As for the usefulness of being able to turn downwind if it quits in cruise, it’s going to depend a lot on your V(bg). Mine is quite slow (50 mph, more or less, from actual testing). So if I’m heading into a 30kt wind, my glide distance downwind will be dramatically further turning downwind than going forwards, and the 180 degree turn will use up a negligible amount of that distance. However, with an aircraft with a low landing speed, generally there are a lot more usable landing spots than with something higher performance (on grass I would expect to be able to stop in 100m from a glide approach into wind).
I don’t remember if Skydemon allows you to enter V(bg) but this will have a significant effect on the shape of the landable area it draws if it does.
LeSving wrote:
That depends. A tank is usually design with the pick up aft in the tank, in a special lowered department. The lowest part of the tank is therefore aft. When low on fuel, you will always get fuel when climbing, but could run out (in the small compartment) when diving, because the fuel is shifted fwd.
In mine, the pickup is at the front of the tank (fuselage tank), but the shape of the tank is such that the front is always the lowest point in any sustainable attitude and will be above the carburettor in any sustainable attitude. The aux tank pickup is at the mid point (the aux tank is external and aerodynamically shaped) and below the carb, so the aux tank is not used for takeoff or landing.
The Cessna 140 I used to have had its fuel pickups about in the middle of the tank. Takeoff was prohibited with the fuel selected onto a tank that was less than 1/4 full (and it would unport if you did, believe me).
In the case of a tank designed as you say, if you’ve got so little fuel that the fuel unports in the attitude for V(bg) then you’ve already made some terrible life choices.
Peter wrote:
From e.g. here it seems that one should commence a change of direction towards a suitable landing site immediately and do this before the usually taught actions (e.g. fuel pump on, alternate air, etc).
Only for a carburated engine (carburator icing), you’d want to get the carby heat in pretty quickly. In any other case common airmanship teaches that there is a very small amount of failure where you could not count 1-10 and still have plenty of time to trouble shoot. I.e. it is possible to setup your backup plan first (glide to a field), then trouble shoot. Particularly if the options are limited over rough terrain.
You are not going to be a happy man if you spend a lot of time troubleshooting whilst flying away from the only landing site… where are you can easily set yourself up for that landing site, then troubleshoot all you like whilst managing your glide path.
POH/AFM usually doesn’t include these airmanship items nor does it prioritize as the situation you are flying in can be so different from time to time.
LeSving wrote:
Lowering the nose further will certainly not help, but raising it, even only for a second, will.
Yes; if you are trimmed at some speed which is not on the back of the curve then power loss should just pitch down the nose and carry on at the same speed.
However there may be a delay in the pitch-down (due to inertia around the pitch axis) and maybe some phugoid oscillation?
Definition of a trimmer ’a simple device that can fly the ’plane better than the pilot’
I think that’s brilliant 
In my PPL (Shoreham, 2000-2001) I was never taught what trim actually does. The trim wheel was explained as something you use to tweak out the force on the yoke! Admittedly that was in a PA38 which has no elevator trim tab (it uses some sort of spring-loaded stick pusher). Later on I had an instructor who showed me the light… it does save an awful lot of work 
If in the cruise all nicely trimmed out, or even in a stable, trimmed climb you probably don’t need to actively get the nose down at all if the engine quits. Definition of a trimmer ’a simple device that can fly the ’plane better than the pilot’ so just let go of the stick and the pitch trim will take care of that for you. I’ve tried this in mine and it does work.
Martin wrote:
The optimum is actually at the stall angle of attack (maximum coefficient of lift), it just wouldn’t be easy to achieve. Question is what is the pilot actually able to reliably achieve (and what would he do). If you haven’t trained it, you might very well stall when trying to rapidly turn
My father made a steep, slow turn after engine failure on the upwind at 500 ft, over a built up area, and made it back because he did. But, very significantly, he was flying a canard design and was able to pull pitch until he felt the characteristic ‘bucking’ of the front wing lightly stalling and unstalling. There was no danger of departure from controlled flight. I do suspect that his flying a canard on that day 30 years ago saved him from injury or worse – he was a competent pilot but no super pilot.
Airborne_Again wrote:
I have a copy of an old (1974) scientific article “The possible impossible turn” which makes a theoretical analysis of what the optimum flight profile should be if you want to turn back to the runway after an engine failure on initial climb-out. The turn itself should be done at 45° of bank at a speed 5% above stall.
I read it years ago as well (I’m not sure about the year, but I believe it’s the same; it was from Rogers). The optimum is actually at the stall angle of attack (maximum coefficient of lift), it just wouldn’t be easy to achieve. Question is what is the pilot actually able to reliably achieve (and what would he do). If you haven’t trained it, you might very well stall when trying to rapidly turn. One of those things you learn while flying gliders.
JasonC wrote:
Ok, so on climb out you get an engine failure, you are going to hold the nose high (or even raise the nose) in the hope that you have a low fuel problem so the engine might restart?
No. What I mean is that if you are low on fuel and heading in a slight downward path toward an airport, the engine can easily stop due to fuel starvation, even with plenty of fuel on board. Lowering the nose further will certainly not help, but raising it, even only for a second, will.
Martin wrote:
Yes, I disregarded it. You’d get the additional complication of how quickly I can turn and with what sink rate (although it’s good to know what bank angle offers a good compromise).
I have a copy of an old (1974) scientific article “The possible impossible turn” which makes a theoretical analysis of what the optimum flight profile should be if you want to turn back to the runway after an engine failure on initial climb-out. The turn itself should be done at 45° of bank at a speed 5% above stall.
That is not quite the same situation as an enroute engine failure as in the initial climb-out scenario you are aiming for a point which is known from the start (the runway), but it still gives a hint that the speed should be lower and the bank angle higher than you might first think.
Noe wrote:
However, now that I think about it, even in flat terrain / no wind, you won’t have a circle: you can’t reach as far back as forward, as you lose non negligible time / distance / altitude / energy in the turn.
Yes, I disregarded it. You’d get the additional complication of how quickly I can turn and with what sink rate (although it’s good to know what bank angle offers a good compromise). I wouldn’t expect any such software to take that into account and Peter wrote about wind. And the fact you can’t reach as far back as forward doesn’t show the issue.
It won’t be oval anyway. Consider turning back (in no wind for the sake of argument). Say you turn 180 ° to the right and then go directly back. You’ll end up some distance (the width of the turn) to the right of the track. The analogous goes if you turn to the left. What if you want to reach a spot right on the track? You’ll have to turn more than 180 ° and you won’t be able to reach as far “down” – a sort of cleft will be created. That’s not circle nor oval nor elipse. I guess one half of it (it would be bilaterally symmetrical) might be a sort of a spiral.
JasonC wrote:
I agree instinctive reaction must be to lower nose.
For me it’s more “watch the speed.” There are situations where I’m sort of spring loaded so to speak. For example, “pushing over” is important in case a winch launch of a glider goes wrong (say the line breaks). At that point, you’re ready for it, you’re practically waiting for it to happen (and in some clubs they botch it from time to time to keep you on your toes). It won’t really surprise you unless you gave in to complacency. I probably won’t be in this mindset in cruise or cruise climb unless I feel there is little margin for error in which case I’ll have a plan ready and will be waiting to execute it. It’s like being pushed into a corner. If I feel cornered, I’ll be looking for a way out and will be ready. Also, when it comes to instinctual responses, I try to keep them in line with what helicopters need as they tend to be less forgiving. And you don’t want to push the stick (the cyclic) forward in a helicopter after engine failure (it would reduce rotor speed).
