Bad Sheila

Bad Sheila

Active Member
:D I have a Dynon d1000 and would like to know how you interpret the color bars for the best glide speed in my RV6
 
I have had the same question for a while and have not found any data. Maybe it is time to develop some data of our own.:) Or at least to see if the indicator is useable for this function. Next time I'm up in my RV-8 I'll set up a glide at best glide airspeed (I use 80 kts) and see what it looks like and if it is a practical solution. I'll try and answer back. Maybe you can do the same in your -6?

-John
 
Bad Sheila said:
:D I have a Dynon d1000 and would like to know how you interpret the color bars for the best glide speed in my RV6
Click to expand...

I posted a long reply to this one two days ago, but it isn't here. I must have forgot to hit "Submit Reply". Arggh!

Short answer - you do the same testing you would if you didn't have AOA, but you note the AOA reading at each of the test airspeeds. After the flight you plot the data, and determine the speed for best glide. Then, you refer to your recorded AOA for each speed and figure out what the AOA value is for your best glide speed.

Long answer - do descents in smooth air at a range of airspeeds, over the same block of altitude for each descent. Start a stop watch at the top of the altitude block, and record the time to descent to the bottom of the altitude block. Also record the AOA at each speed. Fly each speed twice, once with the wind off the left wing, and once the other way with the wind off the right wing. After landing, calcuate the rate of descent for each run, and average the values for the two runs at each speed.

Plot rate of descent vs speed. Draw a smooth curve through the test points. Draw a line from zero rate of descent and zero speed that is tangent to the curve. The point where this line touches the curve is the speed for best glide. Refer to your test data of AOA at each speed and figure out what the AOA reading is at best glide speed.

Do the descents at idle if you are looking for best glide speed with the dreaded "engine stuck at idle" failure. If you are more interested in best glide speed after engine failure do the testing with the mixture pulled to OFF. The best glide speeds will be different in these two cases. Prior to doing testing with mixture OFF, do some practice forced landings with engine at idle. Then do a mixture OFF test at altiude and confirm your engine restart procedure. Do the actual testing close to an airfield with a suitably long runway, to cover the extremely unlikely case where you cannot restart the engine.
 
AOA Questions

Thanks Marty and Kevin... I shall read and do some flight testing. I thought it would be a lot simpler and I am sure others do too. Like... in the green "a stall will not be seen". in the yellow "are you feeling lucky, fella". in the red "you are dead".

I thought it was all to do with Angle Of Attack and not airspeed... I guess I was wrong. :rolleyes: (I'll let you know my results "Boomer")
 
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Would this work?

If you use any or all of the methods I described in my 2010 presentation at AirVenture (see my website) then you should be able to determine your best glide speed in level flight. I don't know if that is the same as what you will get with Kevin's method(s). One obvious difference is prop thrust vs. prop drag. That will be different, too, with CS vs. FP. Another possible difference is the effect of propwash on the airframe. As much as I've played with this, I'm still not sure I've nailed it.

BTW, although I have never convinced Kevin of my methods, I owe him a huge thank you for helping me with the concepts so that I was able to develop them. Any errors are mine, but if I'm even partially correct, he gets a lot of the credit.

Anyhow, I agree that if you can get the best glide speed identified (that's IAS, not TAS for this purpose) at a given moment (it will vary with weight, etc.) then the AOA at that same moment is the right one and it will NOT vary with weight, etc.

I also agree that best glide with engine at idle or stopped is not the same as best L/D for the airframe because of the difference in prop drag. Thus the best glide in an emergency is not the same as in level flight even if all the other factors are ignored.

For me, the simplest and most accurate way to determine best emergency glide speed is to use your EYES. The way we were taught to judge our landing spot as students (spot on windscreen overlaid on the runway) is the correct way IMHO to evaluate your best glide at a given moment. Of course, you have to do this in a zero or neutral wind to be really accurate. To be more specific, the best speed is the one that best keeps the dot moving away from you.

