Short, hot & high takeoff prep
While searching for a report of the crash I mentioned*, I stumbled across this
Taking a Cessna 172 to high and hot airfields
Some interesting points there, including the suggestion to lean to max rpm at full power as BPF suggested. I will start to do that in addition to the normal run-up and checks at 1700. Then go a couple of turns richer when flying to be kinder to the engine?
I guess the key message I am getting here is take this very seriously. These sort of operations are the bread and butter of local bush pilots, but I guess the ones that don't get it right have been weeded-out by the laws of physics. All the comments about the anaemic performance at high DA make me keen to try a low DA! I have never experienced less that 6,500' apparent; I guess that makes me comfortable with nailing Vy on a shallow climb-out as it's all I have ever known.
*[I could not find the official accident report, but I found a press report which said "According to eye witnesses, the plane had not been in the air long when it started spinning in the sky and crashed before bursting into flames."]
Taking a Cessna 172 to high and hot airfields
Some interesting points there, including the suggestion to lean to max rpm at full power as BPF suggested. I will start to do that in addition to the normal run-up and checks at 1700. Then go a couple of turns richer when flying to be kinder to the engine?
I guess the key message I am getting here is take this very seriously. These sort of operations are the bread and butter of local bush pilots, but I guess the ones that don't get it right have been weeded-out by the laws of physics. All the comments about the anaemic performance at high DA make me keen to try a low DA! I have never experienced less that 6,500' apparent; I guess that makes me comfortable with nailing Vy on a shallow climb-out as it's all I have ever known.
*[I could not find the official accident report, but I found a press report which said "According to eye witnesses, the plane had not been in the air long when it started spinning in the sky and crashed before bursting into flames."]
Last edited by double_barrel; 13th Jan 2020 at 05:18.
Join Date: Mar 2014
Location: Way north
Age: 47
Posts: 497
Likes: 0
Received 0 Likes
on
0 Posts
Short field take off.
Most manuals should contain that. something in the line of: "start out flaps up, and at some point when gained speed, throw out a few notches of flaps and rotate into the ground effect, and build up speed there before climbing further".
Read the manual before trying it though!
Most manuals should contain that. something in the line of: "start out flaps up, and at some point when gained speed, throw out a few notches of flaps and rotate into the ground effect, and build up speed there before climbing further".
Read the manual before trying it though!
Join Date: Jan 2020
Location: U.K.
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
Pushing the envelope while sitting in an armchair, or in a discussion forum like this, is an excellent idea. Pushing the envelope in an actual flying machine otoh is an exceptionally bad one. People like BPF and Pilot DAR have already experienced a lot and even when they do something that afterwards they're not so sure about, they're drawing on an awful lot of experience. My strong advice would be to continue pushing the envelope in theory, but in practice just go out and fly as much as you can. You'll experience plenty of "oh s***" moments, that way - trust me - without ever being in REAL danger. As for me, I have 2000 hours, which I regard as just enough to be dangerous.
A 1960 PA22 [150-160 hp Lycoming] manual states the following in section IV: (3) "For take-offs in heavy grass, snow, or in any other speed retarding surfaces, drag on the landing gear can be reduced by raising the nose wheel off the surface during the take-off run by applying back pressure on the control wheel shortly after the throttle is opened. (4) The application of full flaps as take-off speed is approached will reduce the take-off run about 20 percent. Flaps can be pulled down before the take-off run is started but will reduce the acceleration of the plane somewhat if kept down throughout the take-off.
I'm not aware that Piper ever repeated such advice again and I have certainly not found similar advice given by any other manufacturer. Somehow this advice spread and I have known many who believed it to be true for all aeroplanes. In each case, by demonstration, I have been able to disavow these believers by carrying out actual flight demonstrations. Further, for many types handling the manual flap control requires the pilot to stretch to the floor with the possibility of a loss of directional control. Certainly there is an illusion of hoping into the air as if on an elevator but your then left with the distraction of very slowly raising the flaps afterward from maximum in order to climb. Note: drag from the flap set at the start increases with the square of the speed but so of course does lift so I really do not understand Piper's thinking at the time.
I'm not aware that Piper ever repeated such advice again and I have certainly not found similar advice given by any other manufacturer. Somehow this advice spread and I have known many who believed it to be true for all aeroplanes. In each case, by demonstration, I have been able to disavow these believers by carrying out actual flight demonstrations. Further, for many types handling the manual flap control requires the pilot to stretch to the floor with the possibility of a loss of directional control. Certainly there is an illusion of hoping into the air as if on an elevator but your then left with the distraction of very slowly raising the flaps afterward from maximum in order to climb. Note: drag from the flap set at the start increases with the square of the speed but so of course does lift so I really do not understand Piper's thinking at the time.
Last edited by Fl1ingfrog; 13th Jan 2020 at 16:22.
