Maximum glide ratio

[chornedsnorkack]

It seems that the glide ratio L/D of airliners has not changed since 1950-s or even 1930-s. The numbers are something like 16...18.

Gliders are said to have achieved glide ratio of over 60 already in 1970-s. The current record L/D of a whole, manned airframe is held by a powered plane named ETA, and is 72.

Global Flyer is said to enjoy a glide ratio of 37. It has long, narrow wings: wingspan about 35 m, wing area 40 square metres.

Global Flyer is constrained in design by the huge fuel load (10 tons MTOW, 1600 kg ZFW... very limited structural mass available, and needs to stay efficient over a wide range of weights). Also, as a jet it has relatively high Mach numbers and also is constrained by the time the solo pilot can fly without sleeping.

U-2 is said to have glide ratio of 28. And it has wingspan of something like 31 m, wing area of 95 square metres... 1950-s design (back at the time when the L/D of gliders was in 40-s or less, not past 60), a jet plane, flying at high subsonic Mach numbers... and achieved L/D that large.

What is the main technical issue preventing more extensive use of planes having L/D in the 20...25 range?

[garymbuska]

I am not 100% sure that there is one, most designers just do not go into that kind of detail when making a aircraft. If you look into some of the payware aircraft ESP. military they will be more life like and probably include the abillaty to have that kind of a glide slope.
I have two payware aircraft a B727 and a airbus A320 A340. Both of these aircraft are designed with the real aircraft in mind with fully working panels realistic operation and life like dynamics. They put a lot of effort into the aircraft to make it as relaistic as possiable but I have to admit I never cheked out what the glide slopes were and do not fly any of the gliders or helecopters

[Hagar]

I think this should be in the Real Aviation forum.

[Nexus]

It

What is the main technical issue preventing more extensive use of planes having L/D in the 20...25 range?

The ability to drop the inoperative engines. Todays large high-bypass turbofans creates enormous amounts of drag when they are dead, and off course carries a large amount of weight.

Imagine if you could release the huge engines of a 777, the ratio would probably exceed 20:1.
But then again, I'd rather not have a falling engine in my front yard...talk about head ache  :-/  ;D

[chornedsnorkack]

The ability to drop the inoperative engines. Todays large high-bypass turbofans creates enormous amounts of drag when they are dead, and off course carries a large amount of weight.

What is the engine of Global Flyer like in drag generation?