Stall speed and ISA in a slip
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Slim Slag,
As I mentioned in my post, there is a relevant use for high rate of descent sideslipping, ie during a PFL when needing to lose excess height to stop in a required space.
It is not a technique for either slipping 'quietly' into an airfield or as a common practice during a normal powered approach.
The 'wing down' crosswind landing approach is different to the type of sideslipping I was describing: A small angle of bank with rudder to keep straight and power to fly maintain rate of descent is not what I was criticising. It is the few individuals I have flown with who cross control with no power at low altitude to produce a high rate of descent INSTEAD of achieving a stabilised approach.
Side slipping causes accidents in the pattern as well as other reasons, including skidding.
And good practice that is too, but practicing recovering from a mishandled approach is of little benefit if you fly a technique below the height from which it is recoverable. The best idea is to avoid sideslipping - it isn't necessary.
My aim was to highlight the fact it is not a recognised method of adjusting a normal approach, merely a technique to be employed in extremis when no other options are available, ie forced landing.
After flying F16s to 747s as well as 1500hours of light aircraft instruction and pleasure flying (still current), I'm not. But I'm worried that other people don't appreciate their risks.
You should be able to demonstrate a height losing forward-slip to landing to your PPL examiner.
It is not a technique for either slipping 'quietly' into an airfield or as a common practice during a normal powered approach.
Side slips are generally used to land in crosswind conditions, and plenty of students also learn this technique as part of their training.
it's skidding that causes stall/spin accidents in the pattern
In fact at my last BFR, the aerobatics instructor took us to altitude and all we did was cross controlled stalls, late recovery stalls and MCA work
My aim was to highlight the fact it is not a recognised method of adjusting a normal approach, merely a technique to be employed in extremis when no other options are available, ie forced landing.
You shouldn't be worried about them.
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Classic said:
How else are we to fly the many types with poor straight-ahead visibility, and/or no flaps? When flying a flapless Cub, Champ, pitts or a Yak-50/52 from the rear cockpit, or even a Tiger Moth, the sideslip is absolutely common practice for a normal approach. In the big-nosed types it gives you a decent view of where you're going, but on all the above types it also gives you a means of adjusting descent angle very precisely to meet a desired touchdown point, with the advantage (compared to relying on flaps) that you can safely flatten the descent by taking off some sideslip, whereas it may not be prudent to reduce the flap setting on short final.
It is not a technique for either slipping 'quietly' into an airfield or as a common practice during a normal powered approach.
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Pitot Errors
Funny how most of you think that by pointing a pitot to one side gives more errors than pitching it up and down through much larger angles. What is the angle at a straight stall?
Most PEC comes from static pressure error.
Funny how most of you think that by pointing a pitot to one side gives more errors than pitching it up and down through much larger angles. What is the angle at a straight stall?
Most PEC comes from static pressure error.
milt I would agree that most errors come from a duff static system but I would say that there would be a greater error caused by yaw than there would be caused by pitch. If you point the nose up the aeroplane climbs maybe the pitot isn't pointing in exactly the direction of flight but generally it's pretty close. Same for pinting the nose down. In yaw however, the pitot head may be pointing 20-30 degrees off the line of flight which is quite significant.
Classic so how would you land a Tiger Moth? I have nothing like your level of experience but I fail to see what is dangerous about a properly executed side or forward slip to the threshold. I fly an ancient Auster with an equally ancient engine. I far prefer to be high and sideslip into the approach secure in the knowledge that if my engine did quit at the last moment I could safely reach the field and not be picking myself out of a pile of crumpled fabic in the undershoot.
Classic so how would you land a Tiger Moth? I have nothing like your level of experience but I fail to see what is dangerous about a properly executed side or forward slip to the threshold. I fly an ancient Auster with an equally ancient engine. I far prefer to be high and sideslip into the approach secure in the knowledge that if my engine did quit at the last moment I could safely reach the field and not be picking myself out of a pile of crumpled fabic in the undershoot.
Flies for fun
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personally I prefer to set the aircraft 10kts above the approach speed, put the aircraft into a slip and then use my ears as the airspeed speed indicator. I have heard that the ASI is inaccurate in a slip and in any event prefer to keep looking outside the cockpit.
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No doubt duff static ports will exacerbate the ASI readings in slip.
However the reason why it underreads in a slip is not primarily due to static port problems but because the pitot is not aligned with the airflow in a slip.
It is difficult to stall in a slip.
Of course slipping on finals is an extremely dangerous pastime and should only be done by demi-gods not any ol' ATPL/heavy metal driver.
Come on get real!
As others have said, with proper tuition and practise a slip is perfectly safe and useful.
FD
However the reason why it underreads in a slip is not primarily due to static port problems but because the pitot is not aligned with the airflow in a slip.
It is difficult to stall in a slip.
Of course slipping on finals is an extremely dangerous pastime and should only be done by demi-gods not any ol' ATPL/heavy metal driver.
Come on get real!
As others have said, with proper tuition and practise a slip is perfectly safe and useful.
