Flap assisted take off

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Re: Flap assisted take off

Postby Joe Moilanen » Sat Jan 30, 2021 11:33 pm

I have a 650' airstrip at my house that I fly my 170B out of. There is only one feasible direction to take off, because of the downhill slope. there is also trees 300' from the departure end of the strip. I have tried both methods, starting with 20 degrees of flaps and grabbing 20 degrees right at rotation. I clear the trees by more feet when grabbing 20 degrees at rotation. An aspect that I don't think I've seen mentioned in this discussion is: How much propeller propulsion is blanked out by the extended flaps during takeoff roll?? My strip is very hard surfaced and I keep the grass mowed super short. When I takeoff from tall grass strips or strips that are mushy, I start out with 20 degrees to lighten my footprint for better acceleration. Perhaps the extended flaps are interfering with maximum available propulsion? Just an idea.....Jughead?

I have some interesting videos of taking off and landing on my strip if I could figure out how to convert and upload them. I think the one of me landing is an MP4. Maybe I could email it to someone who knows more about video editing etc.

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Re: Flap assisted take off

Postby c170b53 » Sun Jan 31, 2021 12:20 am

Jughead, you are the person I thought of writing the my first sentence.

The rest if my comments pertain to the group I described in my second sentence.

And then there is the rest of us.

i knew what you meant Bruce in your first sentence, when I first read it and I knew what you meant in “ the rest of us “
You were thinking about me,
Thanks D :) :) :)
I enjoyed watching the STOL competitors at Oshkosh and could only wish I had the time to devote to acquire that skill level. I might be in another group as in the rest of the rest of us, those needing just a basic tune up.
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Re: Flap assisted take off

Postby counsellj » Sun Jan 31, 2021 1:00 am

Bruce I knew what you meant.

George, Good discussion. To help keep stuff straight. I formatted my answers to some of your statements or questions in blue.

"I agree ...when it comes to producing flying videos." I don't use techniques, because I produce videos. I produce videos that happen to capture the techniques I use in my daily flying. “But anyone who’s seen Bruce’s demos at Petit Jean will not soon place a money-bet against him.” I didn’t see that, too bad you didn’t produce a flying video about it. Haha. And although not what I’d call “current” in proficiency (more important than ad-hoc personal techniques) ... I’m no stranger to short/rough and “off-airport” operations having spent thousands of hours landing on pipeline right-of-ways, oil-field roads, and Mississippi-Delta levees in my pipeline days.

Jughead, the suggestion to “meet...at a short, rough off-airport... demonstrate how their techniques are better”. ... as you know is not likely to happen....not because it wouldn’t be fun and informative...but because it would require we all use the SAME AIRPLANE under exact same conditions. ...and that is not likely either. I wasn’t talking about comparing different airplanes, I was referring to comparing different techniques in real world, critical situations with your airplane if you are so sure your technique is best.


As you wrote, WEIGHT has a lot to do with successfully operating off short/rough/unimproved fields. Leaving the unnecessary 200-300 lbs of stuff on the ground makes a standard 170 a nice short-field airplane. Even at GROSS weight, I can be airborne in approx. 1,000.’ “And having the “right” propeller subtracts hundreds off the factory distances.” Regardless of what propeller is being used, getting the airplane off the ground as early as possible for any specific prop/powerplant is a function of AOA management and technique.

“The STOL-demo guys you praised are using specialized equipment and are practiced / proficient-in-the-extreme at this... They are NOT operating the typical “fleet” Cessna 170s and their narrow techniques do not apply to those pilots who do”.


They absolutely are operating “typical fleet 170’s. I know of only 1 specialized STOL 170; All the rest are representative of a great many 170’s. Some have 180HP/STOL Cuffs/big gear, others are 100% stock and we see competitors with everything in between. But regardless of their configuration, they all benefit from the same techniques or pulling flaps to minimize takeoff roll. They are more practiced, but so can anyone else.

I’m not saying popping the flaps is the best technique all the time. I don’t use it at really high DA or with really soft, wet, snow surfaces or in tall grass. But for the majority of situations, it will get you airborne at the slowest possible speed.

AOPA recently did a video showing the “book” techniques on a 185 I think it was. They are easy and effective, but nowhere near the optimum answer.


Jughead

Mod note. Edited to clear coding only. No wording was changed- Bruce
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Re: Flap assisted take off

Postby GAHorn » Sun Jan 31, 2021 3:28 am

counsellj wrote:. Even at GROSS weight, I can be airborne in approx. 1,000.’ “ [/color]

Jughead


According to the Cessna B-model Owners Manual getting airborne in approx 1,000’ ... is not all that good, Jughead.

Factory Data states At gross weight, standard day, standard factory techniques.... it only takes 728’ to be airborne.

If you use the factory recommended technique and 20-degrees of flaps.... you’ll be airborne in 618’. :wink:
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Re: Flap assisted take off

Postby Ryan Smith » Sun Jan 31, 2021 4:34 am

Interesting that this should come up, because I did a little experiment a few nights ago with dad.

