What is the Best Airfoil for a USA Part 103 Ultralight?

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Armilite

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As someone said, fabric wings are only roughly the shape you aim at, and that shape changes with the lift and angle of attack. So trying to make \ a precise fabric wing is a waste of time and effort. a 235/70-15 airfoil probably isn't much different to a clark-Y in practice rather than fed it into xfoil. Saying, everyone wants as much lift and least drag, so they optimistically pick something like the Clark Y anyway. No doubt with a lot of math, you could arrive at an optimum fabric airfoil that ends up the right shape when flying, though it starts off 'wrong' on the ground. I'll leave that for someone else...

For a printed, tin, composite or even Coro airfoil, shape can be held fairly accurately on the ground and in the air and concave surfaces are also on.
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Yes, I doubt any Airfoil is going to make that much difference for USA Part 103. Part 103 Ultralights are not flown in any Bad or even Rough Windy Whether. You only have 5 gallons of Gas to play with and most Engines used fall into the 25-35hp catagory, so a 2.0 to 3.5gph, so 1hr to 2hr Tops depending on Engine used. Your Speed Range is set at 28-63mph. Most are flown out of Home Acreages with a 60ft x 400ft Grass Airstrip. A Wing that has a High Lift is most desirable for getting out of them Home Grass Strips. Ideally, a Wing that can carry Max 254lbs + 396LBs = 650lbs so that 99.9% of the People in the World can probably fit. Some of the Tall Zulu's may not. That 396lbs - 30lbs for Gas gives you 366lbs for Pilot & Bags. Lighter People will just have better Performance, maybe a better GPH use.

As I said, the Pheniox 103 Sets the World Bar for Part 103 Ultralights at 396lbs Useful Load using a Hirth 50hp Engine and makes Part 103 254lbs! Using a Simonini Victor 400cc 54hp Single would save you some Weight, about 5-7lbs. Which could add to your Useful Load Weight, also +4hp.

Using those Max 650lbs Spec's, and using the most common used Engine HP's for USA Part 103 Ultralights:
Rotax 277UL (26hp)
Hirth F-33 (28hp)
Rotax 377UL (35hp)
Rotax 447UL (40hp)
Kawasaki 340(35hp)
Kawasaki 440(40hp)
Hirth F-23 (50hp)
Simonini Victor Engines in 44hp, 48hp, 54hp.

So you have a 26hp to 54hp Range! Many of these Older Engines could be Improved to make more HP if needed!

Ideally, for USA Part 103 with only 5 Gallons, 1hr 15min of Flight with a 20-30min Reserve would be nice! If you could Crusie at say 40mph you would have say a 50-mile Radius of your Home. I Average 21 Airports per 50-mile Increment Radius around me.

With some of these different Airfoils, it would be an Interesting Test to see which is maybe better, how much HP is really needed. With EFI you could get better GPH also.
 

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turbolium

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I think it depends on how much precision you put in the wing. If you've got a rigid d-tube back to 30 percent, there are probably big differences in performance, or so I'd guess. I think if you used carbon fiber carefully, you might be able to skin an entire wing in carbon fiber for 20 to 40 lbs of weight. Less if you kept fabric covered control surfaces. And with clever design, maybe that skin can help with bending loads too.
If I understand correctly, you're proposing a leading edge section 30% made from carbon fibre and secured to the main wing spar to create a clean airflow and add strength to the entire wing.

I would be very interested in any more information you would be willing to share on this.

My project is a Challenger ll , I have the wing cross members and probably half the spars but am missing the main spars. I've been thinking of ways to mold the leading edges with carbon fibre and secure them to the spars allowing me to use lighter aluminum tube for the main spars.
Not sure how much can be done to reduce drag and maintain the lift. keeping in mind the bottom of the wing will ultimately have to remain flat. thx.
 

daveklingler

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My rule of thumb is that for part 103, using carbon, it's reasonable to shoot for less than 20 lbs per side.

I also happen to believe that ultralight wings should also be easily removable, using sailplane-style "jeezus" pins. Some people prefer folding wings, and there are simple, well-proven systems for that.
 

turbolium

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Sorry , I'm just getting up to speed on aero foils, are my wings Part 103 or are you using a hypothetical situation?

