Climb Speeds?

[jsharkey]

I have done some initial climb speed tests and Vy seems to be around 105 kt for my RV6. How does that compare?

The aircraft weighs 1021 lb empty with a YO360-A1A & 72/85 Sensenich and has no leg fairings or wheel pants yet. Tests were flown between 4,000' and 5,000'.

With more practice at test flying I think I can get more and better data.

Jim Sharkey

 

[n5lp]

The aircraft weighs 1021 lb empty with a YO360-A1A & 72/85 Sensenich and has no leg fairings or wheel pants yet. Tests were flown between 4,000' and 5,000'...

I'm not sure what the point of comparisons would be between a faired and non-faired airplane. If you do add the fairings, everything is going to change anyway and you will need to do the tests over if you want accurate data.

The fairings make even more of a difference on an airplane with a fixed pitch prop because the fairings affect how make power the engine can produce.

 

[sprucemoose]

I agree with Larry, testing without fairings on won't give you much useful data. It is however good practice for when you do the actual testing.

FWIW- My own testing on my -6 revealed Vy to be 90kts. O-360, 3-blade Catto fixed (66X76) and 1,067 lbs. empty. Just one data point for you.

 

[L.Adamson]

Okay................ I admit, I don't use VX or VY. I just know that I have to make it over that mountain real quick, which is a climb of about 4000'. And I know that I can do it at least three times as easy as a Cessna! Actually it's impossible in the Cessna, without flying back and forth across the foothills to gain altitude...

L.Adamson --- RV6A 0360, Hartzell C/S

 

[N941WR]

Okay................ I admit, I don't use VX or VY. I just know that I have to make it over that mountain real quick, which is a climb of about 4000'. And I know that I can do it at least three times as easy as a Cessna! Actually it's impossible in the Cessna, without flying back and forth across the foothills to gain altitude...

L.Adamson --- RV6A 0360, Hartzell C/S

That doesn't help at all. If Jim's Airworthiness document is like mine, I had to run the tests and document Vx and Vy on the actual document. Without those numbers filled in, I'm not legal.

Like the others have said, the numbers will change once the fairings are installed.

 

[L.Adamson]

That doesn't help at all. If Jim's Airworthiness document is like mine, I had to run the tests and document Vx and Vy on the actual document. Without those numbers filled in, I'm not legal.

Like the others have said, the numbers will change once the fairings are installed.

My numbers are filled in to. Didn't have the fairings at the time, and didn't have that mountain to climb over either. These day's I just don't care much about following VX or VY to the max. I just don't have too.

L.Adamson --- RV6A

 

[n468ac]

In our RV6A

Vx = 70 KTS
Vy = 80 KTS

Normal climb 120 KTS to 10,000 ft - will give inital 850 fpm final around 400 fpm.

Max alt climb 140 KTS 10 14,500 ft - will give inital 700 fpm final around 100 fpm.


normal climb will keep the engine temps below 400 and you can see over the glare sheild.

max climb will keep the engine temps below 400 all the way up to 14,500 and you can easy see over the glare sheild.


IMO - flying under 90KTS on take off, doesn't give you much room for an engine to quit and you to recover. Go up and fly at 70 KTS and pull the power ... it's very close to stalling without power.

 

[jsharkey]

All I wanted to know....

....was how my numbers of ~95 kt Vx and ~105 kt Vy in the open wheeled configuration described compared with the other 2,500 or so RV6s out there

Jim Sharkey

 

[flyeyes]

....was how my numbers of ~95 kt Vx and ~105 kt Vy in the open wheeled configuration described compared with the other 2,500 or so RV6s out there

Jim Sharkey

They seem pretty high. My 200 HP RV-8 pretty much tracks with the numbers in the CAFE report (69 and 91 knots).

The CAFE report on the RV-6A reported 71 and 87 knots.

All of those numbers were in the normal configuration (i.e. with all fairings).

Others have more expertise, but i would expect the increase parasitic drag without fairings to lower both speeds a little.

 

[jsharkey]

Thanks....

....that's what I wanted to know. I need to improve my test technique. I got the same minimum time to climb (+/-0.5 sec) from 4,000' to 5,000' for each of 95, 100, 105, 110 and 115 knots. 90 and 120 knots were significantly slower. Also the nose was very high for the slower speeds.

Jim Sharkey

 

[Kevin Horton]

They seem pretty high. My 200 HP RV-8 pretty much tracks with the numbers in the CAFE report (69 and 91 knots).

The CAFE report on the RV-6A reported 71 and 87 knots.

All of those numbers were in the normal configuration (i.e. with all fairings).

Others have more expertise, but i would expect the increase parasitic drag without fairings to lower both speeds a little.

The power available for an aircraft with a fixed pitch prop increases strongly as the speed increases, due to the increasing rpm. With a constant speed prop, the power available is relatively constant, except for the effect of changing propeller efficiency as the speed varies. The result of all this is that Vx and Vy will be higher with a FP prop than with a CS prop.

An increase in profile drag will lead to a decrease in Vx and Vy. Thus results from testing done without gear leg fairings and wheel pants are not completely valid for the final configuration.

The Vx and Vy values in that CAFE report are listed as coming from the POH. They were not determined by the CAFE Foundation. We have no way of knowing how credible those numbers are.

I've done some of the preliminary work to create diagrams for a climb performance article that I will eventually submit to Kitplanes for their consideration. As part of that project, I played around with some prop efficiency, engine power vs rpm, and airframe drag data to create predicted climb performance for an RV-6A with CS and FP props. The predicted Vx and Vy for an aircraft with a hypothetical FP prop were 78 and 105 kt. With a CS prop, Vx and Vy were predicted at 61 and 96 kt. All values valid at sea level, std day and 1650 lb weight. Vx and Vy will vary with changes in altitude and weight.

Note that these values are only predictions, and many assumptions had to be made, so actual performance might vary quite a bit from these predictions.

 

[AlexPeterson]

I had almost the exact same times (30 to 33 seconds) for my climb tests (something like 3000 to 4000') for 70 kias through 120 kias, WOT full rpm. I have a 180 hp, CS prop. I use the lower speeds for sport in the winter, the higher speeds for cooling in the summer. I decided it would take some very, very careful testing to really nail it down, and didn't bother.

 

[jsharkey]

My Vx is a real SWAG so far...

...since the curve looks more like a table top and the origin to curve tangent intersection point is really anyone's guess.

More accurate flying and testing is needed. The education and recreation just keeps on coming - and I was worried that since I had enjoyed the building so much I would be spooked by or otherwise not like the flying

Jim Sharkey