Sorry I have not come before to clarify the points put to me.

Good day to you, Paulo sir, I am not often here and even less so when I am busy as I have been!

High Wing

Yes, I fly from Bournemouth, and have access to PA-28s (140 to 180), C-152/C-172 and Robin HR200 or DR400 to fly. Would be delighted to help a fellow PPRuNer to improve aviation safety, as many here have done so for me.

TonyR

I agree that if the speed is kept high with no flap then it would be pointless to sideslip into your field. However there are two points: (i) you are using sideslip for an unusual purpose - it is mostly used for adjusting a glide approach or for crosswind landings (I never teach it for the latter; "maintain the runway centreline with co-ordinated use of rudder and pedals") and (ii) the reason I emphasise keeping speed up is because this is a public forum where my advice can be misinterpreted, and speed is a safety factor.

While speed should not be allowed to drop and in theory should rise a little due to the tilted lift vector, in reality angles of bank in the slip are not often high, and speed need only be increased fractionally. However for safety this must be practised a fair amount at high altitude first, as a stall in the slip can cause a spin or at least severe wing drop. Depending on the spin characteristics crossed controls can give complimentary pro-spin input.

This happens at a time when the ASI is unreliable. With a lot of practice you can feel your way all the way down to just above the stall, but get the practice in with plenty of height and an instructor if you feel the need.

Shortstripper

I disagree about the likelihood of spin. While I agree not all aircraft will, some may. Notice that in, for example, a slip left-wing-down, the aircraft has right rudder, the right aileron is down, increasing AoA. You are quite right that the slip and dihedral decrease the AoA of the right wing compared with the left, but we still have a higher AoA near the tip, due to the aileron. Therefore the exact balance of the aircraft comes into play. So the right wing may tip stall, or the wings produce even moments at the stall, with (full) right rudder. These are the conditions for the spin, I had a Robin HR200 go incipient when a student put in similar control inputs, although not from the sideslip.

SC,

Flying too slow in a slip will not cause a spin.

FD

Well, as I said, I had a student use those same control inputs in an aircraft, and it flicked incipient. I'll believe the aircraft.

Wot is that then?

I know of 'flick rolls' and 'incipient spins' but not the 'flicked incipient'

Enlighten us.

FD

SC

If you re-read my earlier post I said that a spin is very unlikely but possibly not impossible whilst slipping. I said this as I believe aeroplanes can always do the unexpected! However, in my experience which is based wholly on gliders and light aircraft, it really would be nigh on impossible to induce a spin whilst slipping ... I've tried and failed on several types. You mention your experience in the HR200 and then say that whilst the control imputs were the same you weren't slipping. What were you doing? if these imputs are put in quickly with a sharp up elevator at the same time, you almost have a flick roll entry, albeit with opposite aileron to normal (which could easily be overcome with powerful rudder and engine torque). In a nicely established intentional slip you have a lot of control and plenty of "feel" which makes the whole thing very controlled. Referance to your ASI is irrellevent as you should fly by attitude in a slip and teach your students the same. If you maintain the same attitude as you were flying pre slip, you will have already built in a safety element. To use a slip to it's full potential though, a higher nose up attitude is required and is still IMHO safe.

Why is TonyR's use of slipping to get into a strip unusual? Most farmstrip flyers and others use slipping for this very purpose frequently.

I'm sorry but I really think that mixing the words slipping, banking near the ground and spinning is inappropriate and could encourage a student/PPL to disregard this useful tool as too unsafe. He/she may then get used to using S turns to loose height in a poorly judged approach. These things tend to balloon at times of stress such as engine failures or even PFL's. It doesn't take much then to end up with an over ruddered skidding turn for fear of banking close to the ground. Now that really IS a SPIN senario!!! :uhoh:

SS

SS,

Well said.

Still waiting to be enlightened what an 'incipient flick' might be.

FD

SS,Could you explain that a bit more? My naive thoughts are that if you hold the same attitude in the slip (with its higher rate of descent), that would give you a higher angle of attack. Where does the 'built in safety element' come from?

