Short field versus Soft field.
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Short field versus Soft field.
Hi, what is the differance in take off technique between short field and soft field. Got asked this by a fellow pilot and did not know the answer.
many thanks
Cheers
SF
many thanks
Cheers
SF
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Short field technique presupposes that you are not disadvantaged by drag from the runway surface, and therefore willing to allow most of the weight of the aircraft to remain on the wheels longer during the run. With the weight on the wheels, you are not trying to coax the aircraft into the air early, thus it will accellerate faster, and reach takeoff speed in less time and runway length. You don't have the aerodynamic drag of the high lift devices (flaps) and deflected elevator trying to pry the nose up early in the takeoff. The short field technique also usually employs a brakes on then full power, then brakes released takeoff beginning. As you reach takeoff speed faster, you rotate on schedule, and you're airborne and climbing as soon as possible over the obsticle.
Soft field technique is based on the premise that you've got lots of space available, but the surface is soft, and getting the aircraft to accellerate to takeoff speed at all is going to be a problem (mud). You will avoid stopping at all if possible from taxi to takeoff, and you will be getting the weight off the wheels as early in the run as possible. You will use more runway length doing this, but you have a much better chance of reaching takeoff speed than carving huge ruts down the runway slowly. Soft field technique will have you off the ground at a low speed, and with less than ideal climb performance until you get the plane cleaned up a little, and accellerating in ground effect.
Soft filed technique is excellent elsewhere too, for example gravel runways, where you are trying to prevent gravel damage to the prop. Get the prop up and away from the gravel as soon as possible. The handling of the aircraft in this way is also more the norm for heavy weight float flying. In these operations, getting one float out of the water first helps immensely. Similarly, getting one of the two mainwheels out of the mud as you accellerate works really well too on some types, but is an advanced flying technique, which requires practice.
Aggressive soft field technique can get you in trouble in some types (PA28) where the aircraft will get airborne, then stuck flying in ground effect. It can be very dangerous in a confined area, and thus, again soft field technique requires training and practice in the aircraft type involved. Some types are nearly useless at soft field ("T" tails) as you just cannot get the pitch authority early enough in the roll to create much beneficial affect.
I hope than helps, Pilot DAR
Soft field technique is based on the premise that you've got lots of space available, but the surface is soft, and getting the aircraft to accellerate to takeoff speed at all is going to be a problem (mud). You will avoid stopping at all if possible from taxi to takeoff, and you will be getting the weight off the wheels as early in the run as possible. You will use more runway length doing this, but you have a much better chance of reaching takeoff speed than carving huge ruts down the runway slowly. Soft field technique will have you off the ground at a low speed, and with less than ideal climb performance until you get the plane cleaned up a little, and accellerating in ground effect.
Soft filed technique is excellent elsewhere too, for example gravel runways, where you are trying to prevent gravel damage to the prop. Get the prop up and away from the gravel as soon as possible. The handling of the aircraft in this way is also more the norm for heavy weight float flying. In these operations, getting one float out of the water first helps immensely. Similarly, getting one of the two mainwheels out of the mud as you accellerate works really well too on some types, but is an advanced flying technique, which requires practice.
Aggressive soft field technique can get you in trouble in some types (PA28) where the aircraft will get airborne, then stuck flying in ground effect. It can be very dangerous in a confined area, and thus, again soft field technique requires training and practice in the aircraft type involved. Some types are nearly useless at soft field ("T" tails) as you just cannot get the pitch authority early enough in the roll to create much beneficial affect.
I hope than helps, Pilot DAR
Is this true ?
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No they are taught, but I suppose if you don't use them regularly it is possible to get confused as both involve rotating at a lower than normal airspeed. There are significant differences, mainly involving the commencement of the takeoff run, and angle of climb is not assumed to be critical in a soft field takeoff... Dig the PPL text books out to refresh your knowledge if you are unsure.
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In actual practice, short field and soft field turn out to be the same thing, most of the time. Short fields are often soft, and soft fields are seldom long. The method provided for most private pilot training for short fields involves holding brakes and applying takeoff power...something sure to suck up rocks and damage airplanes in the real world, and seldom applicable to short/soft field operations.
In either case, short or soft, the goal is the same; get the airplane into the air and off the surface as soon as possible, and one must always be mindful of obstacles.
In either case, short or soft, the goal is the same; get the airplane into the air and off the surface as soon as possible, and one must always be mindful of obstacles.
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With respect, I disagree with:
The soft field technique wants you off the ground asap, the short feild technique does not. I do agree that many runways which will require one technique, tend to need the other as well, but it ends up being a cobled compromise between the two, which works, but does not optimize either.
