REFLECTOR: Fuel pump cooling

Wed Aug 29 08:30:00 CDT 2012

"The two related issues we have seen, however, WRT to the fuel pump may

provide some help.  First, starting at 18,000 ft and above we always turn

our Boost Pump on LOW -- without it, the engine fuel pump seems unable to

provide steady fuel flows and surging and instability can result."

I helped build a Lancair IVP and we installed an automatic switch to turn on the boost pump on low above 18K feet. It was a requirement in the builders manual for the Lancair IVP with the TSIO550. However, we never installed any fuel pump cooling, but we did install a cooling duct and shroud around the gascolator. Never had any issues with unstable fuel flow settings at altitude or quick hot turnarounds.

Best regards,

Nick and Connie Jones
Velocity XL-RG
N10CN
99% done 90% to go

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Bob Jackson (Jax Tech)
Sent: Tuesday, August 28, 2012 11:06 PM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Fuel pump cooling

Scott,

We also run almost exclusively LOP with our (custom and manual wastegate)

turbo IO-550N, so we should have a lot of the same parts as you do.

However, I haven't seen the problem you describe.  Our engine is always

perfectly willing to settle into solid LOP settings and operation after

long, hot climbouts.  We're using dual Lightspeed electronic ignitions, and

I know that facilitates trouble-free LOP greatly.  Our engine is neither

picky about very low LOP fuel flows, or very high LOP MAPs.  And adding

extra MAP really seems to help improve already good LOP cooling.  I

typically use 31-32" MAPs at 2500 rpm and 15-17 gph, and on the other end,

26-27" MAP at 2200 rpm and 12-13 gph for my LOP cruise settings.  The

'oversquare' MAPs really seem to help cooling without affecting power, which

seems mostly determined by the fuel flow.

The two related issues we have seen, however, WRT to the fuel pump may

provide some help.  First, starting at 18,000 ft and above we always turn

our Boost Pump on LOW -- without it, the engine fuel pump seems unable to

provide steady fuel flows and surging and instability can result.

The other time we have trouble with the fuel pump is on Hot Starts.  When

the engine is really heat soaked, even once you get it started and

apparently running smoothly, a half minute or up to a full minute later, all

of a sudden, the engine will try to quit, and can only be 'saved' by a

temporary slug of High Boost.  Apparently this is being caused by 'latent'

air pockets that are still trapped in the hot engine fuel pump that require

High Boost to help clear them out.

Later, maybe we should start a thread again on Hot Start techniques for the

big bore Continentals.  It's been almost a year now since the Reflector last

visited that topic and I think I've finally decided on about the only Hot

Start procedure that really works consistently for me when the engine is

really heat soaked -- but let's save that for a later and different thread

discussion!

Bob

-----Original Message-----

From: reflector-bounces at tvbf.org<mailto:reflector-bounces at tvbf.org> [mailto:reflector-bounces at tvbf.org]<mailto:[mailto:reflector-bounces at tvbf.org]> On

Behalf Of Scott Derrick

Sent: Tuesday, August 28, 2012 9:21 PM

To: Velocity Aircraft Owners and Builders list

Subject: REFLECTOR: Fuel pump cooling

I've had this happen a few times this summer on flights longer than 2.5

-3 hours.  Ran all winter with no problem so I think its heat related.

I typically run LOP, better mileage, lower temps,less pollution.

I can easily setup LOP when reaching my cruise altitude. I rarely have

to re-adjust it after getting in the desired setting.

When its really hot, say 15C+ at 11500, after a couple hours the mixture

seems to wander just a little bit and I have to periodically re-adjust

to get it back.  We are talking less than 0.1 GPH change.

Once I get the engine really heat soaked after a few hours of

flight(when the LOP starts to be work to maintain) and then stop for

gas, take off climb to altitude, now its really hard to get it to run

LOP?  It over  leans, then under leans.  If I then run it for awhile ROP

and let things cool down from the climb, I can get it to run LOP but I

still have that intermittent wandering mixture. Let the engine cool down

over night, next morning LOP is easy again with a engine starting from

cold.  I've had a few departures after it sat for a couple hours after

landing and it leans easy then too. Only those hot fast turn arounds

exacerbate the issue.

I noticed the T210 that uses this same engine has a cooling duct running

to the fuel pup which is shrouded.  I don't have this. I'm thinking

maybe it takes summer temps and a couple+ hours to get the fuel pump

really hot enough to, I don't know, loose it mind?

The turbo setup on this version TIO520 is very sophisticated.  Once you

set the throttle you can climb, descend and change prop rpm and the MAP

doesn't move at all. Very easy to fly.  My fuel pump is from that

original turbo setup.

Lycomings use an entirely different fuel pump so I don't think their

setup would apply.

Any body else see this problem thats running LOP? Is your fuel pump

cooled?  This is a 1986 vintage 520, with I think a similar fuel

pump(carbon vane) is used on later models.

Scott

--

What the superior man seeks is in himself; what the small man seeks is

in others.

Confucius

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