Short field takeoff

[Ulysse]

I cannot see any mention of a short field takeoff procedure in the POH.

How do you handle this ? (brake ON, full power then release ? Cannot it harm the engine/turbo ?)

[exM20K]

It won’t hurt the power plant, but the prop may pick up more pebbles and twigs.  Fewer, though, than would hit the prop if you don’t clear the trees at the end.

there is a bit of lag, mechanical and pilot-induced, to attaining full power, so holding the brakes and running up full-ish power does make a difference.  Try it both ways and report back.

-dan

[Fly Boomer]

9 minutes ago, exM20K said:

Fewer, though, than would hit the prop if you don’t clear the trees at the end.

Ha!  Made me laugh out loud.  Thanks.

[Hank]

7 hours ago, Ulysse said:

I cannot see any mention of a short field takeoff procedure in the POH.

How do you handle this ? (brake ON, full power then release ? Cannot it harm the engine/turbo ?)

The shortest field I've taken my Mooney to was 2000' grass. My limit was 2 people and half tanks, one end was obstructed by a large gravel pile for a cement plant.

Even when departing towards the gravel pile, I didn't go to full power and pop the brakes. Never had any issues. 

But my C doesn't have a turbo.

[steingar]

70% take off speed by midfield, otherwise abort.  Watch for gopher holes, wet spots, gremlins.

[PT20J]

48 minutes ago, steingar said:

70% take off speed by midfield, otherwise abort.  Watch for gopher holes, wet spots, gremlins.

Be a little careful with this. I did the math years ago and this ensures that you will break ground by the end of the runway (barely, no wind, no slope) but if there are any obstacles nearby they they need to be taken into consideration. 

[PT20J]

You can consider that the published performance numbers are short field because Mooney was undoubtedly trying to demonstrate the lowest numbers possible. Thrust is greatest at zero forward speed, so there is a slight advantage to holding the brakes while the engine comes up to full power.

Skip

[kortopates]

FAA Short Field numbers (Vspeeds) = POH Maximum Performance Takeoff & Climb (Vspeeds)

[Shadrach]

As has been mentioned above, all POH take off data was likely performed with the goal of attaining the shortest takeoff numbers. There is no "Short field" procedure.  The internet is full of debates about rolling take offs vs full power brake release take offs.  I think that if the differences between the two seem important, than you likely landed somewhere you shouldn't have.  I personally only do a full power brake release if the runway entrance is at an awkward angle or requires a back taxi. My sense is that in most cases, rolling from taxiway to runway briskly while advancing to max power yields max performance.  A portion of the prop is stalled when full power and stationary so that power is being converted to turbulence, not thrust.  Prop blade AOA decreases with motion and prop efficiency improves.  I think high power/brake release takeoffs create more noise than performance.

The "this much speed by this percentage of runway" can bite.  Better to look at "this much speed by this percentage of expected take off point'.  Calculate your numbers and add at least 30% margin for not being a factory test pilot in a new airplane. The 231POH has a slightly confusing performance graph but it offers a lot of information once you figure it out. 70% of take off speed halfway before calculated take off point might be useful initially, but most of us know if our plane is accelerating as it should.  I think it's more important to be ready to abort early if things appear to be at all questionable. wait too long and all remaining options involve a pooch... I have done a lot of flying out of <2000' fields.  Arrivals are more concerning than departures.  Build in the margin: Light airplane, cool weather, reasonable DA.

Edited May 4, 2022 by Shadrach

[skydvrboy]

I do a rolling start from the taxiway or the 90 degree point if there is no taxiway, which definitely reduces takeoff distance. Additionally, it’s important to get your gear up as soon as you know you’re not going to settle back to the runway and accelerate in ground effect to Vx.  

Most will tell you to clear the trees before raising flaps which is a good idea but Max performance is attained by raising flaps while still in ground effect.  The risk is settling when you raise flaps and I don’t think the minimal performance gain is worth the prop strike risk.

[BDPetersen]

I thought it was long ago established that with brakes set and full power, the cavitating prop really doesn’t become fully effective until forward motion allows it to move out of its own turbulence. In other words, little or no advantage over a smooth but prompt application of power with brakes released or a rolling entry to runway as noted. Maybe if the mixture needs to be tweaked at higher elevations the full power run up could be justified. Otherwise it is just for show. But so cool. Just like Doolittle.