Do you think theres s.t to be done to reduce drag on the first 30% of the wing or should I just be focusing on weight.

thanks!
 

turbolium

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It's good for middle wing.
Expanding it to 16.67%
Out not pose a problem.

View attachment 108548
Thanks for the info.. though I had to google practically everything you said ..sorry I'm in the early stage of wing building :)

16.67% refers to the width or thickness, challenger is an in line 2 seater with overhead wings. I'm increasing the HP by 20% so I could sacrifice a bit of lift for a little less drag. basically looking for an aero foil to match the new engine set up. If I have to go thinner and manufacture new spars ..not a problem but I dont really want to change the profile of the bottom of the wing which is flat.
 
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AeroER

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Pick an airfoil about 15% thick at about 30% to 35% chord with a flat bottom and a reasonably large diameter leading edge.

Then answer the important questions to meet the mission -
- wing area needed,
- span loading needed, then
- aspect ratio.
 

Lendo

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Turbolium, have a look at the Harry Riblett airfoils, get his book it's got all the dimensions for a complete rage of airfoils, bottoms are not flat and have gentle stall.
George
 

Dana

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The good old Clark Y has a long history of working well on low speed aircraft.
 

Jsample40

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Look into original Mitchell Wing B-10 NACA 230-15 airfoil design. It can be constructed out of either wood and fabric ( I have owned/ flown 2 of them), or the aluminum & structural foam version (A-10). I have owned and flown the two seat trainer (T-10) and am now doing a major restoration of the single seat A-10.
They are the finest performance oriented wing design in the Ultralight category available. One can acquire an older B-10 wood & fabric wing very cheaply with a little online research, and the wing can be incorporated into a design which includes a fuselage and tail feathers.

You may contact Jim Gordon at Mitchell Wing online to get help in the acquisition phase. Jim is in touch with MW folks around the world, and has a number of the wood/ fabric B-10s as well as aluminum/ Foam core A-10s available.

No point in trying to start from scratch on wing design, if you can obtain a proven performance design wing, and adapt it to your needs.

Good luck and good hunting on your "Very Great Adventure"

Jay Sample
 

PTAirco

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I always thought that for a Part 103 UL, an airfoil with a really high Cl would be appropriate, since it reduces the wing area and reducing the wing size in an UL has a marked effect on weight. Which is everything on an UL. Fat high lift wing with room inside for a light spar and drag be damned.
 

Gregory Perkins

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What is the Best Airfoil for a USA Part 103 Ultralight, and Why is it? Is their someplace I can download a DXF CAD File of it?
There was only one airfoil ( known to me ) that was created and recommended by NASA for a FAR 103 project and was for the Diehl (sp?) Canard XTC. The airfoil is the E-749 if memory serves correctly and required composite construction to achieve the precision required for what I think was a laminar flow wing. If you can reduce your wing size by increasing the lift and reduce the weight of your motor by reducing the drag, you may well justify the extra weight of a composite wing and still be legal.
It basically looks like a sailplane with with 15 degrees of flaps built in. For a more modern implementation I would look at the wing of a trainer 2 seat ATOS hang glider
to build an UL around. My understanding is that they have added some motors to some of the ATOS trainers and were among the highest performing ULs ever.
 

Victor Bravo

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The slower the airplane, the less sacrifice you make by using a thick high-camber wing. Easy enough to understand even for an uneducated guy like me.

If you have an airplane that is limited to 55 mph by statute, then you can probably get away with a 16-17% thick wing, which makes a lot of lift, which means the wing can be smaller, which means the airplane can be lighter, which means EVERYTHING gets easier to design and build.

The thick high-camber wing will make more nose-down pitch, which means you need a slightly larger or longer tail, and that takes back a little of th gain you made, but you still walk away with a big gain even after subtracting the loss from the larger tail.

IMHO, one of the old antique Eppler glider airfoils that is in the 16-18% range will be a very very good starting point if you want to be successful with a genuine Part 103 aircraft.
 

