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Problem with Top Flite Giant Scale P51 ARF

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Problem with Top Flite Giant Scale P51 ARF

Old 10-27-2013, 04:50 AM
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ibytimmy
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Default Problem with Top Flite Giant Scale P51 ARF

Has anyone had an issue with the wing in a TF GS P51 twisting? A few weeks ago I noticed, while flying, the aircraft starting to behave erratically. I got the aircraft on the ground, and during inspection was able to grab ahold of the wingtip and EASILY twist the being. After i got home, I cut the bottom sheeting off the wing and discovered ALL of the shear webbing was CRACKED. What was odd (to me) was that the webbing was installed with the grain running parallel to the main spars. I have NEVER seen this before, and to my knowledge the webbing should not be installed this way. I was told by TF that they did this on purpose. Anyone care to comment? Anyone have issues like this? Anyone out there that has a TF GS P51 that can verify the direction of the grain on your webbing??????

I would greatly appreciate any feedback.

Thanks!

~Carl
Old 10-27-2013, 05:29 AM
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scale only 4 me
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I have an ARC in the rafters, I'll check later,, but it should be perpendicular for max strength,,of course
Old 10-27-2013, 06:19 AM
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JohnBuckner
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Perpendicular period! only just my lay opinion. The purpose of the webs is to maintain the spacing of the spars as the upper spar will try to fail inward during high upward loads and vice versa. If you think about it to accomplish this the grain of the wood webs needs to be perpendicular and work in compression to maintain the spar separation.

John
Old 10-27-2013, 11:16 AM
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Gray Beard
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Did you ask what this purpose was??? I'm thinking The little people in China really made a big mistake and TF just doesn't want to be replace a bunch of wings. If the plane just crashed most people wouldn't notice the little mistake in the shear webs. Just a guess.
Old 10-27-2013, 03:35 PM
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ibytimmy
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Thanks for the input thus far. I am well aware of the purpose of shear webbing and how it should be installed. my intention was to see if other TF GS P51 owners might take a peek at their models (if possible) and verify the direction of the grain. When I cut mine apart, there was one webb near the retract that was correctly installed. All of the webbing on the backside of the spars were put in with the grain running parallel with the spars.

Thanks for all your help!

If I am on to something, it could prevent more accidents......

Carl
Old 10-27-2013, 03:36 PM
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ibytimmy
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Thanks scale only 4 me.....
Old 10-27-2013, 03:46 PM
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ibytimmy
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Thanks scale only 4 me.....
Old 10-27-2013, 07:58 PM
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Gray Beard
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Maybe if you posted this in the ARF forum there may be a lot more answers about that particular plane? Scale has in in ARC so it is easy to look at before covering. If it is posted in ARFs it will also be something for others to keep an eye out for. Good advanced warning.
Old 10-27-2013, 08:07 PM
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ibytimmy
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Thanks for the suggestion. Haven't used the forums much so I wasn't sure where was best. I will put a couple more up tomorrow in that area.

Thanks!
Old 10-27-2013, 09:21 PM
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Jetdesign
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Interesting thread. I googled RC sheer webbing pics out of curiosity, and apparently it is not *that uncommon for ARFs to come with the grain running parallel to the spars.

I had to think for a minute as neither scenario seems ideal to me. I would think diagonal balsa square stock would be stronger and lighter, but then I also get that from a manufacturing standpoint, the perpendicular-grain sheeting would be more cost effective (labor) and still work for normal operation.
Old 10-28-2013, 04:29 AM
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pacoflyer
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Gentlemen,
This wing problem with the TF P-51 was identified a few years back and the manufacturer,distributor refused to address it. I think it all started when the wing spars started failing with even the most gentle landings possible.
With the sheer webbing running parallel to the spars, there is little support/resistance to the compressive loads applied during landing. Upon repair, where the sheer web is installed properly, with the grain running perpendicular to the spar, the wing becomes rock solid. I'm probably opening a can of worms here, but seen this first hand.

Good flying,
paul
Old 10-28-2013, 04:37 AM
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Airplanes400
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Of all the kits I built (and according to the instructions), as well as my engineering experience and common sense, the sheer webbing needs to be perpendicular.

As per gaRCfield, the ideal method would be diagonal, but in a criss-cross (x) design for ultimate strength (as done in full sized aircraft and bridges with cables.)

