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Date: Fri, 27 May 2005 22:25:37 -0500
From: Jim Sower <canarder@frontiernet.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Sump tank - Velocity version
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I wouldn't guess that'd be a major factor. That said, dynos and even 
chocked airplanes don't have six degrees of freedom.
But I'm sure he'll be fine - he's checked and tested more than anyone I 
ever met ... Jim S.

Joe Hull wrote:

> Al, that was probably standing still in front of your hangar. In the 
> air there’s going to be some sloshing away from your tank pickups 
> –especially when climbing or descending – which are really lousy times 
> to lose fuel pressure!
>
> Joe Hull
>
> Bellevue (Seattle), Washington
>
> Cozy MkIV #991 (working on Engine & Electrical & Finishing)
>
> http://www.maddyhome.com/canardpages/pages/JoeHull/index.html
>
> ------------------------------------------------------------------------
>
> *From:* Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] 
> *On Behalf Of *Al Gietzen
> *Sent:* Friday, May 27, 2005 10:55 AM
> *To:* Rotary motors in aircraft
> *Subject:* [FlyRotary] Re: Sump tank - Velocity version
>
> One other comment while it is on my mind. I have run my 20B at 5300 
> WOT, gravity feeding from one main with about 2 gallons in it, through 
> a 3/8”line; and the low level warning near the top of the sump did not 
> come on. From that I infer that even with only about 3” head above the 
> top of the sump, I had adequate flow; maybe 18 -20 gph (EM2 flow flow 
> not yet calibrated. Normal operation then, with both tanks connected, 
> I would have more than double the necessary gravity flow needed to 
> feed from the mains to the sump.
>
> Al
>
> -----Original Message-----
> *From:* Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] 
> *On Behalf Of *Al Gietzen
> *Sent:* Friday, May 27, 2005 6:52 AM
> *To:* Rotary motors in aircraft
> *Subject:* [FlyRotary] Sump tank - Velocity version
>
> How do we KNOW that the return to the sump is what caused the prob? Are
>
> we talking his redesign or the original install?
>
> We do NOT know that the return to the sump caused the engine out on 
> Paul’s last flight.
>
> My original plan was to return fuel to the sump, but after Paul's first
>
> engine out to also have the sump vent be capable of overflowing into
>
> one of the wing tanks (both of which gravity feed into the sump).
>
> There are sump tanks and there are header tanks. I would define a sump 
> tank as one that is at or near the lowest point in the fuel system, 
> and is gravity fed from the main(s). Any small tank in a system that 
> has to be fed by a pump, I’d call a header tank. Header tanks are a 
> different issue.
>
> Here is a basic summary of my views on sump tanks. I state them as 
> facts, but obviously it is my interpretation of the facts.
>
> A sump tank has the advantage of eliminating the need for a pump from 
> the main tank; and eliminating the need for valves from one tank or 
> the other. Assuming it feeds from the lowest point in mains, it also 
> gives you a single point for collection of water and impurities that 
> may get in the fuel, and a single sample drain. These are desirable 
> and important reliability and safety features.
>
> The Velocity has a true sump tank which is full (or above) any time 
> there is fuel in the main tank. It is also a reasonably large tank; 
> about 2 ½ gal in the RG and I guess 4 – 5 gallons on the FG. A fuel 
> pump at or near the exit from the sump tank; at a level at or below 
> the level of the bottom of the tank, with a reasonably sized line 
> (3/8” or larger) from sump to pump should never see less than at least 
> 1 atmosphere of feed pressure, and therefore be highly resistant to 
> any vapor lock issues.
>
> With the fuel exit from the sump a bit up from the bottom (room for 
> collection of a quart or more of water and impurities) there should be 
> no need for a filter between the sump and the pump that could result 
> in flow resistance. Put the filter (30 micron or less, I suppose) 
> downstream from the pump to catch anything you don’t want going to the 
> injectors.
>
> I don’t believe there is an issue with returning the bypass fuel from 
> the pressure regulator to the sump as long as the sump tank is a few 
> gallons or more. When the engine is running there is always a net flow 
> from the main to the sump. There is not an issue of the sump 
> “overflowing”.
>
> If you have a smaller sump, or if it is reasonable and simple 
> (reliable) to do so; return the bypass to the main tanks (tanks, 
> plural; for gravity feed returning to one tank could result in level 
> imbalance.)
>
> If you are pumping fuel at a rate that far exceeds that burned by the 
> engine, there is a potential for heating of the fuel in the sump from 
> heat picked up in the fuel lines and rail in the engine compartment. 
> Size the pumps so that one pump gives you slightly more than the 
> maximum burn you expect from the engine. More than that; or running 
> both pumps more than just during takeoff, is just circulating a lot of 
> fuel through the engine compartment to no advantage, and causing 
> heating of the fuel. Fire sleeve on the fuel lines is a good idea, and 
> provides some (probably not much, but some) degree of heat insulation.
>
> Monitoring the fuel temp at the bottom of the sump could be a good 
> idea and provide useful information about the amount of heating of the 
> fuel in the sump. I’d expect the worst case to be long periods on the 
> taxiway with a fully heated engine at low power.
>
> Do a power run-up prior to takeoff. (This assumes your cooling system 
> design allows this.)
>
> The reason for circulating fuel through the fuel rail rather than a 
> dead-end system is to keep the fuel temperature from rising in the 
> rail, and to force any air or vapor bubbles (mostly a possibility at 
> or prior to startup) back to the tank. I have found that some period 
> after shutdown of the hot engine, I could hear bubbles feeding back to 
> the sump for a second when turning the fuel pump back on.
>
> In its simplest form (as in the Velocity) both mains and the sump are 
> vented to the atmosphere for air to exit upon fill-up, and for air to 
> enter as the fuel level goes down in the mains. The vents must of 
> course be above the highest fuel level and the lines not subject to 
> filling with fuel that must be drawn upward for air to enter. Keep in 
> mind that the fuel level in the sump will be the same as that of the 
> main tank; meaning that the vent line from the sump will have fuel in 
> it up to the level of the of the fuel surface in the mains.
>
> I realize that there have been or may be other anomalies in the vent 
> system (leaky fuel caps, or whatever) that can affect the function of 
> the vent system (as in Jim’s case); but that’s a separate discussion.
>
> FWIW,
>
> Al
>