Quantcast

Wing design for lightest possible wing

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

nerobro

Well-Known Member
Log Member
Joined
Nov 6, 2011
Messages
1,112
Location
Northern Illinois
Are we talking the same speeds of a 152? What do 152 wings weigh? What features do the wings need?

Just to throw design considerations out there. Each hardpoint is heavy. so the fewer hardpoitns, the better. Those talking about wire supported designs, those wires need hardpoints. So do struts.

I figure the lightest would be some very, very low density foam, as a core for a main spar. Perhaps the main spar might be the whole D front of the wing. most of the wing would be single layer ~whatever skin we chose~ be it aluminum or carbon.

more features are heavier too. Flap tracks, hardpoints for actuator rods, etc...

What's immediately coming to mind, is a large main spar, foam filled with a large diameter hole removed down the middle. The foam mostly there to help with buckling. The airfoil would be built from hollow front and rear airfoil shapes glued on to the front and rear of the spar.

... I wouldn't want to run into a junebug at 150mph, but I can't imagine much lighter, once you start putting coverings on structures weights go up pretty rapidly. this could just live under a coat of paint.
 

proppastie

Well-Known Member
Log Member
Joined
Feb 19, 2012
Messages
4,701
Location
NJ
One other possibility is going massive core. Yeah, that is a lot of foam, but you can skip the composite facings on the inner surfaces of the cored skin, the ribs, the tapes, transferred flanges, and adhesives connecting the ribs to the skins. below 5' chord, you can almost always build a lighter wing with a solid core than with a "hollow" wing...

Billski
Got to thinking With the Aluminum dragon this is not right.....A quick and dirty calculation of the possible foam in my D nose vs the weight of the ribs....it is nowhere close.

The weight of the nose ribs in 1/2 the wing LE was .73 lb.....the weight of the foam in that volume was 25 lb
 

Attachments

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,138
Location
Saline Michigan
I guess the vapors from fuel in root strakes has not effected the Styrofoam?
Many of these birds flown for many years, and no issues that I know of from it.

The strakes on Rutan canards and their derivatives are made of PVC cored skins, while the fuselage is PU foam cored. Fuel safe foams! They do not care about the gasoline diffusing through it. And it is not gases that drive diffusion through those assemblies. Think about what diffusion is here: You have liquid fuel in the strake structure at pressure slightly above atmospheric (just the head of the fuel), and molecules of the fuel are pushed into and through the molecular structure of the resin and foam by that pressure until it finds the air and then these individual molecules are a gas and disperse in the air.

The polystyrene foam core wings are separate structures - getting gasoline into them from the air just does not want to happen. The partial pressure of gasoline in air is a fraction of atmospheric pressure and so is really not driven into and through the resin and foam. And what does enter the resin has an easy path back out the same way it came in, so it does not tend to diffuse into the foam.

Now if you had composite boundary between liquid fuel on one side and polystyrene foam on the other, gasoline will diffuse through the composite and melt the foam to thin little puddles of polystyrene. I have seen it in a post crash (two fatally injured) tear-down of polystyrene foam core wings that were also fuel tanks... It may or may not have played a role in the fuel starvation and subsequent forced landing.

Billski
 

proppastie

Well-Known Member
Log Member
Joined
Feb 19, 2012
Messages
4,701
Location
NJ
The strakes on Rutan canards.....
The polystyrene foam core wings are separate structures -
Now if you had composite boundary between liquid fuel on one side and polystyrene foam on the other, gasoline will diffuse through the composite and melt the foam to thin little puddles of polystyrene. I have seen it in a post crash (two fatally injured) tear-down of polystyrene foam core wings that were also fuel tanks... It may or may not have played a role in the fuel starvation and subsequent forced landing.

Billski
I sure am missing something.....the strake is between the wing and fuselage....is there only a composite structure between the wing and strake?
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,138
Location
Saline Michigan
On a Luscombe type airplane there would be separate metal or plastic fuel tanks to prevent that damage. As long as they are not leaking it should not be a concern. No reason whatsoever to have permanent or integral tanks in this type of wing.
The reason to go wet wings is the same as it always has been - less weight in the airplane.

Then about leaks - therein lies the rub. Your effect from a failure mode of fuel tank leak, fuel line leak, or fuel spill inside the wing is then to immediately ground the airplane and scrap the wing? I would advise against a design with that severe a required response to a common fuel leak or spill.