Intuitively, I think I'd find myself lowering the nose to maintain AoA/airspeed, as I would if I reduced the power. What am I misssing?

Mark

In a good slip there is an balance between the turning force generated by the bank of the wing and the opposite rudder force which you apply to keep going straight.

Due to the fact that the relative wind blows against the fuselage you increase the drag. To overcome this you can either increase the speed or the angle of attack.

When you increase the speed there will come a point where the force the banked wings will become greater than the opposite rudder can compensate for and the aircraft will 'run out of the slip'

When you increase the angle of attack by pulling on the stick the force of the banked wing will reduce and the rudder (if continued to be applied full) will 'win' and the aircraft will start to yaw towards the direction of the applied rudder.

FD

Shortstripper

We were at the point of the stall, no sudden elevator inputs although the rudder was put in quite sharply. There was some power, but in fact it autorotated in the opposite sense to the usual wing drop, although it was with the torque of the prop. Was a stall, wing dropped a lot due to some elevator and the student went rather overboard on the rudder to prevent it.

SC,

Can I comment that for an instructor you use very sloppy terminology.

The movement around the three axis of an aeroplane are: yaw, pitch and roll.

Autorotating is what you do in a helicopter when the engine stops.

Remember the set up for a spin?

When you are doing some slow flying and want to demonstrate a spin you will come up to the stall and when you are there slow down the inboard wing by giving a bootful of into spin rudder and at the same time increase the AOA on that inboard wing by giving opposite aileron.

What happens?

You spin.

Now compare that to the slip.

Which wing will stall first? The same wing as in the pro-spin scenario or the other one?

Think of the falling leaf manoeuvre and you will get the answer.

FD

I was taught in the services and there the term "autorotation" was used in relation to spin entry, also if you use the Trevor Thom books you will find HE uses the same term (Book1 page 188).

Interesting that you should talk about the falling leaf after your comments about fishtailing at low speeds. If you should do this (fishtail at too low a speed) the falling leaf is what you will end up with in most aircraft as you are going to opposite rudder by the time the aircraft has started autorotating (yes that term again) in the first direction - this is not of course the idea in the fishtail and as stated I would normally prefer to sideslip, but is good to have ALL manouvers in your armoury.:=

Flying’Dutch’

May I respectfully suggest that you search out a basic aerodynamic text book and read up on the state of autorotation which is essential for any aircraft to spin. This may lead you to reconsider some of your comments.

Sorry Foxmoth - you beat me to it while I was away typing with one finger!

F,

I was not taught in the services and would obviously not dare to question Thom's so if that is what they call the simultaneous movement around the three axis on spin entry so be it.

Fact is though that if you go too slow in a slip you will NOT spin.

If you go too slow the high wing will stall first and if you whilst this is happening reverse the inputs (as in rudder and aileron) you will end up in a sideslip opposite to the one you started with.

You can repeat this infinitum (obviously height permitting)

FD

Phew! I'm glad FD stepped in there as I'm hopeless at explaining aerodynamics :(

Mark

I didn't really phrase that bit you quoted very well for the reason stated above. I meant that by keeping the same attitude you are giving yourself plenty of margin over the raised attitude slip not over the in-balence flight you are transitioning from. However, it will not be as efficient as a slip held at the correct attitude (which is slightly raised) . In practice it simply means that if you don't raise the nose slightly you will find your speed is same or slightly higher than it was when you straighten up but you will have travelled further for the height you've lost. In a well excecuted slip you will have to lower the nose slightly as you straighten up but you will have lost a lot more height for a given distance. Don't forget that you are not actually flying that close to the stall in the first place, you are at approach speed which is approx 1.3X stall so you have that margin too. If you get much slower it will be difficult to maintain the slip anyway, so the are plenty of clues apart from your ability to fly by attitude. I use the term attitude over AoA simply because I'm looking at it more from a pilotage point of view. AoA is very difficult to think about scientifically as you fly, whereas your training should have shown you that your airspeed is fairly easy to maintain by visual referance to either the horizon or aiming point and is safe enough under normal circumstances.

