Wing in ground effect racer.

[PazHeping]

TL;DR Summary

Working on a very small electric aircraft that will fly mostly in ground effect regime.

Hi All,

I am working on a wing in ground effect racer. I’m a glider pilot with an engineering background. I want to create a very small very simple craft that will operate in the ground effect regime. Think pod racer from the Star Wars prequels. Most simply it’s a single wing in back that will be tailored for WIG and twin shrouded props in tractor configuration in front that will also counteract the main wings pitching moment.

When I talk about the scale of the craft I like to say it’s like a BMX with surfboard sized wings. I have included a drawing that shows a rough plan form and scale and also shows how the pilot will ride in a semi shrouded open cockpit. Like riding on a motorcycle with a fairing and small windshield.

The goal here is to create something super simple and dynamic for short WIG races. Like 2 minutes flight time. I want lots of folks to be involved. And have a craft that teams can put together for less than 1000 USD. The entire design will be open source so people can modify it. And maybe become part of an advanced STEM course. The flight control software is currently running on an arduino nano with a 6050 IMU and will be part of the hackable open source system that I hope folks will want to get into.

There are still lots of things to think about but if you check the picts below you can see I have started building the wings. These wings are to scale but the final wing will be a much simpler molded foam core with fiberglass skin. One thing that is on my mind is the power. The engines will control yaw with differential thrust but I want the safest and most efficient system. I have been looking at large RC electric motors and EDF units. The EDF units appeal to me because I think they might be safer, as far as mitigating prop strikes. I would need 4 or 5, 90mm EDFs clustered on each side for about 60 lbs thrust which would hypothetically be a thrust to weight of about .25 which is small but I think it would be enough in ground effect. Another option would be something like a Rotomax 100cc electric motor that puts out about 7000 watts.

Anyhow, any thoughts? I’ve been thinking about this for quite a few years and am at a good point in my life to do it. So here we go.

thanks in advance,
Paz

 

[Rive]

Anyhow, any thoughts?

Ambitious.

I think some model studies would help you a lot.
Also, I don't think that the real one will be really enjoyable with electric drive. It is OK for small scale models, but a manned one... I would try to look around for suitable ICE engines.

 

[berkeman]

Fun project. What is your projected speed and height of the wings above the ground? Given enough room for your legs and for banking turns, will you really be in the Ground Effect? Unless you are going at airplane type speeds, it seems like your wings will be out of the Ground Effect.

https://www.researchgate.net/profile/Tomasz_Abramowski/publication/228651914/figure/fig10/AS:668618429845514@1536422464598/A-WIG-craft-recently-introduced-to-operation-by-Pacific-Seaflight-on-Alaska.png

 

[PazHeping]

Yes, I have a model...as mentioned before I’m running an arduino with a 6050 IMU. It’s working as a servo controller right now for flaperon stability only and is a baseline for establishing level flight. Currently the model is non flying but it is stand alone and fairly robust. It is based on a quad copter stability system from Brokker.net.

When I became interested in this idea years ago I began reading about sparrow hawk. Sparrow Hawk was an entire redesign of a single seat glider using all carbon composite. One thing they spoke of is the efficiency spiral. Their take on it was this; you make some thing lighter and then all the sudden you can fly on smaller more efficient wings. Which makes your craft smaller again and you can recursively shorten those wings again. I’ve spent quite a long time studying this and there is no way ICE power gives me that win. Then there is also the differential steering issue, ICE power has to ‘spin up’ although piston is faster that a turbine ICE is way to slow for differential thrusting for yaw stability. Also I’m looking for simplicity that electric power provides.

I am certain there is suitable electric power available. Just look at the slew of electric plane startups out there. Also I have had several discussions with Bob at Astroflight. He built the electric motor for a few record setting electric aircraft. He can make anything! Amazing guy and company.

