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John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Fri Feb 26, 2010 10:01 pm Post subject: Fuel Reserve and UL's

> I flew all my two strokes at 5800 rpm cruise.

 	  Quote: 	
		  

 >
	


 	  Quote: 	
		   john hauck

 mkIII

 Titus, Alabama


	




(John, I think we've had this dance before, and still can't seem to agree if 

it's a Cha-Cha or a Foxtrot... Hang in there buddy -  two strokes are evil 

and must be PUNISHED!)



Richard Pike

*************

Richard P/Gang:



Sorry about that.



I think you took my reply the wrong way.



I was not arguing with nor trying to out do you.  Simply stating the way I 

flew and currently fly my airplanes.



I fly normal cruise if I fly 11 miles from my strip to Wetumpka Airport.



I fly normal cruise if I fly around the traffic pattern.



There is more than one way to fly an airplane.



john hauck

mkIII

Titus, Alabama

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

John Bickham

Joined: 10 Jan 2006
Posts: 170
Location: St. Francisville, LA

Posted: Sat Feb 27, 2010 4:30 am Post subject: Re: Fuel Reserve and UL's

Sorry if I'm coming in late on this one.



Don't get lulled into the "30 min reserve" will keep you safe!   Been there, done that, bent the gear in a hayfield in TX. 



I was a heavy iron GA pilot and thought the FAA regs would keep me straight.  Problem is the regs were written for planes that have cruise speeds of 120 mph plus.  Planes that do 60 mph can't get as far as in 30 minutes.  Throw in a little wind in the wrong direction and your options start to vanish quicker.  Next airport just 30 minutes up the road can be well over 30 minutes with just a little bit of the wrong wind.  Don't even think about mid morning radiant fog covering the airport when you get there.



Yes you do have a lot more options of off-field landings.  Farmers around here ain't friendly to ruining their cane fields.  As wet as we have been down here, you couldn't get in and out till summer.

_________________
Thanks too much,

John Bickham
Mark III-C w/ 912UL
St. Francisville, LA

I know many pilots and a few true aviators. There is a distinct difference that I have the greatest respect for.

jbhart(at)onlyinternet.ne
Guest

Posted: Sat Feb 27, 2010 7:34 am Post subject: Fuel Reserve and UL's

At 09:07 PM 2/26/10 -0600, you wrote:

 	  Quote: 	
		  



Hi Guys:



When you all are contributing info on fuel burn, need to include power 

setting, i.e., engine rpm.  There is a great deal of difference in fuel burn 

on two and four stroke aircraft engines at low power settings and higher 

power settings.  To me, 75% power is normal cruise.  Seems most of the 

others who have contributed info on fuel burn, cruise much slower.




	


John,



If you equate 75% power as 75% carburetor slide opening, the 447 will be 

running at max power.  This is due to the fact that the Bing 54 carburetor 

is over sized for the engine.  I found that the 447 will top out at 6,200 at 

about 34% with the throttle at the 34% position.



If you equate 75% power relative to rpm, then .75 x 6,200 gives a cruise rpm 

of 4,650 rpm.  From my flight log, I pulled out the data shown below.  All 

of these flights were from and to Perryville and Painton, MO.   You will 

notice that all of the rpms listed are greater than your 75%.  The rpm/rpm 

indicates that a different rpm was set from the to and return flights.  This 

difference as due to the gps indicated ground speed and the expected gps 

arrival time.  If I had a head wind, I would crank in more rpm, etc. to get 

to the meeting on time. 



Date      Fuel  MPG   Time   RPM   GPH  MPH

          (gal)       (min)        Ave. Ave.  

12/19/99  5.5   19.6   119  5,200  2.8  54.5	

02/20/00  5.5   19.6   126  5,400  2.6  51.4	

09/17/00  4.9   22.0   104  5,800  2.8  62.3	

05/12/01  5.5   19.6   114  ?,???  2.9  56.8	

06/23/01  5.5   19.6   111  5,600  3.0  58.4	

08/19/01  6.0   18.0   112  5,200/ 3.2  57.9	

                            6,200

10/07/01  5.75  18.8   101  5,600  3.4  64.2

11/04/01  6.00  18.0   107  5,700/ 3.4  60.6

                            5,600

02/17/02  6.75  16.0   112  5,200  3.3  57.9

Averages  5.71  18.9   112  5,550 3.06  57.9



I hope this is enlightening.