SC

Surely if you are at the point of stall you would expect an aircraft to possibly do odd things? It doesn't take much of an over imput of anything to diverge from S and L flight. It's a bit misleading to compare this to a properly flown intentional slip. I can see that as an instructor you might want to play it safe with what you say on here but I just think that you are over stating the danger bit. Sure, to begin with you'd want to practice at height, but once you are proficient and used to the slip characteristics of the aircraft you are flying it is essentially a very safe and controlled manouver.

SS

JF,

Did not see your post and happy to stand corrected on the autorotation issue as I posted above. If you want me the reconsider the comments vis-a-vis 'sloppy terminology' then I would be happy to do so.

Maybe you can contribute to the slipping debate on how you see the issues that are raised.

FD

FD

And if you DON'T reverse the inputs?

Never tried.

FD

PS Thinking about it you would then go into a spin, and if you look at it from that perspective happy to concede that SC's experience was an 'autorotation' However this sequence of events is not what was advertised as 'If you slip too slowly you will suddenly end up in a spin'

Oh ******! :\

At least I never said you couldn't spin ... just that it's unlikely :p

Good thread innit? LOL

SS

FD,

The ATPL text I am reading agrees with you so long as there is sufficient dihedral in a low wing configuration or when the a/c has a high wing configuration...which I assume most light a/c are one of.

Standby for Broadcast

(I am sorry but that is a military expression used at the start of a Tannoy broadcast to everybody on a station)

With a conventionally designed aeroplane left rudder will make it roll left.

To enter a steady heading sideslip with this left rudder applied you will have to use the ailerons to the right until the nose stops moving left round the horizon and the aircraft stops rolling left.

This means putting down the left aileron and the right one up.

This aileron action markedly increases the angle of attack of the left wing tip.

This aileron action also reduces the angle of attack of the right tip.

Please be very careful before believing that under these conditions the right wing will always stall first on all aircraft

On many aircraft if you fly slower and slower with left rudder applied you will finish up with autorotation to the left.

If you autorotate left you will spin left.

End of Broadcast

(sorry that is a military expression used when completing a Tannoy broadcast to everybody on the station)

I do hope that is all clear…….

J,

So if I read that back you say that the wing where the AOA at the tip is reduced due to the aileron being moved upwards will stall first. In this scenario the lower wing.

That is not my experience nor the way I understand the aerodynamics to work.

It is my understanding that on a conventional designed aircraft (with dihydral) due to the increased angle of attack (as a result of the relative wind over the wing and the downward aileron on this side) the high wing will stall first.

FD

"Dutch"
I think you have read JFs post wrong, in his example he has LEFT rudder and right aileron, ie. you would have the right wing down in a sideslip and you would roll LEFT ie towards the UPPER wing.
(correct me if i am wrong please John) as you say yourself.
Possibly oversimplifying it - rudder Left- spin left, rudder right - spin right. Not ALWAYS true, but for our purposes I would suggest true enough. (And ALWAYS CHECK the spin direction if unsure for recovery - assuming you have the height:sad: )

F,

So keep the full rudder in left and pick the lower right wing up with the aileron?

That is indeed not how I read JF's post.

Is that how it was meant to read?

FD

I don't know how you sideslip but I always seem to end up with TOP rudder so left rudder means right wing down - but maybe you do it differently:\
Johns post actually saysIf you try this I think you will find the nose does not stop moving left UNTIL you have some right wing down (think about this-if you keep wings level and left rudder you will still turn left. If you are still banked left with left rudder then the nose will swing towards the ground)

Agree with that.

Left rudder means right wing down if you want to slip.

But tell me what in your experience will happen if you manage to slow down so much that you stall in that situation. Which wing will drop? The right (lower wing) or the left (higher wing)

FD

Left (top) wing - which I believe is what JF said:ok:

Nope,

He wrote:

FD

John could you sort please:hmm:

A year or two back, I was curious to see the effect of flying too slow in a sideslip so I tried it in the Skylark. She certainly did not do anything dramatic (she's a real Lady, mind), there was no 'flick into a spin' or anything like that. As I remember, it was just like approaching the stall but with more buffet and general airframe shaking. I think she tended to run out of control to the point where it was difficult to keep the slip on.
I suggest you all go out and try it, at a suitable height, of course.