But yes, that’s my question. Hobby king has motors that produce up to10000 watts of power. Two 10k electric motors will produce 20k watts which is 26HP. The Cri Cri, another small aircraft I have studied extensively runs on two 15HP chain saw motors. And it’s TOW is twice what I’m aiming for. So electric will work. And remember the point of this is short sprint racing. My battery packs will only last for 2, 3 minutes at rated power and then will swap out for another heat.

I’m just looking for safety issues now. I want to make this for my son and his school and as a bigger picture anyone who wants to become involved. I am trying to design something that fails as benignly as possible. A 10kw motor and 26 inch prop throws way more focused energy from a prop strike than say 4 EDFs in a cluster.

I’ve attached a photo of my working flight computer not much to look at but it works and it exists.

 

[PazHeping]

Fun project. What is your projected speed and height of the wings above the ground? Given enough room for your legs and for banking turns, will you really be in the Ground Effect? Unless you are going at airplane type speeds, it seems like your wings will be out of the Ground Effect.

https://www.researchgate.net/profile/Tomasz_Abramowski/publication/228651914/figure/fig10/AS:668618429845514@1536422464598/A-WIG-craft-recently-introduced-to-operation-by-Pacific-Seaflight-on-Alaska.png

View attachment 274892

Yes, I know this picture. While the main lifting wing is in ground effect, the horizontal stabilizer is not. In my extensive analysis, you want pitch stability in the ground effect regime as well. Some of the massive soviet Ektaplans use canard for pitch stability and it’s what’s needed for the efficiency spiral I spoke of in another reply.


Speeds I’m looking at; stall of 30 mph and not going much faster than 60mph. My all up weight of craft and rider I hope to be 250 lbs. Thats why I’m building a full scale prototype along side the models. Because I need to be able to keep this light and simple. Again a BMX with surfboard sized wings. I don’t think I risk leaving ground effect since true flight requires even more power and less drag. My wings are a high lift profile. Max CL is 1.2 with no flap. In ground effect I expect a CL of 1.8. My Cm (pitching moment) is quite high though. 0.08 so the canard propulsion is crucial to keep the nose up. Wings have a 12 foot span and a 2.5 foot cord which gives us a wing loading of about 5lbs/ft2.

edit: Forgot this bit...max altitude will be about 6 feet with sporadic moments outside of that for some ‘style flying’. The BMX with wings metaphors I hope to carry over to all aspects of this project. Not just a small cool aircraft but the flair and community of BMX as well.

 

[anorlunda]

I think you should compare your plans with The Gossamer Albatross and the Gossamer Condor. There should be many similarities, and if you get lucky, you might not need as much power as you think.

edit: and perhaps you can get by with less airspeed than 30 knots. I always always work first on reducing demand, and second on providing power.

 

[PazHeping]

I think you should compare your plans with The Gossamer Albatross and the Gossamer Condor. There should be many similarities, and if you get lucky, you might not need as much power as you think.

View attachment 274905View attachment 274906

edit: and perhaps you can get by with less airspeed than 30 knots. I always always work first on reducing demand, and second on providing power.

Thank you for this. I read the book on the gossamer albatross and condor. Fascinating aircraft. Skinned with double stick tape and Mylar. They made the spar by wrapping an aluminum tube in Carbon tape and after it cured dissolved the inner aluminum tube with swimming pool acid. Far out. I have seen the actual plane at the smithsonian.

I could reduce demand with a longer wing and might do that. But I don’t want to start getting too big. And one of the issues I want to exploit it lack of vortex induced drag from the WIG regime. So a longer wing moves me away from that ‘trick’.

I feel your right about power needs. Bob at Astro flight and I discussed this a few years ago. It’s a question of L/D for straight and level flight. My main unknowns are pilot drag in the semi enclosed tuck; for that I have been reading a lot about Moto GP aerodynamics and my other concern is safety. I’m trying to keep things light and tight and am weighing issues about choosing a prop, a shrouded prop or and EDF cluster. Again, prop strikes, safety, power considerations are all boisterous revelers at this party.

