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Source: Wolfgang Langewiesche - Stick and Rudder; An Explanation of the Art of Flying

  1. Why is it called a mushing glide?

  2. In this glide, does the aircraft point its nose less (or more?) steeply?

  3. How does it steepen the descent?

I find the explanation confusing. At one point it seems that a mushing glide is caused by a high AOA and at another point it seems that a low AOA (pointing slightly above horizon) causes it.

user13197
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user2927392
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2 Answers2

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Why is it called a mushing glide?

The aircraft is not cleanly cutting through the air. It is "mushing" through the air at a high angle of attack creating lots of drag and a slow forward airspeed.

In this glide, does the aircraft points its nose less (or more?) steeply?

The aircraft has its nose pointed up (less steeply) than a normal glide.

How does it steepen the descent?

The low forward airspeed and high drag creates a high rate of sink relative to the forward motion. Low forward speed and relatively high sink rate means the descent will be very steep. A fully stalled condition would be an extreme example of a "mushing" glide.

low AOA (pointing slightly above horizon) causes it.

pointing the nose slightly above the horizon is still a High Angle of Attack, not low AOA.

Federico
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Mike Sowsun
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    The maneuver described in the book minimizes the sink rate, so you have it wrong. To quote the book ("A sailplane--in fact any normally shaped airplane in a glide, will lose the fewest feet of altitude per minute when flown at this gait"). – Tyler Durden Apr 14 '16 at 18:53
  • I guess it depends on how low the airspeed is. If you are on the edge of a stall, you will have a steep angle of descent. Low forward airspeed causes a steep ANGLE of descent but a low RATE of descent. It is sort of the opposite of best RATE of climb vs best ANGLE of climb. – Mike Sowsun Apr 14 '16 at 18:58
  • You said in your answer that the maneuver causes a "high rate of sink". That is not right. A gliding aircraft's sink rate (vertical velocity) will be minimized by increasing the angle of attack. That is exactly what the book says (and the book is correct). – Tyler Durden Apr 14 '16 at 19:00
  • I edited my answer to make it more correct. "low forward airspeed and high drag creates a high rate of sink relative to the forward motion." – Mike Sowsun Apr 14 '16 at 19:02
  • That seems like a weird way to say it. If you look at the numbers in my example which are pretty typical I am not sure if I would characterize that as a "high sink rate". To a glider pilot a high sink rate is -500 fpm. In a so-called "mushing glide", your sink rate actually decreases slightly, maybe from 150 to 140 or 130 at best. Also, the glide slope change is not really that dramatic. I have done this maneuver so I know. Just run the numbers for yourself. – Tyler Durden Apr 14 '16 at 19:10
  • The question was asking how a "mushing" glide steepens the descent. I guess I could have worded it better but I wanted to emphasize that the slow forward speed would produce a steep angle of descent even with a low rate of descent . – Mike Sowsun Apr 14 '16 at 19:17
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    @TylerDurden: Mike is right, and a mushing glide does come with a high sink rate. Once you fly below minimum sink speed, sink rate goes up when you slow down. You may think you have flown this maneuver, but with that low sink rate it was not really a mushing glide. I've done real ones. – Peter Kämpf Apr 14 '16 at 20:55
  • @PeterKämpf At the risk of repeating myself, the author of the book (Langewiesche) himself says sink rate is minimized, the words he uses are "fewest feet of altitude per minute". So, just to be clear the sink rate DECREASES when you pull back on the stick. I actually give practical numbers in my answer. If you are saying sink rate increases after pulling back on the stick, you are controverting what it says in the book the OP cites. – Tyler Durden Apr 14 '16 at 22:34
  • @TylerDurden: Take any glider (I have made the best experience with a Discus; an ASW-20 is less docile) and fly it in a thermal. Preferably late in the day when the thermals are wide and smooth. Then fly the plane at an appropriate speed (90 km/h for 30° roll angle). Note the vertical speed. Slow down to 80 km/h, or to 75 (the Discus will do this without problems). Note the marked decrease in climb speed. Do it with water in the tanks and add 10 km/h to the numbers above. Same effect. What are we even arguing here? – Peter Kämpf Apr 15 '16 at 15:25
  • @PeterKämpf How is this even relevant to the OP's question? You are kind cluttering Sowsun's answer. If you have your own ideas about interpreting the passage in the book, maybe you should make your own answer. – Tyler Durden Apr 15 '16 at 16:12
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    @TylerDurden: How ironic! After 5 comments you are concerned about cluttering Mike's answer. Well, then shut up. Both you and Langewiesche are wrong and Mike is right, short and simple. – Peter Kämpf Apr 15 '16 at 17:04
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  1. It is called "mushing" probably because the controls will be a little mushy (soft). At high angles of attack you begin to lose control authority and the controls can feel soft.

