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fuel system testing

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fehdxl

Well Known Member
The EAA held a webinar this evening about fuel systems and fuel flow testing prior to first flight. Essentially, they stepped through how to determine unusable fuel in various flight phases (climbs, descents, slips, etc).

I know I've read several posts about people excited that there are only ounces of fuel left in the tank after draining through the fuel line (in the hangar). However, I have yet to hear anyone (or Van's) publish how much fuel it takes to ensure the engine receives gas in normal flight conditions...for example a full-rudder slip in the non-optimum direction/tank.

So has anyone in one of the 8000+ flying RVs actually determined realistic unusable fuel? Ideally, each of us would determine our own aircraft's unusable fuel, but I suspect close congruence between similarly constructed fuel systems.

Fly safe,

-Jim
 
A side slip is simply not a normal maneuver and would be used to get to a landing site faster than a normal approach. In this scenario you would not want or need engine power or else you would have no need for a side slip.
Theoretically you could succeed in unporting your fuel pick up with as much as a half tank I guess.
I'd still be interested if someone actually collected some info.
 
Half a tank full deflection, 30 seconds until engine miss. Consider keeping the fuel lever to the high wing on approach.
 
Jim,
During Phase 1 testing I would test my fuel system by flying until my EIS-4000 low fuel pressure light would come on. At that point I would switch tanks, note the fuel level indication on the empty tank, then note how much fuel it took to top that tank back off. By utilizing the low fuel pressure light (set at 1.7 PSI) the engine never missed a beat. Once the light came on it told me the pump wasn't pushing any fuel anymore, however the float bowl had enough fuel to allow me to switch to the full tank and get the fuel pressure back to normal.

I was able to top off the tanks with almost the full 19 gallons which told me that I had almost used the entire amount of fuel in the tank.
 
Tom Martin said:
Half a tank full deflection, 30 seconds until engine miss. Consider keeping the fuel lever to the high wing on approach.
Click to expand...

Wow, that's a lot!

If you are one who maximizes range by running a tank dry, forethought to landing runway and crosswinds would be prudent.

Fly safe,

-Jim
 
curtis said:
I was able to top off the tanks with almost the full 19 gallons which told me that I had almost used the entire amount of fuel in the tank.
Click to expand...

Curtis, Yes that makes sense. But how much was unusable in a 10 degree pitch up climb (go around), or during an extended descent, or slip? The whole point of the EAA webinar was to test in various phases, not just straight and level. Good stuff. Fly safe, -Jim
 
Unusable Fuel Quantity Testin

Below is a response I made to this topic in 2009...

DAGO said:
This topic brings me back 30 years ago when I briefly worked for Cessna Aircraft in Wichita. One of my projects was to conduct unusable fuel quantity tests for the Cessna 404 Titan. The engineers wanted a tank design to reflect about 5 gallons unusable fuel. We had a mock-up tank of the existing prototype installation on the floor of the hangar. The objective was to come up with a published figure to place in the POH.

According to certification requirements, it required 35 seperate flight parameters to test the unusable fuel quantity. Many of these flights had to be repeated. We flew in a variety of pitch attitudes, angle of bank, and coordinated and uncoordinated flight.

For example, we would put just enough fuel into one tank to get us out to the practice area and perform the stated manuever. The manuever could be a 1/2 ball skid, level flight, 15 degree bank turn. We would maintain that attitude until the engine coughed. Switch back to the good tank. Return to the field, empty the tank, and measure the results.

If the results didn't meet the target figure, we would walk over to the mock up, look at the tank baffling and lightening holes, make funny airplane gestures with our hands analyzing the problem, then tell the technicians to move this or that, or make a another hole here or there.

We go drink coffee for a couple of hours, they would make the mods to the tank. Then we would go flight test again. This process, for a certified aircraft was very laborious and costly.

This thread topic brought back some pleasant memories.

Regards,
Click to expand...
 