Im currently at a place were I think I will go with two 5000 watt electric motors with 24/12 props. That should be more than adequate but again... I just don’t know. I figure if I use a layer of Kevlar in my prop shrouds,,, that should mitigate the worse ballistic debris from an unplanned landing maneuver.

If you have a sec, what are you thoughts on this?:

https://hobbyking.com/en_us/dr-mad-thrust-90mm-12-blade-alloy-edf-1600kv-motor-2100w-6s.html

Its a big EDF for RC but small for human flight. I did think I could cluster them to get my thrust to where I need it. But I have zero experience with this power plant and everything I read say EDFs are not suited for slow flight paradigms. But I like the modularity of them. I would get 6 of them for my 250 lb aircraft. That’s marginal but would suit my concept well.

 

[berkeman]

that should mitigate the worse ballistic debris from an unplanned landing maneuver.

Is that what they're calling them nowadays?

 

[anorlunda]

5000 watts or even 2100 watts sounds very high to me. So does 30 knots.

How about starting with an unpowered glider going downslope over a forgiving surface. There's a good reason that the pioneers began at Kitty Hawk. When you get that design working well, then start adding weight+thrust in a propulsion system and see how close you can get to level flight.

I say that because (a) Initial safety. (b) I think of the very small power needed for those Albatross (15 knots and perhaps 150 watts). I suspect that you may be aiming too high on the power&thrust needed. It would be preferable to start low and scale up, than start too high on power&thrust&weight&airspeed and scale back. As you know from flying gliders, the heavier the aircraft the higher the airspeed and the higher the safety risk.

Have you asked around in the hang-gliding community? I wonder if anyone took a Rogalo wing hang glider and tried modifying it with power and a propeller.

I just thought of another way to estimate the power and airspeed needed. Use a winch launch. The winch power is easy to measure. You could measure the L/D ratios at different airspeeds and different vehicle weights in a series of experiments. If you did it over soft sand, and limited the altitude to 2m, it would be pretty safe. When you have the data in hand, you'll know how much power & weight you need.

It was this picture of a NASA experimental glider that reminded me about tows.

You also need to clearly state your requirements before designing. What is your goal? For your son to fly 100 m or 100 km? Max altitude in ground effect? Stalls if the pilot tries to fly higher than max? Flight only over safe ground like soft sand or water, or over more hazardous terrain? Flight only in still air, or a range of weather conditions? Straight and level or full maneuverability?

Maybe your son should learn hang gliding or parasailing or ultralight or autogyro piloting first, so that you don't begin with an experimental aircraft in the hands of a novice pilot.

Design details like motor selection should not be one of the first things in the project plan.

 

[jrmichler]

I highly recommend that you join the Experimental Aircraft Association. And make use of their forums and builder resources, especially the Technical Counselors: https://eaa.org/eaa/aircraft-building/BuilderResources. The Technical Counselors will help you build to aircraft standards, then point you to the EAA Flight Test Manual when it's ready to fly.

I say this because I have experience in this area. Me, about 1976, rebuilding the wings of a Taylorcraft BC-12D:

Jim
EAA Member #92859

 

[PazHeping]

Is that what they're calling them nowadays?

5000 watts or even 2100 watts sounds very high to me. So does 30 knots.

I agree with you 100%. One of the reasons I built my wing ribs first is to learn if I can’t build those, then I can’t build and airplane. Another super wise piece of advice I have listened to is ‘don’t buy your power plant until your fire wall is done.‘ And ,,,, ‘do you want to fly or build?’ That’s one people talk about a lot. Because for the most part builders don't fly because they rarely finish. Especially scratch builders.

I bought a KA6 about a decade ago. Those are the most beautiful aircraft. All wood but with the lines of a fiberglass sailplane. I sold it because my hanger fees were consistently higher than what I was paying for tows.

