Steep Gliding Turns

[Northernflyer43]

Student was asked to perform Steep Gliding Turn during PPL Skills Test.
How would you enter and maintain this?? - as Examiners standard was different to way student had been taught?

Thanks,NF43.

[Sleeve Wing]

1. Climb to suitable Altitude for the exercise.
2. LOOKOUT. Clear area, particularly below.

3. Close Throttle. Select Carb Heat Hot.( if reqd.)
4. Trim for the Glide, wings level.

5. Bank to 30deg. Control speed with pitch.
6. Check Height / ROD.

7. Bank to 40deg. Control speed. (with increment.)
8. Check height / ROD.

9. Bank to 50 deg. Control speed. (with further increment.)
10. CHECK HEIGHT / ROD.

11. When ready, wings level, increase power to climb.
Check Carb.Heat cold.
12. Recover to exercise altitude.

AIM.
To control speed.
To control higher angle of bank.
To appreciate V. high rate of descent.
To appreciate rapid loss of height.
To relate to situation regarding Forced landing without
power.
Spacial awareness.

My 2penn'orth.
Comments welcome.

Sleeve. :8

[homeguard]

Sleeve

Whatever the detailed arguements the important elements that you have ommited are; a) Wing loading and b) stall speeds.

The effecive weight of the aircraft in a 60 degree angle of bank is doubled and the speed at which the aircraft will now stall is increased by 40%.

At angles of bank of up to say 30 degrees the changes are minor but with each further increase the wing loading and the stall speed increase greatly. It would therefore follow that if this fact is not respected a steep spiral dive or a spin may arise.

On test I am looking primarily to see that the candidate lowers the nose and first increases the speed BEFORE increasing the angle of bank in excess of 30 degrees.

So you should modify yours notes 7-10 and also the Aims.

[BEagle]

Enter glide as normal.

Enter descending turn at 30 deg AoB maintaining normal gliding IAS.

Increase to 45 deg AoB turn attitude; progressively increase nose-down pitch attitude to maintain normal gliding IAS.

To recover, reduce to wings level and carry out a normal recovery from a descent.

In a 45 deg turn, the stall speed is only 1.2 x the 1 g stall speed; thus a PA28 would stall at around 68 mph rather than 57 mph, well below the normal gliding speed of 85 mph.

Increasing the IAS above the normal gliding speed is totally unnecessary in a 45 deg AoB gliding turn and would cause an unreasonably high RoD.

No special 'lists', 'aims' or other complications - this is a very straightforward exercise which requires slighter greater skill than a normal descending turn - the principal assessment requirement being to ensure that the applicant appreciates the reduced margin between the gliding speed and increased stalling speed and controls the a/c attitude accordingly.

[FormationFlyer]

homeguard
The effecive weight of the aircraft in a 60 degree angle of bank is doubled and the speed at which the aircraft will now stall is increased by 40%.

However, you missed one vital fact here. The stall speed only increases if you increase wing loading - and the figures you give are for a level turn.

I can achieve 60deg AoB and yet still only be at 1G...

At 60deg angle of bank wing loading does not necessarily increase UNLESS you apply back pressure. You must be pulling 2g for the suggested stall speed increase to occur.

In a steep gliding turn this level of G is NOT encountered therefore the stalling speed does not increase accordingly. However, using back pressure to control the airspeed (as you must) will change the stalling speed. However, not by that much - maybe only around 10%(estimated) even with 60deg AoB - because the wing loading has only increased a small amount.

[orionsbelt]

I was trained and teach it as shown below
However the above posts are valid and food for thought and raise the question 'that is the increased stall speed in a descending glide turn due to:-'
A) Increased AOB,
or B) Increased loading,
or C) combination of A and B

Expert input required please, Genghis comment pls

The text is from:-
Flight Instructors Manual by RD Campbell

The Steep Descending Turn

These turns will be practised from powered descents or glides. The control functions are exactly the same as for steep level turns, but due to the lower nose attitude in relation to the horizon line (particularly in the gliding case) it will be a little more difficult to maintain a constant airspeed. With descending steep turns the entry airspeed should be higher than for a normal glide descent, and this speed increase should be in relation to the pre-selected bank angle, i.e. the higher the intended bank angle the higher the airspeed. This is to ensure an adequate margin above the increased stalling speed during the turn.

''Referring to fig. 15-4 the increase of stall speed at 45° is 18% and at 60° is 40%. Ignoring power effects on the stalling speed and assuming a VSl of 50 kts this will mean that at 45° of bank the stalling speed will have increased to 59 kts and at 60° of bank to 70 kts. Therefore a good principle would be to increase the normal descent or glide speed by 10 kts for a 45° banked turn and 20 kts for a 60° banked turn.''

