Short Field Takeoffs

[EdFred]

Good thing there is an index to your post Opus, so I may read an reflect.

Well, if you think about it, it's much easier to accellerate something that's already moving vs something that's already stopped. So why would the FAA reccommend the least efficient model when it concerns getting off the ground in the least amount of distance. My guess: Because they are idiots.

 

[Clark1961]

Maybe MOI was the wrong term, but more the accelleration of something from a dead stop vs something already moving.

Okay, that I can deal with. Any of the aero knuckle-draggers on the board have an online reference to rates of acceleration for GA aircraft on the departure roll? From the tail dragger thread it's obvious that the rates will vary depending on aircraft configuration but if there is some generalized info it'd be nice to peruse it.

 

[dmccormack]

Well, if you think about it, it's much easier to accellerate something that's already moving vs something that's already stopped. So why would the FAA reccommend the least efficient model when it concerns getting off the ground in the least amount of distance. My guess: Because they are idiots.

Maybe. But my guess is they want the DE to be able to adequately evaluate a examinee.

If he/she places the airplane at the very end of the usable runway, runs the engine to full throttle, holds the brakes, and confirms everything's a go -- that can be objectively evaluated by every DE in every PTS given.

If instead they suggested a rolling start on a short field (which should be a soft as well -- shouldn't be two tasks, but I digress....) there would be lots of subjective -- How fast should the turn be taken? How much runway is now behind that was unused?

All this uncertainty while also placing DEs in a fairly precarious position (42 hour student pilot with a grand total of 10 tries at this rolling turn takeoff thing)

 

[dmccormack]

From the tail dragger thread it's obvious that the rates will vary depending on aircraft configuration but if there is some generalized info it'd be nice to peruse it.

..and conditions (wet grass, long grass, hot pavement, cold air, warm dry air, warm moist air....)

 

[EdFred]

So the reason CFI's teach for testing is because the FAA sets it up that way, and doesn't actually use their collective noggins. And we wonder why some bad habits get passed down the generations of CFIs.

 

[dmccormack]

So the reason CFI's teach for testing is because the FAA sets it up that way, and doesn't actually use their collective noggins. And we wonder why some bad habits get passed down the generations of CFIs.

Not really. I just explained it to you as I would to students.

There is the test, and there is flying, and the two sometimes deviate.

 

[EdFred]

Not really. I just explained it to you as I would to students.

There is the test, and there is flying, and the two sometimes deviate.

I believe they shouldn't deviate. It's also why I run into idiot engineers. Classroom != real world.

 

[dmccormack]

I believe they shouldn't deviate. It's also why I run into idiot engineers. Classroom != real world.

I prefer to think that mastery precedes art.

 

[Clark1961]

I believe they shouldn't deviate. It's also why I run into idiot engineers. Classroom != real world.

That's a funny one.:smile:

I happened to be reviewing some basic info recruiting folks to join my engineering discipline. It noted that some of the highest SAT scores on campus would be in this major. I immediately thought to myself, "maybe that's why there are so many arrogant SOB's in the industry."

Once I get past the attitudes the question becomes, "How do we teach smart people that other folks are smart too?" After all, "we" are nearly always smarter than "me."

 

[EdFred]

That's a funny one.:smile:

I happened to be reviewing some basic info recruiting folks to join my engineering discipline. It noted that some of the highest SAT scores on campus would be in this major. I immediately thought to myself, "maybe that's why there are so many arrogant SOB's in the industry."

Once I get past the attitudes the question becomes, "How do we teach smart people that other folks are smart too?" After all, "we" are nearly always smarter than "me."

I am surprised at how many absolutely basic chemistry lessons I have to give to the engineers I deal with in business.

 

[poadeleted20]

The procedure in the POH was developed through flight testing by the factory test pilots. While you may feel you have a better method, until you conduct a full range of flight test under sufficiently controlled conditions, you don't know whether it really is better or not. I'll stick with the book procedures, thank you.

 

[Ted]

I believe they shouldn't deviate. It's also why I run into idiot engineers. Classroom != real world.

We live in the same world. I'm just an insider.

 

[EdFred]

The procedure in the POH was developed through flight testing by the factory test pilots. While you may feel you have a better method, until you conduct a full range of flight test under sufficiently controlled conditions, you don't know whether it really is better or not. I'll stick with the book procedures, thany you.

Yeah, I forgot that you never like to question anyone above you. Why try and improve on something? Better to just wallow in mediocrity.

 

[steingar]

The procedure in the POH was developed through flight testing by the factory test pilots. While you may feel you have a better method, until you conduct a full range of flight test under sufficiently controlled conditions, you don't know whether it really is better or not. I'll stick with the book procedures, thank you.