I might be an EAA member, they have my address. But I haven’t paid any dues in years. I listen to The Green Dot all the time (their podcast). I’ve jumped off mountains in Nepal as a passenger on a steerable parachute. And skinned balsa models with tissue paper. And have logged more time ridge soaring in a 233 than most folks get a chance to (because the ridge at my airport was on approach so student pilots could ‘try’ to catch the lift and if they couldn’t just bank left for final). I haunted hombuiltairplanes.com and got a bunch of advice there.

One thing I’m not getting from pretty much anywhere is folks who even know what a 6050 IMU is or folks who know even the first thing about the arduino and it’s ability to facilitate autonomous flight. I’m only getting that from a new breed of builders who are into quad copter POV flight,,,drones. That’s where I am at. There really is a old school/new school thing out there. The new school is all about electric power and fly by wire. Things you wouldn’t even consider in a homebuild 5 years ago.

I’m not saying this to prove a point because I’m fairly old and don’t need to do that anymore. But just to say where I’m at.

My speeds and power requirements are in keeping with a craft with a wing loading of 5lbs per square foot. They are are ballpark. Maybe too high. Maybe not. Idk. Hang gliders have a lower wing loading and stall speed. And all of MacCready’s designs were very task specific and have flight characteristics that are very limited.

So to get back to the point. When I started building wing ribs, folks thought/advised that those should be the first thing to build to get a feel for what lies ahead. There was no, what sort of flight computer are you using? But that’s the core of the new breed of aircraft, not just drones but the slew of air taxis people are talking about online.

Pilot control in this new paradigm is a suggestion to a flight computer. when your flight computer knows where you are on the power curve it knows if you can bank left or if you need to drop your nose and increase airspeed first. It’s one of the truly amazing tools we have to work with.

I hope I don’t sound defensive or like I’ve got it all figured out. I’m not and I don’t. I do have a bit of an aversion though, at this point, of going down a separate path. Like running down a genital slope in a hang glider...I know what that feels like. It’s fun. But it has as much of a chance to get me killed or paralyzed than a miss step with my own design. That’s a fact (glider flying is the #1 cause of accidental death).

One thing that I haven’t made clear is that I don’t plan on getting me or my son on this thing until it can fly autonomously in an oval on my local soccer field with 150 pounds of sand strapped to the seat. As far as safety, my biggest worry was debris from a prop strike being thrown from a prop strike and hitting someone. Since we are going to be in ground effect people are going to be closer than usual to the aircraft And prop strikes may be common. Also in keeping with my design paradigm ’A BMX with wings’; Every pilot will have a helmet and full riding suit and HANS PPE.

A friend of mine died on approach about 15 years ago. Took the turn to final and stalled. Basilar fracture. Internal decapitation. Ugh. I used to get grief for wearing a cowboy hat when I flew Because the brim was too big. I am sure if my bud had a HANS system he would have survived. Look at the spills motorcyclists take and walk away from. That’s one thing I decided a while back that I wouldn’t skimp on in my future flying endevours.

So where I am leaning now, based on everyone’s input is using EDFs. I was worried they would be under powered. But what I’m going to do is get my to scale prototype flying autonomously without 150 lbs of sand first. After that I can think about clustering a few EDFs together so I can fly a human or a payload. I think that’s a good safe compromise.

Again, thanks for your input.

 

[jrmichler]

Be advised that the FAA thinks you are building an airplane. Home built airplanes need to be licensed in the Experimental category: https://www.faa.gov/aircraft/air_ce...fication/sp_awcert/experiment/expt_operating/

If you want to fly it unmanned (as a drone), you need to be aware that the FAA also regulates drones: https://www.faa.gov/uas/. And they have special rules for drones weighing over 55 lbs: https://www.faa.gov/uas/resources/e...media/How_To_Drone_Operations_Over_55_lbs.pdf.

The days when a person could just build an airplane, and learn to fly by trying to survive the inevitable (at the time) crashes ended with the Air Commerce Act in 1926. It's possible to get an airworthiness certificate by yourself, but the EAA has extensive resources that will definitely save you time and money.