For the purposes of the size of the TF P-51 Giant scale, perpendicular webbing will be adequate. No need for criss-cross diagonal webbing until a higher weight / larger airframe is utilized. Prob 1/4 scale or greater.

Those kids in China are installing the webbing incorrectly. As you found, parallel webbing is providing no strength. It allows flex, and is simply WRONG. I don't care what Great Planes is telling you.

Open the entire wing and install 3/32" perpendicular webbing on top of the parallel webbibg wherever you can.

Last edited by Airplanes400; 10-28-2013 at 04:46 AM.
Old 10-28-2013, 05:16 AM
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ibytimmy
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Does anyone know if TF corrected the problem with the newer kits? The ARF this happened to is an older version that sat unbuilt for a couple years. I am now actually flying a newer version ARF that is only a year or so old. any reason for me to cut open the new one?
Old 10-28-2013, 05:57 AM
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aghost
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Old concern. Here's a link where an individual posted his fix (page 51, post 1263 I think)
http://www.rcuniverse.com/forum/rc-w...mishap-51.html

Brian
Old 10-28-2013, 08:37 AM
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Jetdesign
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Just FYI, they are called 'sheer' webs because they are there to counteract sheer forces, not compression. When air puts lift on the wing and pulls it up, the top spar goes into compression (forces pushing toward the fuse) and the bottom in tension (forces pulling away from the fuse). A wing rib attached to the top and bottom spar would end up twisting (top in, with right-side-up lift) without proper reinforcement. The sheer webs basically keep the wing ribs square to the top/bottom spar. The wing ribs can handle whatever compressive loads would be present, but they have to be perpendicular/square to do so. This is why diagonal cables can be used in place of ply or whatever else.

If you have this plane or problem and can access the wing structure, a little 3/4oz glass cloth laid diagonally to the grain of the sheer web would be a quick and easy fix. It shouldn't need much. You could also glue a stick of balsa diagonally across each web. Remember that the diagonal bracing is in tension. Balsa is plenty strong for that application.

If you remember learning why triangular patterns are used in bridge structures, it is the same principal.

Last edited by Jetdesign; 10-28-2013 at 08:40 AM.
Old 10-28-2013, 09:08 AM
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retransit
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Not to get off on another aircraft, but I have a Nitroplanes (Projet) Reaper ARF and those wings flex. If I ever have cause to open up the structure, dollars to doughnuts, I will find NO spar webbing.
Old 10-28-2013, 01:10 PM
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flycatch
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Originally Posted by gaRCfield View Post
Just FYI, they are called 'sheer' webs because they are there to counteract sheer forces, not compression. When air puts lift on the wing and pulls it up, the top spar goes into compression (forces pushing toward the fuse) and the bottom in tension (forces pulling away from the fuse). A wing rib attached to the top and bottom spar would end up twisting (top in, with right-side-up lift) without proper reinforcement. The sheer webs basically keep the wing ribs square to the top/bottom spar. The wing ribs can handle whatever compressive loads would be present, but they have to be perpendicular/square to do so. This is why diagonal cables can be used in place of ply or whatever else.

If you have this plane or problem and can access the wing structure, a little 3/4oz glass cloth laid diagonally to the grain of the sheer web would be a quick and easy fix. It shouldn't need much. You could also glue a stick of balsa diagonally across each web. Remember that the diagonal bracing is in tension. Balsa is plenty strong for that application.

If you remember learning why triangular patterns are used in bridge structures, it is the same principal.
Your explanation bears no merit. I say this since I have built many gliders and powered models, all shear webs are installed just opposite of what you are saying.
Old 10-28-2013, 01:36 PM
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Hi

I have prepared 5 of these TopFlite WarBirds , and I have , " ALWAYS " , ripped of the top sheeting and replaced the shear webs , with light ply , where the retracts are . This weak spot in this aircraft ,…………… IS EXTREMELY WELL DOCUMENTED . I learnt from experience .