I'll always believe a pilot who routinely flies out of short unimproved strips over unknown factory test pilots flying unknown strips. I don't know who's way is better, but I have seen plenty of nonsense promulgated by the FAA in the form of regulations in other arenas of aviation.

 

[jesse]

The procedure in the POH was developed through flight testing by the factory test pilots. While you may feel you have a better method, until you conduct a full range of flight test under sufficiently controlled conditions, you don't know whether it really is better or not. I'll stick with the book procedures, thany you.

Yeah, I forgot that you never like to question anyone above you. Why try and improve on something? Better to just wallow in mediocrity.

Like I've said before, it's mostly an issue of providing performance numbers that can be REPEATED. If you're taking a runway with varying levels of energy there is simply no way you can graph that. Since you can't graph that you certainly cannot provide information indicating how long the take-off roll will be.

Starting from a complete stop is a known condition that can be easily reproduced and data can be based on.

 

[gismo]

If you're not making proper rpm or oil pressure, there's no sense in beginning the takeoff...I'm not suggesting NOT checking after brake release, but why even start a takeoff that you know you can't complete?

I was actually objecting to the idea that a full power runnup with brakes was necessary to check the engine.

 

[Trapper John]

Why try and improve on something?

Improve on what exactly? Beating the book figures? Because you just want to, or you have to?

Maybe I'm missing something here, but before I land somewhere, I figure out if I can get back out first. And I add some margin over book, because I figure what I'm flying is old and not perfect like the test plane, nor am I as good as the factory test pilot. I guess if that makes me mediocre, so be it, but I haven't crunched anything yet either.


Trapper John

 

[gismo]

All good points -- but it depends on the field. All the grass fields around here (just west of the Alleghenies) are rough (and get rougher in late summer, early fall).

East of Blue Mountain, the grass fields are pillow soft.

Side load can be increased dramatically when any retractable hits a groundhog hole. The Bo gera is tough, no doubt, but it's meant to collapse in and up -- in the same direction the load will be pushing in a fast turn.

Certainly there is a line between use and abuse and drifting an airplane (any airplane, not just a Bonanza) sideways into a chuckhole doesn't bode well for the gear's longevity. Then again, the Bo gear has a substantial downlock created by an over-center folding arm that provides a very strong support for side loads. I'd be surprised if you could get one to fold with a side load without tearing the tire off the rim and/or breaking the wheel. I wouldn't want to slide one into a deep hole but I wouldn't want to do that in a fixed gear Cessna either.

The Bonanzas I've flown have been the '47 -35 and a 1980 A36 with tip tanks. On both I was warned about fuel unporting. The E-185 had a strange fuel return setup that returned surplus fuel from the carb to the left tank. Thus all takeoffs were done with fuel on Left.

FWIW, I owned a E225 powered '54 E35 for many years and am pretty familiar with their fuel system. You are correct that the carbureted Bonanza models always pass the return flow into the left main tank regardless of the selected fuel source. Later models with fuel injection came with a more complicated fuel selector that diverted the return fuel to the right or left main because the injection system flowed as much as 10gph in the return line (compared to a max of 3gph for the carb).

But that's only an issue if the left main tank is full in which case it's impossible to unport. So the complete answer for a turning takeoff (or slipping landing) is to select the inside (or high one for a slip) unless the left main was within a few gallons of full capacity where you'd go with that one regardless of which might unport. For the injected Bonanzas (with the exception of an airplane that was converted from carb to injection) you can use the same selection procedure or just always go with the high/inside tank.

 

[bobmrg]

Well, if you think about it, it's much easier to accellerate something that's already moving vs something that's already stopped. So why would the FAA reccommend the least efficient model when it concerns getting off the ground in the least amount of distance. My guess: Because they are idiots.

Uhhhh....my post didn't say anything about the FAA but quoted the manufacturer's recommendation. How is it that your knowledge of aerodynamics exceeds that of the folks who design and build airplanes?

Bob Gardner

 

[poadeleted20]

Yeah, I forgot that you never like to question anyone above you. Why try and improve on something? Better to just wallow in mediocrity.

All I said was until you run the full test series under controlled, you don't know your method is better. That's a fact I'll stand by over the suggestion that following the book procedure is "wallowing in mediocrity." So I'll follow the book procedure until someone proves theirs is better, and I hardly think that makes me a "mediocre" pilot.

