Fuel flow test

[Mike53]

I'm about to perform a Fuel flow test on my Onex which uses a 85HP Hummel engine and was hoping someone can confirm my figures

The formula for a Gravity feed system( obtained from EAA webinar on fuel flow test) is HP X BSFC X 1.5 X .36 = ounces per minute

The fuel consumption for the Hummel at full power is approx. 5 gal/hr.or 30 lbs/hr
I obtained the Brake specific fuel consumption from http://www.wallaceracing.com/bsfc-calc.php which was .35

85 X .35 X 1.5 X .36 =16 ounces per minute

So I require a minimum fuel flow of 16 ounces per minute at full throttle in a maximum takeoff climb angle + 5 degrees

Anyone see any problems with the above?

Thanks.
Mike

[sonex1374]

Mike,

When using an 80 HP AeroVee you're likely to see full-throttle fuel flow closer to 6.5-7.0 gal/hr. (This also matches the rule of thumb approximation of 0.5 lbs fuel per hr, per horsepower.) If you use this figure, this gives you a target fuel flow for your test of 23 oz/min (or 10 gal/hr).

I have no way to verify the BSFC of a Hummel engine, but 0.35 is a very good number (e.g. a highly efficient engine on par with diesels). It would be more conservative to assume that the engine is actually less efficient, and therefor may require a higher flow rate. For this reason, I'd encourage you to use the higher numbers.

Jeff

[WesRagle]

Hi Mike,

I agree with Jeff. And I do remember 7 GPH WOT with the Aerovee.

I also installed a 2400 Hummel and just completed my FF test. I was hoping for 10 GPH for the last gallon but was seeing more like 9.5 GPH at 16 deg deck angle. I decided to live with that because, unless you are under propped, you will never see 85 H.P. at max climb angle.

What deck angle did you decide to use?

Wes

[Mike53]

Thank you both.
I based the Max fuel burn on Scott Casler's response to my question on Max fuel burn and he gave me 5 gal/hr.... 2 gal./hr. higher is a significant amount so I will assume he misunderstood my query since the consensus here is 6.5 to 7 gal/hr
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

[Sonex1674]

Thanks for the discussion - wasn't aware of the EAA webinar entitled: "Fuel System Testing". Unit conversion from 5 gal/hr yields 10.6 oz/min - apply the 1.5 factor of safety for gravity systems yields 16 oz/min; and of course 7/5*16=22.4 oz/min. EAA webinar was very informative.

[WesRagle]

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

[Mike53]

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

This was Kerry's response

Hi Mike.

There is no prescribed angle so if you want to test fuel flow at an angle
you can drop the tail into a ditch.

If your fuel system is per plans fuel flow will far exceed what is needed.

Blue Skies....

Kerry

Sonex Aircraft Tech Support


Any suggestions?

[Rynoth]

In reviewing some of my in-flight footage, my typical climb deck angle is very close to how the taildragger sits on the ground. If you can get the tailwheel just a little lower and/or the mains a little higher you'd easily be simulating climb pitch.

I went pretty extreme with my test, at an angle WAY beyond what a sustainable climb would be and still came up with plenty of fuel flow. Fuel system was designed per the plans.

http://www.rynoth.com/wordpress/waiex/2 ... stem-test/

With a tri-gear, just weighing the tail down to the ground would probably be more than adequete.

Next time I'm at the hangar I can measure the angle that the taildragger sits on the ground, I think adding 5 degrees to that would be sufficient to meet the Canadian reqs.

[Mike53]

Thanks Ryan.
Your picks gave me the idea to simply put the Onex back on the trailer designed for it which should give me more than enough leeway to achieve 20 degrees or so.
I would still appreciate your measuring the deck angle on the ground.
Mike

[SonexFactoryTech]

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

We are not sure the intent of Wes' comment. But to elaborate, no we cannot provide a precise answer. Too many variables. What is the density altitude? What is the airspeed at rotation? What is your desired climb speed? Are you trying to get over an obstacle? Are you hanging it on the prop and if so, a climb prop or a cruise prop? Have you built the airplane correctly? Have you modified the fuel system?

The Onex fuel system, installed well and as designed, will deliver enough fuel for the prescribed horsepower. It will do that on a vertical climb while performing aerobatics. To design a fuel system for an aerobatic airplane that couldn't is senseless. The fuel flow test is not a test of the design, it is a test of one particular fuel system installation, the one being tested. Each builder must test their own system to their own needs.

Builders lose sight of the handbuilt, one-off, varying degrees of workmanship aspect of the EAB category. There isn't always one answer, one fix for every question or problem. Sometimes a builder has to define their own specification.

Blue Skies....

Sonex Aircraft, LLC