HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jul 13, 2012, 01:17 AM
This Calls for a Sexy Party
StewieRC's Avatar
Minneapolis
Joined Sep 2010
639 Posts
Discussion
Wing flex, when is too much flex ?

I'm building a Cargo twin by F&T, When i loaded my plane up with full flying weight with cargo, my wing will flex a lot.
When i'm holding it on both wing tips, the wing will flex to almost 45 degrees angle ( but will not break though ).
My wing already have about 15 bamboo spars on LE and center of the wing and cover with Clear packing tape.

Is it the bamboo skewers that are flexible or my wing suppose to flex that much ?

p.s: so a 400g plane flying at 5g mean that the whole thing will weight 2000g ( 2kg ), so if i want to do some crazy pull out, my wing will have to withstand 2 KG without breaking right ?
StewieRC is offline Find More Posts by StewieRC
Reply With Quote
Sign up now
to remove ads between posts
Old Jul 13, 2012, 01:42 AM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
12,425 Posts
To use the skewers for strength, you should try to take advantage of their tensile (pulling) strength as much as possible. Skewers aren't super stiff when you bend them, but obviously if you try to stretch one it won't be as easy.

How you go about this is up to you. Generally it's best if the skewers are glued directly to the foam; simply laying them in place and taping over them won't add much stiffness because they can still move slightly under the tape when the wing is flexed.

As far as the bending force on the wing, remember that in flight the whole wing is generating lift and not just the tips. The wing will still bend, but not as much as it does when you hold it up by the tips.

You might be able to use fishing line or other strong, non-stretchy string to form some type of rigging that'll help keep the wing from flexing upward, i.e. lines from the wingtips to the bottom of the fuselage.
C₄H₁₀ is offline Find More Posts by C₄H₁₀
Reply With Quote
Old Jul 13, 2012, 02:14 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
11,765 Posts
A few observations..
  • The lift of the wing doesn’t all act at the tips, it's spread over the surface of the wing, so if you want to simulate how much flex you will see in flight support the wing in the centre of each wing panel, not at the tips.
  • Your calculation of 400 grams at under 5G loading = 2Kg is correct but for testing the wings you can deduct the weight of the wings themselves from the all up weight of the plane. So if the wings weighed 100 grams, that would reduce the effective all up weight to 300 grams and give a loading of 1.5Kg for testing purposes.
  • For spars to work effectively they need to be spaced as far as possible apart vertically; so one spar on top of the wing surface and one on the bottom. If you can double the depth of the spar (even without adding any extra material to it) you will reduce the deflection of the wing four fold. That's why spars on built up wings have two 'caps' placed on the top and bottom and a 'web' in-between to hold them apart.
JetPlaneFlyer is online now Find More Posts by JetPlaneFlyer
Reply With Quote
Old Jul 13, 2012, 02:20 AM
This Calls for a Sexy Party
StewieRC's Avatar
Minneapolis
Joined Sep 2010
639 Posts
Hey thanks for the info, i hot glue my bamboo skewers under the wing. I'll decided tomorrow on whether to add more spars to make the wing more rigid, i'll maiden without any load, put it though its paces and hopefully everything will come down in 1 piece.

thanks for clearing thing up, if you guys know where to mount the main gear on a Trike landing gear, please let me know. I just know that the main gear have to be behind the CG, but not too far behind it, what happen if i mount it too far behind the CG ?
StewieRC is offline Find More Posts by StewieRC
Reply With Quote
Old Jul 13, 2012, 06:27 AM
Canadian Bacon
flypaper 2's Avatar
Kingston, Canada
Joined Jun 2004
12,913 Posts
Do as Jet plane says and add another bamboo spar on top of the wing about a 1/3 of the way back from the leading edge. Acts like an I beam. How thick is the wing?? 1/4 to 1/5 in behind the CG is fine. If you get too far behind the CG it makes it hard to rotate if it sits slightly nose down as most trikes sit.

