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New Carbon Wing

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mstull

Well-Known Member
Joined
Jun 23, 2005
Messages
1,263
Location
West Texas
Here's my updated specs with the new wing:

Empty weight: 224# Including the parachute and cockpit enclosure
Maximum gross weight: 480#
Cruise Speed: 30 mph to 45 mph
Stall speed: 24 mph
Never Exceed Speed Vne: 70 mph
Engine: 174cc CorsAir M25Y, 22 Hp in its present state of tune
Design Load Limits: +4 -3 Gs
This plane has over 1100 landings and has been looped (I haven't looped the new wing yet.
Span: 30.1'
Chord: 4.0' Not counting the full flying ailerons
Wing Area: 136.4 sq', including the ailerons
Rate of Climb: 400' per minute
Covering: Stitts Poly Fiber
Prop: Powerfin EL2-48P
Belt Reduction: 2.51 to 1
Fuel Consumption: 1.1 to 1.3 gph
 

dustind

Well-Known Member
Joined
May 25, 2004
Messages
146
Location
Saint Michael, Minnesota
I like the new wing, it looks great. The performance looks nice too.

Winter wind... It is not winter until there are fishing houses and lots of traffic driving on the lakes. *mumble mumble he's not even wearing a real jacket in December* :angry: :D

Did you buy the wood at Aircraft Spruce or locally?
 

mstull

Well-Known Member
Joined
Jun 23, 2005
Messages
1,263
Location
West Texas
Yes, I get almost everything from Aircraft Spruce. I had a couple nice flights today... mostly sunny in the mid-60s, light winds. 12-12-05
 

Ted

Member
Joined
Jan 12, 2004
Messages
9
spar hard points

Hello Mark

I was very interested by your instructions on making large diameter
carbon tubes. You mentioned elsewhere that you could also do another whole article about making and planning hard points - I wonder if you ever did? I'd be extremely interested to read that if you wrote or are inclined to write it.

Great plane, by the way, and thanks for the many highly informative (not to say inspirational) posts too.

Many thanks in advance for anything about designing/making hardpoints.

Ted
 

mstull

Well-Known Member
Joined
Jun 23, 2005
Messages
1,263
Location
West Texas
Hard Points

Ted,
A hard point is a reinforced area, designed to withstand the forces where something attaches, and accommodate a fastener. Generally, the reinforced area on a composite structure is just a pile of little squares of reinforcement cloth. You always start with the smallest one, and work larger, so the larger ones cover the edges of the smaller ones. So the first square might be 2" by 2". Then next, 2.5" by 2.5", and so on, until you have enough strength/thickness.

The fastener itself is usually an ordinary blind nut that is pop-rivited to a small (like 1" by 2") aluminum plate (called a nut plate), that is laminated into the reinforced area. If the forces pull from the other side, it can be near the surface, covered by just one ply. If the forces pull from the side it's attached, the aluminum plate needs to be thicker/stronger, and glued to the structure before you add all the reinforcing squares. It helps if you can have a bolt through it from the other side (with parting wax on its threads), so epoxy doesn't fill the blind nut, and there'll be a space for the end of the bolt in your completed reinforced area.
If the forces are in shear, you'll want to laminate a piece of aluminum or steel into the reinforced area to take the side load, unless the layup is very thickly reinforced. Bolt holes tend to gradually wallow out in composite layups without the metal. It is customary to drill the metal with lots of little holes, to give the epoxy something to bite into. Usually this metal plate is only 1" by 2" or so.

On my previous wing, the spar was too large diameter to use through bolts. So I had to cut a hole in the completed spar that was large enough to reach in, and glue a nut plate. It was a nightmare. Then the hole had to be reinforced heavily and widely to get the strength back. Rule of thumb for holes cut in structural members: The patch has to have at least as many plys as the original part, and overlap one inch per ply. You can still use little squares of increasing size. So the first square just overlaps 1" all around. The second overlaps 2", etc.
Planning hard points while engineering your wing takes time and experience. You want them to be hidden inside the completed wing as much as possible, so they don't show up as a bulge. Hard points can add a lot of weight... especially if they're not well engineered... so minimize them by using through bolts as much as possible. I designed my wings as a single wing instead of separate left and right wings, to save the weight of the tremendous reinforcement at the wing root. If you're using struts, its not quite so bad. But a fully or semi-cantilevered wing needs to be super strong there... an engineering nightmare to accomplish without adding a lot of weight.

I have over 1,300 landings on my plane so far. I recently bought my 4th engine for it... a Kawasaki 340 twin. The little CorsAir engine was pretty gutless... making for a very gradual climb at the high density altitudes we get here in west Texas (often 6,000' at the surface). I'll install the new Kaw this month. I wanted better climb, better reliability, and low vibration. It will take my plane up near the legal weight limit. I'll have to move the whole cockpit 9" forward to counter its weight... and that's a lot of work.
 

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Ted

Member
Joined
Jan 12, 2004
Messages
9
Hi Mark

Thanks for that - as always both helpful and interesting!

Ted
 

mstull

Well-Known Member
Joined
Jun 23, 2005
Messages
1,263
Location
West Texas
Kawasaki 340

The Kawasaki 340 snowmobile engine didn't work out at all. I had to fabricate an untuned exhaust system to make the weight limit, but that reduced power too much. Even so, it was too heavy and too loud. It did run smooth though.