I don't know if it has been mentioned earlier but sideslips don't work all that well if the speed is too high. Normal approach speed is about it. Any higher and you just won't get the sideways attitude.

Mike W

I don't know where this is all going, perhaps there are too many of us telling each other how much we all know.

I would like to go back to "why does the average PPL in a light aircraft need to side slip"

I was taught sideslipping as a 17 year old SPPL in various aircraft as a way of loosing height in the least forward distance.

I still use side slipping for the same reason today (30 years later)

Example: PA28 (any model)

You are down wind at a height of 1000 ft, you expect to turn base and fly a 2 1/2 mile final, decending at about 500 fpm at 70 knots,

ATC request you "to keep it tight" and you turn on final at just under 1 mile, but are still at 800 feet, even with with full flap you are not sinking fast enough. If you put the nose down you will speed up and never get in.

This is where it is useful to side slip, to loose the excess height and still land at or near the start of the runway.

Done properly at the correct speed (ie.normal approach speed or slightly less) you will not damage the a/c nor will you spin or loose control in any other way.

Tony R

I was shown sideslipping in a '152 at my last check ride, pretty impressive too, did it with full flap, went down like a brick, intresting noises too at 85kt! What used to worry me a bit is the side loads on the tail, but I'm sure they're well accounted for. I'll have to try it a bit more next I fly (don't know when:( )

SM

Not really. Slipping is not supposed to be a high speed manouver and it does indeed put some strain on the tailplane and sternpost. Besides which, what is the point of slipping at higher speeds? ... OK, I guess if you're in combat there might be a need :uhoh:

JF

Thanks for that answer of yours! ... trust a test pilot to make it sound so complicated ;) I reckon I'd better shut up now as my brain is getting sore with all this thought on what to me is a dark science ... aerodynamics :\

SS

here again a quote from one of my many training books (I left out non essential sentences):

The Slip
The purpose of the "forward slip" is to dissipate altitude without causing airspeed to increase, e.g., airplanes without flaps. In planning the slip, take into cosideration wind direction. Slip into the wind.

Establish normal glide.

Establish slightly less than normal glide speed

Use of elevator: Control speed should be slightly less than normal glide speed.

Use of aileron: Principal control to maintain desired bank. Remember steepness of bank affects angle of descent.

Use of rudder: rudder is used in opposite direction of slip. Another use of the rudder is to keep the airplane from turning and to control the rate of turn.

Maintain original flight path

Note:
check manufacturer's recommendation for use of wing flaps extended during slips

recovery: allow enough altitude for safe recovery. Raise the low wing and release rudder pressure simultaneously to keep the airplane aligned with the runway. Assume normal glide before touchdown. Riase low wing with ailerons. Reduce rudder pressure.


That all coincides with the way I learned it.....

Westy

edited for spelling :ugh:

It is not a good idea to sideslip too fast in any aicraft, 85 knots is too fast in a 152. You could damage the aircraft

Anyway there is no point in slipping fast it defeats the purpose.

Tony

Thats what I thought, I must add that the instructor was showing a way of loosing as much height as possible in the event of the a/c being on fire preparing for a forced landing. I'd prefer to stick to slower speeds for slipping though.

Ah, I think we have the source, of misunderstanding, Mr Shortstripper. I was intending to convey the possibility of a spin in sideslip if the speed reduced and reached the (slightly increased) stall speed. I think you were reading it as an entry into spin as per the spinning exercise - at a high stall speed caused by pulling full elevator. In a sideslip if you keep the speed at normal approacjh speed or above, then you will keep flying. The danger is in an unreliable ASI and in allowing distraction and a low initial speed to bring the aircraft to the stall, hence my warning (remember I am telling people, not demonstrating this with me to keep a student out of trouble) to keep speed up. Wouldn't want to tempt any of our friends here into lethal situations :{