[Shadrach]

15 hours ago, skydvrboy said:

I do a rolling start from the taxiway or the 90 degree point if there is no taxiway, which definitely reduces takeoff distance. Additionally, it’s important to get your gear up as soon as you know you’re not going to settle back to the runway and accelerate in ground effect to Vx.  

Most will tell you to clear the trees before raising flaps which is a good idea but Max performance is attained by raising flaps while still in ground effect.  The risk is settling when you raise flaps and I don’t think the minimal performance gain is worth the prop strike risk.

I cannot envision a scenario where raising flaps in ground effect really comes into play. Even with abysmal performance the plane should be out of ground effect  in ~5 seconds.  If a pilot is playing “let’s hang out in ground effect and see if we can climb before the end of the runway” game, raising flaps is the least of their problems.

[Fly Boomer]

19 hours ago, Shadrach said:

if the differences between the two seems important, than you likely landed somewhere you shouldn't have.
...
abort early if things appear to be at all questionable. wait too long and all remaining options involve a pooch..

Another laugh out loud observation, and good advice.  Thank you.

[201er]

50 minutes ago, Shadrach said:

I cannot envision a scenario where raising flaps in ground effect really comes into play. Even with abysmal performance the plane should be out of ground effect  in ~5 seconds.  If a pilot is playing “let’s hang out in ground effect and see if we can climb before the end of the runway” game, raising flaps is the least of their problems.

Actually I'd imagine that raising flaps in ground effect would worsen climb over obstacle performance both through a momentary loss of lift during retraction and increasing the stall speed, climb speed, and Vx.

[PeteMc]

1 hour ago, BDPetersen said:

I thought it was long ago established that with brakes set and full power, the cavitating prop really doesn’t become fully effective until forward motion allows it to move out of its own turbulence.

I hadn't seen anything on not running up with the brakes as being faster/better.  Is there documentation?

It would also be interesting to see if there's anything on continuing the roll from the taxiway too.  I don't usually like to go into any kind of high speed 90 dgr turn, so my taxi speed would still be relatively slow and wonder if that little amount would make a difference.  Shortest field I typically go into is KBID @2502', but it's almost always on the runway that requires a back taxi.

 

[Shadrach]

3 minutes ago, 201er said:

Actually I'd imagine that raising flaps in ground effect would worsen climb over obstacle performance both through a momentary loss of lift during retraction and increasing the stall speed, climb speed, and Vx.

I can’t say for sure, but my WAG is that a clean airplane climbs better, faster and sooner under all scenarios excepting the aforementioned “not enough lift to climb out of ground effect” situation.

If you’re at Vx with TO flaps, raising them would allow the power that is being used to overcome the drag of the flaps to be used for additional climb or additional speed.

[PT20J]

1 hour ago, BDPetersen said:

I thought it was long ago established that with brakes set and full power, the cavitating prop really doesn’t become fully effective until forward motion allows it to move out of its own turbulence. In other words, little or no advantage over a smooth but prompt application of power with brakes released or a rolling entry to runway as noted. Maybe if the mixture needs to be tweaked at higher elevations the full power run up could be justified. Otherwise it is just for show. But so cool. Just like Doolittle.

Cavitation, as in boat propellers, is due to the propeller inducing a local pressure low enough to cause a phase change in the water from liquid to gas. Air, already being a gas, cannot cavitate.

Maximum thrust is produced at full power with the airplane stopped, and thus maximum acceleration occurs at brake release. 

Skip

[BDPetersen]

Interesting. My recollection, flawed as it may be, was a serious analysis several decades ago determining the premise I offered to be the case. Are not air and water both fluids ?

[PT20J]

40 minutes ago, BDPetersen said:

Interesting. My recollection, flawed as it may be, was a serious analysis several decades ago determining the premise I offered to be the case. Are not air and water both fluids ?

They are both fluids, but water is a liquid and air is a gas. Cavitation occurs in water when pockets of fluid change from a liquid to a gaseous state due to localized pressure reduction. But air is already a gas and does undergo a similar state change.

[T. Peterson]

3 hours ago, Shadrach said:

I can’t say for sure, but my WAG is that a clean airplane climbs better, faster and sooner under all scenarios excepting the aforementioned “not enough lift to climb out of ground effect” situation.

If you’re at Vx with TO flaps, raising them would allow the power that is being used to overcome the drag of the flaps to be used for additional climb or additional speed.

