 at 06:52 PM.
Mar 29, 2015, 10:55 PM
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starting on the larger model, i built the first centrifugal fan. 5" diameter and .78" blade height, 8 blades total. the blades are segments of wood helicopter blades, not ideal i know, but somewhere between flat and airfoiled seemed okay.
I'm also not sure if the motors i have will be able to run them, another test i need to do. it will be easy to mount to a larger motor so long as it has a 3mm shaft.

I've got some work done on the opposite fan as well but won't proceed without running the first one (its already balanced via prop balancer)

with this size fans, the model will be around 18-20 inches long.
Mar 30, 2015, 08:54 PM
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so here is the first test runs of the fan on a larger motor:
5" centrifugal fan test runs (0 min 36 sec)

i wanted to mount the motor under the fan, but because of heat buildup, it will need to be in the fan. this means i will have to come up with a inverted motor mount that is fairly inconspicuous.

it feels like its moving quite a bit of air, even picked up on the video
Mar 31, 2015, 01:20 PM
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Nice fan, got a housing yet?

I'm going to try this setup in a skirted EDF craft soon, it's a delta server rack blower.

Model: BFB1012EH-AF00

Size: 97*94*33mm

Voltage: DC 12V

Voltage range: 7.0-12.6V

Current: 2.94A

Power: 35.28W

Speed: 5300RPM

Volume: 46CFM

Wind pressure: 2.814 InchH2O

Noise: 64d-BA

I'm using a Turnigy rx controlled switch to toggle it from a switch on my tx.

Pretty soon this is going in a small hovercraft as the lift fan, the thrust fan is going to be a 64mm 8 blade edf with 10% reduction nozzle on 3s.
Mar 31, 2015, 02:17 PM
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actually the fans on this will not have much of a housing, the body will have a stator around the fans and an opening in the top. otherwise they are open under the hood.
Mar 31, 2015, 09:03 PM
Registered User
Hope you get it working, do you have any particular method of stabilising the craft as I've found it difficult to achieve any useful amount of lift without a skirt without some type of stabilising arrangement.
Mar 31, 2015, 11:39 PM
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i dont have any ideas about stability yet, because i'm not sure how everything is going to work/react together. it may list whenever a vane is open, or it may not bleed enough pressure to do that, but at this point i can't say for sure.

something i am considering if i can't get it to stop bouncing and going in any direction, is an inner half-skirt, material only attached to the inner plate. it might be cut into little strips so they flow over the ground without catching.. its still not a finished idea though
Apr 01, 2015, 12:50 AM
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I ordered a cc3d module yesterday, I'm going to try using it to control my weight shift pilot. I've got a craft on the bench that has an animatronic pilot with 3dof, forward and back, side to side weight shift and one more yaw axis that doesn't affect the weight transfer.

I'll share what I learn about stabilizing a hovercraft, and any code I write/hack for it.

Cool project though, I might have to try one myself at some point.
Apr 01, 2015, 02:38 AM
Registered User
Ive tried using weight shift and found it effective for steering but not for stability as the response is too slow. Maybe on a large model it could work better. I like the moving pilot idea if its heavy enough. There was a guy on the forum last year had a really good model with a moving pilot, you should check it out.
Apr 01, 2015, 10:29 AM
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My pilot has a 3s 2200 pack for a spine, so there's plenty of weight.

Here's a look at mine.

Hovercraft pilot figure with jacket first test (0 min 7 sec)


Hopefully I'll get time to finish up a few details like wiring and counting the skirt properly today.


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