  2. The nose will be pointed slightly above horizon.

  3. When you pull back on the stick your forward velocity will decrease, but your rate of vertical descent will stay the same or decrease by only a small amount, so your angle of descent will become more steep.

Let's put some numbers on this and make a "real" example. Let's imagine you are in a sailplane which is in a configuration that stalls around 35 mph. You are currently travelling at 45 mph in a level flight attitude, descending at 150 feet per minute. You will be on 2-degree glide slope (confirm this for yourself). Ok, now pull back on the stick until you are going about 37 mph. At this point the controls will start to get soft. Your vertical speed may decrease to about 140 feet per minute. Your glide slope will increase to 2.5-degrees. Thus by this maneuver your glide slope increases (becomes more steep).

Just as a further exercise, let's compute how much we can change our touchdown point by the above maneuver. Suppose we are at 200 feet AGL, then we will touchdown in about 5200 feet in the beginning attitude (confirm this for yourself). Okay, now we pull back the stick to 37 mph ("mushing" descent to use Langewiesche's terminology) and our vertical speed goes to -140 FPM. How much does this change our touchdown point?

If you do the math, you will find our touchdown point changes from 5200 feet to 4650, a difference of over 600 feet. So, by using a "mushing" glide we have changed our touchdown point significantly. Let's just illustrate it with a real airfield:

enter image description here

So, here we see our current position at the circle. If we continue on our current glide path we touch down in 5200. It's too close to the crossover on the runway. We would much rather land at the blue line. By using a mushing glide we could accomplish that.

Tyler Durden
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  • Great explanation. I guess I need to check for myself and "feel" the softness of control surfaces – user2927392 Apr 16 '16 at 12:35
  • @user2927392 If this answers your question, you may want to accept it. I would suggest doing the calculations I describe in my answer for yourself. Doing calculations like this will make you a much better glider pilot since you will know the actual real geometry of the situation, not just visual guesswork. – Tyler Durden Apr 16 '16 at 14:58
  • Yes this answers the question. I think I confused rate with angle.When you maintain pitch above the horizon, you actually decrease the sink rate but increase the sink angle. And I am correct, if you pitch slightly down, you increase the descent rate but you descend less steeply. – user2927392 Apr 16 '16 at 16:31
  • Why not make an S-turn or two to lose altitude, rather than bringing yourself dangerously close to stalling? – Vikki Jan 21 '19 at 05:28
  • @Sean The question was about mushing glides. Normally to shorten the touchdown distance a pilot will use the dive brakes, or slip if a large adjustment is needed. It is a bad idea to maneuver on final. – Tyler Durden Jan 21 '19 at 06:02
  • According to See how it flies (https://www.av8n.com/how/htm/energy.html#sec-power-curve-intro), you don't just get the steeper angle of descent but the descent rate in feet per minute also increases as you pull nose up when in mushing flight. I think it's because at some angle of attack pulling back further starts to reduce the lift but increases the drag. The critical speed where you enter mushing flight is best-angle-of-climb speed. – SMeznaric Nov 05 '21 at 13:22