 

[el con]

I think there are some considerations that make me question the "rules".
First ,if you are on short field or are just attempting a short field T.O. and you must stop at the longest point ,apply full brakes, run engine to check for maximum power output , why is it then ok by the "rules" to T.O. from that same airfield when maybe it's soft now because it rained ,now keeping it rolling. The FAA did'nt just magically make the field longer. Would the engine now run better or decide to produce more power now that the field is wet?
I am not a CFI, so no one should attempt this, but some Authorized "test pilot" might want to do a good run up following all procedures to maximize power,considering prop position,carb lean (for conditions),consider temp.Alt. density etc., tires to proper inflation,etc.,etc, then using modern science and logic, keep the aircraft moving (not losing momentum) ,swing as wide as you can and keeping it as long as you can,accelerate maximum through the turn ( without overly side loading the gear) keep the flaps out till you want to lift off ( avoiding flap drag up to that point( physics again)) pop it in the air and either run in ground affect until you must clear an object or maximise your departure trajectory at an acceptable flying speed ( you know that Vx ,Vy stuff.
It seems like the "rules" or the "book" don't take into consideration that the take off may be a combination of many things.
They both seem to deviate and that modern science or physics are constant and should be taken advantage of at all times. Those who stopped to develop full power may not have walked the field thoroughly enough to see the soft area down field from their starting point.
All the FAA rules have merit and the POH has merit, I would think one would want to use all available knowledge to one's advantage both old way and maybe new better way.
My plane was built in 1972, it's hard for me to fathom there isn't something that couldn't be improved upon concerning procedure in 38 years.
Just IMHO.
The Wright brothers flew, I'm glad I'm not following their procedures today.

 

[dmccormack]

If you're taking off from a field so short, that only a power-on turn will get you out, you're flying far closer to the margin than I'm willing to fly.

 

[EdFred]

Uhhhh....my post didn't say anything about the FAA but quoted the manufacturer's recommendation. How is it that your knowledge of aerodynamics exceeds that of the folks who design and build airplanes?

Bob Gardner

All I said was until you run the full test series under controlled, you don't know your method is better. That's a fact I'll stand by over the suggestion that following the book procedure is "wallowing in mediocrity." So I'll follow the book procedure until someone proves theirs is better, and I hardly think that makes me a "mediocre" pilot.

Point 1) The plane will accelerate quicker (i.e. use less distance) when it is already rolling than it will accellerating it from a dead stop. Physics 101.

Point 2)
(applicable really only to manual flap airplanes that recommend more than 0º flaps) There is less drag produced at 0º flap setting than at say 25º flap settings as in say - a Cherokee. So you will accelerate faster to Vr quicker. Once there - click click 2 notches of flaps. I wouldn't try this in electric or hydraulic.

Point 3) Leaning for max power. "But, but, but the manufacturer says..."
I call BS. As long as you don't spike your CHTs, you are fine. 375º is 375º whether you are taking off, or whether you are in cruise. Which you wont do in a 172, PA28, or 90% of the NA single fleet. The only reason the manufacturers say don't lean below 5k is because when they wrote the recommendation they weren't expecting 8, 12, and 16 channel analyzers to monitor that, so to err on safety, "don't lean below 5000 (or whatever the altitude). And if you are that worried about temps, slowly richen it up once clear of obstacles.

What do we want to do with a short field takeoff? Use the least amount of runway. How do we do that? By getting to Vr as fast as we can.

Which does that ?

MORE drag, accelerating a stationary object, and less than max power?
or
LESS drag, accelerating an already (even if slightly) moving object and max power?

I've done this at near gross on a grass field. I've done this at minimum fuel no pax or baggage on a grass field. I've done this at gross on a paved field, and I've done this at minimum fuel no pax or baggage on paved field. Every single time, I have beaten the takeoff and 50' obstacle clearance compared to following the manufacturer's and FAA "perfect" procedure. After all the FAA and manufacturer is never wrong, oh yeah, except in this case.


I supposed demonstrated crosswind is a limitation too. After all the super awesome test pilots never flew it beyond that.

 

[dmccormack]

Point 1) The plane will accelerate quicker (i.e. use less distance) when it is already rolling than it will accellerating it from a dead stop. Physics 101.

So you roll through the point on the runway you would have been using had you started from a dead stop?

If not, you need to add the unused runway as part of your takeoff roll.

 

[Troska]

If you're not making proper rpm or oil pressure, there's no sense in beginning the takeoff...I'm not suggesting NOT checking after brake release, but why even start a takeoff that you know you can't complete?

I was actually objecting to the idea that a full power runnup with brakes was necessary to check the engine.

How else do you propose to check max static rpm?

If one does not check it, how does one assure full power is being developed?

By the book, and prior to take-off, of course.