My airplane is a stock ‘52. 1205 pounds per the last W&B, bone stock airplane with a 76x53 prop and 6.00x6 tires. I can count on one hand the number of STCs this airplane has with fingers remaining.

I don’t have a 10° flap ratchet, so 20° is the first notch for me. 20° of flap increases downwash on the tail substantially and the tail will rise before the ASI indicates. A “two potato” count and then pulling 40° of flap as I rotate will get me off the ground consistently in 350-400 feet with nil wind, smooth runway, around 1800 pounds close to a standard day at 822 foot field elevation.

“Book” technique yields a 600 takeoff run with the same conditions, literally the very next takeoff. The STOL competition technique is valid and works well, and I use it often. I have zero desire to put any larger tires on my airplane than are on there now, and I’m passively working to get my wheelpants repaired to put them on the airplane after being off since 1979.

I’m not a big backcountry pilot; as a matter of fact, I roll my eyes at a lot of them because it’s a fad and quite frankly, they can be a little obnoxious. That said, I respect a lot of their flying abilities, particularly Jon’s because of what he’s getting out of the setup he chooses to use. He’s a wonderful steward for the sport and balances out the other noise and errata.

These techniques have their place. I HAD to use this when I was departing from a very soft grass strip a couple of years ago while I was airport hopping with Dad. I wanted to get up and get OFF the ground because it was so slick and soft that I was having trouble maintaining directional control and any brake usage would lock the wheel up and it would sink.
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Re: Flap assisted take off

Postby TFA170 » Sun Jan 31, 2021 3:20 pm

Something that seems to be dismissed, especially when discussing raising the tail vs letting it fly off is surface and rolling resistance. While it is 100% factual to state that all of the weight will be transferred to the mains instead of shared with the tailwheel, physics alone should tell you that the rolling resistance of a larger diameter wheel will always be less than that of a smaller diameter wheel. This translates into more of your thrust going to acceleration. Consequently, it's not a simple linear transfer of resistance where there is no net gain.

This doesn't even begin to take into account very wet, muddy, snowy, or otherwise sloppy surfaces where the tail wheel acts more like a skid than a wheel.

Add in larger diameter tires than original, and this function becomes exponentially better because leverage is not linear either.

Another aspect is that often the purpose of "popping" flaps is acceleration in ground effect vs an immediate Vx climb. The goal is simply to get off the ground, lower the nose, accelerate in ground effect where induced drag is less, and then climb - more like soft field technique, but getting off sooner via 'popping"
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Re: Flap assisted take off

Postby GAHorn » Sun Jan 31, 2021 6:15 pm

If the idea is to get up out of a muddy or high-grass strip....Wouldn’t it be logical to think that deployed-flaps begin to take weight off-wheels earlier in the acceleration..?? Whereas “popping flaps” does not lift weight off-wheels until the “pop”...?? (and meanwhile, forcing the tail in the air early adds drag due to the earlier shift of weight onto the main wheels.)

“Popping” flaps requires simultaneous rotation with “up-elevator: to “pop” the airplane up into the air. If the flaps had already been-deployed, the airplane would already be lighter-on-it’s-wheels and the application of “up-elevator” would therefore be even more effective. :wink:

I’m inclined to believe that popping-flaps is merely more dramatic and therefore gives a (false) impression.

And here’s an entirely different micrometer to measure-by.... A takeoff will be shorter at the equator than at the poles (with a standard atmosphere.)
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Postby counsellj » Sun Jan 31, 2021 11:11 pm

George Wrote: "If the idea is to get up out of a muddy or high-grass strip....Wouldn’t it be logical to think that deployed-flaps begin to take weight off-wheels earlier in the acceleration..?? Whereas “popping flaps” does not lift weight off-wheels until the “pop”...?? (and meanwhile, forcing the tail in the air early adds drag due to the earlier shift of weight onto the main wheels.)"

George, do you even read what people write in the replies, before arguing with them? Several people has explained using the "deployed flaps" in those situations already.

Joe wrote "When I takeoff from tall grass strips or strips that are mushy, I start out with 20 degrees to lighten my footprint for better acceleration. "

I wrote: "I’m not saying popping the flaps is the best technique all the time. I don’t use it at really high DA or with really soft, wet, snow surfaces or in tall grass.

TFA170 wrote: "This doesn't even begin to take into account very wet, muddy, snowy, or otherwise sloppy surfaces where the tail wheel acts more like a skid than a wheel.

Add in larger diameter tires than original, and this function becomes exponentially better because leverage is not linear either."
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Re:

Postby GAHorn » Mon Feb 01, 2021 3:01 am

counsellj wrote:
George, do you even read what people write in the replies, before arguing with them? Several people has explained using the "deployed flaps" in those situations already.

."


I didn’t realize it was an “argument”. I thought it was a discussion.
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Re: Re:

Postby counsellj » Mon Feb 01, 2021 3:23 am

GAHorn wrote:
counsellj wrote:
George, do you even read what people write in the replies, before arguing with them? Several people has explained using the "deployed flaps" in those situations already.

