Fuel pump cooling shroud for Lycoming

[rv969wf]

Question: Where are most builders / pilots getting there mechanical fuel pump cooling shrouds from to prevent fuel vapor lock for Lycoming engines on those hot summer days after a heat soak on the ground then firing up and vapor locking on takeoff? What price are folks paying for them? Reason asking is I'm in the process of manufacturing them. Needing ideas or suggestions here if anyone is interested. Thanks AJ

[gmcjetpilot]

Al some one asked earlier and gave them show plane ($65)

http://www.showplanes.com/index_1024.htm



ECI sells them I think? Also Glasair sells them. The Glasair III had potential vapor lock issues ($55)

http://www.glasairaviation.com/optio....html#fuelpump



I think ECI might have them as well. If you make them I'll buy one from you. I plan on adding a cooling shroud. I think it's cheap insurance and well worth the small added weight and installation.

[rv969wf]

[/quote]

I have several prototypes and have tested various designs and the lastest one works the best. I've seen temp reductions at the fuel pump with probes and they do look much different from the ones in the pictures you provided GMC. Not to be knocking on the shrouds that others are selling, but I've tested a few of them and most of them only blast air on one side of the fuel pump and do not capture the air correctly to cool the fuel pump a full 360 degrees where the cooling air is needed. Cool fuel BTW is free Horsepower! Vapor lock issues are bad but they do happen when conditions are right, because I've been there. I am not going to post pictures until I have the finished shroud with all the bells and whistles completed. The shroud will be a bolt on unit without having to remove the fuel pump fittings if one has a flying plane and one not wanting to remove the fittings and such. Top part will be CNC router cut aluminum with a fiberglass molded bottom half that enterlays with each other. I'm working on a CAD drawing so I can get quotes from the CNC machinist on the aluminum top piece. I have tried 1" scat tube along with 1 1/2" scat tube and the 1 1/2" seems to be the ticket. I'll keep everyone posted as things develop. AJ

[DanH]

I realize this is a discussion of the cure, but I'd like to hear more about the problem.

What seems to be the major heat source, radiant heat from the exhausts or conductive from the engine case? Are there other factors?

Alan, can you tell us a little more about your actual temperature measurements? What sort of pump temp is typical in flight (unshielded) vs following a parked heat soak session?

[RV8N]

I've seen LOTS of engine installations on RVs and have never seen a cooling shroud on a mechanical fuel pump. I have never had vapor lock or any hint of it (IO-360).

Karl

[rv969wf]

[quote]

Originally Posted by DanH

I realize this is a discussion of the cure, but I'd like to hear more about the problem.

This question cannot be answered completely because of so many reasons,,,,,, Ambient temps outside, cold AVgas versus sunbaked fuel in the tanks sitting in the sun, the color of you wings, black or dark painted wings on top will have higher fuel temps, engine configuration and cooling airflow needs at the back of the engine around the accessory case / fuel pump, fuel line material, insulated or bare, parking into the wind or out of the wind, not one RV is the same. If conditions are right and you live in the south or someplace where it is HOT, vapor lock can happen as I've seen it on mine one time, and a couple of my friends RVs with injected engines have also vapor locked. The perfect condition for vapor lock is with hot fuel in the tanks from sunbathing, landing the airplane in 100F+++ air, shutting the engine down and letting the engine heat soak for a few minutes, start the engine then take off without a boost pump (injected engines) and spitter spatter the engine starts to run rough, slow down or die. As for temp reductions, I've seen as much as 50F temp reductions at the fuel pump with blast tube and properly designed cooling shroud installed on takeoff. Actual temp of the fuel pump housing at the case? Depends on CHT's, EGT's and oil temps, etc..... You run a hot engine, you run hot fuel pump / AVgas temps. No I did not put a temp probe in the fuel line itself, I used a probe attached to the fuel pump housing, maybe not the best way to test it, but it seemed effective and the probe was not in the airstream of the cooling shroud air. From what feedback I've had and personal emails I don't think it is cost effective for me to make custom fuel pump cooling shrouds at this moment. I had plans to build a very nice cooling shroud to sell, but when others are making them for $60 or so, I'd be loosing my butt with the shroud I designed. So if anyone is interested go buy one of the cheaps ones listed in an earlier thread on this link. Sorry I didn't answer all the questions but I am a firm believer in keeping the fuel cool for safety reasons and horsepower gains.

[gmcjetpilot]

Originally Posted by RV8N

I've seen LOTS of engine installations on RVs and have never seen a cooling shroud on a mechanical fuel pump. I have never had vapor lock or any hint of it (IO-360).

Karl

It's happened. Search the NTSB reports; I did a quick search and turned up almost 300 listed accidents/incidents related to fuel problem, ie vapor lock, and a few where RV's. It happens. I think it's cheap insurance.

You really don't know how close you are to vapor lock. We don't monitor fuel temp. The words "vapor lock", fuel vaporizing from heat cavities the pump and a pressure bubble acts like a dam, blocking fuel flow. We have an electric pump that may save the day, but a cool mechanical pump is helpful in avoiding problems.

Another problem that can occur, is fuel getting to hot in the Carb bowl. If it enters already in a heated state and gains more heat energy, it can boil and actually flood the engine, kind of opposite of vapor lock. This happened with the STC work Petersen did. They tried to get an automotive FUEL STC for older O360 (180hp) powered Mooney's. They solved all the vapor lock issues up to the carb, but could not keep the carb cool enough. Of course that was auto fuel and Av-fuel has greater resistance to vaporizing. Still cool fuel is better, safer and denser.

[Walt]

in that same scenero, Texas heat, giving rides, short turn on the ground so heat under the cowl is really building up. I could tell it was vapor locking because the electric fuel pump was beating it's little heart out with no resistance (almost like a dry pump) and fuel was pressure lower than normal. Kept the electric pump running continuously and it finally cleared but I wasnt taking off until the normal sound returned to the electric pump (which it finally did after a few minutes). To remedy this problem I installed a fuel system purge valve from the carb using a primer valve as the purge valve (already plumbed the line in to the tank when building). Works beautifully and now when it's hot under there I can just flip the momentary purge switch and flush all the FWF hot fuel back to the tank and presto worries are over. Very simple system built with standard fuel system components for simple and reliable operation.

[zav6a]

As far as I'm concerned, the best feature of the purge valve on the Airflow Performance system is ability to cycle cool fuel through the system.

I've also experienced vapor lock a few times. Once high and hot with a quick turnaround (104f in Idaho, 98f at 10,000 DA in Colorado) the other at 50 degrees while expirimenting with auto gas (found out later it had alcohol in it). This is with a shroud and a 1" tube. Three data points to suggest RVs are relatively close to vapor lock.

Looking at the mechanical pump, there is a lot of potential for conduction of heat from the case to the housing and from the hot oil bath that the inside of pump recieves. Is there an engine mount mechanical pump that eliminates these issues?

Seems like a slightly longer arm with a phenolic mounting block for insulation and another diaphram across the housing opening would help a lot. combined with a good shroud, it should eliminate the problem.

[hcccs]

Why would you take off with the electrical fuel pump off when you're aware of the risk of vapor lock? I'm struggling with a used cooling shroud which doesn't fit my RV-4 so I was thinking of leaving it off. Could you ever get a vapor lock if the electrical pump is on?