Fuel flow test

[WesRagle]

We are not sure the intent of Wes' comment.

Hi Kerry,

I was in the middle of responding to Mike. I opened another instance of the SonexBuilders to check on a previous post and saw you response.

This is as far as I got :-)

Like I said, I just finished the FF test and so had/have many of the same questions you have.

Here is my take on it:

1) I'm sure Kerry is right.

2) My tests results were just OK, not stellar. The miniature fuel valve used on my Onex has a smaller orifice than the valve typically used on the Sonex/Waiex. You may be using a similar fuel valve.

3) There are simply too many variables for Sonex LLC to be able to quote a a deck angle for the test.

Examples:

What engine are you using? What is the compression ratio of the engine? How heavy did you build your aircraft? What Prop are you using? The list is endless.

Notice I used the word couldn't, not wouldn't. I was going to point out many of the things you pointed out, but you are so much better at it :-) Anyway, my only intent is to keep the discussion going because Mike has a test he has to perform and needs a number for deck angle. I'm trying to help.

Here's how I came up with a deck angle. I simply estimated a rate of climb and a speed at which that climb would be achieved. If you divide the rate of climb by the speed at which you expect to achieve that ROC, you have the sine of the angle of climb. If you take the arcsin of that number you have the angle of climb.

I used the estimated angle of climb for the deck angle number. This is only an estimate and ignores the angle of incidence and angle of attack of the wing but ..., that is exactly why the test has built in fudge factors of 1.5 x FF and 5 Deg. deck angle.

For my estimate I used an optimistic ROC and a slow climb speed so I would remain on the conservative side.

Example:

Estimated ROC: 1000 Ft. Per Min
Estimated speed for 1000 Ft. Per Min. ROC: 60 MPH (5280 Ft. Per. Min)

Sine ROC = 1000/5280 = 0.1893939

Arcsin 0.1893939 = 10.91 Deg. climb angle.

I rounded that up to 11 deg, added 5 deg and that's how I ended up with 16 deg.

Anyway, that's how I came up with my number for deck angle.

YMMV,

Wes

[Rynoth]

I just read the FAR on the fuel flow test, and the specification for attitude is pretty vague. "...Be shown with the airplane in the most adverse fuel feed condition (with respect to altitudes, attitudes, and other conditions) that is expected in operation.

One could read that as a best-angle climb attitude. One could also read that since we can expect to be aerobatic in our operation, as upside-down, in which case we'd all fail. The climb angle of an 80HP aerovee at 10,000ft would also be a lot different than a 120HP Jab at sea level. I think it's reasonable to assume it means a typical go-around situation with min fuel, which would probably fall in the range of 15-20 degrees of deck angle. I personally don't see going up in altitude would make much of a difference, sea level is probably the worst-case since you'd have the highest fuel flow requirement (more HP!) along with the steepest achievable/sustainable climb angle.

[Area 51%]

Seems there are many variables that could affect the static deck angle (standard gear). Tire size/pressure, gear leg length, how level is the floor? How much difference between planes is an interesting question.

As far as designing/building an aerobatic plane with an inadequate fuel system, the Spitfire wouldn't stay running without a modification to it's carburetor.

To give you something to compare to, I have Tracy O'Brian gear legs (stuck into their mounts all the way to the top) with 4.00X5 tires at rated pressure. The tailwheel is a Peter Anson 6" pneumatic unit filled to the brim with a nitrogen/oxygen/other impurities mix. The floor is, of course, suspect.

My digital angle meter reads 8.4 degrees at the upper cabin longeron on our Waiex.

[Mike53]

Thanks again to everyone who has contributed to this topic..I went out to the airport today to measure the angle with the tail touching the ground and it came out to 11 degrees . I will add 5 degrees as Wes did and rig 16 degrees deck angle. My assumption is it will be a more than adequate fuel flow i.e.: better than or at least 150%

Cheers,
Mike

.