Once you have gone to composite wings to save weight and have fuel safe foam (PVC is advised) as cores, why would you not go wet wings and save some more weight? All of the Rutan canards and their derivatives, all of the Lancairs and the Glasair I,II, III's all built and flying with wet wings this way...

Of course you could get very conservative and go with a separate tank inside a fuel safe foam cored wing structure, but it is more weight in the airplane. Designer's choice on that.

Billski
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,138
Location
Saline Michigan
I sure am missing something.....the strake is between the wing and fuselage....is there only a composite structure between the wing and strake?
http://www.ez.org/pages/waynehicks is a pretty complete and well illustrated build log of a Cozy. Chapter 23 shows the strakes on the fuselage with no wing panels attached. His log is really VERY educational. Chapter 19 shows the wing construction. Two independent structures.

The strakes are built on the fuselage and run from the main spar forward and from the fuselage out the wing a bit. They are there expressly for carrying the fuel. In any good picture of a Long Ez or Cozy you can easily pick out the change in sweep of the leading edge as well as the surface change from strake to wing. The strakes are complete and sealed even with no wing attached. Builders do their gauge calibration, fuel flow tests and ground runs without even attaching the wings.

The wings are bolted on separately and there is air-space between strakes and wings. They run to the root behind the spar and start where the strake ends forward of the spar. Foam covered in glass and epoxy runs all the way to the tips and up into the winglets. There is no fuel inside the wings, just in the strakes. And the gap between them is partially filled at the skin surfaces, but there is air between them.

The wings are thus isolated from the fuel diffusing from the tanks...

Now if someone did merely separate the fuel from foam with a layer of glass-epoxy inside a continuous structure, they, like Jerry Stallings, would have had their foam collapse.

Billski
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,138
Location
Saline Michigan
Got to thinking With the Aluminum dragon this is not right.....A quick and dirty calculation of the possible foam in my D nose vs the weight of the ribs....it is nowhere close.

The weight of the nose ribs in 1/2 the wing LE was .73 lb.....the weight of the foam in that volume was 25 lb
I was not talking equivalents for a 60 knot Vne airplane. The OP talked about a replacement wing for the Luscomb. Luscombs have a Vne much higher than the Aluminum Dragon and have been flown upward of 180 knots. No one is admitting to this illegal flying, but a rewinged Luscomb should probably be designed for that. When q is 9 times higher, you need a lot more torsional stiffness to keep flutter at bay. When you design for the upper end of an improved Luscomb, you must have a much stiffer structure and much stiffer skins. For a 900 pound airplane with a 1500 pound gross weight that must survive at three times the airspeed and 9 times the dynamic pressure, the wing areas may be close, but there is a lot more glass in spars and skins than you might use in your foot launched glider. In the OP's airplane range, he will usually save weight with massive foam cored wings.

Let's run some numbers. Let's say a 48 inch chord, 15% thick, one foot long piece, for a fast airplane. Flaps and ailerons are 25%, so the wing proper is about 70%, let's say 33.6" with a 7.2" thickness. Total cross section area is about 219 in^2 and our foot long piece is 2632 in^3.

Spar is the same for both. Let's say 8.16 in^2, 97.92 in^3, and 4.70 lb.

The rest of the approximations: Full cross section is about 80% of spar depth times chord of the piece. Perimeter of the piece is about 2.2*chord of the piece - we have an overlap at the leading edge for bonding and a drag spar to close out the back edge. Glass-epoxy and adhesives are about 0.048 lb/in^3. Blue foam is 2 lb/ft^3. PVC foam is 8 l/ft^3.

Skin of the solid cored section is 3 UNI, about 0.022 thick, so 1.63 in^2, 19.51 in^3, and 0.94 lb;

Foam is about 183.75 in^3, 2205 in^3, and about 2.55 lb;

So the solid foam wing is 4.70 + 0.94 + 2.55 = 8.19 lb/running foot.

Now for foam cored skins. The outside is still 3 UNI, the inside is 2 BID, total thickness is 0.045", 3.33 in^2, 39.92 in^3, and 1.92 lb.

Foam cores are about 18.48 in^2, 221.8 in^3, and 1.03 lb.

Next we have adhesives. Each side of each spar has a glue line that does not exist in the solid core wing. I get about 0.36 in^2, 4.32 u\in^3, and 0.21 lb.