The important difference between the two techniques in their pure form will be that for the soft field, there is very little change in elevator command to become airborne during the entire takeoff run, the elevators are heald in the position to get you airborne the whole run, only modulated to maintain the optimum pitch attitude.
For Short field technique there will be a distinct rotation (elevator control input) of the aircraft at a piont where the appropriate takeoff speed is reached, but not really prior. If the short field technique includes getting off the ground asap, you're prolonging the ground run (not as short as could have been) because you're pulling along the added drag resulting from lift demanded through the entire takeoff run, instead of just at the point of rotation.
Taken at it's extreme in my experience the PA 28 can be operated to create a dramtic effect (but please don't do it 'cause I said it could be done - hurting the plane is a real possibility). I have previously posted the text which follows, it describes in extreme, an unintentional soft field takeoff through which I once rode, which nearly did not work.
Here you go...
[FONT='Verdana','sans-serif']PA28's have a stabilator rather than the conventional stabilizer/elevator combination. In "normal" operations this is a completely benign difference. Where it does show up, however, is in very low speed, nose high operations. Here's what happens: Pilot commands more nose up at low speed, takeoff being the most likely occasion. Where the conventional stab/elev combination would have a greater deflection of the elevator, the camber of the horizontal tail as a single flying surface is increased (as well as a change in effective pitch angle). As such, it's capacity to create more "down" lift before stalling, or experiencing a large drag increase is better. (okay purist aerodynamicists, have at me, I've got experience with the result, not the theory). On the other hand, the stabilator, has only the opportunity to change angle of attack to create more "down" lift. Like any flying surface, it will reach an angle of attack, where the Cl max has been passed, and the increase in drag is no longer proportionate to the increase in (down) lift. Yes, I'm sure that Piper gave this a lot of thought and test all those years ago, and their engineers know more than I do about this, but...[/FONT]
[FONT='Verdana','sans-serif']I was the right seat check pilot to a junior pilot in an Arrow PA28R-200 many years ago. He rotated prematurely out of a 1000 meter runway. It was a hot day, but we were quite light, and it was a 200HP version of the aircraft, so power was not a problem. The plane was stuck in ground effect, with the pilot holding the controls 'way back. The stall warning was sounding. The aircraft would not accelerate, or climb away. Landing back might have worked, other than the runway end was approaching, and he (well I suppose "we") had allowed the aircraft to drift off the side, so there was not a runway under us any more. I was shocked at the "poor performance" I was experiencing in this aircraft I thought I knew so well. We were nearing the obstacles. We did not wreck the plane simply because I "locked off" and retracted the gear. The resultant reduction in drag was all that was needed to allow the plane to slowly climb away. [/FONT]
[FONT='Verdana','sans-serif']Shocked by what had just happened, I went to experiment. I flew a PA28-140, which I believed to be in good condition, off a very long frozen lake (runway and width length no longer a concern). Sure enough, I could get the plane very nose high, with lots of aft control, and it would not accelerate or climb out of ground effect. My only option was to land back (fixed gear). I repeated this configuration enough to satisfy myself that this is a configuration to be avoided in PA28's (and probably Cessna 177's as well) So I do! The thick wing has great lift, and resists stalling well. The stabilator tail is not ideally matched in this attribute. [/FONT]
In either case, short or soft, the goal is the same; get the airplane into the air and off the surface as soon as possible, and one must always be mindful of obstacles.
The important difference between the two techniques in their pure form will be that for the soft field, there is very little change in elevator command to become airborne during the entire takeoff run, the elevators are heald in the position to get you airborne the whole run, only modulated to maintain the optimum pitch attitude.
For Short field technique there will be a distinct rotation (elevator control input) of the aircraft at a piont where the appropriate takeoff speed is reached, but not really prior. If the short field technique includes getting off the ground asap, you're prolonging the ground run (not as short as could have been) because you're pulling along the added drag resulting from lift demanded through the entire takeoff run, instead of just at the point of rotation.
Taken at it's extreme in my experience the PA 28 can be operated to create a dramtic effect (but please don't do it 'cause I said it could be done - hurting the plane is a real possibility). I have previously posted the text which follows, it describes in extreme, an unintentional soft field takeoff through which I once rode, which nearly did not work.
Here you go...