[petep]

FAA AC90-89B section 11 1-19b (e) recommends . Fuel Flow. A fuel flow and unusable fuel check is a field test to ensure the aircraft
engine will get enough fuel to run properly, even if the aircraft is in a steep climb or stall
attitude, and is accomplished by:
(1) Place the aircraft’s nose at an angle 5 degrees above the highest anticipated climb
angle. The easiest and safest way to do this with a conventional gear aircraft is to dig a hole and
place the aircraft’s tail in it. For a nose gear aircraft, build a ramp to raise the nose gear to the
proper angle.
(2) Make sure the aircraft is tied-down and chocked. With minimum fuel in the tanks,
disconnect the fuel line to the carburetor. The fuel flow with a gravity flow system should be
150 percent of the fuel consumption of the engine at full throttle. With a fuel system that is
pressurized, the fuel flow should be at least 125 percent. When the fuel stops flowing, the
remaining fuel is the “unusable fuel” quantity.
(3) The formula for fuel flow rate for a gravity-feed fuel system is 0.55 times
engine horsepower (HP) times 1.50. This gives a fuel flow rate in pounds of fuel per hour.
Divide the pounds-per-hour number by 60 to calculate pounds per minute, and divide again by 6
to calculate gallons per minute. To get gallons per hour for Avgas divide pounds per hour by 6;
or multiple gallons per minute by 60. For a pressurized system, substitute 1.25 for 1.50 to
calculate the fuel flow rate.

Note that Sonex recommends no take off with less than 4 gallons in the fuel tank so I call that minimum fuel. Lots of individual interpretations in the AC but it is the FAA standard recommendation for flight testing.

[WesRagle]

Hi Guys,

Last Tuesday I made the following post:

I am waiting for Sonex's response to my question about max deck angle in a takeoff.In Canada at least we have to add 5 degrees to that number when performing the test.
Mike

Hi Mike,

Did you get a response from Sonex LLC? I'm betting that they couldn't provide an answer.

Thanks,

Wes

Kerry felt he had to take time out and respond to the post. I think Kerry misunderstood what I meant. I want to take a minute to clarify what I meant so I'll quit feeling guilty about it.

I did not mean to imply any lack of knowledge, competence, or anything of that nature. What I meant was that Kerry Fores, in his official capacity as Technical Representative for Sonex Aircraft, LLC, couldn't answer the question. If I were Kerry's best friend and heard someone ask for a specific number for deck angle I would say "don't answer". If I were Kerry's legal council I would say "don't answer".

Me, I'm just some guy chatting away on a forum. I can guess at a number all day long without consequence. Kerry isn't afforded that luxury.

I feel better now.

Wes

[GordonTurner]

If you are using a factory authorized motor/airframe combination, why would you think the factory wouldn’t provide answer to a technical question?

[WesRagle]

Hi Gordon,

Ill assume you are asking me and that you have read the posts in this thread.

First of all, I do expect the factory to provide answers to technical questions. I've gotten an answer for every question I've ever asked them. I didn't always like the answer but ..., that's just the way of it. I would also point out that Kerry did provide an accurate and useful answer. It's wasn't the type of answer Mike was looking for but it was the correct answer. Also, Mike and I are both using engine/airframe combinations that are not factory authorized so the chance that Kerry could provide Mike with an exact number goes from slim to none. I see you're using an unauthorized engine too, so you're in the same boat.

But, if you want to venture into the hypothetical and assume we are talking about an authorized combination, there are still too many variables in the equation for Kerry to venture a guess. I won't try to enumerate the list because, as I wrote earlier, the list is endless. And, Kerry can't guess. Due to the nature of his job guessing is not allowed. He can't be our "build buddy".

In the past Kerry pointed out to me that homebuilt airplanes start out as boxes of parts. Those parts are shipped to people of varying skills and levels of workmanship who aim to make those parts fly. Ultimately each kit built airplane is unique.

We all have to take responsibility for what we create and as Kerry put it, "Sometimes a builder has to define their own specification".

Wes

[Bryan Cotton]

Hey all,
When you did your fuel flow test, do you just check the last 4 gallons? Or what did you do?

Edit: I see Ryan did 1 gallon, 30 seconds of flow, and used a measuring cup. Anybody else have something to share?

Thanks.

[Area 51%]

With "Chett" high in the front, low in the back, and the fuel valve on, I put gas in the tank till it started to flow, then shut the valve. Took about a quart as I recall. Dumped another gallon in, opened the valve, and timed how long it took for the gallon to come out the other end.

There seems to be a lot of variation in flow tests among our airframes. The guys with the fuel line down around their feet are going to get a much higher rate than having the line supported close to the level of the carb.