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What is worth a few pounds?

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Canuck Bob

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A question in a trade/mission study has always intrigued me.

What would you sacrfice weight for on a design? I'm wondering about were would one add weight specifically.

Assuming a weight conscience builder aiming for the safest low weight possible what would you add for convenience, improved component materials, and for simple whims? I'm looking as much for peoples wish or complaint list as much as a logical choice based on a benefit study.

Me. I am always looking at simple homebuilt designs for cheap recreational flying. Here are some ideas that I often consider.

1- Utilize auto windshield glass rather than the usual plastics. The care required for the plastics and the degraded view with time bugs me. The clarity and easy care of safety glass seems worth a few pounds. I'm refering to the simple flat panel screens like a Fly Baby or a Wittman design.

2- After squezzing my trim 6'2" 280# 56 year old arthritic body head first into the bowels of my Fly Baby cockpit I am willing to sacrfifice weight to allow removeable panels on the sides and bottom of the cockpit area like crop dusters have so one can work on thier machine easily.

3- Designing a comfortable cockpit with a comfortable seat for a fat butt, mine of course. I would never imply anyone else here has a wide rump.

4- The tough engineering questions like how much added weight to sacrifice for lowering drag, ie. cantilevered versus braced surfaces. Or decisions like electric flaps versus manual flaps versus no flaps. Tight tolerance construction suitable to utilize laminar flow airfoils as compared to less critical turbulent airfoils.
 
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Inverted Vantage

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I would definitely sacrifice weight for a well designed and ergonomic cockpit. I'm gonna be spending all my time in there, might as well make it nice.
 

lr27

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I think if you are going to come up with meaningful answers, you'd have to define the mission.

For instance, on an ultralight, if you want very good climb but you don't care much about fuel efficiency, bracing wires are a complete plus because they save weight AND add drag. Adding drag and saving weight let you use a larger engine and get a better climb rate. (There's a legal limit on top speed, so unless you add a gadget to limit the speed some other way, you need some drag to balance out the power.)

On a short range STOL plane, saving drag won't help you all that much but saving weight helps a lot.

Laminar flow doesn't make much sense unless you want to go far and fast, or else turn the motor off and soar. In the latter case it still doesn't make sense unless the entire aircraft is reasonably clean, and you want to get between thermals quickly.

Laminar flow on a crop duster would be worse than useless because of bugs.

Real glass on a Wittman Buttercup and Tailwind might be kind of heavy with all that area, and their windshields look curved. Obviously a good idea on a Fly Baby. I seem to recall off road guys use stick on plastic over the face shield of their helmets that they can peel off layer by layer to get the dirt off. I wonder if something similar might be good for a plastic windshield.

I think I'd want really well designed seat belt attachment points that were at least a bit higher than my shoulders.
 

Dan Thomas

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Sep 17, 2008
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5,473
A question in a trade/mission study has always intrigued me.

What would you sacrfice weight for on a design? I'm wondering about were would one add weight specifically.

Me. I am always looking at simple homebuilt designs for cheap recreational flying. Here are some ideas that I often consider.

1- Utilize auto windshield glass rather than the usual plastics. The care required for the plastics and the degraded view with time bugs me. The clarity and easy care of safety glass seems worth a few pounds. I'm refering to the simple flat panel screens like a Fly Baby or a Wittman design.

2- After squezzing my trim 6'2" 280# 56 year old arthritic body head first into the bowels of my Fly Baby cockpit I am willing to sacrfifice weight to allow removeable panels on the sides and bottom of the cockpit area like crop dusters have so one can work on thier machine easily.
Homebuilt folklore is full of stories of guys who added a little here or a little there for strength or comfort or convenience, and ended up with an airplane that was neither cheap nor flyable.

Auto glass is far heavier than plastic, and way more expensive. Much better simply to replace scratched-up windshields occasionally.

The sides and bottoms of your Fly Baby are plywood-covered for good reason. It's structural. Replacing it with something removable is asking for inflight failure. Better to build something of steel tube (like the crop duster) and do that. The Citabria/Scout series have a belly pan option; I wish we had it. But it adds weight to an already heavy airplane that has too little useful load. A high-wing airplane has doors that allow access to the backside of the panel far more easily. I Modified a Glastar's panel so that the left and right sections were hinged to the sides of the radio stack and could be swung open by removing a few screws. Even that adds weight; all the wires and hoses have to be longer so they can pass near the hinge line or you won't get it open.

An old, experienced homebuilder I knew years ago used to say, "If it weighs anything, leave it out." Some of the other guys in the club found out the hard way that this was true. They had heavy airplanes that flew like dogs.

Dan
 

BBerson

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I did some experiments with used autoglass (laminated windshield). As Dan said, it is heavy because glass is heavy and because is 1/4" thick. Scrap windshields are available at any autoglass replacement shop for free. It can be cut with a diamond wheel and a stream of cooling water. Takes a few tries to prevent sudden cracks, but it can be done.

