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kxo300
02-05-2005, 01:21 PM
PA12, 82-41 Borer, 150-320, extended wing, Horten Hot Tips.

How do you determine the airspeed for the best angle of clime. the best rate is published in the POH and can be measured with VSI or on the 296 vsi.

Will soon be installing the Mircro VG's and suspect that they do lower the stall speed, Will they have any effect on the indicated airspeeds for best rate and best angle?

inquiring minds want to know.

Gary

mvivion
02-05-2005, 02:37 PM
I don't disagree with Supercubber's technique, but the operators handbook for the Super Cub does "specify" in rather roundabout terms, that the best angle of climb configuration is with full flaps and at 45 mph.

In a stock Cub, at least, that is pretty close to Supercubber's procedure.

I think the verbiage in the handbook says something like "if you are trying to climb over an obstruction, yada, yada, a full flap climb at 45 mph indicated airspeed will afford the greatest increase in altitude for the distance covered over the ground....." or words to that effect.

One thing the FAA did that was good was to get all the manufacturers to better specify recommended airspeeds, etc in a standard format, as opposed to hunting around a handbook for "inferences".

With a modified airplane, its up to you to determine what the best speed is.

MTV

kxo300
02-05-2005, 04:52 PM
Thanks for the info.

Where I live in west central MN we have piles of lakes and the topo isn't a problem. When in ONT. Canada the obstructions at the end of the lakes are much greater, at least the lakes I fish (for the big ones, are always in a canyon).

Do you believe VG's help with angel of climb? (Granted the pucker factor as you mis the trees by a skosh might help a little too!)

Gary

Alex Clark
02-05-2005, 06:32 PM
Since all of my planes ahve been heavily modified, I had to go out and test fly them for the best angle and best rates.

Best rate is pretty much how you did it. I used the VSI and GPS VSI. Then I tried the same thing over a two minute period of time and checked the altitude gained by holding at different speeds.

For best angle. I just used a measure distance and the altitude gained in that distance.

We just tried it two of three times at different speeds. Sometimes the most nose up attitude WOULD NOT result in the most altitude gained in a given distance. I think it was mushing along and not climbing as much.

For instance, my PA-11 will fly at and hang on the prop at 40 mph. But not gain the maximum altitude over a 500 foot distance.

BUT, she will gain the maximum altitude in that same distance at 48-50 mph.

Then if I go to 55 mph, that will give me the most altitude over a period of time. Almost 1100 fpm while light and 900 fpm maxed out at sea level.

We did the same thing with gliding distance on floats and off floats.

I was amazed at the gliding distance gained by holding the airspeed just right. A 55 mph glide (on floats) will give me almost a quarter mile more distance compared to 60 mph or 50 mph.

We tried it many times with a full load, and we went all the way to water impact along a lake with markers.

bob turner
02-05-2005, 10:26 PM
The real way to find Vx is to plot rate of climb vs. airspeed on a graph. The top of the curve is Vy; the place where the curve goes through zero is stall, and a straight line through (zero, zero) and tangent to the curve gives best angle. That would be about 45 mph in a Cub.

My Super Cub book doesn't say climb with full flaps. My physics book says that best angle is attained when (thrust - drag) is maximum. Sticking flaps out increases drag. Lift has nothing to do with climb; it is always excess thrust that makes a powered aircraft go up (in still air).

Often Vx and short field takeoffs are combined into one subject. In my opinion, they ought to be taught separately, then combined. Clearing a very close obstacle may well require a greater flap setting, and getting off the water surely requires flaps. But if you just want to go up, minimize the drag and maximize the thrust.

I have recently read things in the popular press that say when hot, heavy, and high, use more flaps on takeoff. My opinion, based on study, is that that is a prescription for disaster!

kxo300
02-05-2005, 10:50 PM
Thanks Alex

you got me in the "testing mode" and thanks for the detailed reply.

As I understand then;
1. Best rate is that airspeed where you get the max lift and the least drag, and this same airspeed also gives you your longest glide?

2. Best angle is an airspeed (always less than best rate) that gives max lift in the least distance covered?

Wish a person could put a dot in the sky to test this one!

I haven't installed the VG's yet. It would be fun to do a before and after and see if these numbers change. Have you done any testing on this?

Gary

Alex Clark
02-05-2005, 11:53 PM
It just happens to also be the best glide speed in my cub.

I lost a bet last year in a C-206 because I was flying to far away from an island.

I was thinking I was within glide range based upon the ORIGINAL specs put out by Cessna.

I had not accounted for it being an old worn out plane, never waxed in 10 years, with a big cargo pod meant for a C-207. And over-sized tires with mud flaps.

I put her at the recommended glide speed and we just mushed. I could not cheat and pull the propeller to max angle since the bet depended on the engine blowing apart. The prop would go to auto-flat pitch in that case and there would be no getting it back.

So I had to pitch down about 10 to 15 knots of speed to get a good controlable glide. At that angle I would have put her into the ice cold water 500 yards off the coast.

The only good thing is that we would have gone into shock and drowned fairly soon.

mvivion
02-06-2005, 12:38 AM
Bob,

Read your cub book carefully, and you will find the reference I noted. Its there, and it says use full flaps. I didn't make it up, believe me. It is a roundabout reference, though. Nothing about it says specifically "best angle of climb".

I also, however, believe it to be correct for a stock cub.

Next time I get close to a Cub handbook, I'll find a specific page reference.

MTV

Alex Clark
02-06-2005, 02:51 AM
PA-18 pre-1974 150 hp handbook.

Page 2. Metal prop at 1750 pounds weight
Best rate 75 mph
Best Angle 45 mph

Page 8. Paragraph 3.
The best angle of climb is attained with full flap.
The best rate of climb is attained without any flap extended.

mvivion
02-06-2005, 01:54 PM
Thanks, Alex,

MTV

Torch
02-07-2005, 12:02 AM
Honestly, I don't know what speed my airplane has the best angle of climb but I can feel it. I haven't looked at the airspeed indicator. I feel the climb. Just the way I fly.

bob turner
02-07-2005, 12:14 AM
Some folks say that best angle with flaps is attainable because the aircraft is moving forward slower - that is, it simply flies slower with flaps extended. This is obviously not true for a Cub; it flies fine at 45 with flaps retracted.

I don't have the drag polars for a Cub, but we did it with a 737, and proved that overall the lesser the flap, the better the climb angle. Then we changed the procedure!

The key is that old lift-weight-thrust-drag vector diagram. If you believe it (and many folks do) you can prove that best angle is attained in the minimum drag configuration. Lift is up, weight is down. Simplify it a bit and make thrust and drag act in the plane of climb - the plane that makes an angle with the horizontal. Climb angle is universally called "gamma", after some Greek guy with his arms up in the air. Vectors can be moved around a bit and added or subtracted if they go in the same direction.

I know that leaves you cold, but it is on the first page of almost any older private pilot study text. Once you get the vectors all arranged, you can readily see that increasing drag, all other things being equal, decreases gamma.

John Lowry, Ph.D., was the Northern Pilot guru, and he helped me understand the simple vector diagram - prior to that I was into the heavy-duty Boeing equations, which will never convince a lightplane driver.

My Super Cub manual says all takeoffs, land and sea, should be made flaps up. I actually disagree with that; a rough or short field, or water, will have me extending flaps. They shorten ground roll. They are not useful for climbing. My opinion. You don't want to hear what we uncovered on "thrust"!