 

[PazHeping]

Be advised that the FAA thinks you are building an airplane. Home built airplanes need to be licensed in the Experimental category: https://www.faa.gov/aircraft/air_ce...fication/sp_awcert/experiment/expt_operating/

If you want to fly it unmanned (as a drone), you need to be aware that the FAA also regulates drones: https://www.faa.gov/uas/. And they have special rules for drones weighing over 55 lbs: https://www.faa.gov/uas/resources/e...media/How_To_Drone_Operations_Over_55_lbs.pdf.

The days when a person could just build an airplane, and learn to fly by trying to survive the inevitable (at the time) crashes ended with the Air Commerce Act in 1926. It's possible to get an airworthiness certificate by yourself, but the EAA has extensive resources that will definitely save you time and money.

A wing in ground effect falls under maritime law. It is considered a boat. Crazy huh?

https://www.navcen.uscg.gov/?pageName=wig

Not that I won’t arouse attention, it’s just that the gray areas that exists will keep me on the ‘right‘ side of the law as long as I operate safely and no one gets hurt.

Edit: just so everyone knows I have no intention of operating as an outlaw. I also have no gripe with FAA or the EAA but the truth is my ‘airplane’ is a boat and the soccer field I plan on testing on is adjacent to a river and is (I believe) on reclaimed wetlands.

 

[anorlunda]

A wing in ground effect falls under maritime law. It is considered a boat. Crazy huh?

https://www.navcen.uscg.gov/?pageName=wig

WOW! That is really crazy. Put in pitch control and the craft can go up and down, in and out of ground effect, between FAA and USCG authority domains several times per minute. It reminds me of tacking upwind in my sailboat on the St. Lawrence River, with each tack taking me to US, Canada, or St. Regis Indian jurisdiction and violating the border regulations of all three by not checking in with customs each tack.

Beware things like chain link fences, trees, or structures, bordering your soccer field.

I still think you can reduce risks by testing with a tow. You could tow it behind a car driving circles around the field. That way, you at least divide testing aerial characteristics and autonomous control into two tests rather than one.

 

[PazHeping]

WOW! That is really crazy. Put in pitch control and the craft can go up and down, in and out of ground effect, between FAA and USCG authority domains several times per minute. It reminds me of tacking upwind in my sailboat on the St. Lawrence River, with each tack taking me to US, Canada, or St. Regis Indian jurisdiction and violating the border regulations of all three by not checking in with customs each tack.

Beware things like chain link fences, trees, or structures, bordering your soccer field.

I still think you can reduce risks by testing with a tow. You could tow it behind a car driving circles around the field. That way, you at least divide testing aerial characteristics and autonomous control into two tests rather than one.

I had already planned on testing with a tether, at the beginning at least. Thank you for your ideas.

The bigger picture here is finding a way to get more youth involved in aviation. When a kid is zipping along at 6 feet about the ground, racing with her friends like on a BMX or a 125cc motocross bike but instead she is F L Y I N G ...woah. And it’s community and teamwork. Then this boat ;) everyone has been working on, getting into the software, painting the wings ... can get a motor upgrade and some wing tips then it’s an FAR ultralight with a speed governor in software to keep it within those rules of min stall and max cruise speed. (This is the reason I came to a physics forum, I didn’t want to overpower this at the beginning but I didn’t want to under power it either) Then they really start learning how to fly...

From there the sky is the limit you might say. Battery tech will evolve and range will open up and this craft that I hope has captured this kid’s imagination like Richard Bach novels captured mine when I was young will really be able to take this person somewhere.

That’s the master plan, the hard work, and the ambitions part.

Thanks for the input.
Paz

Edit: removed a stray thought.

 

[berkeman]

@PazHeping -- We need to tie off this thread. It does sound like you have good experience in this area and are thinking about safety, but we have many, many people who find our threads that have way less experience, and pick up small technical points and get hurt trying to use them.

Please use the other specialized forums that have been suggested. And best of luck on your project. Definitely contain those props, please.