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RV fuel per hour and heat (Low power cruise)

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gmcjetpilot(at)yahoo.com
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Posted: Thu Feb 09, 2006 8:59 am Post subject: RV fuel per hour and heat (Low power cruise)

As long as the engine is in normal limits as Lycoming recommends. Off the top of my head 280 CHT, Oil Temp 190/180 min. There is not truth to doing damage as long as you get it hot enough. Sure you need to check it makes full power, but that happens every takeoff. I am not a fan of babying it on take-off but that would be the next step in fuel saving. Do you need 2000 fpm climb?

   

  Check Lycomings key reprints. They address this.

   

  http://www.lycoming.textron.com/main.jsp?bodyPage=support/publications/keyReprints/operation/lowPowerLowRPM.html

   

   

  Here is the other operational articles that has good info on power settings.

   

  http://www.lycoming.textron.com/main.jsp?bodyPage=/support/publications/keyReprints/operation.html

   

   

  So what do you all think about de-rated takeoffs? I guess if the runway is long and there are no obstacles, but I tend to want to get as high as fast as possible. ON the other hand a Cessna C150 is crawling up at 500 fpm all the time.

   

  George

   

  

   

  From: "Martin Hone" <mctrader(at)bigpond.net.au>



  Hi Jerry,

  I usually run my O-320 powered RV6 at 2250 rpm with a Sensenich 79" 

prop and get great economy as well as good speed -

 like around 6 US gals per hour at 135 kts.. I too have been told to be

aware of burning up the engine, most notably the exhaust valves, as 

well as glazing the bores.  I don't really see how, as my CHT's are all around

310-315 deg F, and the engine is producing approx 55% power.  I know we

didn't build our RVs to go slow, but it is relative, and the fuel 

savings are nice. Cheers Martin in Oz



		

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ronlee(at)pcisys.net
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Posted: Thu Feb 09, 2006 9:55 am Post subject: RV fuel per hour and heat (Low power cruise)

 	  Quote: 	
		    Do you need 2000 fpm climb?


	


Why not?  Your first article discussed ways to save fuel.  One way

is to cut flying.  I don't intend to fly 300 hours this year.  But I will

cruise at normal speeds when I do.   And I buy gas where it is

cheaper.



 	  Quote: 	
		  

   So what do you all think about de-rated takeoffs? I guess if the
	


runway is long and there are no obstacles, but I tend to want to get

as high as fast as possible.



I agree.  Get up to cruising altitude. Full Throttle for a few minutes

is not going to cost that much gas.  Personally, if you are worried

about that amount either sell the plane or cut back a few hours.



It is like buying a Yugo to save gas.  Not me.  I prefer large pieces

of metal around me when I drive and if I have to pay more for gas,

so be it.  Safety is the higher priority.



Ron Lee

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bicyclop(at)pacbell.net
Guest

Posted: Thu Feb 09, 2006 10:45 am Post subject: RV fuel per hour and heat (Low power cruise)

 	  Quote: 	
		    So what do you all think about de-rated takeoffs? I guess if the

runway is long and there are no obstacles, but I tend to want to get as
	


high as fast as possible. ON the other hand a Cessna C150 is crawling up

at 500 fpm all the time.

   

  George



George,

   

De-rated takeoffs at low elevations are probably a bad idea because the

carburetor (and I think fuel injection systems also) run richer at full

throttle than when slightly retarded to increase the detonation margin.

You run the risk of operating too lean and closer to the detonation

margin when at higher than 75% power and low fuel flow. If you were to

use a power setting below 75%, perhaps that would be a non issue. 

At higher altitude airports, your takeoff power is automatically

de-rated by lower air pressure and you may have to lean to achieve

maximum available power. Because you're operating below 75% at anything

above around 7500' density altitude (and normally aspirated), it's

harder to make it detonate by leaning.



I like the idea of maximum terrain clearance as soon as possible for

purposes of having more time in case of power failure. This calls for

full available power for takeoff and initial climb. Power can be reduced

when you feel you're high enough to have viable engine out options. YMMV



Pax,



Ed Holyoke

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