Yes, Fl1ingfrog, I can confirm that the technique taught at Sleap many decades ago for an emergency short-field take-off in a Piper Caribbean (High-wing SEP, tricycle, 4-seats, fixed u/c, might even be a PA22?) was to set full power, check all OK, tighten the friction hard, then let the brake off, left hand on the yoke, the other on the manual flap lever in between the two front seats. As you hit 60Kts (I think was, might have been less), pull 2 notches flap and heave back on the yoke simultaneously, keep straight with rudder. The aircraft would leap off the ground pointing skywards but at 50 ft or so you had to level quickly to avoid a stall, then get the flap in very carefully without losing height, and climb away. It worked, but it wasn't for the faint-hearted.
(In the Auster Autocrats, for a short take-off we would set the parking brake, 1 notch flap, set full power, climb trim, then gently nose down until the tail was well up, brake off, keep level, roll maybe 30 yards depending on wind, back with the stick and climb away, getting the flap in gently.)
(In the Auster Autocrats, for a short take-off we would set the parking brake, 1 notch flap, set full power, climb trim, then gently nose down until the tail was well up, brake off, keep level, roll maybe 30 yards depending on wind, back with the stick and climb away, getting the flap in gently.)
Last edited by old,not bold; 13th Jan 2020 at 18:00.
All the comments about the anaemic performance at high DA make me keen to try a low DA! I have never experienced less that 6,500' apparent;
You should come to Calgary today. Elevation 3750’, DA -630’
In the context of hot and high, I don't think there is ever a situation where you would want to add flap during the takeoff roll in an attempt to get airborne. However this is a recognized technique for float pilots when faced with a glassy water takeoff. Because there is no wind to reduce the required ground speed to achieve lift off airspeed and no waves to help break surface suction when the aircraft stops accelerating on the step adding flap will cause the aircraft to lift off. However this is not a beginner maneuver as care must be taken not to let the aircraft hit the water after lift off but also not climb out of ground effect at too low an airspeed.
It can also be used in very soft fields that are long and have no obstructions at the end. I once went into a grass field in a C172 that looked OK but turned out to be basically a bog. On takeoff the aircraft would not accelerate above about 40 kts. I applied full flaps and the aircraft picked itself up just enough to break free of the ground. Some very delicate flying was then required to allow the aircraft to accelerate without climbing and then settling to a safer airspeed and then allow some flap to be retracted and the aircraft to start to climb away. The only reason I attempted this was because the strip was facing a bay which provided an obstacle free departure path, however in hind sight if I had done a better pre-landing assessment I could have realized what shape the strip was in and not landed in the first place.
It can also be used in very soft fields that are long and have no obstructions at the end. I once went into a grass field in a C172 that looked OK but turned out to be basically a bog. On takeoff the aircraft would not accelerate above about 40 kts. I applied full flaps and the aircraft picked itself up just enough to break free of the ground. Some very delicate flying was then required to allow the aircraft to accelerate without climbing and then settling to a safer airspeed and then allow some flap to be retracted and the aircraft to start to climb away. The only reason I attempted this was because the strip was facing a bay which provided an obstacle free departure path, however in hind sight if I had done a better pre-landing assessment I could have realized what shape the strip was in and not landed in the first place.
It can also be used in very soft fields that are long and have no obstructions at the end. I once went into a grass field in a C172 that looked OK but turned out to be basically a bog. On takeoff the aircraft would not accelerate above about 40 kts. I applied full flaps and the aircraft picked itself up just enough to break free of the ground. Some very delicate flying was then required to allow the aircraft to accelerate without climbing and then settling to a safer airspeed and then allow some flap to be retracted and the aircraft to start to climb away. The only reason I attempted this was because the strip was facing a bay which provided an obstacle free departure path, however in hind sight if I had done a better pre-landing assessment I could have realized what shape the strip was in and not landed in the first place.
But in fact, there even seems to be confusion over what the C172 POH recommends. It says 10 deg flap for short field per se, but no flaps for obstacle clearance. Since these 2 circumstances often appear together it must require careful consideration to decide what is the deciding factor. But everyone I talk to seems to just say "short field = 10 degrees flap".
I begin to realize how real-world differs from theory! In this case surface quality, wind, slope, obstacle all interacted with each other to determine the safest strategy; and the short rwy and high DA made the decision critical. The result was downslope, downwind, no (major) obstacle, 10 deg flap, home for tea and cakes.
Last edited by double_barrel; 14th Jan 2020 at 07:41.
Join Date: Mar 2014
Location: Way north
Age: 47
Posts: 497
Likes: 0
Received 0 Likes
on
0 Posts
I had an instruction lesson in a C172 at one point, he showed me a technique where you start the take off roll 90 degrees off at the runway end, and then use the turn as an initial acceleration, gaining maybe a knot or two extra... Then with full backpressure from the get go, you can pull the aircraft off the ground pretty fast, but remember to push the nose to gain speed before going out of the ground effect.
We did it on a grass field, not short though, but not long either.
I've never tried that manouver again... the 90 degree point of start doesn't suit me.... the other one with full back pressure, wanna experiment with that again, just haven't had my hands on a C172 since (I like my Piper 28-181, and it doesn't help her a lot doing that)
We did it on a grass field, not short though, but not long either.
