Tips and tricks for building a LIGHT aircraft

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Little Scrapper

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Anyone know the weight difference between aluminum and standard fiberglass per square ft? Say on a cowling etc?
 

Eagle

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Sounds like you are attempting to build a fine example of the Cassutt. Do you have any goal in mind after its completion? Will it be used to race or are you just interested in casual flying?
 

Midniteoyl

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Light construction techniques....I'll be following this, for sure.

I met a gentleman who focused on light weight when he was building his plane. "Reduced Hex" nuts were used throughout his build. They might make some uneasy on applications where bolt/nuts are used in tension, but I certainly can't see anything wrong with them for bolts used for shear loads. Hex Nut Lightweight Reduced Dimension On Wicks Aircraft Supply

He also used aluminum washers in place of steel washers. Grams....no doubt, but in the end they all add up and contribute to the number on the scales.

Lynn
As a buddy use to say 'Lose an ounce a day'.. it all adds up.
 

Little Scrapper

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Eagle, just fun I suspect. I just read a lot how a light weight Cassutt is so much fun that I want to experience that. If I'm cognizant of weight and make it a goal it will prevent me accidentally building a 650 pound airplane.
 

plncraze

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If you build it light the ghost of Tom Cassutt will be very happy. He was surprised how heavy some of these airplanes were when completed.
 

Dan Thomas

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I wouldn't go using aluminum washers between steel nuts and steel structure. They could corrode on both sides and let the bolt tension diappear. They're intended for use between a steel nut or bolt head and aluminum structure, so that the washer will slowly sacrifice itself against the steel hardware instead of having the aluminum structure itself suffering the corrosion.
 

lake_harley

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Dan, thanks for the point about dissimilar metals when using aluminum washers.

I don't know if it was on HBA or some other aircraft forum where someone posted that he felt it reasonable to spend up to $100 per pound of weight savings. I guess everyone's threshold varies, but that seemed a reasonable figure to me. Attention to detail and care while building is free other than little bit of extra time, like making parts no larger than they are spec'd. Other lightweight material components, or "lightened" components (think CNC lightened brackets, etc.) can run into some extra $$. One will reach a point of diminishing return though.

Lynn
 

Dan Thomas

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Spending too much to save a tiny bit of weight could actually arrest the whole project. One has to weigh (pun intended) the value of some stuff. If it's going to cost you $3000 more, say, to cover with Oratex instead of Poly-Fiber in order to save ten pounds, I wouldn't do it unless I had really deep pockets. You'll just be a lot longer building the airplane, and as the build time lengthens, the likelihood of finishing it diminishes.

It's hard enough just matching the designer's target weight. Most plans-built homebuilts end up too heavy simply because builders weren't careful to copy exactly the designer's plans. They add a few instruments or a heavier tailwheel or a bigger engine or a few more coats of paint to get that deep gloss. Or they decide that those 1/4" x 1/4" rib capstrips are too fragile and make them 5/16" square instead. Or make them 1/4" thick by 3/4" wide so they can glue the fabric to the ribs to save stitching. Or they use Home Depot wood that has cockeyed grain that splits when you bend it so they have to make it bigger or start patching it or reinforcing it. Or they use oak just to be sure it will be strong enough. Or a metal prop instead of the specified wooden prop because they got a deal on Ebay. One has to watch for the "savings" in time or money that most often end up costing way more than one intended, and resist the temptation to modify or upgrade or spiff up. Weight that creeps in also has a way of making an airplane's CG end up outside the specs so that more weight is necessary, in the form of ballast, to bring it back where it belongs.
 

Little Scrapper

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When you say "I wouldn't do it" what are you talking about? People build light airplanes all the time.
 

Pops

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I cut lighting holes in all of the door sills in my Bearhawk with hole saws. Weighed all the pieces cut out, 8 lbs that I never have to carry around. Local friend of mine makes and sales Carbon fiber doors for the Bearhawk, while not cheap, you save from a 4.5 lb door down to a 18 oz door. Almost a 14 lb total saving.

Dan
 

Kevin N

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I have a lot of .028 wall 4130 in my tubing rack. You can save a lot of weight using it. Piper used a lot of .028 in the J3 too. You have to pick and choose what and where you would use it but it's very noticeable when you pick up parts made from .028 wall tubing. How I came about a large cache of .028 wall tubing is another story. About 17 years ago a lady at my home airport wanted to start an EAA chapter. I attended the first meeting to see if this chapter was going to form. (it didn't) I met a couple of older gents who had went to Oshkosh and came back with Tailwind fever. They ordered enough tubing to build at least three Tailwind fuselages. Wittman spec'd out a lot of .028 for the Tailwind because he built them light as history proves. The two guys built a rudder pedal and decided they would just go partners on a cessna and offered the whole lot of materials to me for about a third of the cost. .028 is expensive so I would never buy it unless I really wanted it. I still have quite a bit of it in my tubing rack. I don't think these two chaps were that interested in being in a local EAA chapter. I think they were looking for a guy like me. Was a good deal for both. Canopy frame, turtledeck formers , fuselage diagonals(intercoastals) lots of places to use light material.
 

Raceair

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If you use 3/32" mahogany (Expensive) for the wing skins, leave the fabric off….Just coat the wood with clear urethane, it will look beautiful, and you will save over 10 pounds….At least two Cassutts I know of were done this way…….Check out Nick Jones' 'Mother Holliday'..
He also had a few random instruments bolted together with a small aluminum rectangle, not really a panel. His Cassutt was right around 500 pounds empty…Maybe a few pounds under 500….
As well, a Grove gear (Expensive) will save several pounds over a steel plans built gear …Finially, consider a lightweight Nitrate / Butyrate paint job for fuse and tail…., Urethanes are heavy…....Ed
 

Raceair

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Tom Cassutt was fanatical about weight. On his second prototype, the little 11M thin-wing, he actually took a grinder and files to the rough edges of the C-85 engine, and shaved off 3 pounds. He weighed every piece of welding rod. He did not varnish the inside of his wing. He painted the airframe with just silver dope, and polished the aluminum cowling. He used a simple 'rudder bar' rather than rudder pedals, to save a few ounces. He left out any fuel tank pressure vent, but blew into a tube on the starting line, to pressurize the fuel tank …(I don't think I would do that)….. The airplane ended up at 444 pounds, (WITH Continental engine!!) actually lighter than he was hoping for! Since then, no Cassutt that I ever heard about came in at below 480 pounds. You might consider the Azusa Mechanical brakes.. Lighter than anything hydraulic, and they 'can' be made to work reasonably well…I have had them on my Sonerais and Zippies…...Ed
 

Pops

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On my C-85 engine, replacing the brass breather elbow that screws into the case with an aluminum elbow saved 8 oz. Made block-off plates for the starter and gen pads. Bob Barrows ( Bearhawk designer) sales a nice spun aluminum oil tank for the small cont's that is lighter than the stock kidney oil tank.

Dan
 

Pops

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One of my old friends has owned 2 Cassutts. Also, a close friend of my wifes family built a Cassutt back in the 1970's. I used to have a set of plans but gave them away. Would have to be fun airplane to fly.
When I get time, I plan on making a spun aluminum oil tank for my C-85. Also after I get the JMR flying, plan on making CF doors, Baggage compartment floor, instrument panel , cowl.



Dan
 

plncraze

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Somewhere there is a story about Leo Loudenslager's last airplane which was not completed while he was alive. He went through the plane and cut off all the extra bolt lengths which stuck out below the nut. The plane is in the EAA museum now I believe.
 
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