FD
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Some good points. I've never done tail wheel flying and it seems there is some validity to side slipping for those aircraft with lots of airframe in front of you. Thanks for that. Good debate means we all learn!
Still not keen on it in a tricycle type undercarriage,though.
Still not keen on it in a tricycle type undercarriage,though.
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Classic, I don't think it's got anything to do with the layout of your landing gear. Of course you don't want to be slipping a 747 on final, and it is a nose-dragger, but I am led to believe that's more to do with it having a swept wing and turbines than anything else.
I was once in the back of a 737 which came in on a very high base leg into SAN, and they slipped it in, not sure about that.....
To all you students. DON"T BE SCARED OF SLIPPING, even in a spamcan. You don't have to be an ace pilot to pass your PPL practical, but you really should be able to slip. Get your instructor to take you through the aerodynamics of uncoordinated flight and concentrate on the angles of attack of both wings, and what happens when you stall one. In a skid you will be flipped upside down before you know it, in a slip not so. Rule of thumb: You will not stall if you are slipping and your nose is pointing down towards the ground, like what is happening when you are on the way to landing.
PS I've even slipped a 172 with full flaps, naughty huh?
I was once in the back of a 737 which came in on a very high base leg into SAN, and they slipped it in, not sure about that.....
To all you students. DON"T BE SCARED OF SLIPPING, even in a spamcan. You don't have to be an ace pilot to pass your PPL practical, but you really should be able to slip. Get your instructor to take you through the aerodynamics of uncoordinated flight and concentrate on the angles of attack of both wings, and what happens when you stall one. In a skid you will be flipped upside down before you know it, in a slip not so. Rule of thumb: You will not stall if you are slipping and your nose is pointing down towards the ground, like what is happening when you are on the way to landing.
PS I've even slipped a 172 with full flaps, naughty huh?
Indeed, slipping should be no problem, I always take some 5-10 kts extra for safety.
To me, danger is present at the "slip exit". It's not the slip itself that is dangerous, but your "stable approach" might become "unstable" when aligning with the centreline.
If you are too high, you can try to slip it in without any danger. However, use commen sense to know how low you can go with the slip. There are pilots who can slip it up to the flare, I wouldn't try it. If I still need to slip at 200-100ft AGL, I'll leave it and call the go around. The reason why I like to do this is speed indeed. What is the speed of the aircraft? You don't really know except that it is too high. In an Archer on approach to a very short strip, every extra knot will give you a nice float up to the end of the strip... So keep in account the runway and its environment.
To me, danger is present at the "slip exit". It's not the slip itself that is dangerous, but your "stable approach" might become "unstable" when aligning with the centreline.
If you are too high, you can try to slip it in without any danger. However, use commen sense to know how low you can go with the slip. There are pilots who can slip it up to the flare, I wouldn't try it. If I still need to slip at 200-100ft AGL, I'll leave it and call the go around. The reason why I like to do this is speed indeed. What is the speed of the aircraft? You don't really know except that it is too high. In an Archer on approach to a very short strip, every extra knot will give you a nice float up to the end of the strip... So keep in account the runway and its environment.
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Take a look at http://www.pprune.com/forums/showthr...5&pagenumber=1
The subject was pretty well covered!
Personally I think forward and side-slipping are essential skills. Certainly, whilst sliping does affect stall speed, it does not raise it in the same way as flaps. By that I mean the drag can be taken off quickly and stall speed reduced rather than drag taken off but stall speed increased! Not unlike the difference between flaps and airbrakes in this particular case. Make sense? ...
Lets say you are trying to get into a short strip at minimum speed (to reduce landing distance) and steepest descent angle (to clear a row of trees in the undershoot). Without slipping you are looking at a full flap, back of the drag curve approach and a quite difficult job. If you find your descent rate is too high you'll have to add power ... or worse reduce flap! Adding power will most likely add speed (remember you are already trying to maintain highest descent angle) and reducing flap will increase stall speed with its associated dangers. However, if you slip off that last bit of the approach, you can constantly juggle the amount of slip and power to suit descent rate and/or angle. You can do this without affecting your airspeed or stall speed adversly. Makes the job much easier!
Ivan
The subject was pretty well covered!
Personally I think forward and side-slipping are essential skills. Certainly, whilst sliping does affect stall speed, it does not raise it in the same way as flaps. By that I mean the drag can be taken off quickly and stall speed reduced rather than drag taken off but stall speed increased! Not unlike the difference between flaps and airbrakes in this particular case. Make sense? ...
Lets say you are trying to get into a short strip at minimum speed (to reduce landing distance) and steepest descent angle (to clear a row of trees in the undershoot). Without slipping you are looking at a full flap, back of the drag curve approach and a quite difficult job. If you find your descent rate is too high you'll have to add power ... or worse reduce flap! Adding power will most likely add speed (remember you are already trying to maintain highest descent angle) and reducing flap will increase stall speed with its associated dangers. However, if you slip off that last bit of the approach, you can constantly juggle the amount of slip and power to suit descent rate and/or angle. You can do this without affecting your airspeed or stall speed adversly. Makes the job much easier!
Ivan
