Airborne_Again wrote:
The problem is to know what the best glide speed with landing flaps is
At first approximation, the delta on VBG from clean/dirty config is about VS0-VS1 (if you just shift polar curve and ignoring 2nd order effect from twisting it at higher speeds), in practice, VBG moves more with headwind, wind gradient and vertical air than with config & weight
In gliders, going for negative flaps pushes VBG as much as it pushes VS without lot of change in best L/D, same for changes in weight (dumping water)
Ibra wrote:
in practice, VBG moves more with headwind, wind gradient and vertical air than with config & weight
In this case it is a matter of energy rather than actual glide angle.
Airborne_Again wrote:
In this case it is a matter of energy rather than actual glide angle.
Energy is a relative concept.
Pilot_DAR wrote:
Practice power off landings from downwind to touchdown in whatever you fly.
That cannot be said loud enough. I am still surprised at how bad my plane glides with prop idling, more so with gear down. Even a PA28 glides well against that. You can configure the plane between “descend badly” and “fall like a brick”. And you sure have to respond quickly to keep it flying, it likes 90 knots (v_bg 91) or more, but all getting a lot better with the fowler flaps halfway down. I had to quit using my earlier used power-off landing technique and adapt because I just never got to my landing destination at first. It’s a bit surprising because it flies so economically and fast, but any wing layout has it’s sweet range.
It’s simple math. Gliding 1:10 on 90 knots (clean aircraft, maybe even a bit optimistic) results in a descent of 1000 fpm. With prop windmilling, gear down and not flying prefectly clean I assume glide rates of down to 1:5 are realistic, resulting in 2000 fpm descent.
The gliders I once flew had between 100 to 200 fpm descent (where those with 100 fpm are amazing…)
LeSving wrote:
Energy is a relative concept.
Please let’s not split hairs. Pilot_DAR was talking about the amount of energy needed to arrest the descent during the flare.
LeSving wrote:
Energy is a relative concept.
My aunt turned 100 last year, and she has a lot of energy, but that’s not relative to this discussion.
It requires the addition of energy to accelerate. If you are in a steady descent, and you would like to stop descending, you’re going to have to accelerate upward from the descent path, so you’re going to have to add energy. In an unpowered airplane, all you have to do that is to trade airspeed, so carry a little more than you need to trade off at the top of the flare. If you’re autorotating a helicopter, bonus, you can store extra energy as airspeed, and some more as extra rotor RPM (‘cause you’re going to need it when you pull at the bottom!). But for airplanes, just airspeed.
If you find yourself with too much energy at short final, a sideslip will help with that (and we practice sideslips when we’re practicing forced landings regularly, right?).
A power off rate of descent exceeding 1000 FPM requires skill and practice to transition into a nice power off landing. When I replaced the two blade Hartzell with a three blade MT, the “onto the step” performance improved. The power off glide suffered. My first practice forced approach was a little terrifying! What had been a 800-900 FPM glide descent rate was now 1300-1400, which meant adding at least 5 MPH to the glide speed to enable a good flare. I found that selecting full coarse on the 3 blade MT got me back the more manageable 900 FPM. It was really lucky that I thought to practice this and found this difference before it happened for real and I had not allowed enough reserve energy to flare.
I find that all of this is rather glossed over with a few practice forced approaches to 100 feet, then power away. That’s not enough training, and incomplete. Power off from downwind to touchdown!
I found that selecting full coarse on the 3 blade MT got me back the more manageable 900 FPM.
Very true, but what if the EFATO is the result of a catastrophic loss of oil pressure, then the governor will fail towards full fine on an SEP.
RobertL18C wrote:
but what if the EFATO is the result of a catastrophic loss of oil pressure, then the governor will fail towards full fine on an SEP
Sorry, I can’t offer suggestions for every eventuality, some situations are simply difficult to manage….. So practice!
Am just pointing out that in the event of a loss of oil pressure EFATO in a SEP the practice of pulling the propeller to coarse may not provide you with the correct practice environment.
Are you not in danger of over complicating things here.
IMO you are conflating 5 different elements.
1/ EFATO at Vx. If the EFATO is rare then the EFATO at Vx is even rarer. Depending on height AGL you only have one choice and that is to get the nose down to your normal approach speed and land as normally as the terrain and obstacles will allow.
2/ Best glide speed. If it’s not in the POH and you have not discovered it beforehand you could use Vy. But the main thing, surely is that you pick a field which you can reach at that speed with enough height to make a normal engine off landing allowing for wind direction and wind speed.
3/ By achieving 2 it allows you to make a normal engine off approach at normal approach speed. The configuration you use will depend on your aircraft and how you have practiced. For instance with a ULM you will likely come in high, point the aircraft at the threshold and aim steeply downwards, by the time you get into the flare you will have lost so much inertia that you will touch down and stop pretty quickly, like the glider tug guys do all the time. If you are in a DA40 coming down final approach with take off flaps and you suddenly go to full flaps you need to remember that it’s like slamming on the brakes.
If you are in a Jodel with no flaps you might need to lose height by side slipping or running ‘S’ s. We have discussed the merits of each of these before. But keeping a little extra height as long as possible so that you can trade it for extra speed (to normal final approach speed and config with engine off which can be practiced regularly at an airfield).
This might be a matter of making allowances when you choose the field you are trying to force land in eg I want to arrive at the vertical of that field at 1000’ .
4/ The flare should be the same as you do every landing with most aircraft. Metal aircraft you need to add a little speed because of the extra weight you are carrying to help you ease it to the ground. Add too much speed and you will be into the wall at the far end of the field without getting the wheels on the ground. Many suggest that Vr is a good figure to aim for if its not in your POH.
5/ The go around which of course does not exist in the case of a real engine failure. But in practice, here again there seems to be a discrepancy between instructors.
In the French PPL handbook it recommends “attitude, power, climb to safe altitude”
The book explains that the reason for this is really a matter of inertia. In a normal light aircraft and starting the go around at low height, adding power could well take you into the ground before the climb can actually start. I am well aware that many UK instructors take the opposite view and I know of one pilot who returned to the UK and received the instructor’s disapproval during his biennial check flight for not doing power first.
Incidentally, for ULMs here, it is power, attitude,climb because adding power on a very light machine is the fastest way to get it to gain height.
Just my 2c but I enjoy studying the way instructors teach and students learn, and when all these “ah but what happens if?” get conflated into the main significant message of “get the nose down” I think many students will just turn off.
