Balliol wrote:
I can’t believe any certified aircraft are unable to round out for a landing from best glide speed?
Oh they can round out, or they would not be certified. However, if you fly at “best glide” speed on very short final, you’d better time and execute your flare perfectly, as there will be hardly any reserve to correct a misjudgement. Consider a single Cessna with a STOL kit installed on the wing. With the changed airfoil, it is capable of a glide at even a slower speed, as the L/D has been optimized. However, in that slower speed, you have not stored much reserve energy, so you pull to flare, and it continues down. In the early days I startled myself with this, and learned. Since then, I have been teaching this during type training. This is particularly important on the water, as a badly misjudged landing will result in sinking the plane, rather than just breaking landing gear. “best” glide results in a safe landing, a safe power off landing will be the result of a little extra speed to stretch out the opportunity to judge the flare well.
For my experience (primarily during an extended flight test of a highly modified Cessna Grand Caravan) I found that the speed for best rate of climb (Vy), Cessna seems to have built in a safety margin. I found this during the testing to demonstrate that ability to make a safe glide landing from Vy at 50 feet, following a sudden engine failure – very scary testing! I could achieve a “best rate” at a speed slower than the POH stated, but I could not glide back from 50 feet to a safe landing from this combination of speed and altitude. That taught me that when landing from a glide, a bit of excess speed is your friend.
For the Twin Comanche, there is an odd relationship to the POH and the FAA approved Flight Manual – they are two different documents. The POH is pretty flashy, and presents lots of information, some of which I found to be accurate. The FAA approved Flight Manual is oddly basic, but for what it presents, very accurate. Make sure you know which you are reading.
Pilot_DAR wrote:
if you fly at “best glide” speed on very short final, you’d better time and execute your flare perfectly,
It really depends on the aircraft I would say. If you fly a modern glider at best glide speed on short final, you can fly all across the airfield, do a chandelle, fly back all across the airfield, perform another chandelle and then still need your spoilers to land it within the field 
… indeed, that is what I see time and again from the (very able!) glider pilots at my home field, especially for the day’s last landing. Only not too sure about that second chandelle 
Yeah, but their props aren’t windmilling, are they?
Pilot_DAR – thanks, I see you’re talking about modified aircraft so I can understand they must be different. For a normal unmodified SEP, gliding at best glide speed down to round out and landing is perfectly normal practice and that is what we teach and examine. Indeed I did a number of glide approaches to touch and go with a student this morning just like this! Approaching any faster will put you higher up on the total drag curve and compromise your glide performance so I can’t see how it can be recommended.
Timothy wrote:
Yeah, but their props aren’t windmilling, are they?
Neither are those of our twins if we follow the checklist and/or memory items ….
My first simulated double engine failure on an IR/MEP renewal I was pretty discombobulated – it’s just not a scenario that I had thought much about. I was far too slow to feather. And that was on an IR/MEP check flight when I knew something devilish would happen.
I just don’t think that most of us would deal with a simultaneous double failure very well, and that might include failing to feather until it is too late. Remember that in a “normal” engine failure, the other engine is dragging you through the air and keeping the failed engine windmilling enough to feather (For SE pilots who have no idea what I am talking about, props won’t feather once their RPM drops below, typically, 1000RPM.)
I now practice double engine failures on the sim, and I teach it, so I hope I would be quicker on the blue levers. But double feathering when way out to sea is a huge decision to take and I wonder how many people would think too long.
It may be another thread, but the whole feather/don’t feather choice is much harder than people give credit to. Several times I have been in the floatdown following a single engine failure when I have been 99% certain that the issue is fuel icing. I have therefore sometimes left it windmilling because I believed that it would pick up at lower, warmer levels. The thing is, once you are feathered, you daren’t try restarting because that way you may very well be committed to have a non-featherable windmilling prop.
discombobulated
Just one more UK peculiarity? Lucky poor old stupid me wasn’t tested for this level of vocabulary for the ELP.
Foreigners, be wary of flying into those abysmal airspaces, though, where R/T may become extremely poetic! Who knows perhaps even the curvatures of the very earth follow such unwonted contortions!
The DA42 has a Vyse of 82kts with Vx being 79kt , Vy 79kts (same as Vx?) with the prescribed Best Gliding Angle Speed being 82kts. For anything that doesn’t have a prescribed speed, I would use Vy for range and Vx for maximum time in the air. The numbers aren’t quite the same as best glide but good enough for the quoted scenario.
That said I can’t imagine any realistic scenario where one would be unlucky enough to have coincident (simultaneous) engine failures; no one can manage fuel flows/balance to the required level of accuracy. We regularly run the outer tanks dry on our PA31s and I’ve yet to see both engines cough at the same time.
Dave_Phillips wrote:
That said I can’t imagine any realistic scenario where one would be unlucky enough to have coincident (simultaneous) engine failures;
There is the famous case of a DA42 which suffered a dual engine failure after takeoff in Speyer (EDRY) in 2007. A total electrical failure was triggered by raising the electrically operated gear (after a ground power start with a wrong setting of the generator switches) which took out both FADECs. Some modifications have been applied to the electrical system of the DA42 since then. Apart from that, the only possible reason for coincident dual failure is contaminated fuel.
