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CTSW Bob

Anyone use more than 15 degrees flaps for take off?

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I always use 15 degrees for take off, but it turns out I inadvertently took off with what I later determined to be 27 degrees of flaps.  My flap selector once again went goofy when my battery died again.  I reprogrammed my -6 setting to get it working again.  All my other settings seemed fine.  I took off the other day with a quartering headwind of 9 gusting to 16.  My 15 degree setting (actual 27) had me jumping off the runway in a startling 400 or so feet and a climb angle that was described by the plane holding short as a kite.  I did two take offs and easily climbed well above pattern altitude before the end of the runway.  It was a substantial difference.

Upon pulling it in to the hangar, I broke out my digital level and determined the 15 degree setting was actually 27.  The others were spot on.  

My question is, has anyone else tried or use higher than 15 degree flap settings for extreme short field performance?  

 

 

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I've done a couple at 30 degrees, and with my light loading it was an elevator ride, even with 15 I'm amazed on every takeoff how well this bird gets up.  The cool dense air this time of year also adds a lot to the mix.  When I bought the plane Tom Jr at Airtime was sharing he had used 40 degrees, gone full power then dumped the parking break and it did very short rolls -  I've yet to attempt 40 degrees.

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I love doing 30 flap takeoffs. Solo I would get airborne in 280 feet and with another person On board it was 400. I could never come close to those numbers with 15 flaps. 
 

caveat: I wouldn’t do this on windy/gusty days. 
 


 

 

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I’ve practiced with 35 flaps on the CTLS, and my guess is that it would clear the trees in a much shorter distance than with 15.  I’ve been thinking about testing this theory, but haven’t gotten around to it yet. Accelerate in ground effect to 50 kts and away you go. I agree that gusty days wouldn’t be good with this technique. 

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You'll break ground faster, but will climb slower.  Best rate of climb is in the lowest drag configuration, but of course you have to get up to the appropriate speed for the config.  You'll roll longer with 15°, but once you break ground you should climb faster than at 30° (even more so with 0°, but man that roll seems to take forever). 

Best use for 30° flaps on takeoff I can think of is to break ground ASAP on a rough field, then accelerate near level and get those flaps up ASAP to climb out.  Or just to play around; getting off the ground super short is fun.   :)

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Yes, it is a great way to pop out of the rough if you need to do that. Although the climb rate will be slower than with 15, the takeoff roll is shorter, you only have to accelerate to 50, and you’re eating up distance at a slower rate during the climb. I’m convinced that the distance to establishing the climb is shorter. It would be interesting to test this at altitude to compare climb angles, then do the math. 

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28 minutes ago, FlyingMonkey said:

You'll break ground faster, but will climb slower.  Best rate of climb is in the lowest drag configuration, but of course you have to get up to the appropriate speed for the config.  You'll roll longer with 15°, but once you break ground you should climb faster than at 30° (even more so with 0°, but man that roll seems to take forever). 

Best use for 30° flaps on takeoff I can think of is to break ground ASAP on a rough field, then accelerate near level and get those flaps up ASAP to climb out.  Or just to play around; getting off the ground super short is fun.   :)

Everything you said is true, but just because you are climbing at a slower rate doesn't mean you are not going up at a steeper angle. 

I once did a test with my CTLS, two take offs back to back. Both with full throttle then brake release from a standing stop. One with 15° flaps and on with 0° flaps, both timed for 1 minute. At the end of 1 minute both configurations put me at 500 feet. With 15° flaps I broke ground quicker, so I had more time climbing. My position was closer to the starting point. With 0° flaps it took longer to get off the ground, so less time climbing to 500 feet. My position was further away from the starting point. It was obvious that the time spent climbing to 500 feet was less with 0° flaps, but if you were trying to clear an obstacle 15° flaps was a better option. A person would need to measure climb rate, distance , and time to determine if more than 15° flaps yields a better option for obstacle clearance.

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16 minutes ago, Tom Baker said:

Everything you said is true, but just because you are climbing at a slower rate doesn't mean you are not going up at a steeper angle. 

I once did a test with my CTLS, two take offs back to back. Both with full throttle then brake release from a standing stop. One with 15° flaps and on with 0° flaps, both timed for 1 minute. At the end of 1 minute both configurations put me at 500 feet. With 15° flaps I broke ground quicker, so I had more time climbing. My position was closer to the starting point. With 0° flaps it took longer to get off the ground, so less time climbing to 500 feet. My position was further away from the starting point. It was obvious that the time spent climbing to 500 feet was less with 0° flaps, but if you were trying to clear an obstacle 15° flaps was a better option. A person would need to measure climb rate, distance , and time to determine if more than 15° flaps yields a better option for obstacle clearance.

Agreed, I was talking best rate and not best angle.

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To anyone thinking about trying this, just be aware that once you break ground, you’ll need to either have substantial down elevator trim or be ready to push the stick forward to allow it to accelerate.  Get the feel at altitude first. 

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Anyone know how much altitude drop you get transitioning from 30 to 15 degrees?  

I ask to see if you recommend a particular airspeed or elevation before taking out the flaps.

I know the POH says there's a 150' drop with flap changes but I just haven't seen that transitioning from 15 to 0.

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10 minutes ago, okent said:

Anyone know how much altitude drop you get transitioning from 30 to 15 degrees?  

I ask to see if you recommend a particular airspeed or elevation before taking out the flaps.

I know the POH says there's a 150' drop with flap changes but I just haven't seen that transitioning from 15 to 0.

If you go to near max speed at 30° (62kt) and pitch up a bit as you change flap settings, you can keep the loss to zero.  You'll need a higher AoA at that speed for the new flap setting to avoid a small sink, which is why you have to pitch up.  You have to then wait for the airplane to accelerate a bit to resume a decent climb.

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You can move the flaps from 35 to 15 even at 50 knots and pitch up to avoid any altitude loss with a little practice. There’s still plenty of margin above stall.  Just pitch to maintain level flight and let it accelerate to Vx or Vy, then continue the climb. Try it at altitude first. 

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Just now, John Vance said:

You can move the flaps from 35 to 15 even at 50 knots and pitch up to avoid any altitude loss with a little practice. There’s still plenty of margin above stall.  Just pitch to maintain level flight and let it accelerate to Vx or Vy, then continue the climb. Try it at altitude first. 

You sure can.  The reason I suggested getting the speed up is the slower you are, the more induced drag occurs from the wing being at higher AoA.  At 50kt the airplane will not want to accelerate very quickly if you are trying to climb out...

 

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