Jack B. Hart FF004

Winchester, IN

slyck(at)frontiernet.net
Guest

Posted: Sat Feb 27, 2010 8:47 am Post subject: Fuel Reserve and UL's

75%power would be a difficult measurement to acquire accurately.  Static prop thrust wouldn't even be accurate due

to inefficiencies with no forward motion.  The only real way to do it would be on a dyno with no prop.

If you had a magic strain gauge between the prop and hub you could get something useful in flight.

On mine I just pull back a few rpm and settle for it.

BB

On 27, Feb 2010, at 10:36 AM, Jack B. Hart wrote:

 	  Quote: 	

 At 09:07 PM 2/26/10 -0600, you wrote:

> 

> 

> Hi Guys:

> 

> When you all are contributing info on fuel burn, need to include power 

> setting, i.e., engine rpm.  There is a great deal of difference in fuel burn 

> on two and four stroke aircraft engines at low power settings and higher 

> power settings.  To me, 75% power is normal cruise.  Seems most of the 

> others who have contributed info on fuel burn, cruise much slower.

> 

 John,

 If you equate 75% power as 75% carburetor slide opening, the 447 will be 

 running at max power.  This is due to the fact that the Bing 54 carburetor 

 is over sized for the engine.  I found that the 447 will top out at 6,200 at 

 about 34% with the throttle at the 34% position.

 If you equate 75% power relative to rpm, then .75 x 6,200 gives a cruise rpm 

 of 4,650 rpm.  From my flight log, I pulled out the data shown below.  All 

 of these flights were from and to Perryville and Painton, MO.   You will 

 notice that all of the rpms listed are greater than your 75%.  The rpm/rpm 

 indicates that a different rpm was set from the to and return flights.  This 

 difference as due to the gps indicated ground speed and the expected gps 

 arrival time.  If I had a head wind, I would crank in more rpm, etc. to get 

 to the meeting on time. 

 Date      Fuel  MPG   Time   RPM   GPH  MPH

          (gal)       (min)        Ave. Ave.  

 12/19/99  5.5   19.6   119  5,200  2.8  54.5	

 02/20/00  5.5   19.6   126  5,400  2.6  51.4	

 09/17/00  4.9   22.0   104  5,800  2.8  62.3	

 05/12/01  5.5   19.6   114  ?,???  2.9  56.8	

 06/23/01  5.5   19.6   111  5,600  3.0  58.4	

 08/19/01  6.0   18.0   112  5,200/ 3.2  57.9	

                            6,200

 10/07/01  5.75  18.8   101  5,600  3.4  64.2

 11/04/01  6.00  18.0   107  5,700/ 3.4  60.6

                            5,600

 02/17/02  6.75  16.0   112  5,200  3.3  57.9

 Averages  5.71  18.9   112  5,550 3.06  57.9

 I hope this is enlightening.

 Jack B. Hart FF004

 Winchester, IN

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Sat Feb 27, 2010 9:24 am Post subject: Re: Fuel Reserve and UL's

 	  John Hauck wrote: 	
		  > I flew all my two strokes at 5800 rpm cruise.

 	  Quote: 	

 >

 	  Quote: 	
		   john hauck

 mkIII

 Titus, Alabama

(John, I think we've had this dance before, and still can't seem to agree if 

it's a Cha-Cha or a Foxtrot... Hang in there buddy -  two strokes are evil 

and must be PUNISHED!)

Richard Pike

*************

Richard P/Gang:

Sorry about that.

I think you took my reply the wrong way.

I was not arguing with nor trying to out do you.  Simply stating the way I 

flew and currently fly my airplanes.

I fly normal cruise if I fly 11 miles from my strip to Wetumpka Airport.

I fly normal cruise if I fly around the traffic pattern.

There is more than one way to fly an airplane.

john hauck

mkIII

Titus, Alabama 	

Nay nay, it was all in fun! I know you, I know how you are, you know me, you know how I am,  - Hey, I see a chain, I think I'll pull it! (Not that you wouldn't) And here we go again! (May I have this dance?)

