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Author Topic: Adding lightness  (Read 1042 times)

Offline Curare

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Adding lightness
« on: August 19, 2012, 08:34:53 PM »
Hey guys, just another thread, this time discussing everyone's favourite topic, weight.

This is slightly out of 1/2a teritory, but is still in the 1-1.5cc mark.

My last trial at building a stuntable 1.5cc model ended poorly, or more to the point, portly.

I had what I thought was enough wing area, but the aircraft was too heavy.

When building a profile fuselage, I used the lightest, strongest, straightest stock I could find 3/8" btw, and the only strengthening was a 1/32" ply doubler either side of the fuse back to the wing's mainspar.

Is 3/8" too much? Should I have used 1/4"?

Also, this was a test bed for cutting foam sparless foam wings, so a complete airfoil without leading, trailing edges or top and bottom spars covered in fibreglass cloth and applyed with polycrylic . I now think after having done this that I'd be better off adding some spars and getting rid of the polycrylic in favour of a low temp iron on covering.

Any thoughts on these topics?
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Greg Kowalski
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Offline Larry Renger

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Re: Adding lightness
« Reply #1 on: August 19, 2012, 09:47:18 PM »
I suspect that no matter what you use to bond 'glass, it is going to be too heavy.  And did you core out the wings or are they solid?  Solid foam wings only nee d strapping tape top and bottom and a low-temp covering to be more than strong enough.  If it is cored out, vacuum bagged brown wrapping paper is sufficient to give you the strength (1/2 the weight of 1/32 light balsa!)

A 1.5cc model should have about 250 to 275 sq.in area and weigh no more than 12 ounces, or 15 ounces with flaps.
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Offline Steve Helmick

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Re: Adding lightness
« Reply #2 on: August 22, 2012, 12:29:32 AM »
A wise guy once said "simplicate and add lightness". There's a lot of truth to that. One thing I am rabid about is tapering the LE, spars and TE.  A bit more work, but significant weight can be saved, and it's in all the right places.  y1 Steve
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Offline Curare

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Re: Adding lightness
« Reply #3 on: August 22, 2012, 01:12:03 AM »
Ok so lets just go thought my processes as I've figured out how to make the perfect baseball bat, but maybe not the best wing.

The cores are 1lb foam, that are solid (not cored out) and over the top 1/4oz tissue (not weave, but similar to carbon veil) was painted on with polycrylic.

That weave took a lot of polycrylic to fill. I wasn't chasing a perfect finish, (far from it) but I had three coats on before it'd stop pulling up the fibres every time I'd get near it with a sanding block.

At any rate, next time I'll probably use spars and maybe hit it with SLC.

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Greg Kowalski
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Offline Trostle

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Re: Adding lightness
« Reply #4 on: September 01, 2012, 07:25:01 AM »
Years ago, I think I can remember when post holes could be ordered from a Sears catalog.  It seems like we should be able to order lightness or whatever it was that came when you ordered a post hole to add to these models of ours.  I guess that "technology" or "unobtanium dust" has been lost with the demise of the Sears catalog.  Packaging was probably a problem.  I think it had to be stored in a plasma flask and those were really really expensive.   Those flasks were fairly small but they required huge amounts of continuous uninterrupted power to maintain.

Keith
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Offline Tim Wescott

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Re: Adding lightness
« Reply #5 on: September 01, 2012, 09:11:44 AM »
You didn't say how heavy.

Once you get your wing weight down, consider making a hollow fuselage with a 1/4" thick core, built up in back and solid in front, with 1/16" sides on it.  That'll be stiffer than a 1/4" thick fuse of the same weight balsa, and lighter.

For that matter -- what's wrong with a built-up wing?
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Jim Thomerson

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Re: Adding lightness
« Reply #6 on: September 01, 2012, 09:26:18 AM »
For a 1.5 airplane the size of a Jr. Flite Streak, 17 oz is OK.
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Offline jim gilmore

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Re: Adding lightness
« Reply #7 on: September 03, 2012, 02:12:39 AM »
I will agree to disagree about your wing size..
I built the topflight hawker hurricane and the tf cosmic wind back around 1969 or so to try and fly stunt. I easily did loops and eights and would glide the plane much better than any of my 35 powered aircraft. but the secret was to build light and keep the paint to a minimum . that was a 144 sq in model.
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Offline Curare

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Re: Adding lightness
« Reply #8 on: September 03, 2012, 07:25:24 PM »
Guys, sorry, I tend to be a bit cryptic at times, this was in aid of a stunt trainer design that I didn't have a lot of success with.

The general consesus was "too heavy" as opposed to my initial thoughts of "not enough power".

Here's the thread that started it all, and if you scroll down you'll see a low res image of the design as it was. http://stunthanger.com/smf/index.php?topic=28145.0


The only reason I didn't suggest a built up wing is longevity of the aircraft. Foam wings take a savage beating before finally becoming a trash-can filler.

My skills necessitate foam at the moment!
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Greg Kowalski
AUS 36694

Offline Tim Wescott

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Re: Adding lightness
« Reply #9 on: September 03, 2012, 07:36:02 PM »
Properly designed wooden wings will take a beating, too (look at the Sig Skyray and Twister, and the Flight Streak).

But if you're comfortable with foam, by all means stick with it.
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AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Curare

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Re: Adding lightness
« Reply #10 on: September 03, 2012, 08:27:08 PM »
If you look at the plan, I originally designed it as a constant chord built up wing, as I know I can make a better lighter wing from balsa than foam, but it takes a few days to get a wing sorted (including covering), whereas a foamy takes a few hours from go to whoa.

That appeals greatly!

If I do another I'll probably core it out too.
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Greg Kowalski
AUS 36694

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