Most glass has a green color.
 

autoreply

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I would accept a minor weight penalty for noise dampening since it's quite tiring (thicker windshields and such) and at the same time (if designed properly) increases the crashability of your cockpit.
 

litespeed

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Canuck,

I would go for the best possible seat structure and seat belt arrangement for comfort and safety.
Forget glass just replace more often if its a small area. The pull off as per dirt bikes is possible- but vision sucks, they only put up with it because it is better than seeing just mud.

Unless you really want speed- forget laminar flow, a cantilever is nice though.

But the absolute biggest safety related item that adds considerable peformance and has no build time or cost ?

Lose some weight if possible from the pilot- nothing is cheaper, and it adds performance, besides a lighter pilot can survive a crash easier as your frame loading decreases and your seat doesn't need as much padding.

I have seen lots of people spend heaps on horsepower for sport bikes and they still get flogged by less powerful ones and don't understand why. Simple, the other riders are a 100 pounds less.
 

Toobuilder

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I think the #1 for me is proper cockpit ergonomics including a comfortable seating position. And if you think about it, this does not need to add any weight, just the time taken to make the seats and position comfortable. As an example, my next project will duplicate the seating position of my car, right down to arm rest height, seat geometry and pedal position. Obviously, going to the junkyard and buying a 6 way electric seat from a Corvette would add far too much weight, but the shape that my body seems to find so appealing could be duplicated with a lightweight composite shell. This approach might weigh more than the typical homebuilt torture chair, but it will be worth it. If you're going to sit in one position for 3-5 hours, you need to be comfortable.
 

N15KS

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Chicago
I use my airplane for practical transportation so I'm willing to trade off some pounds in exchange for convenience, comfort and utility. I routinely trade-off some weight and drag in order to enjoy ground transportation when I land.



I'd give up a few pounds to achieve a spacious and comfortable interior. I'd also trade several pounds to make my airplane engine compartment as easy to access as the one on my car. I would not give up pounds for flashy paint or looks.

I believe a typical laminated car windshield is about 25 pounds. Considering my airplane canopy is a little smaller... minus the weight of the plexi I currently have... it's probably only a 10 or 12 pound penalty. Mostly for safety reasons, I'd consider it because I've met pilots who were seriously cut by plexi during minor accidents. For comparisson, many people have opted to give up 85 pounds for a BRS parachute (85 pounds based on C172 system).
 

Hot Wings

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Plexi = 1190 KG/M3 Glass = ~2400kg/M3.

My .080" thick canopy weighs about 4 pounds (it's thin). Replacing it with .125" thick glass like this:
Shatter-proof pint glasses to be trialled in pubs to fight drunken violence | Mail Online

would weigh about 13 pounds for an increase of ~9 pounds on my 260 pound plane, or about 3.5% increase.

Switching would mean mandatory wearing of eye protection since even safety glass throws pieces around when hit.

Depending on price I'd consider the option if it were available. A few less burgers would even up the TO weight :dis:
 

Rom

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Medina, Ohio
What about the effect of hail on glass at aircraft cruising speed?
Flying in a storm strong enough to produce hail, I would worry more about a damaged airframe. The 20lb goose would be my concern.
My composite fuselage around the cockpit has a little more structure than it needs to be for crash protection. Protecting my person is worth the extra weight.
Adding a ballistic recovery parachute is also on my list. Having 2 near misses, one actually in controlled airspace, I appreciate the extra protection in case of a missing wing.
 

bmcj

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I was thinking more in terms of shattering the glass, making it difficult to see out of. My car's lexan headlight covers take lots of abuse, whereas my windshield has been cracked by small pebbles kicked up by cars ahead of me. Wings can be dented by hail and still land you safely, but multiply that spiderweb crack in the windscreen by hundreds of unanticipated hailstones, and you may not be able to see forward through the glass.

I understand that Saf-T-Glass helps hold the window together even after it shatters, but larger objects (like your 20 lb goose) can still penetrate.

Bruce :)
 

Rom

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My windshield is 60 degrees from vertical and .125" thick plexiglass and bubble shaped so I hope the goose will deflect off rather then impact my noggin. I would like to hear other's experiences in that reguards.
 

bmcj

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My windshield is 60 degrees from vertical and .125" thick plexiglass and bubble shaped so I hope the goose will deflect off rather then impact my noggin. I would like to hear other's experiences in that reguards.
Sometimes it's not the impact of the goose that matters, but what you do to avoid it. A pilot and his wife in my local area nearly died when he reacted to avoid a goose at low altitude. He ended up spinning his Stinson, destroying the plane on impact with the ground.
 

lr27

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I wonder if there's something you could put over polycarbonate to make it harder to scratch and more resistant to sunlight? Polycarbonate is really tough stuff compared to plexiglass. Of course if you've got to have a windshield with double curvature, it's going to be a lot easier to do in plexiglass.
 

cbock

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I'm all for the ergonomics and such. As for the BRS, in anything that I had a hand in it is almost not even an option. I barely trust myself to design a kite.

One additional worthwhile place to add weight is instrumentation. Even the super light guys can benefit from a GPS, Com. I love the idea of working up my own glass panel but if I do that I will have at least minimal backup dials.

Adjustable props, and retracts are worthwhile weight that I waiver on as well.
 
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