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  #1  
Old 05-11-2012, 07:07 AM
s24789 s24789 is offline
 
Join Date: Jan 2009
Location: Hobe Sound, Florida
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Question Fuel flow on takeoff

Looking for other's experiences. On take off we are seeing 13.5 max fuel flow in our carburated o-360 and fixed pitch prop in our 7a. We are also seeing no fuel coming out of the fuel drain in our gascolator mounted on the lower right firewall. We do get flow when we turn on the boost pump. Has anyone else experienced this issue. I am wondering if a vent restrictions keeping us from both seeing fuel at the gascolator drain and also restricting our fuel flow.

Thoughts ?

Thanks
Phelps
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  #2  
Old 05-11-2012, 07:08 AM
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Sam Buchanan Sam Buchanan is offline
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Quote:
Originally Posted by s24789 View Post
Looking for other's experiences. On take off we are seeing 13.5 max fuel flow in our carburated o-360 and fixed pitch prop in our 7a. We are also seeing no fuel coming out of the fuel drain in our gascolator mounted on the lower right firewall. We do get flow when we turn on the boost pump. Has anyone else experienced this issue. I am wondering if a vent restrictions keeping us from both seeing fuel at the gascolator drain and also restricting our fuel flow.

Thoughts ?

Thanks
Phelps
What you are seeing in regard to fuel flow and the gascolator is normal.
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  #3  
Old 05-11-2012, 07:17 AM
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Ironflight Ironflight is offline
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I agree with Sam on the Gascolator - you won't get any flow unless you have the pump turned on.

For your measured fuel flow - have you calibrated the fuel flow system yet? The factor "constant" is oftentimes off by 20%, and you have to play with it by measuring how much fuel you put in after a flight, then tweaking the constant. It is an iterative process, and can take awhile to nail it.

Paul
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  #4  
Old 08-01-2012, 03:39 AM
s24789 s24789 is offline
 
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Quote:
Originally Posted by Ironflight View Post
I agree with Sam on the Gascolator - you won't get any flow unless you have the pump turned on.

For your measured fuel flow - have you calibrated the fuel flow system yet? The factor "constant" is oftentimes off by 20%, and you have to play with it by measuring how much fuel you put in after a flight, then tweaking the constant. It is an iterative process, and can take awhile to nail it.

Paul
Hi Paul thx, yes we have calibrated the red cube. Using Mike Bush's plotting website we generally see 410-420 F at sea level 90 F take off and around 14-15 gph Wf in take-off. After a couple thousand feet with WOT the CHTs settle down. Still wondering if we are not getting enough flow for takeoff. Thoughts?
Phelps
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  #5  
Old 08-01-2012, 04:52 AM
noelf noelf is offline
 
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My set up is O-360, Fixed Pitch, field elevation is 614 ft.

Seems about what I am seeing. Take off run is 13GPH, WOT RPM starts at 2130 and increases as the ground run speed increases. Red cube installed between gascolator and carb.

To drain any fuel out of the gascolator, I have to select one of the tanks using the fuel selector valve. No fuel flows if the selector is in the OFF position.
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  #6  
Old 08-01-2012, 04:53 AM
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RV10inOz RV10inOz is offline
 
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Kevin

Aside from fuel system anomalies and measurement errors, the following is not negotiable in general terms, +/- 5%.

Fuel flow at sea level and ISA is HP/10 in GPH, in your case I assume 18 GPH.

With a fixed pitch prop you may have 85% rpm thus 85% fuel flow, so around 15-15.5 GPH.

CHT on take off should be in the 350-375 F range, if not get your fuel flow right first, then fix your baffles.

Any questions, please ask.

David
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  #7  
Old 08-01-2012, 11:46 AM
N743RV N743RV is offline
 
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Location: Livermore, CA
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Default 15.1 to 15.3 gph at Takeoff

I've just checked the digital records of my RV-7a with a 180 hp Mattituck IO-360 M1B. I have a Hartzell constant speed blended airfoil prop. On full throttle takeoff at my fuel flow ranges from 15.1 to 15.3 gph. My airport (KLVK) is at 400 ft msl and the temperatures I looked at ranged form 48 to 90 F. My fuel red cube fuel flow device is pretty well calibrated (usually well within 0.5 gal at fillups).

This seems to be more than than +/-5% off of the range of 0.1 gal/hp.
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  #8  
Old 05-11-2012, 07:17 AM
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schristo@mac.com schristo@mac.com is offline
 
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Default .1 gph per hp at max power full rich fuel flow

The rule of thumb of .1 gph per hp at max power full rich fuel flow seems to be pretty accurate.
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