."


I didn’t realize it was an “argument”. I thought it was a discussion.


Well George. You aren't reading or comprehending what others said three times, so you tell me what it is.
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Re: Re:

Postby GAHorn » Mon Feb 01, 2021 3:28 am

counsellj wrote:
GAHorn wrote:
counsellj wrote:
George, do you even read what people write in the replies, before arguing with them? Several people has explained using the "deployed flaps" in those situations already.

."


I didn’t realize it was an “argument”. I thought it was a discussion.


Well George. You aren't reading or comprehending what others said three times, so you tell me what it is.

It’s what you make it Jughead. I know what I meant.
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Re: Flap assisted take off

Postby bgiesbrecht » Mon Feb 01, 2021 6:02 am

GAHorn wrote:“Popping” flaps requires simultaneous rotation with “up-elevator: to “pop” the airplane up into the air.


No, it does not. In my experience, I actually have to put a bit nose down if I want to stay in ground effect after popping the flaps. The pop alone lifts me off. There is no traditional "rotation" at the same time as popping the flaps.
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Re: Flap assisted take off

Postby GAHorn » Mon Feb 01, 2021 2:58 pm

bgiesbrecht wrote:
GAHorn wrote:“Popping” flaps requires simultaneous rotation with “up-elevator: to “pop” the airplane up into the air.


No, it does not. In my experience, I actually have to put a bit nose down if I want to stay in ground effect after popping the flaps. The pop alone lifts me off. There is no traditional "rotation" at the same time as popping the flaps.


Yeah, I poorly-described that action. The application of flaps creates/increases a “downwash” of relative wind in front of the horizontal stabilizer, which in-turn increases the effectiveness (downward-lift) of the stab/elevator, resulting in a natural increased AOA of the wing that mimics a rotation.
(BTW, this also assists the natural rise of the tail in a neutral-elevator takeoff.)

The nose-down input you instinctively apply counters the overreaction of that downwash. The effect of popping/deploying flaps also shifts the C/L aft which helps somewhat at that moment (but which already exists in a deployed-flap takeoff technique.)
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Re: Flap assisted take off

Postby ghostflyer » Mon Feb 01, 2021 11:05 pm

Firstly I am no expert pilot , engineering is my forte but saying that I do a lot of take offs and landings in soft sand on beaches or marsh land . I have watched and listen to the experts and tried many methods . I have found the best way for me and the aircraft is to have the best take off in the above mention conditions its to have 10deg of flap and get the tail up ASAP due to it being a brake in the sand . It’s different when landing ,tail down and control column back . My wheel size is 8.00 by 6 and running about 18psi . The best tool for stol take off is GRUNT . That means plenty of pony power. It doesn’t matter what type of engine you are running it’s got to be in a good condition. Correctly timed ,no induction leaks ,baffles working as they should and the carby set up correctly and the right type fitted . Plus ignition leads in good condition as this is when they break down under load . I do not know how many aircraft that come through the shop where ignition timing is incorrect [bad points gap etc etc .] or something has been neglected.
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Re: Flap assisted take off

Postby Metal Master » Tue Feb 02, 2021 6:21 am

Flap Assisted Takeoff.
In my mountain flying training taught by a CFII MEI MFI 20 years ago, one of the things he showed me (he having been an engineering test pilot that worked at Edwards Air Force Base as an engineering test pilot and flew with Paul Bikle as a glider and test pilot, 90 years old now) was that on almost any airplane if you pull the aileron down to its maximum deflection that that deflection is the most deflected a control surface can be on that airfoil at the point where boundary layer separation does not occur and thus the stall. That this is the point where any further deflection starts causing drag beyond the maximum lift (thus creating more drag than lift) that that airfoil can create at any given airspeed. And thus, for short field operations with flaps deployed or popping the flaps you do not want to deploy them beyond this point where the flap deflection is equal to the maximum aileron down deflection. Generally, between 10 and 20 degrees.
“Stalls depend only on angle of attack, not airspeed. However, the slower an aircraft flies, the greater the angle of attack it needs to produce lift equal to the aircraft's weight. As the speed decreases further, at some point this angle will be equal to the critical (stall) angle of attack.”
Thus less weight = a higher angle of attack you can achieve without the stall. This is beyond the published performance data being at gross weight. Which is a safety margin.
Experience and education teach me that Stall speed decreases in ground affect within one wingspan of the ground, thus in landing I can fly well below the bottom of the green arc indicated airspeed as I approach the ground on very a short final, but I do not decrease speed below the green arc that I can see. I am flying by sight picture then. Landing slow and soft three point. I do not like playing with this in the climb. And once clear of the ground in takeoff whether I pop the flaps or take off with 10 to 20 Degrees in my 170A I like to accelerate in ground affect. Obstacles taken into consideration. I push the nose over and I accelerate in ground affect.
Generally you can land shorter than you can take off.
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