I have a couple of flat depron foamies that I fly a lot. One is a fast pusher jet and the other is an aerobatic sport plane.
A while back I started checking them over for cracks in the foam, most of the time everything is fine. Today was a different story, both planes has minor stress cracks that looking at them on the ground I did not see. In fact the cracks on the sport plane were underneath the fuselage and not visible at all from above. The pusher jet had a minor stress crack in the forward part of the fuselage. The crack was only visible when looked at up close. A small amount of foam safe CA quickly repaired both planes and both are safe to fly.
The reason I bring this up is because both planes could have been lost to structural failure during flight brought on by the stress cracks. I was just wonder who else does these post flying checks of their planes and how often do you find cracks?
Years ago I had the GP Fokker Dr1 60 inch size... I flew it aggressively and it was so reliable (and was transported with wings on) so it didn't get a wings off inspection often.
One day it started acting really strange in flight so I landed. Took the top wing off, then the bottom and the middle wing just flopped. it was a essentially a bag of toothpicks in there.
The airplane wasn't worth repairs needed to make it airworthy again... ALL of the structure had severe cracks.
What struck me about depron is it hides fine cracks very well. I don't check after every session, and maybe I should, but after this past flying session I plan to do a once over when I am done flying. You almost have to move the planes major section around to view the cracks. In the case of the jet I actually cut out a small wedge that covered the crack and then glued in a new piece of depron.
Yes, Depron is Brittle and stiff, thats why its a Great foam to build with, other foams twist and bend and cause a aircraft to not fly right with out a lot of Bracing, I always check the glue points, because thats where the Depron will start to crack at, I have some depron planes here that are 4 to 5 years old, and have a few cracks that needed attention from Vibration , OK OK OK From Hard landings too always a good idea to check all planes for cracks, balsa, foam + plastic, you just never know take care and have fun, Chellie
I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
I actually give a light twist test to wings .. tail feathers often as I fly a lot at rough sites ... the landings are always a bit rough on the models. It's common for my fin to be cracked at base ... or a stab to be half broke at fuselage.
About Depron ... I find Depron to be far more forgiving than any other sheet foam I can get in Latvia ... I can bend Depron round a tube - but floor sheet as I use often snaps as soon as you try bending it.
But I must admit - I have flown a model at times without knowing it's cracked !
I flew a biplane once without realizing the bottom port wing was snapped completely in half.
My Bosak Mig 15 back in the 80's cracked it's main spar in the wing and in fact it flew better !!
The model had sweepback to give the rudder authority instead of dihedral, it was 3ch only ... on a 20 IC glow.
Turn control was always there but needed a wide area to sweep round in ... but after the main spar cracked - she turned much better ! The wing was flexing in flight and introducing dihedral when rudder moved ...
Of course I repaired her and did not fly her like that more than once ... but it was so marked a difference I can still remember it ...
I give the superfly delta a slight twist and bend all over to see if any old repairs are still holding or if I need to make new ones. otherwise I mostly fly balsa and don't check for cracks except in the spring tuneup I do on all planes before the season starts and check all moving parts and servos to make sure all ok to fly.
narrow is the place to land...wide is the space to crash....choose the narrow way!
Normally I don't check for cracks, but I do check the connectors and servos arms for problems.
I had my Telelink crack at the wing root once couldn't figure out why it was handling so bad. Landed and checked it out that's when I found the crack in the foam. This week I was throwing it around the sky and noticed it was acting funny again. Landed and I cracked the wing on the opposite side. All fixed, but it is getting a make over to a night flyer. I've beat the snorts out of this plane learning 3D time to retire her to some easy night fun.
I check every thing like we are supposed to Gramps 2361 before and after every flight ! I have had every thing go wrong that can't go wrong with my planes !!
I just lost the Rascal I spent all winter building because the rear former at the tail end
broke in flight and the cable that came with the kit kinked the guide and slammed it down on its tail and wing and tore it apart with just enough left to show me where the problem was !
I am glad I am not the only person looking for cracks in foam airplanes. I have come to the conclusion that foam planes have a finite life time and are basically a throw away item. I do not mean this in a bad way, they are cheap to build, easy to build, and a lot of fun to fly. When they reach end of life, toss them and build another one. That's what I do. I bought a package of depron and build my own.