Are composite planes stronger than metal?

Mid air breakup is extremely low on the list of things that will kill you in an airplane.

Composite airplanes haven't been around very long in the grand scheme of things. I'm not sure enough data has been collected. I don't think comparing a nice new DA40 to a 50 year old Mooney to Cessna is a fair comparison. 737's are made of metal too.

That Pilatus mid air breakup crash wasn't caused by "mid air breakup". It was caused by the pilot flying into a massive T storm. I'm friends with the Insurance Adjuster. That storm would have pulled any plane apart.

 

Had not heard of the Pilatus break up. My understanding is the plane built like a tank. Had the fortune of flying in one several years ago, and while not a pilot, was amazed.

 

If it's this pretty well-known event, it was not the T-storm that broke up the plane.
Pilot error due partly to inexperience.

Pilatus PC-12 Crash: NTSB Points to Surprising Cause | Flying Magazine

 

You'd be just a dead in a composite airplane as you will in an aluminum one..

Composite airplanes primary structure are indeed robust since the FAA and the designers have a hard time trying to make sure that fatigue life and structural margins are met. For that reason they tend to be overbuilt. The cockpit side structure is probably a bit stronger, but face it, it's still not very strong and if you crash you're not likely going to survive. Also, high impact forces will pass through the stiff and strong wing structure and unless you have impact absorbing seats you'd be just as dead as in something that folded up.

The structural limits for aircraft aren't that high compared to the 80 or so g's you get in a fatal accident. If the wing structure is good for 10 g's that would be robust, but compared to the 80+ g's you get in a bad accident even the strong composites will be smashed.

Race drivers survive some horrific crashes when belted into full cage structures and in strong tubs, but in order to survive they are belted in with a full six point harness and have HANS devices and helmets, none of which are going to be found in the typical private airplane. Moreover, most racing crashes are glancing blows into barriers or walls and aren't generally full frontal impacts. Add to that the nature of the frame forward of the driver to absorb the impact over a distance and you have a chance of success. In an airplane the engine is ahead of you and that's pretty much it, and it's supported by a small diameter tube space frame. Good enough to hold up the engine but nothing that will absorb any impact energy.

NASA looked into crashworthiness of light aircraft years ago and found that there wasn't a lot they could do without severely impacting payload. Since that time the laws of physics haven't changed. If you crash a light plane in a bad way the odds of survival are near zero.

 

uh, not so fast

first off, composite structures are subject to fatigue, just not metal fatigue. Fatigue in composite structures does occur, but in ways that is different than metal. This has both positive and negative aspects. Too much to give any detail, just suffice to say it does occur.

second,
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/fbe0c07ed12f99b986257d1e004a78a1/$FILE/2014-13-08.pdf

 

Yes. That's what I said.

 

Every airplane has a max structural G limit. Exceed it and the wings come off. The structural limit for some composite airframes are high because the FAA doesn't really know how to insure that they can meet the design limit load in the future after a period of degradation. So the reality may be that the limit is 10G's for a new airframe and it may actually go down with time but that isn't much of concern since there is some structural margin designed in.

For a composite airframe that has say a 10 G capability, if you aren't going fast enough to generate 10G before stalling then the wings won't come off, the airplane will stall. That's the definition of maneuvering speed. That is the speed above which the aircraft will suffer damage before it stalls. Inflight structural failures don't happen above maneuvering speed (at least they're not supposed to) for just that reason.

So if you have a stronger airframe you can go faster before you damage it and you can have a higher maneuvering speed, but if you exceed the maneuvering speed and encounter heavy turbulence or crank too hard on the controls the wings can come off. No magic here.

 

Well, except for the thunderstorm part.

You said: "That Pilatus mid air breakup crash wasn't caused by "mid air breakup". It was caused by the pilot flying into a massive T storm.
I'm friends with the Insurance Adjuster. That storm would have pulled any plane apart.""


But the storm didn't 'pull that plane apart', the pilot did, the plane was 'some distance away' from the t-storm in every report I've seen.

 

below?

 

The crash wasn't caused by "mid air break-up". The pilot F'd up long before the plane came apart. If I recall the plane was inverted and in a spin as it fell to earth. Horrible horrible situation....... but the pilot put it into a stall. Pilot error.

 

Yes, my mistake, BELOW maneuvering speed...

 

Can only agree with you to a certain extent. Maneuvering speed only covers you if one flight control is moved in one direction in calm air. If you're encountering turbulence, all bets are off.

 

Going further, the FAR's only state that you must be good for the +man load factor at Va. Depending on the aircraft you may or may not hit wing stall or control surface limits prior to that. Further it is a static g value, and all bets are off in turbulence (e.g. a dynamic environment) outside the prescribed limits for that aircraft (weight).

 

The criteria for certification for maneuvering speed is also includes a 50 feet per second turbulence. Moderate turbulence is categorized as between 25 and 35 ft pe second. 35 to 50 ft per second is severe and above 50 ft per second is considered extreme. Think about that for a minute. 50 fit per second is an upward gust of 3000 ft per minute.

So while adhering to maneuvering speed as placarded won't make you bulletproof, it would handle most any realistic turbulence that you'd likely encounter. If it gets really rough and things start banging around the cabin, then slow down another 10 knots and you should be safe.