Tim

 

[EdFred]

So you roll through the point on the runway you would have been using had you started from a dead stop?

If not, you need to add the unused runway as part of your takeoff roll.

Same turn, I just don't stop.

 

[EdFred]

If you're taking off from a field so short, that only a power-on turn will get you out, you're flying far closer to the margin than I'm willing to fly.

If I can give myself more margin, why wouldn't I?

 

[dmccormack]

Same turn, I just don't stop.

It can't be.

The radius of a turn at 20 won't be the same at 3.

 

[EdFred]

How else do you propose to check max static rpm?

If one does not check it, how does one assure full power is being developed?

By the book, and prior to take-off, of course.

Tim

I will do this during my back taxi. If I'm generating it then, I'll be generating it in 15 seconds when I make the 180 to take off, and if I'm not, it was probably going to fail 15 seconds down the runway on the "standard" way to do it.

 

[EdFred]

It can't be.

The radius of a turn at 20 won't be the same at 3.

Who said I'm doing 20?

 

[MauleSkinner]

Improve on what exactly? Beating the book figures? Because you just want to, or you have to?

Maybe I'm missing something here, but before I land somewhere, I figure out if I can get back out first. And I add some margin over book, because I figure what I'm flying is old and not perfect like the test plane, nor am I as good as the factory test pilot. I guess if that makes me mediocre, so be it, but I haven't crunched anything yet either.


Trapper John

Well, say your "acceptable" margin is the much-touted 50% over book.

Now, say you have a 1500-ft runway.

Then, say your "book" value is 1100 feet.

Then, say, after much testing and application of certain variables that AREN'T in the book, you come up with a realistic takeoff distance requirement of 900 feet.

If you use the book, you're giving up a takeoff.

If you use known, realistic performance, with the same 50% margin, you're making a takeoff within your personal limits.

Now, say the "book" value is 1000 feet.

You add your 50%, but the book doesn't account for that 1% uphill slope (that adds 10%) slope or long grass (which adds 25% instead of 10%--and just exactly where does "grass" leave off and "long grass" pick up, anyway?). Since these compounded, not additive, factors, you end up with a realistic takeoff distance of 137% of "book" (100%*1.25*1.1), you end up taking off with ALMOST a 10% margin instead of the 50% you THOUGHT you had. And that's WITHOUT accounting for old airplane, non-test-pilot technique, and all that stuff.

Bottom line, if you don't know what YOU can really do in YOUR airplane, any "safety margin" that you add is just a random number pulled out of somebody's butt.

Mediocre or not, I'd much rather takeoff knowing for a fact that I'll use 1300 feet of my 1500-ft strip than make a guess based on factory data and an unproven "safety factor".

Fly safe!

David

 

[Troska]

I will do this during my back taxi. If I'm generating it then, I'll be generating it in 15 seconds when I make the 180 to take off, and if I'm not, it was probably going to fail 15 seconds down the runway on the "standard" way to do it.

Right, that makes sense for your situation.

But I was questioning Gismo, who said he didn't need brakes and a static runup to determine if the engine is making full power... and I can't think of another way to do it that is repeatable. So I'm wondering what his method is.

Tim

 

[MauleSkinner]

I think there are some considerations that make me question the "rules".
First ,if you are on short field or are just attempting a short field T.O. and you must stop at the longest point ,apply full brakes, run engine to check for maximum power output , why is it then ok by the "rules" to T.O. from that same airfield when maybe it's soft now because it rained ,now keeping it rolling.

Did anybody say it WAS ok to do that?

 

[Dan Thomas]

Point 2)
(applicable really only to manual flap airplanes that recommend more than 0º flaps) There is less drag produced at 0º flap setting than at say 25º flap settings as in say - a Cherokee. So you will accelerate faster to Vr quicker. Once there - click click 2 notches of flaps. I wouldn't try this in electric or hydraulic.

Point 3) Leaning for max power. "But, but, but the manufacturer says..."
I call BS. As long as you don't spike your CHTs, you are fine. 375º is 375º whether you are taking off, or whether you are in cruise. Which you wont do in a 172, PA28, or 90% of the NA single fleet.

Manual-flap airplanes can be pulled off and landed pretty short, shorter than book values, but the pilot ain't going to have a fresh PPL. The POH is aimed at the "pilot of reasonable skill" or something similar, as Cessna puts it, not the 2500-hour guy who's been making his living flying off short bush strips for the last four years. I used to fly an Auster and regularly took off and landed in shorter distances than the specs, but it didn't happen early on and some of the approaches were at 1.1Vso, a dangerous place for any novice to be.

