VansAirForceForums  
Home > VansAirForceForums

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

- Today's Posts | Insert Pics


Go Back   VAF Forums > Model Specific > RV-10
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #11  
Old 02-03-2019, 07:15 PM
Bevan Bevan is offline
 
Join Date: Sep 2007
Location: BC
Posts: 1,585
Default

A few things Iíve learned about preventing vapour lock. Itís caused by one or a combination of factors. This is nothing new for most of you but judging by some of the comments above, and for the sake of the newbies, Iíll mention what Iíve learned.

The higher the elevation, the closer you get to vapor lock conditions when sucking the fuel through a restriction upstream such as a fuel flow sender all things considered equal. In theory, if you could climb high enough, probably any non pressurised liquid will boil at the ambient temperature. Vapor lock is caused by heated fuel, low pressure (sucking rather than pushing the fuel) and sharp corners/obstructions to the flow causing turbulence inducing bubbles to form which then collect in a high point down stream until a bigger bubble is formed (or combinations of these factors and Iím m probably missing a few). The mechanical fuel pump on the back of the engine cannot pump the bubble.

Put a 2Ē flange on the firewall heater control valve exit for a scat tube to control the discarded hot air and route it down to the lower cowl exit area. Do not simply stop airflow from going through the heat muff. Unneeded hot air is dumped overboard to prevent overheating of the muffler/heat muff if this is what you have.

Use a heat shroud around the engineís mechanical fuel pump supplied with a supply of cold air from the upper plenum.

Minimize the volume of fuel on the engine side of the firewall (hot zone). FWF temperatures after engine shutdown increase due to succession of air moving through the engine compartment. Devices that hold a volume of slow moving fuel such as filters and gascolators have more time to transfer heat into the fuel. If you just have to have them, insulate them and protect from sources of heat and radiant IR.

My 2cents worth.

Bevan
__________________
RV7A Flying
O-360-A1F6 (parallel valve) 180HP
Dual P-mags
Precision F.I. with AP purge valve
Vinyl Wrapped Exterior
Grand Rapids EFIS
Located in western Canada
Reply With Quote
  #12  
Old 02-03-2019, 08:58 PM
charrois charrois is offline
 
Join Date: Jan 2019
Location: Legal, AB
Posts: 8
Default

Thanks for the suggestions everyone. It's good to know there is a way of putting a fuel pump shroud on without having to remove the pump entirely. I already have a simple blast air tube directed towards the pump, but I'll look into putting a deflector plate in at the valves, because it should be quick, easy, and relatively straightforward. If that still doesn't help enough, at least the shroud route doesn't have to be as invasive as I thought.
Reply With Quote
  #13  
Old 02-03-2019, 10:47 PM
rv8ch rv8ch is offline
 
Join Date: Feb 2005
Location: LSGG
Posts: 2,501
Default cool trick

Quote:
Originally Posted by bpattonsoa View Post
I put a cooling shroud on my fuel pump without removing it from the engine.

Cut the shroud in half vertically and rivet pieces of hinge to each half. Then you can put it on by removing and replacing the bolts one at a time.
Bruce - very clever! I didn't put a shroud on because I'm not sure I'll need it, and I felt bad removing the factory-installed pump with it's beautiful safety wiring. Your trick changes everything. Thanks!
__________________
Mickey Coggins
http://rv8.ch
Reply With Quote
  #14  
Old 02-04-2019, 06:49 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 8,533
Default

Rather than band-aid the pump with a cooling shroud, try to determine the actual heat sources and eliminate them.

The problem can be broken down into two categories, (1) heating the fuel before it reaches the pump, and (2) heating the pump itself.

The RVs with fuel routed up the cabin centerline can transfer heat to the fuel through the floor; the source is engine cooling air outflow, and exhaust flow. Measure the floor and tunnel temperature. Insulate the belly skin externally if desired. Add tailpipe length or point it/them downward.

RVs with a bunch of firewall forward fuel plumbing upstream of the pump pick up heat from the engine compartment air. Components like filter bodies, gascolators, and fuel flow devices make it worse. Relocate the extra parts to a cool area. Perfect is a short, insulated line from the firewall bulkhead fitting to the pump, and nothing else.

Can't do much about engine block heating of the pump, but I suspect a few measurements would find that block heat isn't a big contributor. The overlooked wildcard is radiant heating from the exhaust tubes. It's not unusual to see a pair of pipes near or under the bottom of the pump. Think about it. The only parts of the pump which can significantly heat fuel are the inlet chamber and the valve disk. Both are at the bottom of the pump, and isolated from the engine block by rubber diaphragms. The thermal conductivity of rubber is more than a 1000x less than aluminum. So if there is no efficient conductive heat transfer path from the 200F engine block, might we consider the 600~800F tailpipes shining on the bottom of the pump...you know, where the fuel is located?

__________________
Dan Horton
RV-8 SS
Barrett IO-390

Last edited by DanH : 02-04-2019 at 07:24 AM.
Reply With Quote
  #15  
Old 02-04-2019, 07:01 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 4,964
Default Inlet fuel lines pressure tested?

Don't forget, a tiny leak on the suction side will create many of the same symptoms.

Tunnel temps? It is a 10, right?
__________________
Bill

RV-7
1st Flight 1-27-18
Phase II 8-3-18
Repairman 11-15-18
Instrument Currency 12-17-18
Shrunken Exit = ??
No Photo? => PM me.
Reply With Quote
  #16  
Old 02-08-2019, 09:24 AM
msausen's Avatar
msausen msausen is offline
 
Join Date: Oct 2008
Location: WI
Posts: 11
Default Showplanes pump shroud

Incidentally I have a Showplanes shroud that I was planning to use when I lived in TX. Don't really need it now that I'm back in the frozen tundra of WI so PM me if anyone is looking for one.
Reply With Quote
  #17  
Old 02-08-2019, 09:39 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 4,006
Default

Quote:
Originally Posted by DanH View Post
The overlooked wildcard is radiant heating from the exhaust tubes. It's not unusual to see a pair of pipes near or under the bottom of the pump. Think about it. The only parts of the pump which can significantly heat fuel are the inlet chamber and the valve disk. Both are at the bottom of the pump, and isolated from the engine block by rubber diaphragms. The thermal conductivity of rubber is more than a 1000x less than aluminum. So if there is no efficient conductive heat transfer path from the 200F engine block, might we consider the 600~800F tailpipes shining on the bottom of the pump...you know, where the fuel is located?
This would be my primary area of concern if I was chasing your issue. I was dealing with boiling fuel in my injector lines (a unique installation problem) on my 6 and undertook several steps in an attempt to reduce absorption of heat across the fuel distribution network in the cowl. I made heat shields (easy to make from .063 6061) for the exhaust pipes near the servo, as I believed that I was picking up a lot of heat from there. It made a noticable difference. Radiant heat from the exhaust is often much more problematic than the hot air blowing around.

Larry
__________________
N64LR
RV-6A / IO-320, Flying as of 8/2015
RV-10 in progress
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 02:11 AM.


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.