During steep descending turns the tendency for the nose to lower will be more marked and a quicker reaction to this must be made by bank reduction and increase in back pressure. A useful practice manoeuvre is the steep descending turn with flap lowered to stimulate a situation where the pilot is inadvertently operating at steep bank angles during the final stages of a spiral type descent whilst positioning for a final approach for an actual forced landing without power.
The procedure is exactly the same as for a gliding steep turn with flaps up, but the actual speed used will have to be compatible with the flap limiting speed, and wherever possible the speed chosen should be at least 10 kts lower than the maximum speed permitted with flap down. The main difference in handling will be in the steeper nose attitude necessary to maintain a safe speed, and the rapid lowering of the airspeed when the nose is raised even by quite small amounts.

Cheers Orions***

[FormationFlyer]

More thoughts...AoA in a descending turn is less than for a climbing turn....

Im not saying the stalling speed does not increase - Im saying It does not increase by 40%. There may be some increase as per my last post to account for the need to control airspeed using pitch - but nowhere near the figures quoted.

If AoB were a consideration then think about this. During a slow roll an aircraft will go through 90deg, to remain level would induce significantly high G loading and would therefore result in the stalling speed increasing beyond the capability of most light aircraft. Why does the aircraft executing the slow roll not flick out at 90deg?

Reason - the wing does not stall - there is little loading. A slow roll is a +-1G manoeuvre. Therefore the stall speed does not increase significantly.

I have examined ALL of my books on aerodynamics and cannot find explicit reference to stalling speed in a descending turn - only level turns. Indeed the RAF flying manuals themselves only give stalling speed changes in relation to wing loading - not against AoB.

Now I did a steep descending turn in a glide recently demonstrating an emergency descent following a simulated engine fire - I dont recall feeling 2G....To be honest I would have put the G level experienced (no G meter) at less than 45deg turn - even though I had 60deg AoB. This means the stall speed increase would be an absolute max of 17%.

An aerodynamics expert would be greatly appreciated.

[squawking 7700]

I'd go with FF's explanation, anybody here actually banked to 60°
and flown at a speed lower than the 'suggested stall speed' and not pulled 2G, yeah that's right it doesn't snap round on you.

Haul back to up the wing loading (and AoA) and you get a good example of wing drop, most of my experience of this is in gliders (it's not demo'd that much in power flying).

Go and try it.

Oh and if that doesn't kill you - carb heat hot first (if applicable) before closing the throttle and carb heat cold before opening the throttle.


7700

[MadamBreakneck]

In my gliding days long ago, I was told that best angle of bank for amount of turn per height lost was 45degrees - is that the case or does it depend on type and slipperiness? I wouldn't have thought so and I still use it as a rule of thumb in PFLs.

Obviously issues of speed and control still arise as discussed above.

:8 Anyody run the numbers to confirm or correct this?

MadamB

[FormationFlyer]

During my Eng Fire->PFL example above I normally have the VSI off the clock - in fact if the student doesnt get it off the clock Im not happy!

The idea behind using say 60deg AoB instead of 45deg AoB is the movement of the lift vector....for instance a glide at 80kts vs a glide with 60AoB at 80 kts - the one with the higher AoB will yield a much much higher RoD - which when you are trying to get out of the air due to fire is a worthy thought...

The idea is that compared with zero AoB a steep turn 45/60 will yeild a higher RoD as the lift vector has now been moved and is now only partially supporting weight. At 90deg AoB you would have no lift acting in the vertical plane (no pun!). However, a 90deg AoB brings with it other complications, not least the ability to control the descent path appropriately, and more importantly the airspeed.

I cant say that I have compared 45 or 60 to see which gives the greater - I would have thought 60 due to the reduced amount of lift acting against weight...but I might be missing something.

[BEagle]

It was part of one of the RAF PFL lessons to demonstrate that height lost in a 360 deg turn at 45 deg AoB was less than at 30 deg AoB due to the increased turn rate having a greater effect than the increased descent rate at 45 deg AoB.

[homeguard]

Some have questioned as to whether the factors affecting the stall speeds vary from level flight vs gliding decending turns. Here are some figures taken from the Pilots Operating Handbook.

Cessna 150 (Glide 70mph)

Aof B-------Stall
0------------55
20-----------57
40-----------63
60-----------78

In the case of the C150 the stall speed exceeds the best glide at 60 degrees Aof B by 8mph.

Socata TB10 (Glide 86kts)
Aof B--------Stall
0-------------60
30------------65
45------------72
60------------84

In the case of the TB10 the stall speed is within 2kts of the best glide at 60 degrees Aof B.

Therefore it is obvious that the speed should be increased to maintain a safe margin before initiating an increase of Aof B greater than say 35 degrees.

[Northernflyer43]

Thanks for all the interesting replies! - Just to let you know, the Examiner used power to control ROD.

NF43.

[BEagle]

Hardly 'gliding' in that case....

[Northernflyer43]

Well thats what I thought!

[Sleeve Wing]

Now I know where I have been going wrong.
:hmm:

[machonepointone]

A long time ago I was told that an increase of speed is required not so much for the turn itself, but to cater for the situation where the nose needs to be raised in order to regain the correct gliding attitude for the turn. Flown accurately I suspect nearly all aircraft will quite happily and safely maintain at least 45 degrees of bank, if not sixty. It is only when making corrections that the extra few knots may be useful.