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Fuel flow

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clemwehner

Joined: 02 Feb 2009
Posts: 32

Posted: Sun Aug 18, 2013 8:25 am Post subject: Fuel flow

Our KF-IV has the plastic header tank behind the seat. Since the header tank is lower than the carbs, how can the engine run from the header tank in the event fuel flow stops from the main tanks for some reason? Some guys have said that there is about 10 minutes of fuel in the header tank. How is that possible with no gravity flow in level flight?



Does the engine fuel pump suck fuel from the header when it's running?



thanks,

Clem

Oklahoma

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Sun Aug 18, 2013 9:07 am Post subject: Fuel flow

On 8/18/2013 9:25 AM, clemwehner wrote:

 	  Quote: 	
		   Our KF-IV has the plastic header tank behind the seat. Since the header tank is lower than the carbs, how can the engine run from the header tank in the event fuel flow stops from the main tanks for some reason? Some guys have said that there is about 10 minutes of fuel in the header tank. How is that possible with no gravity flow in level flight?



 Does the engine fuel pump suck fuel from the header when it's running?

    

In a "normal" IV installation the mechanical pump will draw fuel from 
	


the header at any sustainable pitch angle. Interestingly, I could find 

no specification in the install manual for the minimum fuel level (below 

the pump) that the pump would draw. Note that the mechanical pump works 

with many aircraft that have low wings and therefore much less head 

pressure than even your header tank.



Guy Buchanan

Ramona, CA

Kitfox IV-1200 / 912-S / Warp 3cs / 500 hrs. and grounded

Now a glider pilot, too.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

mikeperkins

Joined: 22 May 2007
Posts: 123

Posted: Mon Aug 19, 2013 6:30 am Post subject: Re: Fuel flow

The Mikuni fuel pump is spec'd to pull fuel against gravity to a height of 24 inches. However, I assume that's at 1 G. When the aircraft is at 2 Gs, so is the fuel. So if the assumption is correct that 24 inches is at 1 G, then the distance at 2 Gs becomes 12 inches. But I'm not sure how the fuel lift distance was specified (if it spec'd at 1 G or if it is spec'd at more than 1 G). Anyway, here's a writeup on the Mikuni fuel pump: http://www.ultralightnews.ca/mikuni/



Also, most Kitfoxes have fuel caps with ram air vents, but I'm not sure how many inches of fuel pressure they add.



That having been said, I plan to never count on the fuel remaining in the header tank alone because with a failed fuel pump, the lack of head pressure with empty wing tanks will create an unpleasant situation.

_________________
Mike Perkins
Havana, Illinois
Model I, 532, B gearbox, GSC prop

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Mon Aug 19, 2013 7:28 am Post subject: Fuel flow

Mike,

     Not too many people launch with empty wing tanks, and if you do, I 

guess you get what you asked for, eh? Fortunately the head pressure in 

level flight is nearly even, with most of the "loss" of pressure 

attributable to friction and other mechanical losses. I don't know if 

anyone else has done this but when I get to the end of this installation 

I'll be testing without the fuel pump to see if the wing tanks will 

gravity feed and at what attitude. There's some conjecture that the 

vibration of the carbs allows a pure gravity feed in spite of the lack 

of 2.5psi static pressure.



Guy Buchanan

Ramona, CA

Kitfox IV-1200 / 912-S / Warp 3cs / 500 hrs. and grounded

Now a glider pilot, too.



On 8/19/2013 7:30 AM, mikeperkins wrote:

 	  Quote: 	
		   That having been said, I plan to never count on the fuel remaining in the header tank alone because with a failed fuel pump, the lack of head pressure with empty wing tanks will create an unpleasant situation.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

mikeperkins

Joined: 22 May 2007
Posts: 123

Posted: Mon Aug 19, 2013 8:00 am Post subject: Re: Fuel flow

Hi Guy, 



You're right to say that no one would (or should) launch with empty tanks, but someone who encountered something unexpected enroute might wind up accidentally landing with them empty. In that case, a go-around would put the behind-the-seat header tank pretty dang low. 



I once did a differential measurement of my Kiftox I's behind-the-seat header tank and the carbs. I discovered the aircraft's supply of fuel would depend upon a working fuel pump. But I don't remember the distance.

_________________
Mike Perkins
Havana, Illinois
Model I, 532, B gearbox, GSC prop

lcfitt(at)sbcglobal.net
Guest

Posted: Mon Aug 19, 2013 8:40 am Post subject: Fuel flow

Interesting discussion. On another forum a guy measured fuel flow beyond the 

fuel pump at the carburetors and he found that the flow there didn't  come 

up to the FAA recommendations.  So the fuel will flow past an inop pump. 

