VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 02-18-2019, 08:08 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 8,671
Default Soft Spot Plenum Lid

RV-8 builders know stuffing an angle valve Lycoming into an RV-8 cowl results in very tight engine to cowl clearance above the front cylinder corners, and down the left side. It gets worse with a plenum lid, a classic case of stuffing six pounds of stuff in five pound sack.

My plenum lid has routinely bumped the inside of the upper cowl. If I look close, I can see some fine spiderweb cracks in the cowling clear coat, so if allowed to continue surely it will develop an ugly spot. In recent times it has not been bumping so much, but that was because the mount isolators were sagging. With new isolators, it was time to fix the bumping.

The problem spot, both sides:



For a first cut, I simply sanded a big flat spot on the lid and glassed it over, in an attempt to lower the height of the lid in the contact area. It wasn't enough to truly cure the problem, so I decided to try an experiment...plenum soft spots.





We've had past conversations about soft membrane lids and similar. These are partials. They are made from two plies of 9 oz plain weave fiberglass cloth, with rolled-in Permatex Ultra Black (Loctite 598) silicone sealant to fill the weave. Process is like the cylinder seal wraps; roll in the silicone between two sheets of 4 mil plastic, cut to shape right through the plastic, peel one side, stick into place, allow cure and peel the other plastic sheet.

Here the forward edge and outboard edge of each soft panel is clamped under fastener strips. The inboard and rear edges are simply 2" overlaps of the plenum glass, and rely entirely on the shear strength of the sealant (which for UB/598 is quite good).

The soft inlet ducts are now at 850 hours and 8 years. They are still doing fine. It's a similar fabrication, a single ply of 9 oz and room temp cure urethane rubber. I'll see how the silicone soft spots hold up, and if generally satisfactory, I may replace them with urethane panels. A very future mod might be to make new inlet ducts with a considerable extension rearward, i.e. make the soft inlet and the soft panel as one piece.

More later.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #2  
Old 02-18-2019, 11:50 AM
Bob Martin's Avatar
Bob Martin Bob Martin is offline
 
Join Date: Jan 2005
Location: Richmond, Virginia
Posts: 1,153
Default Thanks

Dan,
Thanks for pointing out this problem and actually showing a FIX.
I know you have a 0-390.......but this problem exists even in a 0-360 with vans baffeling. Well may not be exactly the same but......
This was one of many issues that urged me to convert to a James plenum and Cowling. Paying attention to the "corners" in the install. Fixed my issue.
So far anyway....
__________________
Bob Martin
RV-6, 0-360 Hartzell C/S, Tip up, 1150+TT
James extended cowl/plenum, induction, -8VS and Rudder. TSFlightline hoses. Oregon Aero leather seats.
D100-KMD150-660-TT ADI2- AS air/oil seperator. Vetterman exhaust with turndown tips.
Louisa, Virginia KLKU N94TB

Last edited by Bob Martin : 02-18-2019 at 12:21 PM.
Reply With Quote
  #3  
Old 02-18-2019, 12:33 PM
rocketbob's Avatar
rocketbob rocketbob is offline
 
Join Date: Jun 2006
Location: 8I3
Posts: 3,279
Default

Curious why you're using fiberglass. In my opinion, it's an obsolete material.
Kevlar would be a better choice in this case. Just an uninvited ombudsman's opinion.
__________________
Bob Japundza CFI A&PIA
N55BC RV-6 borrowed, flying
N678X F1 Rocket, under const.
N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
Not a thing I own is stock.
Reply With Quote
  #4  
Old 02-18-2019, 12:59 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 3,894
Default

The Five Rules for Good Engineering are:

1. Part of the art of being a good engineer is knowing where to steal good ideas.

2. Get it good enough and get on with it.

3. The best way to solve an engineering problem is to guess the right answer.

4. Any **** fool can figure out another way to do it; i.e., the first solution to a problem is often entirely adequate.

5. If you can't fix it, feature it. There's always a way to market the problem as a benefit.

--- written by Mark Drela.

Seems to me that Dan has hit number two pretty well.

Dave

Last edited by David Paule : 02-19-2019 at 09:24 AM.
Reply With Quote
  #5  
Old 02-18-2019, 01:36 PM
mtnclimber mtnclimber is offline
 
Join Date: Apr 2010
Location: Nathrop Colorado
Posts: 66
Default Thanks Dan!

I've been using glass impregnated with black RTV for the RV-8 ducts as you taught us, and also have used it to seal the corners of the flap seal on my 9-A. It's in contact with the upper cowl continuously, and neither the RTV or upper cowl show any abrasion damage after 300 hours.

Now if I could just move on with your cut-and-buff tutorial!

Roger
Reply With Quote
  #6  
Old 02-18-2019, 01:45 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 8,671
Default

Quote:
Originally Posted by rocketbob View Post
Curious why you're using fiberglass. In my opinion, it's an obsolete material.
Kevlar would be a better choice in this case. Just an uninvited ombudsman's opinion.
It would be a better choice, technical speaking. On the other hand, (1) the fiberglass is hanging in there pretty well in the duct application, and (2) I'm too cheap to buy the special scissors which will actually cut kevlar.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #7  
Old 02-18-2019, 04:51 PM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
 
Join Date: Mar 2005
Location: Calgary, Canada
Posts: 5,244
Default

Dan, you're the only guy I know with plenum featuring a finish as fine as the outside of your plane... Nice
__________________

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 433.4 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi2.htm


Reply With Quote
  #8  
Old 02-18-2019, 05:44 PM
humptybump's Avatar
humptybump humptybump is online now
 
Join Date: Feb 2011
Location: Eastern Shore of Virginia
Posts: 3,139
Default

From an uneducated, what are the benefits of Kevlar vs fiberglass? and to add to the mix, where does carbon fiber fit (or not) in this specific discussion?

Thanks.
__________________
- Glen, ESVA
RV-8 FP IFR | Track my RV-8 | 53VG
Reply With Quote
  #9  
Old 02-18-2019, 05:57 PM
Mike S's Avatar
Mike S Mike S is offline
Senior Curmudgeon
 
Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 14,766
Default

Quote:
Originally Posted by humptybump View Post
From an uneducated, what are the benefits of Kevlar vs fiberglass?
Bulletproof.

If you throw a rod...........
__________________
Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
Reply With Quote
  #10  
Old 02-18-2019, 06:03 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 8,671
Default

Quote:
Originally Posted by humptybump View Post
From an uneducated, what are the benefits of Kevlar vs fiberglass? and to add to the mix, where does carbon fiber fit (or not) in this specific discussion?
Fatigue resistance. Pretty sure they rank (best to worst) kevlar, glass, carbon. I'm too lazy to look up the numbers. If the membrane would be subject to a lot of flexing, it might be worth consideration. Here? Naaa.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 02:15 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.