Comment

Comment by ben duarte on January 20, 2012 at 4:54pm

I know I'm late, but just read this. My first plane I decided to increase all tube walls by one increment [tube and fabric] No reason, just thought it was good. Next plane, more fiberglass and resin. No reason, just thought it was good. They didn't break, but I had thousands of extra pound/miles for many years.

Unless you have a reason to point to, ie, someones plane broke, don't mess with the design. Changing anything that can affect the stiffness of a flying surface will affect dynamics [frequencies and transfer of loads] and you enter a realm that has not been tested or analyzed. Personally, I would not fly in a plane, at least in its first 100 hrs, that had such a modification done to it as I would consider some probability that it could be less safe than a stock built plane. When I say that I mean that many 750's are flying with stock design with no flying surface problems leaving me to accept the testing and analyses to be valid. Changes invalidate everything.

That said, increasing the thickness of a bracket, or cable size, or heavier eng mount, etc, would be fine if it makes you feel better, in my opinion, you just have to eat the weight. For my 750, plans only for flying surfaces.

Comment by Brian Fitzpatrick on October 26, 2011 at 8:57pm

Jesse:  I'm building a 750 and rightly or wrongly add a bit of extra material here and there.  Gives me peace of mind thinking I may have made a truly great aircraft greater. When I strap the floats on I may be glad I did.

Brian

Comment by Chris Aysen on October 19, 2011 at 11:08am

Jesse -  There are some parts that can accommodate flexability in material make-up. However on the wings you may want to try stiffiners of some geometric design. I personally added 3 rear ribs to both wings to stiffin the outer skins; with rivets it added just under a pound per wing....Elsewhere on the frame; if I had to do it again, I would use a slightly thicker material on the angles that attach the horiz. stabl. to the fuselage. The process of beading that Andre talks about is also a good way to stiffin sheet material. My two cents.

Chris

Comment by Andre Levesque on October 18, 2011 at 11:28pm

Jesse, i just added another tool to my collection...a bead roller. Why I'm telling you this ?  i like you was doubting the strength of some parts being used...-:) Building the gaz tank I used the bead roller to stiffened the skins...wow what a change that makes to the structure of the skins. I learn noew things every day....LOL

But yes...keeping  to the plans is probably wiser.

 

Comment by Jesse Hartman on October 18, 2011 at 7:07pm

Yea I think its smart to stay with the plans.  Thanks guys

Comment by Bob Pustell on October 18, 2011 at 6:20pm

For sure, check with the factory or the designer before you substitute thicker skins. Besides adding weight, they can (in some designs) alter the stress distribution characteristics of the wing (or other structures) and can therefore move the stress from a part or mounting point that is built to take the force, and put the force elsewhere in the structure, possibly to a part that cannot handle the stress or force. I do not know if that is the case here or not, and neither do you. Personally, if it is good enough for Chris Heinz, it is good enough for me. I am building to plans.

Comment by Andre Levesque on October 18, 2011 at 2:09pm

Jesse, ss a scratch builder we are always tempted to alter the material because we (i do) feel its kinda flimsy in some part of the plane but in reality it's more then adequate for the type of plane it is.
Changing the skins for thicker materials and other parts like rudder horn, door gussets, landing gear attachments etc... slowly it adds weight and as for the design characteristics...I'm not sure what the impact would be !! ...
it would be nice to hear from someone that has that kind of knowledge. I've seen 701's with larger rudders, longer flapperons, 750 wings on a 701 etc.... what does all that mean? EXPERIMENTAL...-:)
I hope we get some feedback on that becasue i had the ,,still have the same questions as i build.
My opinion