[FONT='Verdana','sans-serif']PA28's have a stabilator rather than the conventional stabilizer/elevator combination. In "normal" operations this is a completely benign difference. Where it does show up, however, is in very low speed, nose high operations. Here's what happens: Pilot commands more nose up at low speed, takeoff being the most likely occasion. Where the conventional stab/elev combination would have a greater deflection of the elevator, the camber of the horizontal tail as a single flying surface is increased (as well as a change in effective pitch angle). As such, it's capacity to create more "down" lift before stalling, or experiencing a large drag increase is better. (okay purist aerodynamicists, have at me, I've got experience with the result, not the theory). On the other hand, the stabilator, has only the opportunity to change angle of attack to create more "down" lift. Like any flying surface, it will reach an angle of attack, where the Cl max has been passed, and the increase in drag is no longer proportionate to the increase in (down) lift. Yes, I'm sure that Piper gave this a lot of thought and test all those years ago, and their engineers know more than I do about this, but...[/FONT]
[FONT='Verdana','sans-serif']I was the right seat check pilot to a junior pilot in an Arrow PA28R-200 many years ago. He rotated prematurely out of a 1000 meter runway. It was a hot day, but we were quite light, and it was a 200HP version of the aircraft, so power was not a problem. The plane was stuck in ground effect, with the pilot holding the controls 'way back. The stall warning was sounding. The aircraft would not accelerate, or climb away. Landing back might have worked, other than the runway end was approaching, and he (well I suppose "we") had allowed the aircraft to drift off the side, so there was not a runway under us any more. I was shocked at the "poor performance" I was experiencing in this aircraft I thought I knew so well. We were nearing the obstacles. We did not wreck the plane simply because I "locked off" and retracted the gear. The resultant reduction in drag was all that was needed to allow the plane to slowly climb away. [/FONT]
[FONT='Verdana','sans-serif']Shocked by what had just happened, I went to experiment. I flew a PA28-140, which I believed to be in good condition, off a very long frozen lake (runway and width length no longer a concern). Sure enough, I could get the plane very nose high, with lots of aft control, and it would not accelerate or climb out of ground effect. My only option was to land back (fixed gear). I repeated this configuration enough to satisfy myself that this is a configuration to be avoided in PA28's (and probably Cessna 177's as well) So I do! The thick wing has great lift, and resists stalling well. The stabilator tail is not ideally matched in this attribute. [/FONT]
My softest field takeoff was from sand in a C-172 with four people and full tanks.
The start of the takeoff was with full back stick to about 35 kt, then it was necessary to lower the nose to accelerate faster.
PilotDAR makes a very good point
Those of us with less knowledge of the a/c will want to keep the nosewheel well clear of the ground until we have enough speed to lighten the weight on the wheels and bring the nose down to takeoff attitude.
The one good thing about a soft field is that if you become doubtful about the take off, it is very easy to stop
And yes, taildraggers are more suited for soft fields.
Gliders do well in soft fields. I paced out my last outlanding at two glider lengths. The glider dug a trench with the wheel and came to rest sitting on the gear doors. I felt fortunate that I could get the trailer to the glider and the loaded trailer out without having to beg for a tractor
The start of the takeoff was with full back stick to about 35 kt, then it was necessary to lower the nose to accelerate faster.
PilotDAR makes a very good point
for the soft field, there is very little change in elevator command to become airborne during the entire takeoff run, the elevators are held in the position to get you airborne the whole run, only modulated to maintain the optimum pitch attitude.
The one good thing about a soft field is that if you become doubtful about the take off, it is very easy to stop
And yes, taildraggers are more suited for soft fields.
Gliders do well in soft fields. I paced out my last outlanding at two glider lengths. The glider dug a trench with the wheel and came to rest sitting on the gear doors. I felt fortunate that I could get the trailer to the glider and the loaded trailer out without having to beg for a tractor
Last edited by RatherBeFlying; 3rd Jan 2010 at 15:51.
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Take off
Hi all,
Thanks for your comments. I'm sure I was taught both techniques during my PPL but temporarily lost that information
(forgot). I have now been reminded and will now go and practise both as soon as the snow has melted. (Ifor that would be great. 07989.515576)
Pilot DAR, thanks for your very specific explanation of the different techniques for soft and short TO. It is very much appreciated.
Cheers
Scottish Flyer.
Thanks for your comments. I'm sure I was taught both techniques during my PPL but temporarily lost that information
(forgot). I have now been reminded and will now go and practise both as soon as the snow has melted. (Ifor that would be great. 07989.515576)Pilot DAR, thanks for your very specific explanation of the different techniques for soft and short TO. It is very much appreciated.
Cheers
Scottish Flyer.
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IME, neither is taught in the UK PPL.
IMHO, the soft field method is less than effective in avoiding prop damage from gravel, because the maximum gravel damage risk is when the plane is moving forward slowly - the "maximum vacuum" situation.
And that condition is unavoidable... unless one does a gentle low power run-up to maybe 20kt and then goes to full power; that will play havoc with one's calculated takeoff performance, obviously.
