Posted: 1/4/2010 22:53:02
I am looking at buying an older homebuilt glider and am quite interested in the Schreder HP-14/16/18 series. One of the questions I have is: how are the foam ribs holding up after 30 years of flying/sitting/aging, and how do you know how the structure is still OK? Has anyone any experience, good or bad with this?
P.S. Moderator: Compuker trubbles - this is the third try, so if you would dump the previous two (if they haven't disappeared into cyberspace). Thanks
Posted: 1/5/2010 21:48:52
I don't know the answer to the question, but I like the aircraftin your avatar. What is it?
Posted: 1/6/2010 00:27:10
It's a Schiebe SF25 Rotax Falke. The picture was taken at Wasserkuppe several years ago. With a 100 horsepower turbo Rotax it was used as a towplane and for motorglider training. I was quite keen on flying it, but at 2m (6ft 7 in) tall I was not able to fold into it and close the canopy....
Posted: 1/6/2010 17:07:17
I sill don't know the answer to your question, but if you knew or could find out the brand or type of foam and adhesive used, someone might make a reasonable guess based on the expected life expectancy of the materials.
Hope this is some help.
Posted: 1/16/2010 15:20:34
I do not know how good the foam ribs of the HP-14/16/18 are after 30 years, but we have a lot of older composite gliders flying here in Germany. That's the encouraging part of my comment. There is only one way to decide about the airworthyness of a plane: thorough inspection and that's annually done on all sailplanes in Germany. This starts with the aircrafts logbook. Is there any damage history? Who did the repair, if any? Than do a thorough visiual inspection of the whole plane, pay especial attention to the wing attachment areas, brackets, bolts, the empennage, the control surfaces and so on. A very important point to judge about the structural integrity of the glider is the eigenfrequency. This is measured in a quite simple way: The glider, sitting on the ground supported on its wheel, is held in wings level attitude by the inspecting person. Then a vibration is excited by tipping periodically on the wing tip. The number of osscillations is determined and compared to the specified value. If there are discrepencies, mainly frequency drops, you have a new restrauration project.
I hope that gives a rough idea.
Posted: 1/21/2010 22:22:10
How does someone find out the eigenfrequency and the correct way to compare the number of ocsillations to the specified value? Sounds like a technique that might apply to more than gliders.
Posted: 1/25/2010 21:28:32
The biggest hit a composite structure (foam included) sees over time is exposure to Ultra Violet “UV” light. If the aircraft has been stored inside a hanger or covered trailer this should not be a problem. A Light color top coat with a Black under coat provides the most protection against UV. If you can look thru an inspection hole make sure the foam is not turning to dust, it should look, feel and act like the same kind of foam as if you where to purchase it today. i.e. polyurethane, polystyrene, pvc…
Check for “spider cracking” near the high stress areas such as the spar, hinges, spar to fuse connection and stabilizer to fuse connection. This is the biggest thing to look for on an older composite aircraft.
EAA Composites Technical Counselor # 5426
Posted: 1/26/2010 00:19:35
Appreciate you taking the time and the gift of your knowledge.
Posted: 1/26/2010 09:28:50
More help might be found at Yahoo Groups, hp-gliders. There are two web sites for Schreder glider designs, hpaircraft.com and soaridaho.com Enjoy, Erich
Posted: 1/30/2010 01:14:54
Saying hello to my long wing buddies.
I flew motorglider made of wood,wood frame is usually inspected by sound.
That means knocking, tabbing gently every rib above the cowering,
with one Dollar (Euro)coin.No matter if the
cower is canvas, plywood or Dural sheet.And judging by sound if the rib is still
solid and attached to cowering.