Flight test results for N957BH - Tell me yours

[captain_john]

Hey All,

While we have been testing 7BH we have some typical numbers that I thought I would share. The plane is an RV-6 with an O-360 and a Sterba wooden prop. No wheel pants or leg fairings.

2300 rpm =154 mph
2500 rpm = 177 mph
110 mph = 1500 fpm roc

Oil temp = 160-180
Fuel pressure = 3-5 psi

I have tested up 10,000 feet and begin leaning at 5,000. Fuel consumption is about 9.5 gph.

Does this all jive with your findings? It is pretty much textbook Vans.

Off thing happened on climb out last night. Pitched for 90 mph with boost pump off at 2,000 - 5,000 feet the fuel pressure dropped down to about 1 pound. Close to the airport, I chose to monitor the problem. When I got to 5,000 I turned the boost pump on and pressure came up to 4 psi. When I leveled off at 6,000 I shut boost off and pressure stayed at about 3-4 psi.

Engine never stumbled or faultered during the whole event.

...a concern? I dunno. We are going to install a supplemental fuel pressure gauge and fly with that and monitor the issue some more.

What's your take?

CJ

[cjensen]

I don't know how you can fly mph...I just can't get used to it...

I'll post some numbers this weekend after a couple more test flights!

Not sure on the 1psi reading. What kind of gauge? EFIS?

[bullojm1]

CJ,

This manual states the fuel pressure range for the O-360:

http://monrv-3.fr/docs/o360.pdf

"0.5-8 psi" is the normal range. I think you're fine with your 1psi shown.

- Mike B

[Brantel]

I have seen my fuel pressure read 0 without the boost pump.... It drives me crazy but I have never had the engine even bump wrong when this happens.

After a while it will come back up.

Some say the sensors we use are not accurate enough and that the change in ambient pressure from the climbs and decents screw them up????

[painless]

It is a common finding to see low fuel pressure on climb out in RVs. There was a thread about that in the other RV forum.

Sounds like it's doing normal stuff CJ.

[captain_john]

Chad, Bill has the Vans instruments... airspeed, fuel gauge et. al..

We do know that carbs don't need much pressure at all to run. We are going to cross check the instrument regardless. Might as well, nothing else is really wrong with the plane anyway! (I am happy to say!)

The bottom plugs are fouling a bit after taxi to the runup area. Standard mags are being used.

Gonna see about switching to REM37BY plugs for less fouling. Wicked Stick sent me this link from Sacramento Sky Ranch.

http://www.sacskyranch.com/faqsparkplug.htm

CJ

[captain_john]

OH! I know what else...

What are you guys running for tire pressures?

We are fairly high and coming down. Started at 40 and now down t 32. Thinking of even lower.

Pro's and con's?

CJ

[Thermos]

Off thing happened on climb out last night. Pitched for 90 mph with boost pump off at 2,000 - 5,000 feet the fuel pressure dropped down to about 1 pound. Close to the airport, I chose to monitor the problem. When I got to 5,000 I turned the boost pump on and pressure came up to 4 psi. When I leveled off at 6,000 I shut boost off and pressure stayed at about 3-4 psi.

Engine never stumbled or faultered during the whole event.

...a concern? I dunno. We are going to install a supplemental fuel pressure gauge and fly with that and monitor the issue some more.

What's your take?

CJ

Same thing used to happen to me when I was instructing in a Piper Seminole. We would be in a climb attitude, airspeed ~100 KIAS and while climbing, fuel pressure on the right engine would slowly roll back to around 1 psi. Other engine was fine. Turning on the electric boost pump brought the pressure right back up and once the airplane was established in cruise, fuel pressure came back up on its own.

Why it happened on one engine and not the other, I have no idea. I suspect it was heat-related which is why the problem went away at higher speeds - and that's consistent with what you're seeing on Bill's airplane. But I don't know what needs more cooling...fuel line? Boost pump? Pressure sender? I dunno.

It was unnerving the first couple of times it happened - the first time was out over the water around 20 miles southeast of NYC, and I thought I was going to lose the engine - but it kept running and since then I've heard of other Lyc O-320/360s doing the same thing.

HTH

Dave

[cjensen]

OH! I know what else...

What are you guys running for tire pressures?

We are fairly high and coming down. Started at 40 and now down t 32. Thinking of even lower.

Pro's and con's?

CJ

I'm running 34psi at the advise of our shop guys. Granted I've only flown twice, but it seems to be working just fine so far.

[captain_john]

Dave, That makes me rest more easily, I s'pose...

Chad, 34 psi for the tires. Got it!

They look right with that pressure. Will see how they wear.

