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Old 02-19-2014, 03:45 PM
cfiidon's Avatar
cfiidon cfiidon is offline
Join Date: Apr 2008
Location: Goodyear, AZ
Posts: 665

I's kinda like conservation of angular momentum. You know it exists, empirically and mathematically, but I could never draw you a picture of it.
RV-8 QB Titan ECi 191HP XIO-360
WW200RV Dynon D180 HS34 AP74
GNS430 SL30 GTX327 PS8000B Uavionix Echouat
"Pilots are alchemists... we turn gold into lead."

Last edited by cfiidon : 02-19-2014 at 03:55 PM.
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Old 02-19-2014, 05:38 PM
sailvi767 sailvi767 is offline
Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,467

I can't add much more to what has been posted except that wind also effects your optimum range best AS in powered flight also. The computer figures it out in my day job and speeds up into the wind and slows down with a tailwind to generate max range. In my non computer days we had a rule of thumb on how much to speed up going into the wind. My tired old brain can't remember it now.

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Old 02-19-2014, 07:16 PM
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n5lp n5lp is offline
fugio ergo sum
Join Date: Apr 2006
Location: Carlsbad, NM
Posts: 1,912

Originally Posted by BobTurner View Post
...But add a headwind, and the heavier plane wins over the lighter one, which is why, again already noted, gliders engaged in racing can carry water ballast (used if the first leg is into the wind).

Edit: I see Gil 'published' something similar to the power required curve while I was typing
Well, it doesn't really take a headwind, just reasonably strong conditions to need water ballast for best cross country speed. Where I live, on most competition days gliders will carry enough water to take them to maximum gross weight (or maximum contest rules weight) until right before landing. Only if they are in danger of landing out will most people dump water.

In olden days before each glider was weighed at the start of each day, people were known to cheat by loading saltwater into their gliders, rather than fresh water, for more weight. It really is astounding to experience the huge performance increase caused by carrying more weight in a glider.

I enjoy telling looking at power pilots when I tell them about how the increased weight helps the performance so much. It isn't intuitive to most people but is something we need to understand to understand our aircraft.

The essential thing is that best glide ratio is essentially the same with increased weight but the best glide angle occurs at a higher speed with increased weight.
Larry Pardue
Carlsbad, NM

RV-6 N441LP Flying
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Old 02-20-2014, 04:04 AM
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Kevin Horton Kevin Horton is offline
Join Date: Jan 2005
Location: Green Bay, WI, USA
Posts: 2,369

Originally Posted by dbuds2 View Post
Sunday was a glorious day for blue sky flying. Didn't have any real objective so I decided to do Vg testing.

RV-8, Solo, Fixed Pitch Whirlwind prop, Idle engine, 20-15 gallons of fuel, decend thru 5000' to thru 3000' at 100knots, 90 knots, 80 knots, 70 knots and let the Skyview record the data.

The results are different than I've read for other RV's, i.e. best Vg is much slower than I expected, probably the prop at idle???
There is almost certainly thrust from a FP prop at low speed, with the engine running at idle. The amount of thrust will be higher at low airspeed. The thrust from the engine at idle will affect the measured glide ratio and the airspeed for best glide ratio.

Another possible factor is the effect of wind, unless you used specific test and data analysis techniques to remove the effect of wind from the calculations. The method of calculating glide ratio is also a possible explanation of these results. Some people use some very creative, but incorrect, methods to calculate glide ratio.

Which data from the Skyview did you use to calculate glide ratio for each of those airspeeds?
Kevin Horton
RV-8 (Sold)
Green Bay, WI, USA
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Old 02-20-2014, 08:08 AM
MedFlightDoc MedFlightDoc is offline
Join Date: Nov 2009
Location: WI
Posts: 76

Having just been through this experience awhile back, but at 8-900' AGL, one thing I might add as a caution is that I would be very careful about trying to fiddle with your GPS in an engine out situation while you are also trying to figure out why the engine quit...!


Don't mean to insult anyone's intelligence, but I learned a lot about how one can get distracted and almost stall the plane...

So I just thought I'd throw that out there to keep in mind.

-Ryan in Madison, WI
(RV-6 Glider pilot, and former sailplane pilot)
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Old 05-16-2022, 10:58 AM
moespeeds moespeeds is offline
Join Date: Apr 2021
Location: Cherry Hill, NJ
Posts: 164

I just calibrated my AFS 4500 AOA indicator on my EFIS. The AOA manual claims it can show best glide. Curious if anyone has ever tested this with one of these things?
Moe Colontonio
Cherry Hill, NJ
RV-8 N495T
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