Archie wrote:
You simply cannot assume that you can get to 50 ft then abort the take-off and land back without having a serious mishap. TODR is the take-off distance required to a screen height of 50 ft.
Slight misunderstanding perhaps. If you are performing a short field takeoff, and you have an engine failure over the obstacle (50 feet), a safe land back should be possible if: You achieved a speed adequate to enter and maintain a glide, and there is a suitable landing area ahead. This has happened to me, as an engine failure after takeoff, and I landed with no damage ahead in the next field, just after the engine quit over the obstacle trees. The key is maintaining a suitable speed.
A short field performance chart is going the show the distance required to clear the 50 foot obstacle, and when over the obstacle, you will have the speed to land back safely. You can clear the obstacle in a shorter distance, but a safe glide back will not be possible. For that reason, the manufacturer will not provide that data, even though the plane could be capable.
Rwy20 has presented (thanks very much) a gold mine of understanding as to this situation with the referenced article. If you are going to leave ground effect in a minimum performance situation (like a short field obstacle clearance) you really should understand this. I have done the testing. It was the most un nerving flight testing I have ever flown. I really did fear I would crunch a Caravan (the one pictured earlier). The increase in drag was so much that the plane could no longer achieve the minimum required rate of climb for approval when flown at the POH "after takeoff speed. To achieve approval, my only choice was to after takeoff climb at a slower speed (80 KIAS, rather than 87 POH value). It worked, the required climb rate could just be achieved, but now I was required to demonstrate an engine failure land back. I could not do that – I would have bent landing gear in the hard hit. Approval was conditionally issued with this shortcoming considered. I learned a few important lessons vividly!
For those wishing to further their understanding of the article Rwy20 has kindly posted, do some reading on “height velocity curve” or “dead man’s curve” for helicopters, and understand the concept. It’s about the same for fixed wing aircraft, with the variation that a helicopter can store energy as rotor RPM (up to 110% of normal RPM, build up during the descent) and airspeed. An airplane can only store this energy as speed. This stored energy will be required to arrest the inevitable rate of descent during the power off arrival.
This is an important, yet poorly understood topic within the powered flight community. It is because of this poor understanding that all forced landing training I do while training others will conclude in a touchdown, particularly for water landings. It’s fine to practice gliding down to 100 feet, then powering away over surprised sheep, but that left the lesson very incomplete. That’s a whole other topic worthy of it’s own valuable discussion, and thread drift tot he original topic here. But it all goes to planning your departure to be most safe – clear the obstacle if there is one, clear it with a reserve of safety if you can. If you must clear the obstacle at the cost of the understanding you cannot maintain a safe glide back speed, understand that, and minimize your time in the risk zone. Those showoff pilots who climb away after takeoff, hanging on the prop with no obstacle, are failing this miserably.
I get your concerns and I think they are valid. However I also think that your concerns “concern” pilots that do not fly the plane in accordance with the POH/AFM/normal envelope and don’t have the proper response to an engine failure.
Pilot_DAR wrote:
Those showoff pilots who climb away after takeoff, hanging on the prop with no obstacle, are failing this miserably.
Pilot_DAR wrote:
A short field performance chart is going the show the distance required to clear the 50 foot obstacle, and when over the obstacle, you will have the speed to land back safely. You can clear the obstacle in a shorter distance, but a safe glide back will not be possible. For that reason, the manufacturer will not provide that data, even though the plane could be capable.
Rwy20 wrote:
No, he is not. Pilot_DAR talks about a trajectory on takeoff which would allow you to keep flying if the engine stops, as opposed to plummeting to the ground.
Archie wrote:
I assume by “glide back” you don’t actually mean a turn back, but a glide to land straight ahead. I think it is foolish to assume you can do this safely without injury as I pointed out earlier. There may be forest, ditches, rocks, houses, cars, water, fences in the way.
Yes, glide back to earth, not the departing runway – we land straight ahead following EFATO. This should be a safe and injury free event, unless you hit something, which is not an aircraft performance issue, but rather bad planning (takeoff path) or bad luck (the hard thing was there, and nothing you could do about it). However, a properly conducted takeoff should always have a safe power off, land straight ahead option (assuming suitable area to land in). Other than a possible brief period before the obstacle is cleared, an engine failure during a normal takeoff should leave the aircraft retaining enough energy, and controllable to return safely to earth.