That's why, at Elstree (covered in loose stones), I would start the takeoff roll from a spot on the runway which is clear of gravel.
IMHO, the soft field method is less than effective in avoiding prop damage from gravel, because the maximum gravel damage risk is when the plane is moving forward slowly - the "maximum vacuum" situation.
And that condition is unavoidable... unless one does a gentle low power run-up to maybe 20kt and then goes to full power; that will play havoc with one's calculated takeoff performance, obviously.
That's why, at Elstree (covered in loose stones), I would start the takeoff roll from a spot on the runway which is clear of gravel.
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It should be taught, though it often isn't. It's also not exactly the easiest thing to practise given our slavish devotion to licensed airfields for PPl training. It's not easy to find short, rough, soggy grass strips whilst training for the PPL unfortunately.
I was taught soft field for my FAA PPL back in 1990. However, I was taught the technique on either hardtop, or dry grass which really isn't very soft.
I learned soft field at Indiantown, Florida. They get a lot of rain down there. Fortunately the grass at indiantown is about 7000' long. I was getting a checkout there in an ancient C172. Least I assume I was, it crossed my mind after that the old dude instructor could have just been an airport bum hopping a ride. Anyway, I got to the end of the runway, had 20 degrees flaps, kept it going, got to the end and firewalled it. I got the nosewheel up early, rotated back to a nose up angle, and held it. We would accelerate, then hit a big puddle and slow down. It was pretty impressive, water flinging off the wheels and hitting the wings. Happened a couple of times. So I made an adjustment, and got the nose up attitude to a little more than I was comfortable with. Same thing. We are bombing along, using up 3000' so far, and no joy. So, with another 4000' to the fence, I tried something different. I pulled the yoke all the way back, got the nose really high, then I got the stall horn going off. Then I knew I had it. It staggered off the ground, I milked the yoke in and kept it 1" off until I got up to flying speed. We burned up 4000' on that first attempt. After I found I could get off a lot sooner, though it sure took more runway than usual. Landings were fun, I would end up at the backside of the power curve nose high, plunk the mains on and keep the nose up with power.
I also flew a J3 out of there. And, when it was that wet, the J3 required really no special technique. It was easy.
So, I would maintain that you can be taught, and still not know. I bet the majority of pilots, either here or anywhere, don't do any real soft field. Not to say that some of you don't.
-- IFMU
I learned soft field at Indiantown, Florida. They get a lot of rain down there. Fortunately the grass at indiantown is about 7000' long. I was getting a checkout there in an ancient C172. Least I assume I was, it crossed my mind after that the old dude instructor could have just been an airport bum hopping a ride. Anyway, I got to the end of the runway, had 20 degrees flaps, kept it going, got to the end and firewalled it. I got the nosewheel up early, rotated back to a nose up angle, and held it. We would accelerate, then hit a big puddle and slow down. It was pretty impressive, water flinging off the wheels and hitting the wings. Happened a couple of times. So I made an adjustment, and got the nose up attitude to a little more than I was comfortable with. Same thing. We are bombing along, using up 3000' so far, and no joy. So, with another 4000' to the fence, I tried something different. I pulled the yoke all the way back, got the nose really high, then I got the stall horn going off. Then I knew I had it. It staggered off the ground, I milked the yoke in and kept it 1" off until I got up to flying speed. We burned up 4000' on that first attempt. After I found I could get off a lot sooner, though it sure took more runway than usual. Landings were fun, I would end up at the backside of the power curve nose high, plunk the mains on and keep the nose up with power.
I also flew a J3 out of there. And, when it was that wet, the J3 required really no special technique. It was easy.
So, I would maintain that you can be taught, and still not know. I bet the majority of pilots, either here or anywhere, don't do any real soft field. Not to say that some of you don't.
-- IFMU
Moderator
Its important to remember that the various techniques which are known, and taught, were developed out of need first, then packaged and taught as a "technique" to newer pilots. There are many instances where a "tribal knowledge" technique is very common in the tribe, but never taught in pilot training or described in flight manuals. An example of this would be rolling one float out of the water first during a floatplane takeoff to reduce distance on the water.
Pilots who went before us simply figured out how to do what they needed to do. As aircraft manufacturers competed for customers, they caught on to the need, tested their aircraft, and documented and marketed their aircraft to make the most out of certain capabilities. I've never looked in a Piper Tomahawk flight manual for the soft field technique, but from considerable experience flying one out of a small grass runway, I can tell you, that there really isn't much capability there for that -but that's not what the Tomahawk was designed to do in the first place!