As far as leaning goes, read the POH on short-field takeoffs. Cessna says to apply brakes and full throttle, lean for for maximum RPM, and go. Slowly enrich the mixture after the obstacle has been cleared. We teach this in seven Lycoming-powered airplanes and all of those engines are still exceptionally healthy at TBO. The key is to keep the runup time to a minimum.

Turning tightly with the RPM well up raises the gyroscopic forces on the crankshaft and prop hub. Aerobatic airplanes have shorter TBOs on their engines partly because of this, and more than a few have lost their props. There are ways to abuse your airplane, and this is one of them.

Dan

 

[el con]

Again, turning through the stopping point would not put undue stress on the engine, this is aprox. the same speed as everyone taxis,about the same as is you are doing in the soft field "recommended " procedure.
I feel doing this same turn through procedure ( after a proper run up brakes on)is good idea as you don't have to remember all the different procedures, it becomes natural and takes care of all factors soft ,short, wet ,tall grass,tall trees, electric wires,deer, geese,etc.,etc. and it works. it's putting all these good things together.
"Some pilots have done this many ,many times with better results than what is stated in the book at a grass field somewhere north of here. Granted you guys that fly off pool tables it may not be much of a difference but it does if your wheels sit and settle into soft ground. We are doing nothing wrong it's a by the book soft /short field T.O.combo as you are allowed as PIC. I prefer to get off the ground quicker ,in the air faster, climb higher, and be safer than any slight chance of not developing enough power. If your airplane can't be reliable to produce enough power 100 ft before you turn, then I would'nt trust it stopped at the beginning of your roll. Again would the book tell you to ever do a soft field T.O. if it was unsafe,NO, they tell you to keep up your momentum.
Why not have the best of both worlds You have all done this procedure (soft field)if you have ever been taught by a CFI worth his salt.
And no this is not just Ed, a very good friend ,CFI,20,000 + hrs of flying ,see's no problem and recommends this, maybe just not to the 10 hr. student. This is only to be done by pilots who can multi-task and do more than just one thing at a time
Flaps:Johnson bar flaps good, you electric flap cessna guys you have a higher percentage of failures, not so good.
Do all you guys still drive your car with your hands always at 10 and 2?

 

[RogerT]

Why not check that part way into your takeoff roll when there's still plenty of room to stop? I'm not suggesting that checking this before brake release is wrong, just that IMO there's not much benefit either.

On a short field takeoff I prefer to have the major focus outside and at least start out knowing everything is good. The way for me to do that is to check everything before I start rolling. Your mileage may vary and you may be just fine doing all that at the beginning of the takeoff roll.

 

[EdFred]

As far as leaning goes, read the POH on short-field takeoffs. Cessna says to apply brakes and full throttle, lean for for maximum RPM, and go. Slowly enrich the mixture after the obstacle has been cleared. We teach this in seven Lycoming-powered airplanes and all of those engines are still exceptionally healthy at TBO. The key is to keep the runup time to a minimum.

1982 Cessna Skyhawk Model 172P Information Manual says:

5. Mixture -- RICH (above 3000 feet, LEAN to obtain maximum RPM).

We are below 3000' here in the Great Lakes.

Turning tightly with the RPM well up raises the gyroscopic forces on the crankshaft and prop hub. Aerobatic airplanes have shorter TBOs on their engines partly because of this, and more than a few have lost their props. There are ways to abuse your airplane, and this is one of them.

Where did I ever say I was making the turn at max/high rpm? You are making assumptions. Aerobatic airplanes also make a lot of abrubt power changes, it's not just from turning. Plus, I'm not pulling 6Gs on my turn to takeoff.

This is exactly what I am talking about. Someone injects their own thoughts into what was actually saying, and then make it look like that's what I was trying to say.

 

[dmccormack]

This is exactly what I am talking about. Someone injects their own thoughts into what was actually saying, and then make it look like that's what I was trying to say.

Then just say what you mean.

You blast anyone who applies a proven, tested configuration, yet fail to provide an alternate.

Can't have it both ways...

 

[Ted]

Can't have it both ways...

I agree.

Book procedures are written for reasons. They are rarely optimal, but they serve their purpose which is to provide repeatable, safe operation for the masses who use the aforementioned products. I would agree that the standard short field procedure is not optimal, but it is safe and repeatable.

 

[EdFred]

Then just say what you mean.

You blast anyone who applies a proven, tested configuration, yet fail to provide an alternate.

Can't have it both ways...

Wouldn't matter. As it was both Dans added/implied things I did not say. I teach it in person, not on a message board. If you want the alternate, come to 6Y9.