Stretched polypropylene
 

I use polypropylene hinges for my rotor hinges. This has been satistactory but today an odd thing happened. I went to our flying grounds but did not fly - neither did anyone else. The wind was too strong. The plane stayed in the car where I guess it was rather warm. When I got home the blades had sagged to the extent they would have hit the fin!. Anyone else had this happen? The hinges had apparently stretched.
Colin Duthie

RE: Stretched polypropylene
 

Colin,
I have had the same think happen to me, when I used polypoplene from a Milm carton or Ice Cream bucket.. But not from sheet poly.

Jim

RE: Stretched polypropylene
 

Yes, my hinges were indeed from an ice cream bucket. My polypropylene has come from two scources, - one the ice cream containers and the other has been sheet code 5 plastic table mats I found in a shop. These were clearly labelled code 5 polypropylene and may be the better material. Nevertheless odd that my hinges stretched - inside the car was not overly hot, but those hinges sure stretched, giving not only excessive droop but a heck of a lot of upward movement too. If I had got flying it would have been OK in the air but on landing the vertical tail would have been knocked off, or worse!

RE: Stretched polypropylene
 

Hi tintrax,
I would have said you used polyelthylene for hinges until you mentioned Symbol "5" which definitly is PP.
On my smaller gyros I use .032" thk PP.
On larger .25 sized machines, I use .062" thk. PP.
You will certainly need to add shims to eliminate that downward blade movement.
I hope this helps & good luck,
Bob G