Glide approaches
 

In the old days they used to do glide approaches all of the time presumably due to the unreliability of engines. Gliders still do glide approaches.

Then we started doing powered approaches, presumably because the airlines need to do powered approaches (on the back of the drag curve) and instrument approaches demand the 3 degree thing.

When did the switch happen in the PPL teaching world?

When things reversed, and engines became more reliable than instructor skills.....

18G,

I read about these in Alex Kimble's book "Think Like a Bird", even in the 50's it seems to be regarded as the old way of doing things. Other than good practice, I don't think I really understand the logic. If anything the engine is less likely to fail at a low power setting during final when compared to any other part of the circuit (carb ice discussions to one side for the moment, that is down to equipment and technique).

Are you suggesting that an aircraft should be in glide range of the runway from any point in the circuit? If so I don't suppose that would be very practical for many airfields. with all the traffic and noice restrictions we have.

Tony,
I guess I am lazy, I fly a tight tight circuit and if i'm on my own and theres no one ahead then i'll chop the thottle and glide from abeam the downwind numbers, delighting from the joy of kissing the numbers and taxiing off at exit 1. It saves time, its quieter and you get loads of circuits per hour (and being constantly s*** scared of the inevitable engine failure I take every chance I can to practise glide approaches). And other than noise abatement why should we land any other way?

If the guy ahead goes so far out I feel uncomfortable I'll cut in (politely) or more likely go around.

Being in glide range of the airfield (or a good alternative) at all times makes me feel better. I'm not sure whether that affects glide or powered approach argument.

Pilot DAR,

I think you may have nailed the argument. However its just as hard to teach a 2 mile final with power as it is to teach a glide approach.

The change started with the replacement of the Tiger Moth as the school training aircraft.

I know one CFI who still teaches and insists on glide approaches on all normal circuits

I was taught glide approaches in the 1970's by ex RAF instructors. Our trusty mounts were Cessna 150s in which one could select 40 degrees of flap and dive near vertically but never exceed 80 mph.

Great fun, and it imbued me with a lifelong aversion to the 'modern' cross country circuit and powered approach.

I once read a book (wriiten many years ago) in which it was suggested that gentlemen should never "motor in". As a result I never have:ok:

Except when piloting things that glide like a brick:eek:

Sir George Cayley

I think it was later than that. Glide approaches were taught to me as being the norm in the 1970's. Still the best way; with power for those who can't judge it properly, as I was taught, or who wish to land very short.

At some point the training reversed to make power the norm. Hence the daft size circuits. Perhaps it was after the CAA, with their fine minds, made a CPL a requirement for instructing. Then students had to pretend they were flying the airliner the instructor probably thought he ought to be flying.

The owner of what was the finest flying club in the world used to say that the three most useless things in a light aircraft were, a step ladder a stiff broom and a commercial pilot. I make no comment about that.

I too, do what 18greens does. I always glide approach if there's nobody else around, or if there's nobody in front of me - for two reasons.

1) I like to get the practice - having past experience with an engine failure at 200ft AGL you can never, EVER be too practised. EVER!

2) I'm lazy at the end of a long working day. I can't be assed flying big circuits and spending five more minutes on finals when it's not necessary.

And I always call "glide approach".

:ok:

Personally I prefer glide approaches, but then I'm a glider pilot ;)

Seriously - having picked up power also, I'm generally uncomfortable with the 'what happens if the donkey coughs' factor on a powered approach, but I'm lead to believe that it's better for the engine - particularly doing circuits, glide approaches = shock cooling, and bad for the cylinder heads.

My preference is for glide approaches, but when it gets cold, the engine needs to be kept warm, especially for a touch and go.

So in cold weather, more flap or sideslip to counter the extra revs.

Calling glide approaches
 

I note with interest the requirement to call glide approaches. Surely the only requirement is to establish circuit priority (unless local rules require glide approaches to be called.)

When does an approach become a glide approach. I've never seen anything written down about what is a normal circuit (how far out, when to turn etc) with exception of the noise abatement approaches. Theres no requirement to call extra wide circuits.

A glide approach in a motor glider could be flatter than a powered approach in a cessna and a powered approach in a pitts will be steeper than a glide in a cessna. What's the reason to call a glide approach?

The comment about shock cooling is noted.

I must admit that calling a glide approach is a new one on me. If there is a particular circuit size or routing that is what you fly. (I've been based at strips for the last 20 years and so have a near religious observance of these things). For a glide APPROACH it will actually have no effect. OK if you're flying a different type of circuit be it low level or a gliding CIRCUIT then fine call it because it will help people work out where you are.

Once you've decided that the throttle can be closed things really will not look a great deal different apart from being a little above the usual 'glidepath'. Actually of course you are on the glide and all the others are flying below it. Which neatly brings us back to go. I try and fly all my approaches as glides and that gives plenty of time to avoid shock cooling by gently reducing power in the earlier part of the circuit.