It's all good. Finished getting the rust off the steel root rib for the left wing and welded up the hole for the clevis pin. Can you believe it was wallowed out to almost 3/8"? And somebody was flying it that way? So yes, there is more than one way to fly an airplane, in the case of this basket case we bought and cannibalized, by someone who apparently didn't mind rattling and flopping through the sky... 

Richard Pike

N420P (420ldPoops)

cedavis

Joined: 05 Jun 2006
Posts: 23
Location: Malvern, PA

Posted: Sat Feb 27, 2010 9:31 am Post subject: Fuel Reserve and UL's

My Firefly gets 2.5gph at 55 MPH turning 5300-5400 RPM. It's empty weight is about 280 lbs (from memory; too lazy to get my weight and balance).



If Terry Franz is reading, I believe he's say's his 103 Firefly get's closer to 2.0 gph, but he's done more optimization then I have.

 



Chuck Davis

Firefly, N7057K

  [quote][b]

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sat Feb 27, 2010 4:23 pm Post subject: Fuel Reserve and UL's

I hope this is enlightening.



Jack B. Hart FF004

I have been enlightened.



Thanks, will try to explain the way I do it somewhat later tonight.  Right 

now it is time for the Atlanta Supercross Live.  



john hauck

mkIII

Titus, Alabama

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

GeoB

Joined: 16 Jun 2009
Posts: 207
Location: Fresno, CA

Posted: Sun Feb 28, 2010 12:58 pm Post subject: Re: Fuel Reserve and UL's

 	  jbhart(at)onlyinternet.ne wrote: 	
		  If you equate 75% power as 75% carburetor slide opening, the 447 will be running at max power.  This is due to the fact that the Bing 54 carburetor is over sized for the engine. 	




Also note that this carb, like MANY others, has no linear relationship between throttle-slide movement and cross-sectional area of the throttle bore opened.



Butterfly carbs have a similar problem.



I thought there was an 'official' definition of 75% power. I don't recall for sure but it seemed like it was something like 100% rpm, then back off 10% rpm.

_________________
GeoB

"Members of Congress should be compelled to wear uniforms like NASCAR drivers, so we could identify their corporate sponsors"

jbhart(at)onlyinternet.ne
Guest

Posted: Sun Feb 28, 2010 1:03 pm Post subject: Fuel Reserve and UL's

At 08:42 PM 2/26/10 -0600, you wrote:

 	  Quote: 	
		  



Richard P/Gang:



I flew all my two strokes at 5800 rpm cruise.



My 582 powered mkIII cruised 80 mph at 5800 rpm and burned 5.5 gph.



My 447 powered FS cruised (can not remember the cruise speed) at 5800 rpm 

and burned 3.5 to 3.75 gph.



My ULII02 powered US cruised (can not remember the cruise speed) at 5800 rpm 

and burned 3.5 gph.



My 912UL powered mkIII cruised 85 mph at 5,000 rpm and burned 4.0 gph.



My 912ULS powered mkIII cruises at 88 mph at 5,000 rpm and burns 5.0 gph.



I flew/fly all my two and four stroke engines at aprx'ly 75% power.  They 

all were happy at that power setting and the airplanes and I were too.




	


John,



 	  Quote: 	
		  From being on the list for a few years, I questioned your 75% power cruise 

statement because it countered my impression of how you flew your planes.  I 
	


checked with http://www.rotaxservice.com/rotax_engines and using the numbers 

proved from the various engine model spec sheets this is what I found.



engine max hp  max hp .75 max .75 max |John's   hp   % max

model  (cont') rpm       hp     rpm   | rpm   (dev')   hp

582     65     6,500     49    5,300  |5,800    61     94

447     40     6,500     30    5,200  |5,800    37     93

912ul   79     5,500     59    4,000  |5,000    74     94

912uls  95     5,500     71    4,200  |5,000    89     94



Approximately 75%?



Jack B. Hart FF004

Winchester, IN

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sun Feb 28, 2010 2:11 pm Post subject: Fuel Reserve and UL's

>From being on the list for a few years, I questioned your 75% power cruise

statement because it countered my impression of how you flew your planes.

