Best Glide Speed And Bank

[subpilot]

...that shows your experience.....do a 60 degree banked gliding turn without loading the wing and see if you can avoid the Vne dive! You certainly can see 2 or more g's in a steep spiral!

How does the acceleration to Vne relate to the wings being loaded?

 

[Ziggyfuzz]

How does the acceleration to Vne relate to the wings being loaded?

If all you do is roll into the turn, coordinate it and add no back pressure you will enter a spiral dive and quickly reach Vne, greater load (by pulling) equals greater AOA( and less nose down attitude for accelleration with gravity) and both load and AOA increase drag keeping you from reaching Vne. If that doesn't answer it for you, then just try it...that's the best way I can explain it!

 

[fish314]

There. That should make it clear to those folks.

A more than fair critique! I tried to explain what the terms mean... but I realize that math is definitely not everyone's cup of tea.

 

[shdw]

Adrock,

You initially had the correct reasoning. The bank requires an increase in lift assuming you want to maintain steady state flight. With no configuration changes, the only ways to increase lift are to increase AOA or increase speed. Since L/D_max for a given configuration is only a function of AOA, you can't change AOA and still keep the "best glide" condition. As such, speed has to be increased in order to make a best glide turn.

Note that the steady state condition does NOT require you to maintain altitude as a few have mentioned. It does require that you are not accelerating vertically – that is, your vertical speed is constant.

Mike

:yeahthat:

Aerodynamic weight increase effects v-speeds in the exact manner as an actual increase in weight. Does it change with an actual increase in weight? If that answer is yes than the answer for it changing from g-load will almost certainly be yes also.

I never saw a more rigorous mathematical explanation of it, though, so I never fully trusted that explanation.

The optimal 180 would require minimum altitude loss and radius/max rate of turn. Agreed? This being the case we need to shoot for a bank angle that will correspond to stall speed being at minimum sink speed while taking into account that minimum sink speed will increase with g-load increase. I don't remember calculus well enough solve this, maybe you do?

For what it is worth I always simplified this by just finding the bank angle that yields stall equal to 1g minimum sink. It isn't perfect, but it is better than just winging it. This is also how I was taught to find the optimal bank angle for flying in a thermal during my glider training.

 

[shdw]

Disregard above, didn't see there was a second page here when I checked at work.

 

[Autothrust Blue]

The following three PTS tasks are all different: ...

Not to be (more than normally) flippant, but an emergency landing might just include two ore more of those "TASKs".

There's the PTS, then there's reality, which are occasionally divergent. As Ziggyfuzz pointed out a savvy examiner will use the maneuvers in conjunction...which is a fairly realistic application.

"Hey, the field is made, and our engine is still dead. And it's on fire now. Let's spiral down over the airport and GET DOWN!"

 

[mhcasey]

For what it's worth in the F-16 during a flameout (or simulated flameout) approach we use the same airspeed whether flying straight ahead or in a bank. The pitch attitude in a 55 degree bank (supposedly optimum if turns are required) is about 5 degrees lower than without bank to maintain the same airspeed. I'm no engineer, but someone at General Dynamics long ago decided the airspeed for the F-16 for best glide should not change in a bank, and I'm inclined to think with the lower operating speeds of most GA aircraft that would hold true there as well.

 

[fish314]

For what it's worth in the F-16 during a flameout (or simulated flameout) approach we use the same airspeed whether flying straight ahead or in a bank. The pitch attitude in a 55 degree bank (supposedly optimum if turns are required) is about 5 degrees lower than without bank to maintain the same airspeed. I'm no engineer, but someone at General Dynamics long ago decided the airspeed for the F-16 for best glide should not change in a bank, and I'm inclined to think with the lower operating speeds of most GA aircraft that would hold true there as well.

We did similar in a T-6, but held 30 degrees once over the field in a normal forced landing pattern. The 60-70 degrees was just for the quick turn around with excess air speed... but even after that we weren't at "true" best glide. Our dash 1 had us at 125 knots, regardless of weight. True best glide airspeed varies with weight (although glide ratio remains constant), and 125 ensured we were always at or slightly above. Best glide was typically around 100-110, usually +/- a knot or 2 of 105 (clean, straight and level), IIRC. The slight excess above best glide was a safety factor for maneuvering and to make up for poor pilot technique, since stall speed wasn't much lower.

I imagine a similar thing probably played in for the F-16...

Again, I'd love to see the math that backs up the analysis for other starting conditions. The math link above proves the case of 45 degrees as the best angle (and it should hold regardless of aircraft), but ONLY based on the assumptions by which they defined the problem (very near 45 degree bank stall speed when engine is lost with no excess air speed to trade for altitude). With significant excess airspeed, I'm sure the answer is probably different... but don't really know how to set up the analysis to prove it.