When you look carefully in flight manuals, you may see a technique briefly described, but no supporting performance data, because the conditions and technique are just too variable to detail in performance charts. On the reverse side, aircraft changes (like STOL kits) can enable much better performance than the manual describes. During a recent flight with an instructor friend of mine, I demonstrated in my STOL C150M getting airborne with she and I and 3/4 tanks, at 35 MPH, and steadily accellerating and climbing away (though slowly). I repeated this type of takeoff two weeks later by myself, while leaving my home runway, which was covered in 6 inches of crusty snow. It took near full power to get the plane moving at all, but the ground roll in still air was just over 400 feet (tracks in the snow measured against my runway lights). I had expected to use most of the runway. Accellerating to a typical 60 MPH rotation speed would have been hopeless.
It is my opinion that there is no excuse for these techniques not being trained and practiced with some frequency (along with stalls and spins, but that's another thread!). The next time you're flying, whatever you fly, and conditions are suitable, read the manual, and employ the technique described. You will find that you gain skill, and a feel for aircraft in general. Then when you happen onto a gravel runway, or foolishly land on grass in the spring, without first enquiring about its firmness, there is a better chance you'll handle the situation as well as possible.
I pay for the maintenance of my plane, including the propeller, and nose strut. Every takeoff has my nosewheel light, and off the surface as early in the takeoff as possible. In 23 years, I have never nicked my prop, or slammed my nosewheel. It keeps repair costs down!
I once employed a soft filed technique to taxi out a 172 to the runway. It had been hangered for some time, and I suppose forgotten, as they ploughed up the field between where it sat in the hangar, and the runway. With a soft field technique (and the owner and his daughter (of perfect mass) sitting in the back for ballast), I was able to taxi the aircraft out 500 feet, slowly picking my way around the big lumps, with the nosewheel never touching the surface. it worked just fine, and we flew out minutes later. You never know when you may need a trick up your sleeve, may as well practice!
Pilots who went before us simply figured out how to do what they needed to do. As aircraft manufacturers competed for customers, they caught on to the need, tested their aircraft, and documented and marketed their aircraft to make the most out of certain capabilities. I've never looked in a Piper Tomahawk flight manual for the soft field technique, but from considerable experience flying one out of a small grass runway, I can tell you, that there really isn't much capability there for that -but that's not what the Tomahawk was designed to do in the first place!
When you look carefully in flight manuals, you may see a technique briefly described, but no supporting performance data, because the conditions and technique are just too variable to detail in performance charts. On the reverse side, aircraft changes (like STOL kits) can enable much better performance than the manual describes. During a recent flight with an instructor friend of mine, I demonstrated in my STOL C150M getting airborne with she and I and 3/4 tanks, at 35 MPH, and steadily accellerating and climbing away (though slowly). I repeated this type of takeoff two weeks later by myself, while leaving my home runway, which was covered in 6 inches of crusty snow. It took near full power to get the plane moving at all, but the ground roll in still air was just over 400 feet (tracks in the snow measured against my runway lights). I had expected to use most of the runway. Accellerating to a typical 60 MPH rotation speed would have been hopeless.
It is my opinion that there is no excuse for these techniques not being trained and practiced with some frequency (along with stalls and spins, but that's another thread!). The next time you're flying, whatever you fly, and conditions are suitable, read the manual, and employ the technique described. You will find that you gain skill, and a feel for aircraft in general. Then when you happen onto a gravel runway, or foolishly land on grass in the spring, without first enquiring about its firmness, there is a better chance you'll handle the situation as well as possible.
I pay for the maintenance of my plane, including the propeller, and nose strut. Every takeoff has my nosewheel light, and off the surface as early in the takeoff as possible. In 23 years, I have never nicked my prop, or slammed my nosewheel. It keeps repair costs down!
I once employed a soft filed technique to taxi out a 172 to the runway. It had been hangered for some time, and I suppose forgotten, as they ploughed up the field between where it sat in the hangar, and the runway. With a soft field technique (and the owner and his daughter (of perfect mass) sitting in the back for ballast), I was able to taxi the aircraft out 500 feet, slowly picking my way around the big lumps, with the nosewheel never touching the surface. it worked just fine, and we flew out minutes later. You never know when you may need a trick up your sleeve, may as well practice!
Upon further review, 7000' is a slight exaggeration. Only 6300'. Maybe part of it sunk.
AirNav: X58 - Indiantown Airport
-- IFMU
AirNav: X58 - Indiantown Airport
-- IFMU
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I was referring to the length of the grass
(Sorry
)
Originally Posted by flybymike
British humour lost on the Americans?
-- IFMU
PS over here in the states I have never seen grass longer than 500'.