Kevin Horton said:
I posted a long reply to this one two days ago, but it isn't here. I must have forgot to hit "Submit Reply". Arggh!

Short answer - you do the same testing you would if you didn't have AOA, but you note the AOA reading at each of the test airspeeds. After the flight you plot the data, and determine the speed for best glide. Then, you refer to your recorded AOA for each speed and figure out what the AOA value is for your best glide speed.

Long answer - do descents in smooth air at a range of airspeeds, over the same block of altitude for each descent. Start a stop watch at the top of the altitude block, and record the time to descent to the bottom of the altitude block. Also record the AOA at each speed. Fly each speed twice, once with the wind off the left wing, and once the other way with the wind off the right wing. After landing, calcuate the rate of descent for each run, and average the values for the two runs at each speed.

Plot rate of descent vs speed. Draw a smooth curve through the test points. Draw a line from zero rate of descent and zero speed that is tangent to the curve. The point where this line touches the curve is the speed for best glide. Refer to your test data of AOA at each speed and figure out what the AOA reading is at best glide speed.

Do the descents at idle if you are looking for best glide speed with the dreaded "engine stuck at idle" failure. If you are more interested in best glide speed after engine failure do the testing with the mixture pulled to OFF. The best glide speeds will be different in these two cases. Prior to doing testing with mixture OFF, do some practice forced landings with engine at idle. Then do a mixture OFF test at altiude and confirm your engine restart procedure. Do the actual testing close to an airfield with a suitably long runway, to cover the extremely unlikely case where you cannot restart the engine.
Click to expand...
 
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Disagree with the article

I just noticed that the article by Mr. Kolano states that the best glide angle and the best range angle are the same. This is only true in a case where there is no drag from the prop and no extra drag from prop wash or where the two are somehow equalized.

If you doubt me on this, look at the extra slides in the back of my 2010 presentation linked on my website. First look at the Cessna 152 POH page that gives best glide. Then look at the results of the no-prop test on the same model airplane by Norris and Bauer in 94 or 95. I also have the links to the original article they wrote, on my site. You will see a huge difference in favor of the no-prop version.

I "tested" a C-152 to see if the best glide speed reported by Norris and Bauer was correct for level flight. The short version is that I came within 5% in one try and stopped the test because the conditions were not going to allow better precision. I did not repeat the test because I was paying normal rental rates for the airplane and an instructor to fly it for me.

If the best CAS for glide is different, then so is the AOA for the same weight. Given these findings, Kolano cannot be correct on this one point. That said, I have and use AOA and I think everyone should, too.

Here is the quote:

"Yes, a single AOA value will always yield the maximum no-wind glide distance. Believe it or not, that same AOA will also provide the maximum cruise range for your airplane."
 
Fidelity??

I've not yet flown behind one but from what I've seen I don't imagine there's enough fidelity with the colored light display to be useful for this. I've used indicators that displayed degrees AOA and you could hold a precise number. These were great for precision flying, but don't know if you can do this with the light bar displays.
 
AOA frustration!

I read the article: http://www.oshkosh365.org/saarchive/eaa_articles/2001_05_19.pdf but it didn't help much. (I am not a test pilot and the numbers were a little above my ATP pay grade!):eek:

I have a Dynon D1000 and will calibrate the AOA with a number of stalls and button pressing. Then I will have to do all the tests you guys recommended and then have to work out the color bars for best glide, (prop stopped and windmilling) max cruise range, short field approach speed, etc.

I thought there would be someone out there that has already done all this and would be able to give us some indication of what to expect. I guess that guy is going to be me... I will post my findings.:cool:
 
Will not work

Went out yesterday (sorry for the delay) and looked at the Dynon AOA indicator at slower airspeeds. In my RV-8 best glide (i.e. L/D Max) is around 80 kts. At that speed all the green bars are in view from 80 and remain so to above 120 kts, so there is no way to use the indicator for best gluide AOA. Seems to be an indicator limitation, and I wish the Dynon display was calibrated in degrees or some other units from zero (zero G) to the stall point. Would be more useful, IMO.

-John
 
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