AJLiberatore

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Imitation might be the sincerest form of flattery.

Why has no one mentioning the Ribblett GA-30618 used on the Hummel UltraCruiser and H5.

Watch one fly in person, perhaps that might expand your choices what sections to consider.
 

Lendo

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AJ, I mentioned the Riblett, however the GA 306 18 is symmetrical I believe.
George
 

Armilite

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The slower the airplane, the less sacrifice you make by using a thick high-camber wing. Easy enough to understand even for an uneducated guy like me.

If you have an airplane that is limited to 55 mph by statute, then you can probably get away with a 16-17% thick wing, which makes a lot of lift, which means the wing can be smaller, which means the airplane can be lighter, which means EVERYTHING gets easier to design and build.

The thick high-camber wing will make more nose-down pitch, which means you need a slightly larger or longer tail, and that takes back a little of th gain you made, but you still walk away with a big gain even after subtracting the loss from the larger tail.

IMHO, one of the old antique Eppler glider airfoils that is in the 16-18% range will be a very very good starting point if you want to be successful with a genuine Part 103 aircraft.
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First, for any Part 103 Aircraft to qualify, it has a Max Full Power Speed of 55 knots = 63.29287 mph, not 55mph. Has to meet a Stall Speed, I believe with a 170 lb person which is 24 Knots = 27.61871mph. Which with that Criteria probably means Max 36-38hp for 55 knots!

The 24 knot Stall Speed is probably the hardest thing for most Aircraft meet. Most Manufactures take advantage of the FAA Part 103 Stall Formula using the 170lbs. The Vast Majority of Pilots Weight today falls between 180 lbs and 235 lbs. Today, we also have many people over 235 lbs. Not really a problem with Airframe at 254 lbs + 30 lbs Gas = 284 lbs. A 660 MTOW - 284 lbs = 376 lbs for Pilot & Bags. A 650 MTOW - 284 lbs = 366 lbs for Pilot & Bags. A 600 MTOW - 284 lbs = 316 lbs for Pilot & Bags. So probably covers 99% of the People in the World.

Most Ultralight & Small Kit Airplanes MTOW falls between 450 lbs and 660 lbs. If you use the 1lw for 10kg Power to Weight Ratio. 85% of the Part 103 and many Small Kitplanes out there Flew with a Rotax 277UL rated 26hp/28hp! The 26hp version actually Dynoed Max 25.4hp!

450 lbs = 204.1166 kg / 10 kg = 20.41166 kw = 27.37249 hp to Fly Well!

600 lbs = 272.1554 kg / 10 kg = 27.21554 kw = 36.49664 hp to Fly Well!

660 lbs = 299.371 kg / 10 kg = 29.9371 kw = 40.14631 hp to Fly Well!

Since Part 103 is limited to Max 55 knots, and like I said, I bet 36-38hp would Push/Pull most of them 55 knots if you want to be Legal. Most people are more interested in their Stall Speed and Quicker take-offs from short fields, which means more Lift needed.

So over the years, I have seen only 5-6 different Airfoils mentioned. Most of these Tube & Fabric Ultralight's doesn't really use a Numbered Design Airfoil. Simplicity to make is also important.

Standard Part 103 Wing Airfoil looks like this one for the Affordaplane. Using different Widths & Lengths.
Affordaplane Wing Ribs.jpg
 

Gregory Perkins

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Depending on the level of sophistication and time you wanted to invest, borrowing from the glider community to gain max performance would be a good idea.
For a wooden cantilever wing, that does not require composite precision, I cannot think of a better place to start than with the Wortmann FX 63-137 as used on the German ULF-1. The whole wing would have to be re engineered for higher gross weights for the 103UL. Another effective glider wing would be the one used by
the F,R. E. D. which originated with the early German training gliders. I have never seen the concept taken further to heavier planes but with the wooden cantilever VJ-23 hang glider, it had a relatively large span with a 16inch thickness at the inboard spar attach and tapered to the tip. If you re-engineered that wing to a gross weight of 600 pounds you would likely have the very lightest wooden cantilever wing possible.
 
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