A fuel-saving announcement from your ASI

[Webb]

Has anyone read this from AOPA yet?

http://www.aopa.org/aircraft/article...080825asi.html

For best economy according to the article....."After takeoff, simply cruise climb at (1.31 times VY) as high as possible with the throttle wide open. When you?ve reached the maximum altitude at which you can maintain your target IAS with the mixture properly leaned, you?re done."

If Vy for a RV is 110 mph, then the cruise climb would be 144 mph according to the article. I'm sure it's going to take O2 for an RV also.

I wonder what the most fuel efficient altitude for a RV is?

[Geico266]

Interesting, gives me another excuse to drag the plane out and go flying!

[Webb]

Larry - it probably gives an excuse to put O2 in the plane also......"but honey, I really neeeeeeeeeed it to save $$ when I fly.......

Let us know what you find out.

[Geico266]

I still find LOP to be the best way to get somewhere fast and cheap. The mighty IO-540 can suck a lot of fuel, 20 GPH on take off if pushed hard, but I can get 10.5 GPH LOP and still be moving 175MPH. Thats economy to me.

Flying at 144 MPH is just find too. Anytime you slow down it's gonna improve economy.....to a point.

[jonbakerok]

Originally Posted by Webb

Has anyone read this from AOPA yet?

http://www.aopa.org/aircraft/article...080825asi.html

For best economy according to the article....."After takeoff, simply cruise climb at (1.31 times VY) as high as possible with the throttle wide open. When you’ve reached the maximum altitude at which you can maintain your target IAS with the mixture properly leaned, you’re done."

If Vy for a RV is 110 mph, then the cruise climb would be 144 mph according to the article. I'm sure it's going to take O2 for an RV also.

I wonder what the most fuel efficient altitude for a RV is?

Actually, VY is more like 90, not 110. Most guys use 110 as their standard climb speed. 1.31 VY would be 118, which is a good WOT climb speed for adequate cooling. The idea is to get to altitude as quickly as possible. At 144, you wouldn't even be making 1000 fpm and the climb would take forever.

But I absolutely agree with the article. The idea is to go WOT and leave it there until you're ready to come down. You're using altitude to control engine power. When power gets to the 50% range, you're down in the 6 gph range. The problem is, RV's climb so high that 50% occurs well above the altitude where you need O2, so I never could get there in my RV6. I had to pull the prop back to 50%, once I got to 9,500.

Somebody ought to make a chart that shows WOT engine power at each 1000' altitude up to 50%.

[Tomasz]

Originally Posted by jonbakerok

But I absolutely agree with the article. The idea is to go WOT and leave it there until you're ready to come down. You're using altitude to control engine power. When power gets to the 50% range, you're down in the 6 gph range. The problem is, RV's climb so high that 50% occurs well above the altitude where you need O2, so I never could get there in my RV6.

Somebody ought to make a chart that shows WOT engine power at each 1000' altitude up to 50%.

It's not that hard - you loose 1" of MP per 1000'. At WOT 50% power means 15" of MP or more depending on RPM. Which means about 15000' of altitude.

No matter in which airframe you install the engine it will have no more than 50% it's power above 15000' (assuming we are speaking about non charged engines). The difference is - if the airframe will allow you to go that high and how long will it take. Lighter (less lbs/HP) and cleaner airframes will get you there much sooner and will allow you to fly faster but still the engine will produce only 50% of it's max power there.


Power charts for IO-540 show 55% power between 10k' and 15k' depending on RPM setting.

[tmbg]

I would think that best l/d speed is going to be your most efficient point... if you trim for best l/d, full power, and climb until it won't as described, I'd imagine that'd be your absolute best fuel economy.

[osxuser]

Good information to know but... winds at higher alts often don't favor going that high.

Weathermeister.com, run LOP and plan for winds. No matter what altitude you end up at, run whatever power setting gets you max l/d speed.

[Ironflight]

I thought that the article was an interesting refresher on the power/drag curves, and what they can tell us. I remember looking at those points many years ago, and I agree with the author that in a no-wind condition, that would be a pretty good place to run. But as others have pointed out, winds will probably play a bigger part in altitude selection than anything.

I find that the Miles per Gallon readout on my EFIS is probably the best way to maximize my efficiency overall.

Paul

[Mike S]

Originally Posted by Ironflight

I find that the Miles per Gallon readout on my EFIS is probably the best way to maximize my efficiency overall.

Paul

Yep, nice thing this here "Experimental" aviation.

But dont forget this is from AOPA---------and they cater to the certified crowd.

And they ----certified------cant tap into the current crop of EFIS's from the experimental world.

Unfortunately, the certified EFIS's cost is often so high that is is not economically worth putting them in older planes.