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Jan 21, 2020, 02:54 AM
Duane, LSF IV
Wazmo's Avatar
Here's an extreme example to illustrate. Suppose you fly directly into the wind at a normal airspeed/angle of attack, and the wind speed is equal to your airspeed. Your ground speed is zero, so your plane does not appear to move forward, but it is still flying at cruise airspeed. Now, suppose you start climbing while maintaining zero ground speed (let's say a thermal passes through). Your climb angle is 90° because the plane rises straight up over the ground, but your angle of attack is certainly much less because the plane is still travelling forward through the air. So, the apparent climb angle from the ground is steeper in wind.

For your DLG launch example, the plane sees a higher air speed because of the wind. Once it leaves your hand, the wind only matters when maneuvering with respect to the ground (e.g. landing) and it only affects your ground speed. If you try to keep a normal ground speed on launch, your climb will be less because you're flying at a higher and less efficient airspeed.
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Jan 21, 2020, 04:10 AM
In F3J size does matter!
roydor's Avatar
The biggest mistake people do is not trim the pitch and not mix the correct amount of elevator to throttle required for a pitch stable model under power. They fight to maintain the pitch all the way up.
I trim the model under half throttle for a slow and steady climb with no pitch up tendency and then mix the required amount of elevator to throttle so the model brings up the nose very very slightly when adding power but doesn’t want to bring the nose up to vertical. End result is I have a model that I can climb with after setting the climb angle at the start when its low and close and requires very little adjustments all through the climb.
For a low power setting, maintaining air speed similar to cruise will give you best climb. For a higher power setting you need a bit of practice to find the “best angle” but as written above, close to 60 deg works well.
Jan 21, 2020, 04:18 AM
launch low, fly high
Quote:
Originally Posted by Dave80H
...

I recall from many years ago (in one of the RC mags) that someone had worked out that the best rate of climb for any model is achieved when it flies at 57 degrees to the horizontal.. Could this (or something like it be true)?
There was a specious derivation for the optimum climb angle ins a model aerodynamics book that claimed 57 degrees as the optimum climb angle for a high powered aircraft. A quick look through the derivation showed that there was a flaw in the assumptions in the derivation. It turns out that the sine(alpha) does not equal alpha for large alpha... I remember Jerry Bridgeman talking to me about this "optimum" in the early '90s, and I pointed out at that time the mathematical error in the derivation.

The optimum climb angle depends on a lot of factors, including aircraft weight, motor kv, gearbox, battery, prop diameter and pitch, etc. I was a bit surprised, I have one F5J aircraft that can barely climb vertically, there is just enough excess power to do so but the climb speed is slow enough that it doesn't handle well at all if climbing vertically. I did some tests, and it turned out that the optimum climb angle was still vertical despite the "slow" climb speed. If you have a speed oriented prop, then it may make some sense to climb less than vertical even if there is enough excess power to climb vertically. It just depends as to whether the prop efficiency increase outweighs the profile drag increase... (motor efficiency is also a pertinent factor, but the prop efficiency with airspeed vs profile drag trade is typically the most important one for climb rate optimization.
Jan 21, 2020, 06:03 AM
Registered User
Thread OP
Thanks to all for your input, it is much appreciated.... I can lay my ghost of 57 degrees to bed...

It also means that my idea of allowing the comp entrants their individual motor run times based on 4Ws/g (or so) will work as well as any other means of limiting climb as the actual height gained will be so effected by the way it is flown to height (and where, for that matter).
Last edited by Dave80H; Jan 21, 2020 at 01:47 PM. Reason: Removed non related text.
Jan 23, 2020, 01:09 AM
AMA 7224
Leadchucker's Avatar
Quote:
Originally Posted by roydor
The biggest mistake people do is not trim the pitch and not mix the correct amount of elevator to throttle required for a pitch stable model under power. They fight to maintain the pitch all the way up. ..........
Thumbs work just fine for me with no mixing stuff. No fight what so ever,just switch on ( I have only full power or none) and climb out. Climb is rarely if ever a straight line of trajectory any how when ranging to a point to start looking for lift.
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Jan 24, 2020, 01:46 AM
Registered User
For a small prop, it makes sense to fly fast when climbing, at a shallow angle. This was especially apparent on the original Allegro Lite, which had a direct drive Speed 400 with a six inch prop. As long as you kept it moving, the climb rate was reasonable.

If you are flying near a pyramid, the best strategy,may be to use ground effect most of the way up. ;-)


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