Webb

Webb

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Has anyone read this from AOPA yet?

http://www.aopa.org/aircraft/articles/2008/080825asi.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?
 
Excuse for Oxygen

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.
 
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. ;)
 
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We need a chart

Webb said:
Has anyone read this from AOPA yet?

http://www.aopa.org/aircraft/articles/2008/080825asi.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?
Click to expand...

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%.
 
jonbakerok said:
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%.
Click to expand...
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.
 
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.
 
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.
 
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
 
Ironflight said:
I find that the Miles per Gallon readout on my EFIS is probably the best way to maximize my efficiency overall.

Paul
Click to expand...

Yep, nice thing this here "Experimental" aviation. :D

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.
 
How to Verify Best Rate

After reading this I went into the Google world to try and find something on how to establish Best Rate in a unique experimental with no history or POH applicable to the particular combination of engine, aerodynamics etc. in the plane. I found an EAA article that described it but was missing some visuals and there were other articles with it that were not available. Can anyone point me in the right direction?
Thanks!!
 
CS vs FP

tmbg said:
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.
Click to expand...

I find that with FP prop set up for cruise the best climb rate is higher than the best glide speed. I suspect that with CS prop best L/D would be best climb rate speed.

This effect is even more noticeable for best angle of climb which should correspond to minimum sink but that really doesn't work for FP.
 
RVadmirer said:
After reading this I went into the Google world to try and find something on how to establish Best Rate in a unique experimental with no history or POH applicable to the particular combination of engine, aerodynamics etc. in the plane. I found an EAA article that described it but was missing some visuals and there were other articles with it that were not available. Can anyone point me in the right direction?
Thanks!!
Click to expand...
The following procedure can be used to determine the IAS that gives the best rate of climb at a particular altitude (the IAS for best rate of climb will decrease as the altitude increases):
  1. Check the upper wind forecasts to determine the predicted wind direction at a range of altitudes.
  2. Go flying, and find a range of altitudes that has very smooth air.
  3. Pick the bottom and top of an altitude block in the smooth air, such that it will take you at least one minute to climb through the block.
  4. Pick a heading that is at 90 degrees to the forecast wind in the altitude block.
  5. Pick a test airspeed. Start sufficiently below the altitude block so you can be nicely stabilized on the test airspeed at full power as you hit the bottom of the block.
  6. Start a start watch as you hit the bottom of the altitude block.
  7. Stop the start watch as you hit the top of the top of the altitude block. Record the test airspeed, time to climb through the block, and any comments on air quality, accuracy of airspeed control, etc.
  8. Descend back below the block, and repeat at the same airspeed, but on a heading 180 degrees to the original heading.
  9. Repeat with two reciprocal heading climbs on a range of airspeeds that are expected to cover the expected speed for best rate of climb.
  10. After landing, do some math work to determine the rate of climb for each test point. Average the rates of climbs for the two runs at each airspeed, and make a graph of rate of climb vs airspeed.
  11. Draw a smooth line through the points on the graph.
  12. You will note that some points seem to be above or below where a smooth curve would go. Study the remarks you recorded to see if perhaps those outliers are explained by rough air, or poor airspeed control. If so, you are well justified to not put the line through those points.
  13. The speed at the top of your curve is the IAS for best rate of climb at the test altitude and weight.

For improved accuracy, you can also:
  1. Carry a second person to run the stop watch, record data and look out for traffic, allowing you to concentrate on accurately flying the desired test airspeed.
  2. Instead of only recording the time to climb through the whole altitude block, record the stop watch reading and altitude at several altitude intervals during the climb. Then for each run, plot stop watch reading vs altitude, and draw a straight line through those points. Measure the slope of that line to determine the climb rate for that run.
  3. Repeat the same set of tests on more than one day, as results from any given day can be affected by weather conditions, variations in piloting technique, accuracy at recording data, etc.

Note, the above procedure ignores the effect of air temperature and aircraft weight. The results will only be valid for one temperature, weight and altitude, but you can use ballast to do the test at the weight of interest, and repeat the test at several altitudes to determine the variation of Vy with altitude.
 
Thank you!

Thanks Kevin. Will make up a notepad and try it out.
PS: Best wishes for a great first flight when you get home!
 
