Hello,

May I just say I am new to both planes and this forum, though I am highlyfamiliarized with the technology that goes into planes. I am doing a project where I need to build a scale commercial aircraft with a complete chassis and cabin where an egg can be secure. The plane needs to be able to land in rough terrain while minimizing impact force, I am thinking of making the wings detach on impact. Any advice on whether I should do a bi tri or single wing plane? I am trying to maximize lift.<br type="_moz" />

Hmm, doesn't sound like a useful project if the wings detach on impact? I'd concentrate on landing gear. But you will need to know the moments of inertia at impact and read up on oscillatory motion, in particular a critically damped oscillation. Look at long wheelbase, wide track, several points of contact, spread it out....put the egg at the CG

Welcome to both, Mike!

What scale your model would be?

The classic method for avioding damage to a wing during a bad landing is to attach the wing using rubber bands so the bands secure the wing to the fuselage. The forward bands go onto dowel stubs sticking out of the fuselage that are pointed forward. This allows the bands to hold the wing on in normal flight but duing an impact the wing slides forward and pushes the bands off the forward pointed dowels. The bands spring loose and the wing continues and impacts the ground in a more kindly way on it's own. You'll seen this style of wing hold down a lot on cabin style models. The rear anchor dowels are merely a sideways mounted dowel that passes through the fuselage and holds the rubber bands on.

You'll have to define "rough terrain". Keep in mind that a regular grass field to a model is like a full size light plane landing in a field of wheat or waist high grass where there's lots of big mole hills and roughness. Operating out of an area with rocks, very uneven dirtand other hazards would not be a realistic scenario at all. It would be like a real plane being asked to operate from a boulder strewn field that had just been bombed. You can compensate to some extent with oversize wheels but in the end the field needs to at least be a realistic attempt at a grass playing field or the model will just flip over.

Padding an egg to avoid damage is as simple as molding or forming a block of foam around the egg so any pressure is distributed over the whole end of the shell facing the impact. With such a molded bed and a hard box shell around the inner bedding you can drop the box from the top of a house and the egg will still be intact. Mother Nature did a really good job on the basic design. You just need to ensure that the forces reaching it are spead out by using a firm material for the bedding.

As for the plane you don't design for high lift by using some sneaky feature. There's really only two factors involved. Keep the model light and make the wing big enough to lower the wing loading so it can fly slower. You also want to use an airfoil with lots of camber, up to a point, so the stall speed is lower. But the two key elements are the low weight and big wing area. If you don't have those the higher camber airfoil won't be enough to save the day. And don't worry about crash damage. A light but intelligeintly designed model will be tough and resiliant because it carries less kinetic force to do harm to it's own structure. Light but well designed models will bounce instead of busting. But you need to know where to build in the toughness and where to keep it light. The wing spar and the nose of the model are two areas where you can justify using a bit more weight for tougher materials. If you can keep those two parts strong then the rest can be quite light.</p>

EPP is a excellent material for this type project.
It absorbs high load very well
It is not a familiar medium for many modellers but those who have built or purchased models made from it , can attest to the fact that it absorbs energy extremely well
Basically you shape it as needed for appearance and add localized bits of ridgid strips as required

By rough terrain I do mean a field, the idea is to simulate a commercial plane crash and the wings detach to reduce impact

You are looking for impact absorption by the structure failing in a way as to reduce the transmitted impact forces to the egg, correct? A biplane will not necessarily be more beneficial. A better bet would be to build a low wing thick airfoil with a lattice type structure to give more material a chance to break during the impact. The fuselage sand landing gear should also have a more complex structure. As the structure fails it will absorb the impact over more time allowing the forces to taper off gradually. Using weaker materials with a more complex structure would be more beneficial. Just my .02.

How have you come to the conclusion that wing separation will lessen the impact forces on the fuselage/egg? To me it seems that given a certain velocity, the aircraft(less wings) would have less mass and therefore would slow down more rapidly. This would induce higher deceleration forces into the remaining fuselage structure.

Um... I just noticed in re-reading your first post the reference to "scale commercial aircraft".  So this is more about trying to model full size plane crash damage and an egg is the payload you're trying to protect?  Then you can forget about the whole show right now.  If the goal is to replicate and study how full size aircraft can protect the cargo by sheding parts to absorb the energy of the impact then your egg is hardly a good indicator of the sort of human cargo that you're trying to protect.  And model structures made from our usual wood, foam or fiberglass just don't "shed" in the same way during a crash due to the wildly different design and construction methods used.  Not to mention the differences in how the forces affect the model due to the size scale and mass moments. 

To do such a study properly you'd need to replicate the full size structure using material analogs that rip and tear in a manner that can be equated to the aluminium parts used in the full size aircraft and factor in the shifts in mass-moments and try to equate the way that the parts shed and related this to the full size aircraft.  Just finding such material, or using actual aluminium in reduced section sizes, is far, far, far beyond the scope of anything you'll find in the hobby model airplane world.   And equating how such a model were to perform to how the larger and heavier full size aircraft would work makes my brain hurt just thinking about it.  There's so many factors that I'm not even sure a model of anything much smaller than 1/4 scale would even give results that are actually useable.

First time around I had read this to be that you wanted to make a model that would fly in a rough field and land without damaging an egg.  I figured that it was another one of the oddball airplane related school contests or lab assignments that seem to be so popular these days.  And if that is the case then designing a model and flying it with an egg as the prototype is not hard with some packing and accepted model design.   The only thing that would make it interesting would be if there were a severe weight and size limit placed on the design of such a model. 

If I'm wildly out in both interpretations then how about filling us in more on how this got started. the sort  of size of the model and what the goal is intended to achieve.  Because as it seems now it's just a wild goose chase with no meaningful outcome.

In that case I will talk to my teacher about it