So I rebuilt the little CorsAir engine, and stuck it back on. Decarbonizing it totally revitalized it. It climbs great now. I ordered an MZ201 engine, that I'll try running direct drive. It's the only light engine I've found that has enough torque to turn a prop direct drive. It should come out 10 to 15 pounds lighter than the Kaw. I'm a bit concerned it will vibrate and be loud. 626cc is a huge displacement for such a light engine.

I found this face shield at a welding supply store, and modified it to use instead of a windshield. It works great with the headset, is comfortable, aerodynamic, inexpensive, and way easier than making a windshield. I like the included sun visor.
 

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Nilsen

Well-Known Member
Joined
May 12, 2006
Messages
91
Location
New York City
Hi,

Great work!

How did your trim setting change when you added your new wing? I saw your old wing didn't have much camber, did your new wing add a larger pitch moment that needed to be corrected?
 

Ted

Member
Joined
Jan 12, 2004
Messages
9
mz201

Hi Mark

Did you see my comments on the MZ201? I put them in the 2-stroke section where you started a new thread for this. Any help? I'm also interested to know how you're getting along with this new engine.

Ted
 

mstull

Well-Known Member
Joined
Jun 23, 2005
Messages
1,263
Location
West Texas
Camber

Nilsen,

The new wing's center of lift is farther aft because of the deep under camber, relative to the percent of chord. In other words, the CL of the old wing was about 30% of chord. The new wing's is about 35% of chord. But the new wing has a 6" shorter chord. So the center of lift, relative to the leading edge is relatively unchanged.

In any case, the CG of my plane is adjusted by moving the cockpit forward or aft. I have to move it after any significant change.

After the Kawasaki didn't work out, I went back to the little CorsAir engine for a little while.

Then I tried running an MZ201 direct drive. I tried everything, but couldnt get enough thrust to climb well. So I added the stock reduction belt to it. It climbs great and cruises faster. The weight is getting close to the limit.
 

mstull

Well-Known Member
Joined
Jun 23, 2005
Messages
1,263
Location
West Texas
MZ201

The MZ201 engine is working out great. It's the most reliable engine I've tried, with about 70 hours on it so far. I'm still on the original belt. I get 1.6 gph, using a float/slide carb I adapted. The muffler is difficult to mount reliably. A re'drive housing broke, but was replaced for free with an upgraded one by the dealer.

It's turning a Powerfin BL2-58P on a 2.08 belt re'drive. It could use an even bigger prop with that ratio. That's the biggest diameter that will comfortably fit between the empennage booms on my plane. I may eventually go to a taller re'drive ratio. I'm cruising at about 50 mph at 4,000 RPM.

I got the optional single ignition, and no electric starter to save weight. This engine took my plane very near the weight limit. It's at 250# plus the 24# parachute.

I'm using a throttle stop to limit power to about 30 Hp at 4,600 RPM. It would overheat at a higher throttle setting. Free-air cooling is pretty marginal on a pusher. They have a fan cooler option for this engine. But I think it only works with electric start.

I'm building a new set of ailerons, designed to aerodynamically counter adverse yaw... totally experimental. They're stiffer and stronger to resist flutter too. I'll let y'all know how they work out.
 

mstull

Well-Known Member
Joined
Jun 23, 2005
Messages
1,263
Location
West Texas
The new ailerons fluttered. So I improved one of the aileron hangers with a strut brace to the wing spar, and put the old ailerons back on. They work better than ever. I'm still thinking about the new ailerons. Flutter is a fickle beast. Here's a photo of the new ailerons.
 

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CAB

Well-Known Member
Joined
Nov 26, 2004
Messages
128
Location
Colorado
What airfoil are you using for your ailerons? The bottom looks too flat to me. I would also move the hinge point back a little. Mass balancing has also cured flutter- if you can afford the weight. OK- enough criticism from someone who really has no clue what he's talking about!!

CAB
Bearhawk #862
 

mstull

Well-Known Member
Joined
Jun 23, 2005
Messages
1,263
Location
West Texas
Thanks CAB,

I designed the flat bottomed airfoil myself. I assume you mean to move the ailerons back to move their hinge point forward. In my experience, that is very effective for reducing flutter... although the ailerons do get heavier in the stick.


I'm flying with the old ailerons. They still work fine with no flutter, and a very light feel. They even got better becuase I left the hanger brace on from the new ailerons.

I love to experiment. I wasn't holding my breath the new ailerons would work. So nothing is lost. My Mom used to say, "Nothing ventured, nothing gained."

I flew the last 4 days in a row. I figure I'd better fly while the weather's still nice. I have about 400 hours and 1,700 landings on my plane so far. The MZ201 engine is still working great.
 

CAB

Well-Known Member
Joined
Nov 26, 2004
Messages
128
Location
Colorado
I look at the underside of your wing and it appears (to me) that the airflow would be directed somewhat downward at your ailerons. When the air comes around the leading edge of the ailerons and hits that flat section it looks to me like it would seperate- like a wing in stall. I wonder if that is the flutter you feel? The fix (I think) would be a symmetrical airfoil allowing the air to follow around more cleanly (I just learned about the Cuoanda[sp?] effect recently).

And, I did mean to move more aileron forward (hinge point aft). This makes them ealier to mass balance. This could also move the "nose" of the aileron closer(up) or farther from(down) the trailing edge of the wing- opening and closing the gap- kinda like Friese(sp?) ailerons. You had reported a lot of adverse yaw earlier- maybe this could help?

I am by no means an expert; just a lurker who has enjoyed your posts and admires your work. Keep it up and best of luck to ya!

CAB
Bearhawk#862
 
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