RV10

Nick Allen · Post by **Nick Allen** » Tue Jan 27, 2009 9:21 am

Are the MCRs actually fragile or simply as strong as they need to be...?

J.C. · Post by **J.C.** » Tue Jan 27, 2009 9:46 am

I suppose that depends on your definition of " strong enough." Strong enough to be flown by a very competant pilot from smooth runways or strong enough to be used by a hairy a***d bush pilot in Oz ?

Rod1 · Post by **Rod1** » Tue Jan 27, 2009 9:53 am

That’s an interesting view. I would expect my composite airframe to last for ever, but some of the metal bits will require replacement / de corroding from time to time. The high time10 year old MCR’s I have looked at have been fine. I would however hope that the design will be obsolete 20 years from now, with better engines and even more efficient airframes. My old 180hp machine was burning £4000 more fuel a year than my MCR, so I get a “free” aircraft quite quickly in fuel alone. The only thing I would change is the lack of aerobatic capability, which is the VANS big plus.

Rod1
PS my machine is based on a strip, and has no problems.

J.C. · Post by **J.C.** » Tue Jan 27, 2009 11:21 am

Maybe we will see examples of both at the BB FLY-IN in a few weeks !
DELIBERATE PLUG INTENDED!

Rod1 · Post by **Rod1** » Tue Jan 27, 2009 6:34 pm

“permit aircraft are not used for flight training”

That is true in the UK but in enlightened countries like France they are using home built MCR’s for training with no problem.

Rod1

Steve Brown · Post by **Steve Brown** » Tue Jan 27, 2009 7:18 pm

...and how many Austin Allegros, Morris Marinas and Lancia Betas are left?

bertdeleporte · Post by **bertdeleporte** » Tue Jan 27, 2009 8:36 pm

Hello all,

just two comments to lighten the discussion:

-the first all-composite certified aircrafts were French (less than 300 years ago

), built by Wassmer. The Pacific, Baladou and (I forgot the name) series were covering 100HP fixed gear and prop to 180HP RG VPP IFR machines. Most of them are still alive, with no major structural problems. I have to check, but I think the composite was polyester-glass. I have no idea if some were used for training.

On the other hand, composite materials are known for one caracteristic: their fatigue test curve. A fatigue test will impose to a material sample a cyclic load. You can find consistant litterature with "Wöhler fatigue test" for instance. If you make a graph on cyclic load (vertical scale) vs number of cycles before failure (horizontal scale), materials used for aeronautics are roughly behaving as follows:
-Steels are assymptotic, you can thus design structures to be under the fatigue load (as for ships, for instance), set @ 100 000 000 cycles.
-aluminiums are quite linear, which means even with a very small load, you will at some stage reach the failure of of the part. The bigger the cyclic load is, the shorter the life is.
-composite materials will present a 90° counterclockwise turned J curve: for a wide range of cyclic load, the "life" or number of cycles before failure is quite constant, but it will abruptly drop at a certain number of cycles, whatever the cyclic load is.
Nothing is perfect, and on the cycle side point of view, composite as aluminium are unfortunately bound to fail one day. One of the big point of composite is the chemical stability, and natural corrosion proof of the structural elements.

For the time being, nobody can predict how will last a MCRs or Sirrus', we can only say we still see flying every day 20, 30, 40, 50 years old Cessna, Pipers and Mooneys. Aluminium which has survived corrosion is still a lasting material, will composite behave the same? I don't know.

The only infinite cycles material I know so far is wood. So, maybe at some stage, we will rebuild wooden aircrafts, and seek for eternity for our machines...

Bertrand

Steve Brown · Post by **Steve Brown** » Tue Jan 27, 2009 8:40 pm

It was a bit tongue in cheek. Even so did the Reliant & Europa fail due to their glass body or their chassis corroding? Or nutty drivers? Were they (the cars) polyester or epoxy based? Chopped strand mat vs cloth weave. Crazed gel coats and sun damage/water absortion was rife in the early GRP days. Much has been learnt ref UV protection and composite design over the years. But wood and alloy have had a head start.

Simlarly alloy a/c that were not corrosion proofed are unlikey to have lasted unless well cared for, particularly in salty atmospheres. Likely need repainting too.

I guess it is horses for courses - as usual!

Nick Allen · Post by **Nick Allen** » Tue Jan 27, 2009 10:11 pm

Composite gliders have been around for over thirty years, and gliders don't have an easy life; the Grob 109 is nearly thirty years old and appears not to turn to dust (and I tried very hard on some of my landings when I was learning!). On the other hand, perhaps "durability" is overrated and some controlled obsolescence would be a good thing in terms of innovation...