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Best Glide Vs Best Sink... RV7 numbers ?

BillSchlatterer

Well Known Member
Just curious what folks are using for Best Glide and Best Sink rates in the RV7A with 360/CS or similar 7 or 8? What are you putting in your POH if you have one?

I'm using 85-90 MPH for best sink and 100-105 MPH for Best Glide. Anybody done any real measurements ??


Thanks Bill S
 
Just curious what folks are using for Best Glide and Best Sink rates in the RV7A with 360/CS or similar 7 or 8? What are you putting in your POH if you have one?

I'm using 85-90 MPH for best sink and 100-105 MPH for Best Glide. Anybody done any real measurements ??


Thanks Bill S

Bill, not sure about best sink, but the best glide (tangent to curve) with my RV7, engine at idle (4 test points) was 103KTAS (87KIAS) for my plane at about -940 FPM. With the engine windmilling (mix pulled) I only got two points the one closest was 105 KTAS , -1000FPM as measured resulting in a 9.7 glide ratio. Tanks were near full, 160lb in cabin, empty GW is 1140lb. The test was between 9-8000 ft. While speed (103KTAS) and descent rate (-940) are taken from the graph/data points, the other info is from memory. If it is important, it can be verified. Prop pulled out fully. I have the Hartzell composite and at fine pitch, glide is much different (8% less).

Important note: This if for reference and will not likely represent any other aircraft model or serial number.
 
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I'm using 85-90 MPH for best sink and 100-105 MPH for Best Glide. Anybody done any real measurements ??

Anyone who has built their plane should have real measurements derived from phase 1 testing, and every plane will be a bit different due to static/pitot/asi instrument/weight particulars. Bottom line, you really need to do this testing for your plane and, in any case, is probably beneficial anyway for a non-builder to help them get to know their plane better. It’s easy to do and good for polishing piloting skills as well.

Have fun.
 
I did some testing with my RV-7 and came up with a best glide speed of 80 KIAS, 1,6 NM still air distance per 1000ft, gliding range almost 1:10. Most testing was done with close to max weight and between 5000 and 10000 ft with power at idle (windmilling) and prop at low pitch. Numbers are rounded as they are dependent on weight and so a little variable.
 
Interesting discussion

In my case (RV-7) best glide is around 110 mph, fixed pitch Catto 3 blade with heavy sabre spacer and landoll ring approximating a CS weight up front. Rate of descent around 500 ft per min (approximated prop windmilling at idle rpm).

I actually built a glide range chart (no wind) with altitude and terrain height as one of my check lists to quickly see if I could make a runway when punching "nearest" on the 796 in case of an engine failure, now superseded by the glide range ring in Foreflight.
YMMV
Figs
 
Some recent retesting to more accurately find Vbg found ~95 KIAS, pilot + passenger, no baggage, about 3/4 tanks.

Seems in line with most others, but then I see some that are WAAAY lower, like 75 or 80 KIAS.

How can there be such wide variation in the same airframe? They're all RV7s, probably about the same weight give or take a little...75 knots all the way up to 103 knots? That's nearly 40% increase from 75 to 103...doesn't make sense to me.
 
Some recent retesting to more accurately find Vbg found ~95 KIAS, pilot + passenger, no baggage, about 3/4 tanks.

Seems in line with most others, but then I see some that are WAAAY lower, like 75 or 80 KIAS.

How can there be such wide variation in the same airframe? They're all RV7s, probably about the same weight give or take a little...75 knots all the way up to 103 knots? That's nearly 40% increase from 75 to 103...doesn't make sense to me.

I think we are all reporting in different conditions, altitude, temperatures, props, and weight. I reported 103 KTAS, at 9000 ft. Precisely, that is 87 KIAS for barometer and temp of that day. I am not a test pilot so did not know how to report in "standard" conditions. A recent Kitplanes article by Nigel, recommended testing a several altitudes. I only tested in one region. If you have a recommendation of a correction procedure for this testing, and a standard condition, please post, I'll do the calculations and report accordingly.
 
I think we are all reporting in different conditions, altitude, temperatures, props, and weight. I reported 103 KTAS, at 9000 ft. Precisely, that is 87 KIAS for barometer and temp of that day. I am not a test pilot so did not know how to report in "standard" conditions. A recent Kitplanes article by Nigel, recommended testing a several altitudes. I only tested in one region. If you have a recommendation of a correction procedure for this testing, and a standard condition, please post, I'll do the calculations and report accordingly.

Good point about the different atmospheric conditions/altitude. I don't have a procedure or analysis for computing Vbg at a specific altitude/density altitude, but someone might (given, say Vbg at another specific point). I did miss that you were reporting TAS, whereas I think most people understand all V-speeds other than Vne to be in IAS.

Still...quite a range of values for similar aircraft.
 
Good point about the different atmospheric conditions/altitude. I don't have a procedure or analysis for computing Vbg at a specific altitude/density altitude, but someone might (given, say Vbg at another specific point). I did miss that you were reporting TAS, whereas I think most people understand all V-speeds other than Vne to be in IAS.

Still...quite a range of values for similar aircraft.

It's always interesting to read what pilots get out of their machines, much can be learnt from these pages:) I Like the last bit, VNE to be in IAS, I still hear pilots say VNE is what's on the dial at high Altitudes, now that's a worry!
 