Jack B. Hart FF004

OK



john hauck

mkIII

Titus, Alabama

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

herbgh(at)nctc.com
Guest

Posted: Sun Feb 28, 2010 8:49 pm Post subject: Fuel Reserve and UL's

71 hp divided by 12 hp per gal per hour...comes to abt 5.9 gals 

hour... Seems a bit high...I am guessing that the 912uls burns about 

5.5 gals hour at 75 % power?   Herb

At 04:10 PM 2/28/2010, you wrote:



 	  Quote: 	
		  --=======AVGMAIL-29A51582=======

Content-Type: text/plain; charset=us-ascii




  >From being on the list for a few years, I questioned your 75% power cruise

statement because it countered my impression of how you flew your planes.

Jack B. Hart FF004

OK



john hauck

mkIII

Titus, Alabama



--=======AVGMAIL-29A51582=======

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Content-Transfer-Encoding: quoted-printable

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Checked by AVG - www.avg.com

34:00



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<pre><b><font size=2 color="#000000" face="courier new,courier">

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Mar 01, 2010 4:51 am Post subject: Re: Fuel Reserve and UL's

The power curve in Rotax (and other engine manuals) shows the maximum power available for that engine at that RPM at sea level on a standard day, not the actual power being produced at that rpm under other conditions. The actual power being produced at a given rpm depends upon two primary variables. One is the density altitude and the other is the prop loading. 



The power curve is valid only at DA of zero and at wide-open-throttle (WOT). The actual power being produced in straight and level cruise at normally encountered density altitudes at partial throttle is less than that shown on the power curve.



John's 75% power at 5,000 rpm are pretty close at typical DAs in lowlands knowing he pitches his prop generally for 5500 rpm WOT in S&L flight. At a density altitude of about 8,000' the 912 engines will produce only 75% of rated power with WOT at 5,500 rpm, not 5,000 rpm. As you go higher still, the maximum available power continues to decrease.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

GeoB

Joined: 16 Jun 2009
Posts: 207
Location: Fresno, CA

Posted: Mon Mar 01, 2010 8:57 am Post subject: Re: Fuel Reserve and UL's

 	  Thom Riddle wrote: 	
		  The power curve in Rotax (and other engine manuals) shows the maximum power available for that engine at that RPM at sea level on a standard day, not the actual power being produced

	




I hear you saying that to be very close to actual 75% power you would have to solve an equation that relates temp, humidity, altitude and prop attributes. It sounds like if you had a glass panel you could have a read-out of your %-power. Funny! It doesn't even involve the engine!



Thanks for your post.

_________________
GeoB

"Members of Congress should be compelled to wear uniforms like NASCAR drivers, so we could identify their corporate sponsors"

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Mar 01, 2010 9:21 am Post subject: Re: Fuel Reserve and UL's

GeoB,



As I've said either here or elsewhere, I think one of the easiest ways to know what your current engine power output is under whatever conditions you are flying, is a fuel flow meter. A 4-stroke engine maintained and operated according to the manufacturer's instructions will consume roughly .45 lbs (+ or - .03 lbs) of gasoline per hour per HP being produced. 



For example:

An engine with rated sea level max continuous power of 80 HP, when running at 75% power (60 HP), no matter what the rpm or density altitude required to make that power, will be consuming approximately 4.2 - 4.8 US gallons per hour. If your 4-stroke engine is burning less than that your engine is producing less than that amount of power. Again, assuming it is maintained and operated properly. Another way to look at it is each US gallon/hour is equivalent to roughly 12 1/2 to 14 hp.



Most Rotax 2-stroke engines run closer to .6 lb/hp/hr BSFC.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Mon Mar 01, 2010 10:28 am Post subject: Re: Fuel Reserve and UL's

 	  Thom Riddle wrote: 	
		  GeoB,



As I've said either here or elsewhere, I think one of the easiest ways to know what your current engine power output is under whatever conditions you are flying, is a fuel flow meter. A 4-stroke engine maintained and operated according to the manufacturer's instructions will consume roughly .45 lbs (+ or - .03 lbs) of gasoline per hour per HP being produced. 



For example:

An engine with rated sea level max continuous power of 80 HP, when running at 75% power (60 HP), no matter what the rpm or density altitude required to make that power, will be consuming approximately 4.2 - 4.8 US gallons per hour. If your 4-stroke engine is burning less than that your engine is producing less than that amount of power. Again, assuming it is maintained and operated properly. Another way to look at it is each US gallon/hour is equivalent to roughly 12 1/2 to 14 hp.