However I seem to have heard that if the diaphragm has been breached, fuel 

will preferably simply flow into the crank case - not sure on this.  I would 

think an easy fix would be an electric aux pump between the header tank and 

the mechanical fuel pump.  I have one on mine and the on switch is within 

thumbs reach with my hand on the throttle.

Lowell



--------------------------------------------------

From: "mikeperkins" <flybyewire(at)gmail.com>

Sent: Monday, August 19, 2013 9:00 AM

To: <kitfox-list(at)matronics.com>

Subject: Re: Fuel flow



 	  Quote: 	
		   



 Hi Guy,



 You're right to say that no one would (or should) launch with empty tanks, 

 but someone who encountered something unexpected enroute might wind up 

 accidentally landing with them empty. In that case, a go-around would put 

 the behind-the-seat header tank pretty dang low.



 I once did a differential measurement of my Kiftox I's behind-the-seat 

 header tank and the carbs. I discovered the aircraft's supply of fuel 

 would depend upon a working fuel pump. But I don't remember the distance.



 --------

 Mike Perkins

 Havana, Illinois

 Model I, 532, B gearbox, GSC prop





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=407039#407039

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Mon Aug 19, 2013 9:24 am Post subject: Fuel flow

On 8/19/2013 9:39 AM, Lowell Fitt wrote:  	  Quote: 	
		  However I seem to have heard that if the diaphragm has been breached, fuel will preferably simply flow into the crank case - not sure on this.  I would think an easy fix would be an electric aux pump between the header tank and the mechanical fuel pump.  I have one on mine and the on switch is within thumbs reach with my hand on the throttle. 	
 

 'Course if it's true about the diaphragm, the aux pump isn't going to help you much in that failure mode. (I've never heard of anyone pumping fuel into the case, though.)

 

 Guy Buchanan

 Ramona, CA

 Kitfox IV-1200 / 912-S / Warp 3cs / 500 hrs. and grounded

 Now a glider pilot, too.

 

 

    [quote][b]

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

redrocketrider

Joined: 13 May 2011
Posts: 67
Location: Nervino airport

Posted: Mon Aug 19, 2013 9:53 am Post subject: Fuel flow

I agree, the only way to fly, Back up for the mechanical.  Bob & Toodie KF 

4/1200/ O02, High Sierras.

--------------------------------------------------

From: "Lowell Fitt" <lcfitt(at)sbcglobal.net>

Sent: Monday, August 19, 2013 9:39 AM

To: <kitfox-list(at)matronics.com>

Subject: Re: Re: Fuel flow



 	  Quote: 	
		   



 Interesting discussion. On another forum a guy measured fuel flow beyond 

 the fuel pump at the carburetors and he found that the flow there didn't 

 come up to the FAA recommendations.  So the fuel will flow past an inop 

 pump. However I seem to have heard that if the diaphragm has been 

 breached, fuel will preferably simply flow into the crank case - not sure 

 on this.  I would think an easy fix would be an electric aux pump between 

 the header tank and the mechanical fuel pump.  I have one on mine and the 

 on switch is within thumbs reach with my hand on the throttle.

 Lowell



 --------------------------------------------------

 From: "mikeperkins" <flybyewire(at)gmail.com>

 Sent: Monday, August 19, 2013 9:00 AM

 To: <kitfox-list(at)matronics.com>

 Subject: Re: Fuel flow



> 

>

> Hi Guy,

>

> You're right to say that no one would (or should) launch with empty 

> tanks, but someone who encountered something unexpected enroute might 

> wind up accidentally landing with them empty. In that case, a go-around 

> would put the behind-the-seat header tank pretty dang low.

>

> I once did a differential measurement of my Kiftox I's behind-the-seat 

> header tank and the carbs. I discovered the aircraft's supply of fuel 

> would depend upon a working fuel pump. But I don't remember the distance.

>

> --------

> Mike Perkins

> Havana, Illinois

> Model I, 532, B gearbox, GSC prop

>

>

> Read this topic online here:

>

> http://forums.matronics.com/viewtopic.php?p=407039#407039

>

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_________________
Keep the dirty side down/Blue skies. Bob

cliffh(at)outdrs.net
Guest

Posted: Mon Aug 19, 2013 5:48 pm Post subject: Fuel flow

I had a fuel pump failure last spring.

The engine would only run for less than a minute at full throttle.

Would run fine at cruise setting.



Fkoran Higgins

Helena, Mt.

Speedster

912 ULS

---

Dorsal

Joined: 29 Mar 2008
Posts: 34
Location: MA

Posted: Thu Aug 22, 2013 3:41 pm Post subject: Re: Fuel flow

Clem,

I initially ran my engine (without priming) off the header tank alone and it was happy to start and reach full power. This was on the ground, normal flight attitude on a 912ULS.

_________________
Dorsal ~~^~~
Series 7 Flying
912S Warp Drive

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