Tips and tricks for building a LIGHT aircraft

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Little Scrapper

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Guys. Looking for tips on building a very light Cassutt. My goal is to build the lightest Cassutt possible without re-engineering the plane.

So let's hear your thoughts. I'd like to cover every possible square inch of this airplane from light weight finishes to light weight washers and everything in between. Firewall forward? Everything. Cowling? If I have to hand shape it from aluminum I will. I want this LIGHT.

There's a lot of smart people on this board, I'd like to hear from everyone possible even if it's just an idea.

Thanks, Scrap.
 

TFF

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First light weight might cost more money because you have to buy more materials. Why, because you have to search for the lightest. Spruce, now not just rejecting it for bad grain or warps, now you have to reject wood that does not meet the lightest version of the wood. Metal has to be the nominal thickness; if ordering .045 you reject if it is .046. The range that is acceptable to call it .045 is not good enough. Hand beaten cowls and wheel pants. Of course no elelctrical system, and the lightest gauges you can buy. Wheels, brakes, prop, seat, seatbelt, paint will all be measured for weight. Bolts exact grip length needed. Going racing?
 

Little Scrapper

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Doubtful TFF. Light planes are just better all around. I think with the Cassutt it's even a bigger deal. The general consensus seems to be that a heavy cassutt is quite different than a light one so I want to head in that direction. I don't think I even want an instrument panel, probably something like a crotch rocket instrument cluster.
 

don january

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I'd say don't try and cut to many corner's on your build. Think about the in air factor's you will have to deal with once off the ground.
 

TFF

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"Simplify and add lightness" I agree the lighter the better, On my rebuild project, I am about trying to cut weight to see if I can do it. 100lbs is my goal if I go with hand propping. I will see when I get an engine. Moderation or obsession is your decision. ;)
 

lake_harley

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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
 

Little Scrapper

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Lynn, watch the ounces and the pounds take care of themselves. I know a guy who built a Pitts using those light weight bolts and nuts etc.

I'm not sure what's all available for items such as brakes and wheels but there's gotta be a difference and people here who have been through this.
 

rtfm

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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
Hi,
I just think this is silly.

Lose a Kg or two, and forget all the silly little micro-gams of weight savings.

Duncan
 

Kevin N

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Hi,
I just think this is silly.

Lose a Kg or two, and forget all the silly little micro-gams of weight savings.

Duncan
No it's not silly. Lose a pound or two off the body AND build as light as practical. As posted scrapper, you don't really need an instrument panel. Just the minimum gauges held in place. Not as easy or popular but eliminating four 3/8" bolts and associated spools at the firewall save weight. Just makes firewall fabrication a little more work. Many cassutts were built this way.
 

Angusnofangus

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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
Those MS21042 nuts are actually fine for tension loads.
 

Little Scrapper

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SVSUSteve, it's possible I suppose. Kevlar and composite construction is something I know nothing about so there's a learning curve for me on this.
 

SVSUSteve

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SVSUSteve, it's possible I suppose. Kevlar and composite construction is something I know nothing about so there's a learning curve for me on this.
I don't have THAT much experience it with either but from what I do have, I would wager that learning to make a composite cowling is easier than to hammer a compound curve into a piece of sheet metal.
 

Cubman

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Hi scrap,

The spruce you select must still be at least the minimum specific gravity in order to achieve the strengths shown in, for example, the ANC-18 tables; this will work out to 27lbs/cubic foot at 15% moisture - wood density matters.

An AN364-4 nut weighs about 0.0056 lbs and a 960L-4 washer about 0.0002lbs so if you used alloy versions you might save half the weight. If you had say 500 items that's a saving of about 1.5lbs. Not to be sniffed at. But the point being the potential savings there are quite tiny as a percentage of the whole - even though every little helps.

Solid wood spars and steel tubing won't produce super light-weight structures for obvious reasons, but will be easy(ish) to build so there will be a limit to your efforts; this is where R & D will pay dividends, which is to say Ripoff and Duplicate - copy the lightweight opposition's ideas...

However, I think the greatest single savings to be made will be (1) with a lightweight finish using minimum dope/paint. and (2) bearing in mind that apart from the engine, the heaviest single item as a percentage of the empty weight will be the pilot, so, without being facetious, keep in trim!

Bonne chance

Cub
 

BJC

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Lots of good suggestions above. I will repeat some.

Build the II wing. Save material costs, hangar space, and weight. It will have a higher stall speed.

Cut the spar planks ends with a long taper. (IIRC, and it has been a long time, the specified taper is fairly short.)

The plans specify balsa for the wing tips. Use foam and CF.

Cover the wing with light weight Dacron. Use minimum coatings.

Use fabric to the greatest extent possible. Ailerons, forward fuselage, etc. Use just enough removable covering to allow access to service the brakes and rudder pedals.

Keep fairings light. Use minimum size and thickness of aluminum, or use CF.

Use a CF spinner and a CF cowling.

Use a composite propeller.

Use a small (removable) battery for XPDR and hand held COM. Wire a Battery Tender connector to it.

No alternator, no starter. Use a modified glider tow hook on the tailwheel that you can release from the cockpit. Always have it tied down for propping and entering the airplane. If you absolutely must have a starter, use a lightweight starter and a GPS plug that can be unplugged while sitting strapped into the airplane. One PB to energize the starter.

Extend the longerons to be the four major tubes in the engine mount. That will complicate the firewall installation, but it will save weight. Check alignment three times before welding.

Do add the little bit of weight over stub exhausts by having exhausts that point rearward, not down.

Keep the throttle control as simple (light) as possible. Ditto carb heat. Take alternate air from inside the cowling. No air filters, just a screen a la Pitts.

Keep the fuel tank small. You can have lots of fun with a fuel capacity of one hour with a half hour reserve. Use the lightest off / on fuel valve that you can find.

C-85-8 (if you can find one) with O-200 innards.

Keep the top former of the fuselage aft of the cockpit as minimal as possible. Keep its height as low as possible. Use CF. It does not need to extend down to the upper longeron, it just needs to be big enough to form the curve.

Use a sling seat with a five point harness. You will get dissenting comments on this item, but if light weight truly is your priority, it is an option. (Aerobatics? Go seven point, but then you need an inverted system, etc., so not a minimal weight Cassutt. Note that it will roll so fast that it will not have time to lose oil pressure in a roll, unless you deliberately slow it down.)

Leave the fuselage interior aft of the rear spar open. Do not make a baggage compartment. Note: The first landing will sound like the TW came off, with that open fuselage acting like a megaphone.

Keep the canopy hinges and latches dirt simple and light. Use Plexiglas, not Lexan, for emergency exit considerations.

Use lightweight brakes and wheels. If it is light, slowing down is easy.

Use CF wheel fairings.

Use the smallest aluminum gear that Grove makes, unless you want to land slower, then use the taller gear. I would probably go taller. YMMV.

I don't recall the details of the lower longeron reinforcement for the LG. Probably minimal since it was designed to be a race plane. For a routine flyer, I would refer to the Pitts mods and emulate them, even thought it might add weight.

Use a direct steering rod on one side of the TW, with no spring. Talk to others to get the geometry right. You won't be able to spin it around during taxi, but it works well. Cut off the unused steering horn on the TW.

Use sheer bolts where appropriate, with thin washers and the small nuts mentioned above.

Use small instruments. A panel isn't needed.

No lights, although, depending on the amount of traffic where you fly, you may want to consider adding an LED "strobe" powered by the above mentioned removable battery.

Keep us posted on your decisions and build progress.


BJC
 
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