Flanges are applied at the leading edge and at the drag spar. I get 16 plies 2" wide and 0.009" thick for 0.29 in^2, 3.46 in^3, and 0.17 pounds.

Ribs, are still needed, let's say one is used every three feet. Each will have about 171 in^2 of area, and they run about 0.5 lb/ft^2, or about 0.59 pounds. Each one foot section has about 1/3 of that or about 0.20 pounds.

Each rib also has flanges, I count 10 plies per rib 2" wide and 0.009 thick, at about 0.75 pounds per rib or 0.25 pounds per running foot - Yeah the flanges weigh as much or more than the ribs themselves. Seen it over and over.

Hmm, 4.7 + 1.92 + 1.03 + 0.21 + 0.17 + 0.20 + 0.25 = 8.46 lb/ running foot.

I have run these sorts of numbers over and over. In faster airplanes - where you can justify a 100% composite structure - massive foam is lighter. In an airplane with much lower wing loadings and tiny q, the composite amount drops, but the foam amount won't and yeah, the foam might weigh more than the internal parts to replace it. But not in faster airplanes.

Billski
 

proppastie

Well-Known Member
Log Member
Joined
Feb 19, 2012
Messages
4,701
Location
NJ
the foam might weigh more than the internal parts to replace it. But not in faster airplanes.

Billski
One of my general rules is "do not glue aluminum"......my thoughts were if one was to just replace the aluminum ribs in an aluminum aircraft.....
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,138
Location
Saline Michigan
Are we talking the same speeds of a 152? What do 152 wings weigh? What features do the wings need?
And do you want the current legal Vne or the one each airframe is capable of running?

Birdus talked about C152 and about the Luscomb. Maybe he was thinking about 65 hp Luscombs, but why re-wing a 65 hp bird? At that power level, changing the wing to a lighter one will not materially change the character of the airplane. There is one for rent at a nearby airport with 150 hp. Another was sold out of here with a 120 hp engine and it would cruise above the marked Vne. Folks have been flying them much faster. The current structure is up to that as evidenced by folks exploring Vdive in them above 180 knots without flutter. I just took that ball and ran with it.

Both airplanes Birdus cited are single strut with ailerons and flaps, so I guess you are starting there. The 152 has electrically actuated Fowler flaps too, just to add some weight and complexity. IIRC the 152 has lower wing loading and lower real Vne than the Luscomb, so you really gotta decide, do you want a lighter wing than the Luscomb or the 152? And do you want to maintain the higher speed capability of the base Luscomb wing, or do you want to preserve the Vne of the Luscomb.[/QUOTE][/QUOTE]
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,138
Location
Saline Michigan
Oops found a mistake in my file. Density of fiberglass epoxy is more like 0.062 lb/in^3

In my example, the massive cored wing becomes about 7.28 lb/ft while the hollow one at 9.00. That is more like my other runs. Big win in the fiberglass and massive foam design. But if you are going to store fuel or water ballast in the wing, you go hollow.

I also ran massive foam with two plies graphite vs the favored graphite sandwich (one ply per side of the core), again with the same spar. 4.09 pounds per running foot with massive core, 4.76 in a hollow wing. Massive core is still lighter there too.

And as we were discussing above, if you are doing much lower wing loading, you do not build this way... Skins are lighter, ribs are lighter and fewer, and massive core can become the heavy way to build this.

Billski
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,587
Location
North Carolina
I explored many dead ends looking for a way to build a rigid skin with low wing loading. I am trying something very experimental...
 

birdus

Well-Known Member
Joined
Apr 3, 2012
Messages
185
Location
Tacoma, WA
No reason whatsoever to have permanent or integral tanks in this type of wing.
Is there reason not to? If I made the wings of carbon/foam sandwich panels, then it seems like that would be a nice, simple, light solution.

EDIT: It looks like Bill actually thinks this is a good idea. Will keep reading, watching, and learning.
 
Last edited:

birdus

Well-Known Member
Joined
Apr 3, 2012
Messages
185
Location
Tacoma, WA
Birdus talked about C152 and about the Luscomb. Maybe he was thinking about 65 hp Luscombs, but why re-wing a 65 hp bird? At that power level, changing the wing to a lighter one will not materially change the character of the airplane. There is one for rent at a nearby airport with 150 hp. Another was sold out of here with a 120 hp engine and it would cruise above the marked Vne. Folks have been flying them much faster. The current structure is up to that as evidenced by folks exploring Vdive in them above 180 knots without flutter. I just took that ball and ran with it.