More important to call flapless approach than glide approach for following traffic otherwise the flapless pilot extends downwind with the following pilot turning base in the normal position and oops we meet near finals.

'Shock cooling' more folk lore!!!!!!!!!!!!!

Much more important to fly the A/C rather than make any of these 'glide approach' or 'flapless approach' calls, none of which I can find any reference to in CAP413.

Flapless
 

Thats another one, why do flapless approaches need to be flatter or go out further than normal approaches? If you have such a surfeit of energy why not just apply less power and maintain the glide path. Given the wide variety of approach methods and variety of ac you do see one mans long final is another glide approach. Talking of steep approaches have you ever followed one of those powered hang gliders.

So the priority is to ensure everyone knows where everyone is and getting a priority of landing established. What value is there in calling glide or flapless?

In a light aircraft at least flapless landings don't require a flatter approach path and the approach profile is so similar to a normal landing that I don't think it's worth calling. A 10kt or so increase in threshold speed is the only difference usually.

Also if you say on the radio: 'Flapless approach' (which I have heard before) it doesn't really help other pilots much....if you are going to extend the downwind...the say so, it's much more meaningful than saying 'flapless approach'.

I'd always call a glide approach...I think the approach profile is different enough to warrant it.

'Shock cooling' more folk lore!!!!!!!!!!!!!

Chit, now I have to go and use black out on all my P&W and Wright radial engine manuals.....

Especially my manual for the C117 because there are many " Warning " notices in that outlining the danger of cylinder choking due to shock cooling.....

....we could get into reverse bearing load caused by high RPM and low manifold pressure but I won't go there now.

If shock cooling is a factor in engine life in big radial engines can someone explain why the laws of physics should be different for other air cooled piston engines?

How about because all the cylinders are exposed directly to the airflow in a radial and not in other layouts as found in most Uk training aircraft, hence the lack of similar placards.

In a well discliplined circuit with max 4 aircraft(which should be an 800 feet oval for my money) everybody would always be in the same position. However the circuit pattern at a lot of airfileds is just a free for all based more on need than organisation and management

How about because all the cylinders are exposed directly to the airflow in a radial and not in other layouts as found in most Uk training aircraft, hence the lack of similar placards.

Well...lets examine air cooled engines.

Do they need airflow evenly past all cylinders to properly cool each cylinder?

Is it possible that because engines such as the little Continentals and Lycomings do not have their cylinders evenly exposed to the air flow like a radial the engine manufacturers require baffling to evenly spread out the airflow to evenly cool all cylinders?

Anyhow this will get us nowhere.

The tighter the circuits the better i think not only does it mean u can glide in but that you can save about £5 by not doing bomber circuits. But never cut othjer people up.
David

Tighter circuits produce better handling pilots, in my experience

I was told that in the early days of flying many engine failures occurred as the pilot altered the power setting on his engine as he approached the air field, especially after the engine had been at one power setting for a long period. As to why the engine should suddenly fail at this point is not clear to me, but this was the reason given for his instruction. “Always be within gliding distance of the air field before you make any power reduction”.

Could this be the origin of the military method of chopping power when opposite the numbers on the down wind, and make a curved dead stick approach and landing?

Personally I look upon each landing as a unique event, and treat it as such. I do whatever I need to, in order to hit the numbers. :ok:

Regards,
White Bear.

Seems that lots of people here think that practicing glide approaches (with the engine throttled back to idle) and then doing the same thing, with a genuine engine failure, will enable them to reach the airfield on that awful day.....have they never witnessed the difference in the gliding performance of an aircraft with an engine throttled back, as opposed to a genuine "deadstick" engine???? Guess not.

Regarding "the Shock cooling, more folklore" well Chuck you are right ....its beyond help!!
UV

UV

Yes.

True deadstick, no - and I hope not to have to, but I'm expecting significantly worse glide performance, and hope I'll be able to cope.. after all, the 172 at idle glides a lot worse than a duo discus in just about any config ;)

As for shock cooling, plenty of cracked heads on pawnee glider tugs would indicate a genuine problem, as would the SOP's glider clubs come up with to look after the things.

Mark1234

:hmm:

I suggest you find an experienced instructor and give it a go.

A 172 at idle glides a lot worse than a AS-K13 in it's only configuration.. :)

Shock cooling
 

When I learned to fly, in 1960, the term shock cooling just wasn't heard. I'm sure I never heard it once. I was taught that the reason you rev the engine occasionally when flying throttled back, perhaps during a PFL or a glide approach, was to prevent the plugs oiling up in our inverted, in-line engines. The only time we consciously managed our engine temperatures was immediately after starting and when we cooled the engine after landing, immediately prior to shut-down.

The engines in use then were the air-cooled, in-line, inverted, four-cyllinder de Havilland Gypsy Major and Blackburn Cirrus Minor II. And the majority of our instructors then were ex-wartime military pilots with extensive experience on a whole variety of engines including big air-cooled engines.

