KidEpoxy

What do you guys think of building in an impact absorbing area behind the firewall,
so the nose will shatter but make it easier on the engine/firewall & rest of the fuse?

I was just fixing a DNU after the ground assaulted my innocent plane,
(ok, perhaps the radiospikes I was dealing with on the bench had something to do with it)
and had to cut out some of the nose sheet & squares that crumpled. It turned out just one side of the firewall got pushed back 1/8" and the sheet blew out the front 2-3" to allow that. I thought this was a great feature, that the doubler & bulkhead area was fine, as was the motor (yes, I suffer the burden of electric flight shame ) [)]& firewall.

The question is, to build stronger with doubler all the way to the firewall,
or go the other way with it and cut the sheet for a 1" gap & use 1/4sq "shear pin" splints to hold a strong front-nose to a strong rear-nose.... kinda like a front box & rear box with sacrafice connecting 1/4sq in the corners.

ptulmer

My Feedback: (5)

KE, instead of doing the stick thing, just bring the vertical grain doubler all the way to the firewall. Minimal weight gain and a lot more strength. If you precut it to plan dimensions, you can rebuild around it and it will still be far stronger.

KidEpoxy

PT-
Thanks for the tip,
but I had already cut a clean hole & fit a drop in buttsplice patch piece of 1/16 diagnal grain to replace the bad fuse side area. Elmer with 3 CA dots to hold it, and slapped a 1/2" strip of elmers soaked paper on the inside to 'fuse' the seam. As I was putting some doculam over the fix I thought about the crumple saved the rest of the bird, and thought I maight make that a more pronounced feature.

Sure, I thought about running the doubler all the way on the next one, I have weight to spare cause I run the span out an extra rib bay on all my DNUs (easy handlaunch). Just wondering it that would put more hurt into the motor/firewall & rest of the bird.

It really is an opinion thing, strong enough to not need fixing,
or shearpins to simplify fixing & limit damage.

Of course, there is always the chance it wont crash,
but not crashing isnt my particular flying style. [&:]

cyclops2

All my planes pass the insurance frontal impact test.

combatpigg

My Feedback: (3)

The generous span wing, low pitch prop, light weight model will out perform the heavier version in most areas and leave you with fairly simple repairs, even if you have to graft an entirely new nose onto the "box". How hard is it to rebuild one end of a box?
The difference between flying a 12 oz and 14 oz 1/2A plane of the same size is like night and day. One is like driving your Moms station wagon, the other is like driving a sports car.

ptulmer

My Feedback: (5)

KE, you may have something with the crumple zone. When the Langolier went in with a doubled front end, that was all that was left. The empennage was broken off as a piece and the front was still intact. Far, far more damage than I'm used to seeing in a 1/2a. Maybe too much to be repaired!

KidEpoxy

"Maybe too much to be repaired!"

All damage can be repaired,
it just might end up needing a .15 afterward to pull all the extra splints, patches, & glue [&:]

The more thought I put into it, I realize the fine balance between light enough crumplezone to reduce other damage, and keeping enough structure that the front dont snap off when we try to start a flooded cylinder engine.

Yuu

I like the 'crumple zone' approach. I built an RCM-5 [for .049] and used the doubler in the front as per plan. Every crash would break the tail off just ahead of the stab. The inertia of the heavy tail area would just 'bring it around' and leave it hanging by the nyrods. After a friend demolished the fuse on a three ton bolder, I built a new fuse w/o the doubler. Much easier to re-extend the nose than trying to "align" all the tail feathers, IMO. I also found that 'tyvek' will absorb water and expand, maybe 3%, but Elmers white mixed w/ a little water and let 'sit' five minutes so it enlarges, the glue will hold it as it drys. Cheap 'crumple zone'.

digital_trucker

...or you could just try not crashing it. Don't build 'em to crash, build 'em to fly! Not only will they fly much better, but they'll suffer less crash damage as well. Most models are horribly overbuilt (and thus overweight...and thus more prone to rekitting on impact).

smoknDave

Absolutely what Digital Trucker said! Never build thinking about crash survival.

Dave

combatpigg

My Feedback: (3)

Crash energy seems to travel through an object looking for a weak link. Planes made with spongy foam are good at spreading the force out in all directions. I think a clever substitution for balsa fuselages would be that EPP foam, too bad it is so toxic to work with.
One of the most miraculous sites is to see a C/L combat plane hit the ground nose first and just bounce off the dirt, then get immediately relaunched.

digital_trucker

I know it's not 1/2A, but take a good look at how Great Planes' Ultra Sports are engineered. They're very lightweight, and tremendously strong (I can attest to how strong by the heaps of abuse I piled on my old .40 size version). It flew THROUGH a tree, hit straight on the nose from a vertical (unpowered) dive, cartwheeled, landed inverted in the weeds, and numerous other oopsies...all these on separate occasions. Grand total of airframe damage one broken prop, three cracked ribs, a little cracked wing sheeting, ALL the monokote blown out of the open bays in the wing, numerous dings along the leading edges of the wing and stab.

As an example of how lightweight and strong they are, I'm currently flying a .60 size version. Built with ambroid (the 'glass on the wing is attached with it too), flying weight with an HP .61 is an even 6lbs. This one has been cartwheeled once too (engine failure, caught the weeds on the edge of the runway and danced down the runway). No damage. I've since replaced the go-unit with a nice shiny new .91 surpass...no more engine troubles and the vertical is unlimited, and takes off in about 10 feet with the flaperons down.

My point is that no matter what size the plane is, properly engineered with an eye for weight and strength and an airframe can suffer horrible abuse and emerge unscathed. This Q-Tee is built basically the same way but with elmer's wood glue instead of ambroid, it's immensely strong (it's been cartwheeled too). I finally broke it a few weeks ago when it caught a wingtip and snapped the cabanes. I figured they were going to be the weak point in the structure...I'm sure the fact that it's very overpowered and I fly it wayyyy out of it's design specs didn't contribute or nuthin'.