VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #21  
Old 05-31-2017, 12:46 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 4,459
Default

Quote:
Originally Posted by AX-O View Post
What function is that? Where do you turn it on and off?
IIRC it is just there - I don't think you can turn it off. Put your plane into a descent and look at the Hx's map page. Out in front of you you should see a green arc. That's where you'll hit the ground, if you continue at the same horizontal and vertical speed. If you make smooth adjustments to your speed while gliding, you can watch that arc move further away or closer to you, until you find the best glide speed for that day's weight and wind.
Edit. BTW, I use that arc all the time, e.g., to see if I'm at the proper descent rate to arrive at an airport not too low or high.
Edit. Please see post 25 for correction to this post, thanks, Dynon

Last edited by BobTurner : 05-31-2017 at 02:44 PM.
Reply With Quote
  #22  
Old 05-31-2017, 01:22 PM
Robert Anglin Robert Anglin is offline
 
Join Date: Mar 2008
Location: houston, texas
Posts: 667
Default

Quote:
Originally Posted by BillL View Post
Hi Bob, I was curious about this a found this:

"Variations in aircraft weight do not affect the glide angle provided that the correct airspeed is flown. Since it is the lift over drag (L/D) ratio that determines the gliding range, weight will not affect it. The glide ratio is based only on the relationship of the aerodynamic forces acting on the aircraft. The only effect weight has is to vary the time the aircraft will glide for. The heavier the aircraft is, the higher the airspeed must be to obtain the same glide ratio. If two aircraft have the same L/D ratio but different weights and start a glide from the same altitude, the heavier aircraft gliding at a higher airspeed will arrive at the same touchdown point in a shorter time. Both aircraft will cover the same distance but the lighter one will take a longer time to do so."
Reference: http://www.skybrary.aero/index.php/Glide_Performance

As a practical matter, it would appear either AoA or known glide speeds vs weight should be documented for ones serial number - right?
Thanks for the wright-ups. I can tell you we do sink faster when at gross Vs solo. It may have to do with me. I try to hit my air speed and stay on it after I use what is left to get that last little bit of climb from any speed above that. I do not try to very my speed per my weight, I just try to stay on it and work the problem and landing sights. So far I have not had to dead stick this one in, but it has been known to happen. Yours, R.E.A. III #80888
Reply With Quote
  #23  
Old 05-31-2017, 01:27 PM
snopercod's Avatar
snopercod snopercod is online now
 
Join Date: Aug 2016
Location: Asheville, NC
Posts: 671
Default

Quote:
Originally Posted by dcurrier View Post
Does that sound like a solid plan?
Yes. Pick a calm morning day and a remote area away from mountains so you won't have updrafts and downdrafts. What I did was begin my descents at 5,500', stabilize at the test airspeed, and start the timer when passing 5,000'. You can double up and determine your best rate of climb speed on the way back up.
__________________
(2017 dues paid)
Reply With Quote
  #24  
Old 05-31-2017, 01:38 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 4,459
Default

The variation in best glide speed is the square root of weight. A good approximation is to use half the percentage difference. E.g., if best glide at gross is 80 kias and you are 10% below gross, then reduce the gross weight number by 5%, or 76 kias. Remember too this is for no wind. Into the wind you'll want to increase the speed by 1/3 - 1/2 of the wind speed. In a lot of common training scenarios, these two effects cancel out. e.g., you may be 10% below gross, calling for a 4 knot reduction. But on final, you may have a 10 knot headwind, calling for a 4 knot increase.
If you try a few power at idle landings on a day with a 20 knot headwind, it's pretty easy to get set up where an approach at published best glide will bring you in short; but increasing airspeed by 7 or 8 knots will let you make the runway.
Reply With Quote
  #25  
Old 05-31-2017, 02:19 PM
dynonsupport's Avatar
dynonsupport dynonsupport is offline
 
Join Date: Jun 2005
Location: Woodinville, WA
Posts: 1,491
Default

Quote:
Originally Posted by BobTurner View Post
IIRC it is just there - I don't think you can turn it off. Put your plane into a descent and look at the Hx's map page. Out in front of you you should see a green arc. That's where you'll hit the ground, if you continue at the same horizontal and vertical speed.
In most EFIS systems, this arc shows when you will intercept the altitude bug, not hit the ground.

The thing lots of EFIS systems have is a ring around the plane all the time that shows if the engine failed, where you could glide to. This needs performance data for the plane as this ring is drawn even when you are climbing. Most of these systems also offset the ring for wind (if it's known).
__________________
_______________________
Dynon Avionics
support@dynonavionics.com
425-402-0433
www.DynonAvionics.com
Reply With Quote
  #26  
Old 05-31-2017, 02:41 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 4,459
Default

Quote:
Originally Posted by dynonsupport View Post
In most EFIS systems, this arc shows when you will intercept the altitude bug, not hit the ground.

n).
Yes, you're right, my error. I forgot, I just reflexively set the altitude desired to the airport traffic pattern altitude on descent.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 03:42 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.