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Short Cut to Start Kevin's Method

1. (only with variometer or good EFIS) fly the climb with reference to the indicated rate of climb, changing airspeed slowly. That will give you the starting point for using Kevin's method and save a lot of time.

2. (only with recording EFIS) record the trials and analyze them on the PC later - aids accuracy.

If anyone actually tries this I'd be curious to see how much difference there is between the test pilot procedure and just flying the rate of climb meter. And I'd also be curious to know how much difference in the best ROC speed there is for different weights (I know the ROC will vary; I'm asking about the best speed.) If there is as much difference for different altitudes and weights as between methods, then maybe flying the meter is the best practical way to go? Yes, I know there is a lag in the instrument and I know that there are some inherent measurement distortions when changing altitudes and temperatures.
 
In a nutshell.....,

.....cruise climbs are definitely the way to go. Solo, in my -6A with a seriously pitched cruise prop, I can get right at 1000 FPM during the cooler months, at 160MPH. I've demo'd that to students here many times, with great visibilty and good cooling to boot.

Regards,
 
Missing the point

I think some are missing the point of the article and my question. I swear, some of you would agrue with a rock.

Let's start over. If I read the article correctly....and if I am wrong, let me know.

Per Mr. Norris, an aeronautical engineer (who knows more about the physics of aerodynamics than most of us will ever come close to) there is an altitude that you will enjoy best economy and have little loss of speed (and yes, LOP was mentioned in here).

Mr Norris is pointing out that 1.31 times Vy (best rate of climb) gives you best speed vs the increased drag. If you cruise climb (1.31 times Vy), there is a point that WOT won't allow you to maintain that speed. Once you hit that altitutde, you're done and know what it is. Obviously we must adjust our altitudes for best winds when we travel.

With the current status of fuel prices, the ability to knock off 20% of fuel cost vs only an 8.2% loss of speed is attractive to me. A previous post suggested we need a chart and I agree. Best economy speed for different altitudes. Also, don't forget that IAS is going to be less that TAS and the gap will change as you increase altitude.

Since RV's are so efficient, I am just guessing as to what that altitude is. No doubt it will be in oxygen required areas of the world.

Since I'm at the paint shop now, I can't tell go out and tell you what that altitude would be if I were to set my cruise climb.

If someone has a chance this weekend, would they consider giving it a try and let us know what that altitude is? Also let us know what they used for Vy and the cruise climb speed.

To clarify my question.....WHAT IS THE BEST ECONOMY ALTITUDE?
 
The best altitude is going to vary based on prop, winds, temperature and pilot preferences.

Generally, 10,500 gives very good WOT economy cruise performance at low engine rpm, which I prefer for comfort. If you want to run higher rpm, you'll likley be up at 12-15000 feet depending on temperature and of course, winds rule. For fuel economy, climbing into a headwind is silly, and with the tailwind, you'll climb even higher.

Sorry to not answer your quesetion, but if you specifiy EXACTLY what conditions you will be fliying, and exact answer will come to you.

Specify, prop C/S or fixed, Temperature deviation ISA, estimated winds?, desired cruise RPM etc.

Bob
 
And to clarify an answer; there IS NO ONE ANSWER. It varies by airplane, engine, prop and loading configuration, as well as temperature, atmospheric conditions etc.
Talk about arguing with a rock.....:rolleyes:
 
This rocks question.

RVadmirer said:
And to clarify an answer; there IS NO ONE ANSWER. It varies by airplane, engine, prop and loading configuration, as well as temperature, atmospheric conditions etc.
Talk about arguing with a rock.....:rolleyes:
Click to expand...

Fair enough. Gotta laugh at others and myself too!!

For the sake of arguement, in general my assumption is RV's will have a similiar Vy. Yes, engine, prop, and load will be a limiting factor as to that altitude at which they could not maintain the cruise climb speed.

I know that there is not ONE answer but I suspect there are a bunch of similiar ones.

I'll try it again (yes, mud on my face)...Can anyone tell me what THEIR results are. I'm just curious as to way to expect when I try it. It would also help to know their configurations.
 
Webb,

The answer to your question is even more open ended than some make it sound - too many variables.

However, the long range cruise I normally use in my RV-8 (blended airfoil constant speed hartzell, 180 hp IO-360) is 165 kts true at around 16000 ft with wide open throttle and 2200 rpm. This gives me a burn of 6.2 gallons per hour leaned LOP.

One data point,

Pat
 
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