Exactly. It's a PITA, but it should really be done for each aircraft. Props, especially, make a big difference. Here's how I found the "best glide" on my plane, and the Vy and Vx are done the same way, only climbing. This is just the 80 KIAS run, and I also did them at 90, 100, and 110. My Garmin Virb allowed me to dictate the numbers into the Intercom and also see the numbers on the panel.I'm assuming you just go figure it out by testing various speeds?
there are also FAA Advisory Circulars that will help.
How exactly did you determine these numbers?
I would appreciate some of the numbers that were determined for the RV10.
Thanks.
Johan
How exactly did you determine these numbers?
I would appreciate some of the numbers that were determined for the RV10.
Thanks.
Johan
EAA has a Hints for Homebuilders video on finding Vy and Vx: http://bcove.me/8ch18ik8This is one of those flight tests where the additional pilot program or an autopilot that has an IAS function comes in real handy.
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.
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
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.
Thankfully, Foreflight Glide Advisor does that for me.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.
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....the FAA requires us to know those speeds and sign off on a statement...
Originally Posted by BobTurner
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.
Fly faster into the wind and slower with the wind for best "true glider" range. Luckily, if the winds aren't too strong and our RVs best glide is high enough it won't make too much practical effect.
rl]
Thanks for that Glider link. There's a wealth of information in there, some of which I had forgotten... like the part about adjusting your best glide speed for headwind/tailwind. The chart on page 5-11 has a note "With flaps set to ?8 degrees, sink rate does not change significantly but airspeed increases." I can reflex the flaps on my plane -7 degrees, and this reminds me that I need to re-perform my best glide tests with the flaps reflexed rather than in trail.ForeFlight isn't as smart as a sailplane final glide calculator/display which will give you speed-to-fly...
Do the same for glide:
- bottom of curve gives minimum sink
- tangent from origin gives best glide - Vbg
!
And the tangent drawn, not from the origin but, say, 20 knots to the right of zero, will give you the best glide speed with a 20 knot headwind.