Fuel flow test

[racaldwell]

I have a 3300 with a Bing carb so I have the Facet 40105 fuel pump installed in the cockpit. I noticed the fuel flow through the Facet pump depends on how much head pressure there is. With about 8" of head, there is just a trickle through the pump. With several feet of head, there is lots of flow.

This indicates to me that with the tank in climb attitude, the fuel is moved to the back of the tank. This increases head pressure. So to get a worse case scenario on fuel flow, the tank would need to be tilted forward.

If I had known how dependent the Facet pump is on head pressure, I would have installed it down near the low point which for me is the about 3" above the floor. Instead, I have it only about 6" below the tank outlet. Good thing I have a glider:)

Rick Caldwell
Xenos 0057

[GordonTurner]

Hi Rick

You sure you have a good pump?

Gordon

[racaldwell]

Hi Gordon,

I do not have one to compare it to. I verified it is the model Jabiru supplies. It came from their firewall forward kit. There is a little white plastic piece inside the inlet which I took as a check valve at first. But this pump doesn't have a check valve. Anybody else have a 40105 boost pump and have looked inside the ports? Is there a white plastic piece in the inlet?

The flow was good with head pressure but a near empty tank will have unuseable fuel. I have not tested that yet.

Rick Caldwell
Xenos 0057

[GordonTurner]

I have one of those pumps, I will check if it’s the exact same number, but it pumps same flow rate, which is pretty good, from full to sucking air.

[racaldwell]

Hi Gordon,

Just to clarify, I was referring to fuel flow through the pump turned off. Just the gravity flow, since this will be the case with the engine driven pump off and the boost pump off. I did open up the ports on the engine pump because I drilled and tapped for AN fittings...but the carb still has the stock brass tube for connecting a hose. I added a male brass 1/8" NPT fitting over it so I can connect AN fittings on the hoses.

Rick Caldwell
Xenos 0057

[GraemeSmith]

You might consider the Pitch Attitude/AoA at stall.

From a general discussion for GA wings at:

http://www.av8n.com/how/htm/aoa.html

AoA1.png (10.52 KiB) Viewed 4366 times

So something like 14 degrees pitch for a stall at 18.5 AoA

Add 5 degrees for your Canadian reg

19.5 degrees pitch

YMMV

[Bryan Cotton]

I used to fly a PA25 with a cowl tank similar to the Sonex. You could not do a power on stall as the engine would quit dramatically first. It had a bit more power than the Aerovee.

[Scott Todd]

18.5 degrees is a bit misleading. I've seen that quoted before in other discussions without source reference. A highly cambered wing (which we DO NOT have), may get there in ideal conditions. In addition, that data is always taken in a wind tunnel where the wing section goes from wall to wall. In the real world we have tip losses and other factors. We typically use something around 15 for rough calculations. And with flaps deployed, we can get a higher lift coefficient but the wing may stall earlier Angle of Attack wise.

But to the point, Angle of Attack is relative to the oncoming air. But like Graeme points out, for fuel flow discussion, its only about the incidence. Of course you can't be too safe. I think I always test at 16 degrees or so with 30 minutes of fuel in airplane. I like to see fuel flow of 2X even though 1.5 is the minimum. I've tested a handful or Homebuilt airplanes and NEVER seen less than 2X. Just saying... :)

[GraemeSmith]

18.5 degrees is a bit misleading.

Hence my reference to PITCH angle - rather than AoA

[builderflyer]

In doing fuel flow testing, the stall AOA is irrelevant. What matters is the power available to pull the aircraft through the air at a given airspeed while sustaining a given climb rate. For my lightly loaded 3300 powered Sonex, I assumed a 60 mph forward speed while climbing at 2,000 fpm which turns out to be a pretty good estimate. If I haven't made an error in the calculation (angle whose sine is...), the angle comes in at 22 degrees. This is close to what others, including the factory (see the tail in the ditch photo), have used......20 degrees or so.

Art,,,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,,,Jabiru 3300 #261