Most Rotax 2-stroke engines run closer to .6 lb/hp/hr BSFC. 	




Thom, math is the weakest of all my weak skills, so given that I typically burn 4 gph at 5300 rpm, how do I set up the equation (using a 2-stroke) to figure out how much horsepower I am using to do it? Knowing the answer to that tells me how much horsepower it takes to push my MKIII at 63-65 mph.



Thanks,

Richard Pike

MKIII N420P (420ldPoops)

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Mar 01, 2010 10:42 am Post subject: Re: Fuel Reserve and UL's

Richard,



Assuming my statement is correct, that most Rotax 2-stroke engines use about .60 lbs of fuel per hour per horsepower, you take the known fuel consumption of 4 GPH and  multiply it by 6 lbs/ US gallon to get 24 lbs/hour fuel consumption.



4 GPH x 6 lbs/US gallon = 24 lbs/hour



Then divide the 24 lbs/hr by the approximate .60 Brake Horsepower Specific Consunption (BSFC) figure as follows:



24 lbs/hour / .6 lb = 40 HP



It turns out to be pretty easy math to do in your head with a 2-stroke BSFC of about .6 since each US gallon of fuel weighs 6 lbs. If your 2-stroke engine if you throttle back to 3.5 gph your engine is producing approximately 35 HP.  In other words, about 10 HP per GPH.



I hope this helps.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Mar 01, 2010 10:44 am Post subject: Re: Fuel Reserve and UL's

OOOPs.



BSFC stands for Brake Specific Fuel Consumption. I got my words twisted around and mixed up. Aging ungracefully, as you can plainly tell.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

NeilsenRM(at)comcast.net
Guest

Posted: Mon Mar 01, 2010 10:52 am Post subject: Fuel Reserve and UL's

Thom



I don't mean to throw cold water on you calculations but. Throttled engines 

waste a lot of power working against the vacuum behind the throttle plate. I 

have no idea how much fuel is burned at idle throttle but your power per 

fuel burn calculations would be off the charts. A calculation of 75% power 

by fuel consumption needs to take into account of this non liner fuel 

efficiency and might give you only 70-73% power.



Rick Neilsen

Redrive VW Powered MKIIIC

---

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Mon Mar 01, 2010 2:04 pm Post subject: Re: Fuel Reserve and UL's

Rick,



You are correct about it not being linear over a wide RPM range but it is close enough for first order estimates at any reasonable cruise RPM.



There is usually one most efficient engine rpm, i.e., the rpm at which the engine produces the most amount of power for each ounce of fuel consumed. Attached is an image from a Rotax 2-stroke manaul showing how the BSFC varies with RPM for the 582. Notice that it is most efficient at about 5,700-5,800 rpm. This assumes a correct prop loading among other things. Since the number I quoted is really only valid at or near normal cruise RPM, where it is most efficient, the efficiency drops off somewhat on either side of that RPM, as you can see on the cruve. BUT the BSFC and the known fuel consumption with a little arithmetic does give a rough estimate of the HP being produced during cruise at any altitude. The RPM alone is not a very good prediction of HP being produced over a wide range of density altitudes, at least not as good as fuel consumption in normal cruise rpm range.

582 BSFC curve.jpg

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_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Mon Mar 01, 2010 3:56 pm Post subject: Fuel Reserve and UL's

At 01:50 PM 3/1/2010, Richard & Martha Neilsen wrote:



  	  Quote: 	
		  I don't mean to throw cold water on you calculations but. Throttled engines waste a lot of power working against the vacuum behind the throttle plate. I have no idea how much fuel is burned at idle throttle but your power per fuel burn calculations would be off the charts. A calculation of 75% power by fuel consumption needs to take into account of this non liner fuel efficiency and might give you only 70-73% power. 	


 That makes sense... if it's 0.6 lb/hp-hour, then at 3.3gph (cruise at 5700 rpm) my Cuyuna should be producing 33hp... a wee bit more than 75% power...



 -Dana

 --

  Capital punishment: people in the Capitol need to be punished...    [quote][b]

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