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Foam Ribs

Posted By:
Ted Sorensen
IAC MemberVintage Aircraft Association MemberWarbirds of America Member
3
Posts
0
#1 Posted: 1/4/2010 22:53:02

Hi Guys,

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?

Thanks

Ted

 

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



Ried Jacobsen
194
Posts
26
#2 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?

Ried



Ted Sorensen
IAC MemberVintage Aircraft Association MemberWarbirds of America Member
3
Posts
0
#3 Posted: 1/6/2010 00:27:10

Hi Reid

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....

Cheers

Ted



Ried Jacobsen
194
Posts
26
#4 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.

Ried



Thomas Stute
15
Posts
1
#5 Posted: 1/16/2010 15:20:34

Hi Ted,

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.

Good luck

Thomas



Ried Jacobsen
194
Posts
26
#6 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.



Spencer Gould
Homebuilder or Craftsman
32
Posts
1
#7 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.

 

Spencer

EAA Composites Technical Counselor # 5426



Ted Sorensen
IAC MemberVintage Aircraft Association MemberWarbirds of America Member
3
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0
#8 Posted: 1/26/2010 00:19:35

Thanks guys,

 

Appreciate you taking the time and the gift of your knowledge.

Ted



Erich Pfalzer
Homebuilder or CraftsmanAirVenture Volunteer
2
Posts
0
#9 Posted: 1/26/2010 09:28:50

Ted,

      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



Martti Mattila
Homebuilder or Craftsman
1
Post
0
#10 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.