I've never tried that manouver again... the 90 degree point of start doesn't suit me.... the other one with full back pressure, wanna experiment with that again, just haven't had my hands on a C172 since (I like my Piper 28-181, and it doesn't help her a lot doing that)
Moderator
a technique where you start the take off roll 90 degrees off at the runway end, and then use the turn as an initial acceleration, gaining maybe a knot or two extra...
Then with full backpressure from the get go, you can pull the aircraft off the ground pretty fast,
If I'm on soft ground, and total takeoff distance is less a concern, then I will always use the greatest flap setting permitted, and the highest I can get the nose on takeoff (without banging the tail), and allow the airplane to leave the ground at the slowest possible airspeed (it flies when it's ready), then allow it to remain in ground effect as long as practical to gain speed, before climbing away.
Practice: Unless I'm flying with sensitive passengers, every takeoff I do will be either soft or short field technique, simply for the practice. I rarely do "normal" takeoffs, it's simply a waste of an opportunity to practice a different and useful technique. I suggest DB, that as you train with your instructor, you brief each takeoff: "This will be a soft field takeoff, flaps set at... speed...." or, "This will be a short field takeoff, flaps set at... speed...".
Further to that DB, the C 172 POH gives pretty specific procedures for different takeoff techniques, and answers some on the point you raised. Now that you're thinking about the detail, go ready that section again...
You must always have in your mind that to raise the nose wheel you create a downforce with the tailplane and this makes the aircraft heavier, the main wheel friction increases and there is an increase in induced drag. The trade off therefore will always require a careful consideration in the handling so not to increase the total drag. Over pitching could mean you never leave the runway at all.
Re flap settings for short field takeoff's for the C 172.
For C 172's to C172 N the POH advised that 10 deg flap be used for short fields without obstacles and 0 flap for short field obstacles. For C172 P/R/S the POH says to use 10 deg flap for all short field takeoffs
Like Pilot DAR often says, it is important to read the POH for the aircraft model you are flying not some generic one or Flight School-ism that have no basis in fact but are just mindlessly handed down from instructor to instructor
For C 172's to C172 N the POH advised that 10 deg flap be used for short fields without obstacles and 0 flap for short field obstacles. For C172 P/R/S the POH says to use 10 deg flap for all short field takeoffs
Like Pilot DAR often says, it is important to read the POH for the aircraft model you are flying not some generic one or Flight School-ism that have no basis in fact but are just mindlessly handed down from instructor to instructor
Last edited by Pilot DAR; 14th Jan 2020 at 19:14. Reason: typo
Thanks all. This has been a super helpful discussion, it really helped to fix the issues in my mind.
P_D, I like the idea of always doing some kind of 'special' takeoff. I will start to do that, it sounds like a great way to get experience eg simulate soft-field with an early lift and staying in ground effect, but with a mile of bitumen ahead of me in case I screw-up.
P_D, I like the idea of always doing some kind of 'special' takeoff. I will start to do that, it sounds like a great way to get experience eg simulate soft-field with an early lift and staying in ground effect, but with a mile of bitumen ahead of me in case I screw-up.
Join Date: Mar 2014
Location: Way north
Age: 47
Posts: 497
Likes: 0
Received 0 Likes
on
0 Posts
Don't mix up your procedures here. Full back pressure on a 172 takeoff is a soft field takeoff, not a short field take off. You will get off the ground at a slower speed, but you will spend noticeably longer stuck in ground effect because of the high drag you created for yourself as you left the ground. The total takeoff will be longer....
Moderator
a great way to get experience eg simulate soft-field with an early lift and staying in ground effect, but with a mile of bitumen ahead of me in case I screw-up.
If the airport you normally fly from has lots of hard surfaced runway, and better, features which allow you to estimate how much runway you have used, you can familiarize yourself with varying techniques for getting airborne. In particular, the only takeoff for which I would deliberately "rotate" a Cessna 150/152/172/182 would be for a short field takeoff, where I have let the plane accelerate to the desired speed before applying much up elevator. Other than that (so, most of the time), it's either a soft field takeoff, or letting the plane fly itself off. So, for both of those, I'll have the nose light from the beginning of the takeoff roll, more nose high for a deliberate soft field.
Most of my flying is on my C 150, from my grass runway, so always a soft field takeoff, because I want the nosewheel off the ground as early as possible - I pay to maintain it! If the nosewheel is not supporting weight, it's not suffering wear and tear. Otherwise, if I'm taking passengers, or flying someone else's plane, I'll hold the nose light, and allow the plane to gently lift off when it is ready. A very few types don't react so well to this (Piper T tail planes), otherwise it's generally fine, and results in a very gentle takeoff. The only thing to be aware is that when you don't "rotate" as a deliberate action, the plane is lifting off when it is ready (which is my intent), so a crosswind will begin to affect the plane as it gets light on its wheels, so you'll have to be aware, and compensate when needed. It works fine, as long as you're paying attention.