CJ

[cjensen]

Okay...when the email came across, I thought I had read your post wrong...

[Thermos]

Dave, That makes me rest more easily, I s'pose...

Well...I never liked it, which kinda begs the question "why the was I flying the airplane?". Like you, I'm not happy with "it always does that" explanations.

Seems like somebody, somewhere (maybe on The Other Site) had a decent explanation of why this happens but I couldn't find it. If you can solve the problem, you'd make a lot of people rest a lot easier!

Dave

[cjensen]

Hey All,

While we have been testing 7BH we have some typical numbers that I thought I would share. The plane is an RV-6 with an O-360 and a Sterba wooden prop. No wheel pants or leg fairings.

2300 rpm =154 mph
2500 rpm = 177 mph
110 mph = 1500 fpm roc

Oil temp = 160-180
Fuel pressure = 3-5 psi

I have tested up 10,000 feet and begin leaning at 5,000. Fuel consumption is about 9.5 gph.

I have some results to post from my flight this evening...

I'm running it pretty hard right now, so fuel flow is running 12.1 to 14.9, fuel pressure is running 2-4psi.

At 4500', 2500rpm = 138kts (159mph) indicated, 149kts true, at 2600rpm = 150kts (173mph), 162kts true.

110kts = 1650fpm roc

Oil temp has been running a bit hot 207-227 at high power settings.

I have tested to 6500' so far, and leaned for the first time on tonight's flight, down to 12gph, but no further yet.

More flying tomorrow I hope.

[hydroguy2]

looks like pretty good numbers with no fairings, things should pick up as you get broke and a faired up

[cjensen]

Did a four way GS check today at 6500'...158kts true, so the EFIS is just about spot on. Can't wait to see what this thing will do with the fairings on it!

[captain_john]

Okay...when the email came across, I thought I had read your post wrong...

Yah!!! I had to edit. I was thinking that you were talking about FUEL pressure!

Hahahaha...

I got it! We are leaving them at 32 and monitoring wear.

Dave, Yup... I agree. I am not a fan of 1 PSI. But it is better than NONE psi! What is really odd is that sometimes we get about 6 without the boost on. Weird, huh?

Chad, those numbers are pretty consistent with ours (as I might have suspected)

Speaking of Speedpants... We have just named our local A&P IA that! hahahaha

We are going to put SPEEDPANTS on his golf cart! He is gonna love that!

Here is a pic of Speedpants in the foreground:



Bill is talking to me before a subsequent launch and checking engine parameters.

Here is a pic of the -6:



Gonna have to fly some more tonight!

CJ

[Thermos]

I did a little checking on this whole fuel pressure issue. There's a theory going around that your typical fuel pressure sender has a small hole in it that vents one side of the sensor to outside air pressure - and that affects the fuel pressure the sender measures.

As this theory goes, the sender is actually an automotive part - somebody here can probably confirm or deny that - and the pressure vent hole is pretty small. So small, in fact, that when outside air pressure changes quickly as in a climb it takes the pressure sender awhile to vent down to ambient pressure - and that error translates to an abnormally low fuel pressure reading.

So John, if you're up for a test...you can stabilize in level flight and let the fuel pressure reading catch up. Then with the boost pump off, slow down to approach speed or slower while maintaining altitude. See if the fuel pressure changes or remains the same. Then speed up and check the pressure again. If there's no change, that hole-in-the-sender theory may be right. If it changes, there's something else going on.

You may already have enough observations to confirm or deny this theory...

Cheers,

Dave

[Lycosaurus]

I did a little checking on this whole fuel pressure issue. There's a theory going around that your typical fuel pressure sender has a small hole in it that vents one side of the sensor to outside air pressure - and that affects the fuel pressure the sender measures.

The fuel pressure goes back up when using the electric fuel boost pump. Wouldn't that eliminate the 'sender theory'?

[captain_john]

Yes Dave, I am up for a test on that theory. After all, isn't that why we are here!?!



I can agree with the likelihood that it is (as is the mechanical pump) an auto part.

Lyco, I would say... Maybe.

The reason I say maybe is because the boost pump could be (and likely IS) making more pressure than the mechanical pump.

If the gauge goes from 1-4 lbs with boost on, it is probably ACTUALLY going from 2-maybe 8 in true numbers. No?

Hmmmm???

Won't fly today. Might fly tomorrow. Need to get secondary gauge t do a true double check.

CJ

[Spike]

The fuel pressure goes back up when using the electric fuel boost pump. Wouldn't that eliminate the 'sender theory'?

Might not. The sender really measures differential between two points right? Oil pressure against a spring, or atmosphere, etc. I would think that boosting the pressure with a pump would change the differential pressure while the body was bleeding down.