BTW ,………….. don,t ask TopFlite ( Idid ) ,…………………. There R&D , is the best , There modo , sell the kit ,………………………….. have a nice day

Michel
Old 10-28-2013, 04:10 PM
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I have also redone the shear webs in my TF P-51 wings. I do it prior to glassing or covering. Also check any and all glue joints to the landing gear blocks and reinforce them if needed.
Old 10-28-2013, 04:31 PM
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Glad I bought a kit.
Old 10-28-2013, 04:36 PM
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Michel
 
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Hi
Absolutely ,……………. There was , " NO GLUE " on many of the webs ( I took them out by hand , no ***** ) , and the retract area , they are very poorly built . And what about the guide tubes for the elevators and rudder , they were laser set , ( NOT ) LOL . They were all binding , . If you have a 500 oz servo , you're cool .

Very poorly built model , and a would never buy nor advise anyone ,……………….. to buy this model unless there willing to do the mods , and again , " YES " it is all documented .

Michel

Michel

Last edited by Michel; 10-28-2013 at 04:37 PM. Reason: bad spelling
Old 10-28-2013, 05:38 PM
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vertical grimmace
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Originally Posted by ibytimmy View Post
Has anyone had an issue with the wing in a TF GS P51 twisting? A few weeks ago I noticed, while flying, the aircraft starting to behave erratically. I got the aircraft on the ground, and during inspection was able to grab ahold of the wingtip and EASILY twist the being. After i got home, I cut the bottom sheeting off the wing and discovered ALL of the shear webbing was CRACKED. What was odd (to me) was that the webbing was installed with the grain running parallel to the main spars. I have NEVER seen this before, and to my knowledge the webbing should not be installed this way. I was told by TF that they did this on purpose. Anyone care to comment? Anyone have issues like this? Anyone out there that has a TF GS P51 that can verify the direction of the grain on your webbing??????


I can promise you that you should never install shear webbing with the grain parallel to the spars. The best would be to alternate the grain at something like a 45 degree angle, but that is a lot of work. It is standard to install it with the grain vertical to the spars. The whole purpose of shear webbing, is to keep the spars from shifting in shear. Parallel grain adds no strength and is really doomed to fail. Especially with a heavily loaded aircraft like this. If this was done on purpose, Top flite engineers need to go back to school.

I would greatly appreciate any feedback.

Thanks!

~Carl

I can promise you that you should never install shear webbing with the grain parallel to the spars. The best would be to alternate the grain at something like a 45 degree angle, but that is a lot of work. It is standard to install it with the grain vertical to the spars. The whole purpose of shear webbing, is to keep the spars from shifting in shear. Parallel grain adds no strength and is really doomed to fail. Especially with a heavily loaded aircraft like this. If this was done on purpose, Top flite engineers need to go back to school.
Old 10-28-2013, 05:44 PM
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vertical grimmace
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Originally Posted by gaRCfield View Post
Just FYI, they are called 'sheer' webs because they are there to counteract sheer forces, not compression. When air puts lift on the wing and pulls it up, the top spar goes into compression (forces pushing toward the fuse) and the bottom in tension (forces pulling away from the fuse). A wing rib attached to the top and bottom spar would end up twisting (top in, with right-side-up lift) without proper reinforcement. The sheer webs basically keep the wing ribs square to the top/bottom spar. The wing ribs can handle whatever compressive loads would be present, but they have to be perpendicular/square to do so. This is why diagonal cables can be used in place of ply or whatever else.

If you have this plane or problem and can access the wing structure, a little 3/4oz glass cloth laid diagonally to the grain of the sheer web would be a quick and easy fix. It shouldn't need much. You could also glue a stick of balsa diagonally across each web. Remember that the diagonal bracing is in tension. Balsa is plenty strong for that application.

If you remember learning why triangular patterns are used in bridge structures, it is the same principal.
I think you are right here about the easy fix. Glassing the balsa would be best. Amazing with these ARF's what people are really getting. Really a shame. These all seem to be disposable planes.
Old 10-28-2013, 05:58 PM
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Hi

What you don,t see ,……………………………………….. doesn,t bother you ,……………… till after you,ve payed . I love TopFlite I love TopFlite I Love TopFlite .

Especially there R&D team .
Sorry ,……….. but they deserve this .
Michel
Old 10-28-2013, 07:57 PM
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Chris Nicastro
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I know a fellow flier here that took the ARF and removed the lower skin to strengthen the landing gear and spar only to find there was hardly any glue in the wing assembly!!! Many parts were void of glue as well. He just completed the wing mod and will be flying it as soon as the weather cooperates. I wish he took photos of it inside, he was just telling me about this the other day.

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