Both airplanes Birdus cited are single strut with ailerons and flaps, so I guess you are starting there. The 152 has electrically actuated Fowler flaps too, just to add some weight and complexity. IIRC the 152 has lower wing loading and lower real Vne than the Luscomb, so you really gotta decide, do you want a lighter wing than the Luscomb or the 152? And do you want to maintain the higher speed capability of the base Luscomb wing, or do you want to preserve the Vne of the Luscomb.
A couple points.

1) Let's forget the 152.
2) I would probably want to maintain the original VNE of the Luscombe.
3) I don't own a Luscombe yet, but intend on purchasing one. If the one I get comes with a fabric wing, I probably would not follow through with this project, as those wings are already pretty light. If it has metal wings, then I would consider continuing with this project.
4) I'm hoping to get a 100HP plane. Many of them have been upgraded to an O-200.
 

birdus

Well-Known Member
Joined
Apr 3, 2012
Messages
185
Location
Tacoma, WA
In my example, the massive cored wing becomes about 7.28 lb/ft while the hollow one at 9.00. That is more like my other runs. Big win in the fiberglass and massive foam design. But if you are going to store fuel or water ballast in the wing, you go hollow.

I also ran massive foam with two plies graphite vs the favored graphite sandwich (one ply per side of the core), again with the same spar. 4.09 pounds per running foot with massive core, 4.76 in a hollow wing. Massive core is still lighter there too.

And as we were discussing above, if you are doing much lower wing loading, you do not build this way... Skins are lighter, ribs are lighter and fewer, and massive core can become the heavy way to build this.

Billski
Just to make sure I understand what you're saying, Bill: for a plane like a Luscombe, with a light wing loading, it would be lighter to go with carbon/foam sandwich panels, because I could use thinner layers of carbon fiber, whereas in a fast, highly loaded plane, you'd need enough thickness of fabric on two sides of the foam that it would become much heavier and you'd be better off going with solid core. Do I understand that correctly?

Thanks,
Jay
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,138
Location
Saline Michigan
A couple points.

1) Let's forget the 152.
2) I would probably want to maintain the original VNE of the Luscombe.
3) I don't own a Luscombe yet, but intend on purchasing one. If the one I get comes with a fabric wing, I probably would not follow through with this project, as those wings are already pretty light. If it has metal wings, then I would consider continuing with this project.
4) I'm hoping to get a 100HP plane. Many of them have been upgraded to an O-200.
I would not fool with a new wing on a 100 hp Luscomb. First, you will have to relicense it as an Experimental Exhibition or some such, with restrictions on it. To sell it, you would have to either change it back to its original airworthiness form or STC the new wings. HUGE Job. There might be other ways or reasons. Second is that you might take out some weight, but it will still fly and land pretty much the same, just get you a little more useful load.

Billski
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,138
Location
Saline Michigan
Just to make sure I understand what you're saying, Bill: for a plane like a Luscombe, with a light wing loading, it would be lighter to go with carbon/foam sandwich panels, because I could use thinner layers of carbon fiber, whereas in a fast, highly loaded plane, you'd need enough thickness of fabric on two sides of the foam that it would become much heavier and you'd be better off going with solid core. Do I understand that correctly?

Thanks,
Jay
No, not saying that at all. I was talking about shaving some weight from a 150 or more horsepower Luscomb.

Staying in a 100 hp Luscomb, well, going graphite might save some weight, and that could gain you some useful load if you can also stay inside CG limits with it. You would have to start off with current weights and then diligently design a carbon wing, and see how much different you can make it after you include all of the hardpoints, connections, controls and control surfaces, etc. Evaluate it for robustness too. If you play with lighter graphite cloth, it could become really fragile.

Said it before, I'll say it again: Slow airplanes are usually lightest in rag and tube. This is a slow airplane. Then there is the fuss over how to license it with a new wing...

Billski
 

birdus

Well-Known Member
Joined
Apr 3, 2012
Messages
185
Location
Tacoma, WA
Although I may not end up doing this project, this has been an interesting thread and I've learned some things. Thanks for all the input.
 
Top