I don’t have the ability to describe things in the technical terms of which  many of you are capable, but in my simple mind, flaps enable me to use a shorter runway but the cost is decreased climb performance. As you stated, the best climb performance is a clean wing but requires a longer runway and reduced abort options. Higher takeoff speed probably also increases tire wear and possibly other negatives of which I am unaware. Of course V1 and V2 considerations are paramount in the twin jet world.

 I think the gentleman advocating raising flaps in ground effect is attempting to take advantage of both optimums, but I rather agree with the fellow that said if you’re attempting that you probably landed somewhere you should not.

Torrey

[Shadrach]

27 minutes ago, T. Peterson said:

I don’t have the ability to describe things in the technical terms of which  many of you are capable, but in my simple mind, flaps enable me to use a shorter runway but the cost is decreased climb performance. As you stated, the best climb performance is a clean wing but requires a longer runway and reduced abort options. Higher takeoff speed probably also increases tire wear and possibly other negatives of which I am unaware. Of course V1 and V2 considerations are paramount in the twin jet world.

 I think the gentleman advocating raising flaps in ground effect is attempting to take advantage of both optimums, but I rather agree with the fellow that said if you’re attempting that you probably landed somewhere you should not.

Torrey

I agree with you. I always use flaps on takeoff. Not only does it enable shorter take off rolls, I think it makes for a much more positive transition to flight. However once airborne with positive rate the flaps come up right after the gear 

Edited May 4, 2022 by Shadrach

[BDPetersen]

Well I see only 1 way to settle this. I challenge thee to a drag race! You hold the brakes and run up, I will leave the brakes off and promptly apply power.

[skydvrboy]

I don't know about the rest of you, but my POH clearly states in two places that best angle of climb is gear up, flaps up.  Basically short field takeoffs are an exercise in drag reduction.  You want to minimize rolling resistance drag, wingtip vortex drag, gear drag, and flap drag.  So, get off the runway as soon as possible, accelerate in ground effect, and get your gear and flaps up as soon as it's safe.

How short the runway is determines how closely you have to follow the best performance procedure.  When you are at full gross and the runway is under 2000' you need every advantage you can get.  According to my POH ('67F model), at 5000' elevation, 80 degrees, and gross weight, takeoff roll is only 1560' and distance to clear a 50' obstacle is 2395'.  My guess is you have to take advantage of all of the above to duplicate those numbers.

[A64Pilot]

I’ve done a lot of flight testing getting a heavy crop duster off the ground and to 50’ in as short a distance as possible, and being very precisely measured via a transit on the roof of the plant.

In my testing full brakes and max power before brake release and or leaving the flaps up for decreased drag until just before takeoff and pumping the tires up to high pressure pretty much were all rounding errors, sure you could argue a few feet possibly, but it wasn’t enough to be significant, neither did forcing the tail to come up under the theory of putting thrust horizontal, which equates to us holding back pressure before rotation.

The difference between all of the tricks being employed and simply having the aircraft trimmed properly and it flying off all by itself was minimal. It’s very possible to drag an airplane into the air at such a slow airspeed that it’s difficult for it to climb out of ground effect, which by the way is equal to wing length

I also used to do a whole lot of off airport flying in my Maule landing on river banks and pastures etc.

We all want to think by using our superior skills and techniques like snatching full flaps on manual flap airplanes just at rotation will make a big difference, but it doesn’t really.

Within reason do what your used to and can maintain control. with the possible exception of taxiing to the very end of the runway.

Soft field of course is different.

There is an AC that specifies how exactly in flight testing to do takeoff testing now that wasn’t in effect when most of our aircraft were built. the old way had you horsing the thing to 50’ and if you did it right you pretty much stalled at 50’ meaning of course that’s as high as you can get without increasing airspeed, but it was the shortest distance possible to 50’. Not very realistic so that’s why the AC came about.

Edited May 5, 2022 by A64Pilot

[carusoam]

Some of these things are goofy ideas….

They sound really good until you try them…

The goofiness proves itself nearly immediately…. 

 

Many of the things that don’t work… actually require a lot of practice…. To prove they don’t work… 

Fortunately… We have an App called CloudAhoy… combined with a WAAS source… we can actually measure our machines and skills….

In the flap/no flap arena… the plane with flaps is off the ground before the plane without… a function of the reduced stall speed…

So… waiting to start the improved climb may not make a lot of sense…. 
 

Use a long runway… collect your data… and show it here…

Non-WAAS sources need not apply… their accuracy will be really disappointing for this exercise…

PP thoughts only, not a mechanic or CFI…

Best regards,

-a-