Gord.
flypaper 2 is online now Find More Posts by flypaper 2
Reply With Quote
Old Jul 13, 2012, 10:54 AM
This Calls for a Sexy Party
StewieRC's Avatar
Minneapolis
Joined Sep 2010
639 Posts
honestly i don't want to add any spars on top, the top of my wing is simply nice, clean and beautifu.
StewieRC is offline Find More Posts by StewieRC
Reply With Quote
Old Jul 13, 2012, 11:08 AM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
11,765 Posts
Quote:
Originally Posted by StewieRC View Post
honestly i don't want to add any spars on top, the top of my wing is simply nice, clean and beautifu.
Recess the spar into the foam and tape over, you wont even know it's there. Anyway, putting form before function is never a good idea when it comes to building airplane wings
JetPlaneFlyer is online now Find More Posts by JetPlaneFlyer
Reply With Quote
Old Jul 13, 2012, 12:33 PM
I fly 3-C Crash,Crunch,Crumble
Mr. foambuilder's Avatar
USA, NM, Clovis
Joined Feb 2010
1,084 Posts
Quote:
Originally Posted by StewieRC View Post
honestly i don't want to add any spars on top, the top of my wing is simply nice, clean and beautifu.
Next time invest in some flat Carbon Fiber spars. They are thin, and have exceptional strength along with low weight. Roy ps: you slit the foam and put them in on edge.
Mr. foambuilder is online now Find More Posts by Mr. foambuilder
Reply With Quote
Old Jul 13, 2012, 01:16 PM
Glow 😡 no no no
Australia, SA, Evanston Park
Joined Mar 2010
4,807 Posts
Quote:
Originally Posted by Mr. foambuilder View Post
Next time invest in some flat Carbon Fiber spars. They are thin, and have exceptional strength along with low weight. Roy ps: you slit the foam and put them in on edge.
In my mind the best answer so far +1, why bamboo when carbon is longer and one piece.
aeromaniac is online now Find More Posts by aeromaniac
Reply With Quote
Old Jul 13, 2012, 01:19 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,411 Posts
Also think about wing twist when you have a 'flexible' wing.

Dihedral isn't a major problem, ......until either the wing tips touch , or the wings part company with the fuselage .

Flexible wings that allow twist chord wise can be a real major problem at speed. In a turn the affect of the aileron can cause the outer wing section to also twist. If the leading edge twists down enough to cause 'dig in' as it is sometimes called. Then the plane can become very unstable and spin out or the turn.

The other potential problem can be wing flutter, where the wing will flex and then start oscillating, (similar to blowing across the top of a sheet of paper). It is more likely to happen to a control surface, even on a stiff wing, but I have seen a model lose a wing at speed when the wing started fluttering, (hell of a noise), then disintegrate.

Flexible is Ok up to a point with slowish speeds, but for anything fast, stiffer wings are a good safety feature.
eflightray is offline Find More Posts by eflightray
Reply With Quote
Old Jul 13, 2012, 02:07 PM
miniture aircraft pilot
rcshirt's Avatar
United States, FL, Tampa
Joined Oct 2007
1,341 Posts
if inverted flight is not planned... fiber stranded packing tape... use to use that on 1/2a model foam wings in the days of the old
rcshirt is offline Find More Posts by rcshirt
Reply With Quote
Old Jul 14, 2012, 10:09 AM
buyer of the farm
United States, FL, DeLand
Joined Mar 2009
4,425 Posts
This is too much flex:


Parkzone Radian on a winch. The wings did not break. The plane flies fine afterwards. This was not a trained professional but you should not try this at home anyway. Your mileage may vary.
Rockin Robbins is online now Find More Posts by Rockin Robbins
Reply With Quote
Old Jul 14, 2012, 03:09 PM
Glow 😡 no no no
Australia, SA, Evanston Park
Joined Mar 2010
4,807 Posts
Quote:
Originally Posted by Rockin Robbins View Post
This is too much flex:


Parkzone Radian on a winch. The wings did not break. The plane flies fine afterwards. This was not a trained professional but you should not try this at home anyway. Your mileage may vary.
Lol
aeromaniac is online now Find More Posts by aeromaniac
Reply With Quote
Old Jul 14, 2012, 07:06 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
12,425 Posts
Errrm, why was the Radian getting fired off the winch? Was there actually a specific reason, or was it just like "Hey guys, let's see what happens if we winch-launch this Radian!"?

Cool picture either way
C₄H₁₀ is offline Find More Posts by C₄H₁₀
Reply With Quote
Old Jul 14, 2012, 07:28 PM
I like to fly!
United States, WI, Monona
Joined May 2011
227 Posts
As long as they're not separating from the aircraft, it's not a huge concern. Wingflex really pisses me off when I fly, though. It just makes the plane handle strange from the wings flexing around. It's the number 1 problem I tend to fix in planes. Carbon fiber strips work great to get rid of it.
Alex
alexkmmll is offline Find More Posts by alexkmmll
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Adding Capacitors, what voltage and how much is too much? aerosoardude Electric Power Cars 7 Jul 16, 2012 08:48 PM
Discussion how much wing damage is too much damage ?? :-) khooke Micro Ready-to-Fly 15 Jun 13, 2012 11:13 AM
Discussion When is too much too much? highflyer9 Power Systems 3 Dec 31, 2007 09:50 AM
Question How much is too much wing flex TXTATE Foamies (Scratchbuilt) 6 Sep 21, 2006 11:24 AM
SS wing Dihedral, how much is too much? too little? Keesercc Beginner Training Area (Aircraft-Electric) 17 Jun 28, 2003 02:08 AM