VansAirForceForums  
Home > VansAirForceForums

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

- Today's Posts | Insert Pics

  #1  
Old 12-29-2008, 11:05 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 7,528
Default Baffle Mod

Lycoming cylinders have a classic baffle problem. I don't know if anyone else has taken this particular approach to solving it (lots of ways to skin a cat), but maybe the pictures will help the new guys understand the issue.

Here's the root of the problem. The intake side of the head has no fin depth in the area indicated by the pencil. but standard baffles for the left front and right rear cylinders place a plate directly against this area. There is plenty of air at "A", but there is no way for air to circulate down to area "B"



Here's the standard baffle (right rear) against the head. Flow to the lower fins and baffle wrap is blocked by the zero-depth fin area identified by the green tape. The standard "cure" is to place a washer or some other spacer between the head and the baffle, but that opens a gap along the entire length of the baffle plate.....in particular the area outlined in a black rectangle above. Any air sneaking past the area in the rectangle is pure leakage.



It is quite easy to hammerform a small duct of sorts in the baffle plate. The "duct" is nothing more than a fancy dent knocked in the sheet.



The result is a passage to bypass the no-depth fin area (arrow). Now air can flow down the back of the head and pass in between the lower fins where you have a baffle wrap. The reminder of the baffle plate is not spaced away from the head and cylinder, reducing undesired leakage. Any air not passing between fins is pure drag; it didn't do any cooling work.



Not all builders have metal forming hammers, or may not want to try beating on an expensive baffle part as their first metal forming experience. I'll do the left front baffle using an alternate method and get it up here soon.

Have fun.

----->>>>POSTSCRIPT: See posts 24 and 25
__________________
Dan Horton
RV-8 SS
Barrett IO-390

Last edited by DanH : 07-01-2015 at 07:11 AM.
Reply With Quote
  #2  
Old 12-30-2008, 05:29 AM
carguy614's Avatar
carguy614 carguy614 is offline
 
Join Date: Aug 2007
Location: Shallotte NC
Posts: 594
Default Baffle Mod

Great idea Dan. For sure, the clearance is an issue, as I lost 25 degrees just by adding a washer to the back of that baffle. This looks like a much more elegant solution. I'll give that a try on my next one.

Thanks for the tip!!

Chris
__________________
Chris Schmitt
Shallotte, NC
RV9A 90970 N614RV
Sold to nice folks in Texas and badly missed.
RV9 in progress
Reply With Quote
  #3  
Old 12-30-2008, 03:44 PM
Captain Avgas Captain Avgas is offline
 
Join Date: Oct 2005
Location: Melbourne, Australia
Posts: 1,653
Default

Quote:
Originally Posted by DanH View Post
I'll do the left front baffle using an alternate method and get it up here soon.
A really interesting topic Dan. I'm looking forward to your front baffle solution. Very timely for me....guess what I'm working on.
__________________
Regards
Bob Barrow
RV7A
Reply With Quote
  #4  
Old 12-30-2008, 04:59 PM
RV7Guy's Avatar
RV7Guy RV7Guy is offline
 
Join Date: Jan 2005
Location: Chandler, AZ
Posts: 2,800
Default Great Idea

I used a couple of larger spacers. I really like the idea of hammering a dent to make it work. How great to get to use a hammer in a productive, non destructive manner
__________________
Darwin N. Barrie
Chandler AZ
www.JDair.com
RV-7 N717EE-Flying (Sold)
RV-7 N707EE-Building
EMS Bell 407,
Eurocopter 350 A-Star Driver
Reply With Quote
  #5  
Old 01-01-2009, 09:00 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 7,528
Default

Here's the alternate method.

Cut a hole in the baffle, carefully deburr it, then make a spacer (0.065" to 0.080" thick) and a cover plate:



When assembled, you have a duct to bypass the no-depth fin area:



There is a structural brace (a length of angle) above the inlet ramp and across the face of the cylinder. Space it forward a little so it doesn't block the duct.

Here's the other side:



The 90 degree flange on the cover plate is important.

Dimple and countersink as necessary, rivet flush on the cylinder side.
__________________
Dan Horton
RV-8 SS
Barrett IO-390

Last edited by DanH : 07-01-2015 at 07:06 AM.
Reply With Quote
  #6  
Old 01-02-2009, 10:01 AM
Wicked Stick's Avatar
Wicked Stick Wicked Stick is offline
 
Join Date: Feb 2005
Location: Marion, MA
Posts: 236
Default

Great Post Dan. !
__________________
Dave "WS" Rogers
RV-8 N173DR
Reply With Quote
  #7  
Old 01-02-2009, 05:32 PM
aerhed aerhed is offline
 
Join Date: Dec 2008
Location: Big Sandy, WY
Posts: 2,566
Default

A dent in the baffle, BRILLIANT!
Reply With Quote
  #8  
Old 01-02-2009, 07:23 PM
Rick S. Rick S. is offline
 
Join Date: Mar 2005
Location: Las Vegas
Posts: 735
Default

Great eye...do you lay awake at night thinking of these great ideas/fixes? I love your posts!! Even when the flames are flying!!
__________________
Rick Sked
Las Vegas
Reply With Quote
  #9  
Old 01-03-2009, 05:55 AM
Tom Martin Tom Martin is offline
 
Join Date: Jan 2005
Location: Ontario, Canada
Posts: 1,351
Default

Another method, that I have used many times, is to rivet a piece of 1/8" flat bar to the outside of the area that Dan is modifying. The flat bar goes in the location where the mounting hole to the cylinder is. It is about a couple of inches long. This is a simple modification, solves the cooling problem, and strengthens the baffle at the attach point.
__________________
Tom Martin RV1 pilot 4.6hours!
CPL & IFR rated
EVO F1 Rocket 1000 hours,
2010 SARL Rocket 100 race, average speed of 238.6 knots/274.6mph
RV4, RV7, RV10, two HRIIs and five F1 Rockets
RV14 Tail dragger flying #153

Fairlea Field
St.Thomas, Ontario Canada, CYQS
fairleafield@gmail.com
Reply With Quote
  #10  
Old 01-04-2009, 06:39 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 7,528
Default

Thank you everyone for your kind comments.

It is an air-cooled engine worth more than my first house, so really good baffles are worth thought and careful fabrication.

BTW, I can't say if a 1/16" or an 1/8" or any other particular dimension is "correct" for this duct. Can't even say if the left front and right rear cylinders should have the same duct size; different pressures in their respective plenum areas. I am sure an install which doesn't allow any air to a whole section of the cylinder head finning is bad, and likewise, all leaks are bad.
__________________
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 11:12 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.