During the presentation, it was alluded that Van's has done some testing. Although they didn't state which models.

I would be curious if anyone had that data.

Scott/Joe, is this something that you can publish?
 
certification? ...makes for interesting systems.

This makes me think about how many certified aircraft seem to have unecessarily complex fuel systems, often to their detriment.
Perhaps that odd header tank that is plumbed into the fuselage is there just to satisfy an otherwise troublesome wing tank dynamic.... that made it nearly impossible to certify with a reasonable minimum fuel level !
The advantage of course is when you run the mains dry, you have a reliable and quantifiable reserve, that should flow in all attitudes. ( although the accident record may show otherwise...humans being what they are!)
 
flyboy1963 said:
Perhaps that odd header tank that is plumbed into the fuselage is there just to satisfy an otherwise troublesome wing tank dynamic....
Click to expand...

Yes. Last evening during the Webinar, they spoke about the Glassair (if I remember correctly) that would flame out on long, fast descents from fuel starvation...a header tank was the fix.

In the world of experimenting, sure is nice to know some background as to why things are the way they are so we can refrain from making the same mistakes Clyde Cessna, Bill Piper, Bill Lear, Joe Taylor, etc made in the last century develping the certified planes of yesteryear.

Fly safe,

-Jim
 
I am not sure if anyone mentioned being coordinated in a turn with regards to this thread. If the turn is coordinated, it wouldn't matter which tank is the high tank or not.

Also, in regards to a Un-coordinated turn.. Depending on how the turn is uncoordinated, even the low tank can have the fuel try to run out to the tip.

Also, In building the RV, the Trap door is put in place and if working correctly helps keeps fuel in the inner bay at least temporarily. To get specific numbers on this as requested, testing would need to be done on each specific aircraft I would assume.

Just my thoughts
 
Back to Fuel System Testing

I attended the same webinare. As I am about to do my first engine start and hopefully first flight, this is an issue I would really like to address.

I wrote Van's asking them if they could tell me the angle of flight associated with Vx in an RV 8. Their reply was, well it depends on loading, power, etc. I suppose that is true, but definitely dodged the question. They said that they mostly put the wheels on blocks, put the tail wheel in a hole and then checked the flow.

Can't say that I was the least bit impressed with that answer. Does anyone here have a decent notion of what angles we ought to be looking for? Obviously the slip test needs to be done during flight but there ought to be some information from experieneced pilots about roughly what angles of inclination and declination I should use for static tests.

Regards,

Michael Wynn
RV 8 Finishing
San Ramon, CA
 
fehdxl said:
Yes. Last evening during the Webinar, they spoke about the Glassair (if I remember correctly) that would flame out on long, fast descents from fuel starvation...a header tank was the fix.

-Jim
Click to expand...

I think the reference made here is to the Glasair GlaStar and the later Sportsman 2+2 aircraft. There had been an incident where an engine had flamed out in a descent because the fuel pickups are at the aft end of the wing tanks. It seems strange that a high-wing aircraft would encounter fuel starvation in a descent but that seems to be the case.

The solution to the problem was to install a header tank, nestled into the welded tube cage structure just behind each of the doors. These headers hold enough fuel to sustain the engine in a steep power-off descent from something like 10,000 or 12,000 feet. It's only in this kind of descent that the tanks will un-port. Since implementation of these header tanks there hasn't been a report of anybody flaming out and a lot of these airplanes are operating in the back country where such descents are often necessary.

Of note, the Canadian amateur-built regulations require a fuel flow test be completed before the Minister's Delegate - Recreational Aviation will sign the aircraft off as being airworthy. This flow test is done with the aircraft configured in the configuration most adverse to sustained fuel flow. In the case of the Glasair Sportsman, that means a 16degree nose up attitude (this figure was calculated and provided by Glasair - suspect that Van should be able to do likewise).

If the EAA seminar was delivered by Dave Prizio it's worth noting he's built both a GlaStar and a Sportsman.
 
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