Best glide speed (range) in 757?
 

Lost my copy of the sleep-inducing "Mishandling The Big Jets" book. Bext angle (Vx) is 235, best Rate (Vy at about 90 tons) is about 275kts. If both donkeys died, what would be the best for glide range? I think it is Vx as best angle of climb must be the same as best angle of "un-descent"?

PS in the sim you can lose them at 3000 off the end of the runway at EGCC and still have to lose height to make it back onto the departure runway!!!

Lacking a AOA indicator, I'd go to Vref+80.

Any particular reason why?

For best glide, you want to go to L/D max. Usually L/D max is somewhere around 3.8 AOA I think, but it depends on the airfoil. Since civil airliners are rarely fitted with AOA indicators or vector bars, you can't really determin AOA easily and accurately. In absence that AOA readout, Vref+80 (low GW) or Vref+100 (high GS or high altitude) is a decent rule of thumb.

757 Optimum Glide Speeds
GW Vref Op Glide
160 117 203
200 133 226
240 148 246

767 Optimum Glide Speed
GW Vref Op Glide
220 119 203
300 141 236
360 159 257

Commercial flight manuals are notoriously sparse of detailed data and charts. Maybe someone else has a better ROT. Sorry, that's the best I can do for you with the data I have.

Thanks for the info! Nice to get some sort of reply.

Since nobody else is responding on this subject....Bar is open....drinks are on me! :p

It might not be a bad idea to check out the in-flight start envelop that will come on to the EICAS display. Hopefully at least one of them can be caught before it rolls back too far. If that's not a player, I also would shoot for approxiomately Vref+80 initially.

The best glide speed is Vref+80 in clean configuration.:p

We do this as a sim exercise for a double fail after T/O, to simulate losing them entering a CB/rain at about 3000 feet. We've got Vref +80 on the clock when both fail. I used 235kts as it equated to best ANGLE of climb (best angle of non-descent?) Inflight start on eicas says 240 for a relight using the fuel control off-then-on method to reset the starter logic for a quicker relight.

Guess I just hate not getting a definative answer.

Thanks for the input, guys!

Best angle is L/D max. Good for both descent and climb and holding (best endurance), assuming no other factors or restrictions.

Has there ever been a case of a 757 or 767 haveing both engines stop on takeoff at 3000 due rain?
Take off directly into an active cb and heavy rain is never recommended and was banned in my company for all their jets including the 767/757.
The ignition selector should be Both after start and in the cruise as it ties in with the engine ant ice system use after flaps are up.
I asked your question and told vref+80kts was the speed you sought.
I note you nolonger land straight ahead but are given height enough to return to the field.

What do they tell you is the "minimum" height for the 757 for this manouvre to work at max tow?

Hope the light aircraft pilots do not pick up on this 757 sim manouvre and attempt this at lower altitudes.

QRH sez....
300kts minimum blo fl300.....
no restart.....then
it may be neccesary to reduce to Vref30 +100 to increase range

subsequently
descent approx 400ft per nm
360 degree turn loses 5000 feet
aim to cross OM /4 dme at twice normal height, Flap 5, Vref30+40
gear down flap 20 after OM/4dme

Best angle = best glide... I hope you are never flying my airplane... Best rate speed will more co-inside with best glide because that is the speed where it is most efficient... I hate to make sense but... I guess all you airline guys were asleep at the switch today...

Best rate of climb speed occurs where the difference between available engine power and required power for level flight is greatest; this is max excess power. In a turbine, at slower speeds, available power will increase with speed at a faster rate than required power, so best rate of climb speed will be slightly greater than minimum power speed. Minimum sink rate occurs at the minimum power required to sustain flight speed, this gives best loiter time, max endurance.

Best angle of climb speed occurs where max thrust minus drag is greatest. Thrust does not vary much with speed, so max climb angle is obtained near minimum drag speed. Minimum glide angle will occur when the weight component acting in the direction of flight will just balance drag, for the most efficient operation this occurs at the minimum drag speed, that is where the least amount of weight is acting in the direction of flight. As stated minimum drag speed is the same as minimum glide angle which is the same as best angle climb speed. Minimum glide angle will give the greatest horizontal distance.

- confusing isn’t it.
:)