As mentioned, you need to test to find your own numbers, Also bear in mind that whatever you come up with, these are theoretical numbers. It is generally preferable to fly slightly on the fast side for several reasons:

- it makes little difference to the glide angle
- helps with any headwind
- further from the stall especially as some heavy maneuvering might be required
- leaves a bit more energy for that final glide to touchdown if you are a bit short
 
Best glide

As mentioned, you need to test to find your own numbers, Also bear in mind that whatever you come up with, these are theoretical numbers. It is generally preferable to fly slightly on the fast side for several reasons:

- it makes little difference to the glide angle
- helps with any headwind
- further from the stall especially as some heavy maneuvering might be required
- leaves a bit more energy for that final glide to touchdown if you are a bit short

I would add that it gives you a little margin for the natural tendancy pull up as you speed towards earth without power.
Been there!:p
 
Best glide is like engine out VY , (feet per MILE!) (92 KIAS in my aircraft, windmilling, prop coarse pitch).
Minimum sink airspeed is like engine out VX (Feet per Minute) is (77 KIAS - same configuration as above)

So, 77 knots will give you most time in the air, and 93 knots will give you most distance.

DAR Gary
 
Best glide is like engine out VY , (feet per MILE!) (92 KIAS in my aircraft, windmilling, prop coarse pitch).
Minimum sink airspeed is like engine out VX (Feet per Minute) is (77 KIAS - same configuration as above)

So, 77 knots will give you most time in the air, and 93 knots will give you most distance.

DAR Gary

Very good explanation.
 
Best glide is like engine out VY , (feet per MILE!) (92 KIAS in my aircraft, windmilling, prop coarse pitch).
Minimum sink airspeed is like engine out VX (Feet per Minute) is (77 KIAS - same configuration as above)

So, 77 knots will give you most time in the air, and 93 knots will give you most distance.

DAR Gary

I think you got Vx and Vy backwards.. Vy is RATE (Altitude per unit time) while Vx is ANGLE (Altitude per unit horizontal distance)
 
My opinion is it’s too hard to say with enough certainty to put it in your POH. These are not type certificated airplanes. Meaning there’s lots of variability. For example, you didn’t say what prop, engine, static port location etc you have installed. In exchange for the privilege of building your own comes the responsibility to test and make your POH based on actual testing. If you do, your POH and flying skills/knowledge will be better for it.

Bevan
 
For those with Garmin G3X, there is a new software update which will paint the glide area capability, based on the best glide entered by the operator, and terrain around the aircraft terrain. (Wind can still be a big variable).
DAR Gary
 
Just curious what folks are using for Best Glide and Best Sink rates in the RV7A with 360/CS or similar 7 or 8? What are you putting in your POH if you have one?

I'm using 85-90 MPH for best sink and 100-105 MPH for Best Glide. Anybody done any real measurements ??


Thanks Bill S

An accurate Best Glide speed may be your best & ONLY friend one day. So wouldn't it in your best interest to determine what that number is - for your aircraft with your airframe/engine/prop model/C0fG/etc... combination?
While you're at it, get the EAA Flight Test Manual & build your own accurate for your airframe POH. Web POHs are for the most part good templates - but you should edit the content to your specific test resulted numbers.

Just a thought...
 
Distance Vs Altitude Loss.....

The question between distance or altitude depends completely on the situation. If you are quite a distance from an airport, then obviously you want distance. OTOH, if you are relatively close to a suitable airport, then you might opt for minimum altitude loss so that you might have more time to troubleshoot the power-loss problem. I have a VHS tape from many years back that does a very good job of demonstrating all scenarios. The tape was from ABC's "Wide World of Flying". I think it was Barry Schiff flying a C-182. He demonstrates both glide distance and altitude loss with engine at idle (with both fine and coarse prop positions) and with prop stopped.
I'll see if I can find it and give more information.
I had to take Ann to the emergency room yesterday, so I'm a little busy right now.
As said before, you need to find the best numbers for YOUR airplane.
 
...
I had to take Ann to the emergency room yesterday, so I'm a little busy right now.
...
Mel, I hope she has a speedy and full recovery! Not the place you want to be right now with the holidays and other stuff going on. Take care!
 
Glide distance based on an external reference

During phase I did some engine out glide numbers in the 5k down to 3K' test range (actual stopped prop, 3 blade Catto, -7) at different headings towards the airport to account for wind. GPS data was recorded and pulled from the Dynon HDX for analysis. Depending on weight, the best range glide speed was in a range of 75 to 80 kias.

The best info from these tests came from the concept of judging glide distance based on an external reference on the aircraft.

A talented Cub driver worked with me on the idea (he uses it in his Cubs) and we found that at my seated height, everything that was under my left wingtip was reachable in a power off glide. We did the calculations based on the computed data from my tests and converted it into a glide angle.

I've done more tests with power at idle, reduced power etc and have been pleased with the results.

Being able to look out the window when the noise stops and have a quick idea of how far you can make is nice. I find myself doing it all the time during cruise while playing the "what if" game. Keep in mind that this data applies to an aircraft already at best glide speed, so if your cruise is well above that number (as it normally is), that extra airspeed is all gravy.

Fly well

Cheers
 
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