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  #11  
Old 08-13-2017, 09:42 AM
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Auburntsts Auburntsts is offline
 
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Originally Posted by ChiefPilot View Post
It's not hard to hold an indicated airspeed to within one knot for 90 seconds of climb or descent given an electronic airspeed indicator and reasonable conditions. I doubt autopilots in our birds could do any better.
Didn't say otherwise-- did it myself solo and my autopilot doesn't have an IAS mode. But you missed my point, which is having some help, whether human or mechanical, when trying to fly a precise profile, collect data, and look for traffic can be beneficial. IOW, it's not about having the autopilot fly a better profile, its about having the autopilot reduce the workload so the flight can be conducted safer and perhaps produce better results.
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Last edited by Auburntsts : 08-13-2017 at 09:50 AM.
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  #12  
Old 08-13-2017, 10:45 AM
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Quote:
Originally Posted by Auburntsts View Post
Didn't say otherwise-- did it myself solo and my autopilot doesn't have an IAS mode. But you missed my point, which is having some help, whether human or mechanical, when trying to fly a precise profile, collect data, and look for traffic can be beneficial. IOW, it's not about having the autopilot fly a better profile, its about having the autopilot reduce the workload so the flight can be conducted safer and perhaps produce better results.
If you have a Skyview system - and I presume any of the other similar units - the task of collecting data has become trivial.

Just let the software do it and take the data home on a USB stick...
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Last edited by az_gila : 08-13-2017 at 10:50 AM.
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  #13  
Old 08-13-2017, 01:24 PM
BigD BigD is offline
 
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For some ballpark numbers for your airplane you can look at the Pilot Operating Handbooks (POH's) that Doug has via a link on the home page. Another way to determine best glide is to record time to descend through a set altitude (1.000 or 2,000 ft for example) at various speeds and then calculate the ratio. I found it more accurate (and simpler) doing it this way rather than trying to determine a distance over the ground for each run. The references already mentioned are a good start. I also read Vaughan Askue's book which was of some limited help, particularly the performance chapter.

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  #14  
Old 08-13-2017, 02:30 PM
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Originally Posted by BigD View Post
For some ballpark numbers for your airplane you can look at the Pilot Operating Handbooks (POH's) that Doug has via a link on the home page. Another way to determine best glide is to record time to descend through a set altitude (1.000 or 2,000 ft for example) at various speeds and then calculate the ratio. I found it more accurate (and simpler) doing it this way rather than trying to determine a distance over the ground for each run. The references already mentioned are a good start. I also read Vaughan Askue's book which was of some limited help, particularly the performance chapter.

=dave=
N102FM
After watching I had some major concerns over the EAA video referenced a few posts back.

I presume it came from a flat land area with moderate temperatures.

The video had no mention of temperature (hence Density Altitude) and of aircraft weight. These are both significant items that need to be taken into account and should used to "normalize" your performance numbers.

I am going to carefully examine the certified POH from my Tiger and try and try to extract some simplified mathematical corrections from it.

I'll start a new "Testing and Numbers" thread later tonight, so please post replies to the above on that thread.
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  #15  
Old 08-13-2017, 03:47 PM
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Default Vx and Vy Debunked

Just to splash some gasoline on the fire, here's John Deakin's Vx and Vy Debunked. Deakin demonstrates that using a Vx or Vy climb (or Vx then Vy) really doesn't do much for you. He also brings up the "Carson Speed", the speed that uses the least fuel to a given altitude. It's Vy x 1.3. Personally, I think it's good to know all those numbers, although we seldom use them in real life flying. Besides, should my engine quit on takeoff, I'll be using my AoA indicator rather than airspeed.
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Last edited by snopercod : 08-13-2017 at 03:52 PM.
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  #16  
Old 08-13-2017, 04:26 PM
BobTurner BobTurner is offline
 
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For best glide: if you measure distance over the ground you will have to account for any wind, to come up with the no-wind best glide speed. Remember the actual best glide speed in any situation depends on both wind and weight. I think it's more accurate to measure descent rates vs airspeed, and calculate glide ratios. Of course up or down drafts will affect this measurement.
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  #17  
Old 08-13-2017, 04:35 PM
BigD BigD is offline
 
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I agree that differentiating between Vx and Vy can be seen as a mostly academic exercise in the RV family because of the already excellent rate of climb, which is also offset somewhat by cooling problems if the slower climb speed is maintained for any length of time.

The Carson speed is a cruise speed above max range that optimizes the excess fuel used vs the speed gained, or, as he put it, "the least wasteful way of wasting fuel." Here's a link to the paper for those interested:

http://cafe.foundation/v2/pdf_tech/M...B.H.Carson.pdf

Hurry up and start that new thread...

=dave=
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  #18  
Old 08-13-2017, 05:14 PM
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Exclamation What the FAA says...

Quote:
Originally Posted by snopercod View Post
Just to splash some gasoline on the fire, here's John Deakin's Vx and Vy Debunked. Deakin demonstrates that using a Vx or Vy climb (or Vx then Vy) really doesn't do much for you. He also brings up the "Carson Speed", the speed that uses the least fuel to a given altitude. It's Vy x 1.3. Personally, I think it's good to know all those numbers, although we seldom use them in real life flying. Besides, should my engine quit on takeoff, I'll be using my AoA indicator rather than airspeed.
Maybe debunked, however the FAA requires us to know those speeds and sign off on a statement including those speeds at the end of Phase I testing -

Compliance with FAR 91.319(b) must be recorded in the aircraft records with the following, or a similarly worded, statement: “I certify that the prescribed flight test hours have been completed and the aircraft is controllable throughout its normal range of speeds and throughout all maneuvers to be executed, has no hazardous operating characteristics or design features, and is safe for operation. The following aircraft operating data has been demonstrated during the flight testing: speeds Vso ______, Vx ______, and Vy ______, and the weight ______ and CG location ______ at which they were obtained.”

Admittedly a bit wishy-washy on actual loading conditions (is it for Gross Weight and Aft or Forward CG positions?) and altitude conditions but a sign off is legally needed.
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Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
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  #19  
Old 08-13-2017, 06:17 PM
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Originally Posted by BobTurner View Post
For best glide: if you measure distance over the ground you will have to account for any wind, to come up with the no-wind best glide speed.
Thankfully, Foreflight Glide Advisor does that for me.
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  #20  
Old 08-13-2017, 06:31 PM
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Originally Posted by az_gila View Post
...the FAA requires us to know those speeds and sign off on a statement...
Well yeah, we all need to do that. Thankfully, the best glide curve on my plane is almost flat between 90 KIAS and 100 KIAS so I won't have to obsess about my airspeed while I'm looking for an emergency landing spot and trying to get the engine running again.

Funny story: I was taking a BFR a few years ago in a C-172 and the CFI had forgotten to do the "emergency landing" portion. So he decided to pull the power while I was in the pattern abeam the numbers. So I set up to go right in and land, and the guy basically screamed at me, "NOOO! You have to set up your best glide speed!!!" What I should have set up was my Minimum Sink Speed (which I think is 60 KIAS in a C-172) so I would have maximum time to troubleshoot the problem, but this guy was "by the book".

Y'all be careful out there, y'heah?
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