When I returned to flying a couple of years ago, I encountered this concern with shock-cooling for the first time. And the concern was real. I know for a fact that today gliding clubs in particular do have a constant problem with cracked cyllinders, caused after dropping the tow and returning as quickly as possible to the launch point to collect the next tow.

I wonder whether the current concern with 'shock cooling' could have something to do with the fact that for most of the last forty years private flying has been utterly dependent on the Lycoming and Continental engines. I wonder if these engines are more susceptible to variations in temperature than the engines we used to use.

Broomstick.

Broomstick, you've probably got a point there - I was looking at a Gypsy Queen today (I think!), actually two of them in a Devon. They clearly have a great deal more mass, and possibly less efficient cooling, than your average small Lycoming or Continental.

These later engines with less mass and more efficient (relatively!) cooling will alter temperature at a faster rate, potentially leading to greater thermal stress and the cracking etc that others have noted. Just the same sort of thing where you can heat up a glass, then dunk it in cold water to make it crack - but if you heat it up slowly to the same temperature, then cool it slowly it won't destroy itself. Somewhere in between these two extremes will be a level of change that is acceptable for the glass, or engine, in terms of both thermal stress and practical use. There are also a number of other factors involved with engines, including changes in clearances due to temperature etc.

I'll admit that, like Chuck, I've been made more aware of this with respect to the P&W engines but from a first-principles perspective it's a no-brainer and almost any engine could be affected in some way.

As Pilots we have the ability to make or break the engine, particularly over time. Amongst other things smooth changes in throttle level and being aware of the induced temperature changes and resultant stresses involved will assist in ensuring a longer-life engine as well as improving the life chances of the Pilot & Pax. It doesn't really cost anything, and in the long run could save money, so why not?

Going back a bit in the thread, I know.

So what's wrong with good practice? And can you casually put carb ice discussions to one side?

What I cannot understand about this thread is why anyone would want to carry out a low, powered approach when they don't have to under normal visual conditions, as opposed to a glide final approach from the start of the base leg or from a straight-in approach. Unless the wings fall off a glide approach is going to succeed, assuming you chop the power and set carb heat at the right moment, and you can always get rid of excess height in a slip. A powered low approach carries a risk of engine failure, however small. Why take the risk if you don't have to?

As for big wide circuits with long approaches for ab initio students, I have always thought they are fraudulent. To only get 4 landings in an hour's flying is a total waste of a student's money, and students are well-advised to avoid schools where this happens, which probably means avoiding schools based on busy airports.

PS The reason I was taught to use a 15-sec burst of power with any engine with a carburetor (spelling?) every 500 ft in a PFL or such-like was to get rid of/prevent carb ice, as well as, with a Gipsy Queen only, to clear the plugs and see if the mass of iron was still functioning at all.

So a glide approach succeeds, if you do it right. A forced landing following an engine failure is also succesful, if you do it right. But which are you more likely to screw up; one out of 1,000 approaches with the engine running, or 0.01 approaches with an engine failure?

Which accident type is more common: Having an accident (no, not that kind! :E) after suffering an engine failure during the approach, or flying oneself into an accident by misjudging the landing, either going off the far end or crashing during a mishandled go around?

If one agrees that landing accidents due to misjudged approaches are much more common than accidents following engine failures during approach, and if one further agrees that a powered approach is easier to judge and control than a glide approach, I think one should limit glide approaches to what is necessary for engine-out proficiency and let powered approaches be the normal procedure.

Which, incidentally, is how I'm being instructed to do it...

I would suggest that if you can only land with assistance from the engine then you are severely limiting your options.

Fine when you're learning to fly and the work load is already high but if you skill levels require engine assistance for all landing you chances of getting it right on the occasion you reaally need to is going to be pretty small.

Quote::::


As Pilots we have the ability to make or break the engine, particularly over time. Amongst other things smooth changes in throttle level and being aware of the induced temperature changes and resultant stresses involved will assist in ensuring a longer-life engine as well as improving the life chances of the Pilot & Pax. It doesn't really cost anything, and in the long run could save money, so why not?

Sorry for the thread drift:

Kiwichick:

I'd be interested to, however you're rather lucky to find an instructor who will even contemplate deliberately stopping the fan in flight - it leaves little option if the scenario doesn't go according to plan. I'd take bets that 99% of pilots are in the same boat as me!

Maybe I'm in a better place than most in being an active glider pilot, or maybe I'm just cruising for a fall (hope not!), but I can't see the biggie - the whole plan is you have to work to what the aeroplane is achieving in the glide; fly a different plane, and the parameters change, as they do having a truly dead engine. Forget the formal rectangular circuit, and fly the circuit to get you there - roughly a constant angle to aiming point. Should be quite achievable.

I'm more concerned about what happens when: 1) It coughs on final with full flap and a 1500rpm powered approach. 2) What if the fields along the nice straight course you're flying aren't very landing friendly? I'm told to trust the engine, but low hours powered, and still flying with a slightly different mindset!

While on that: how many have actually touched down in a paddock on a (P)FL? Have done a few live landouts myself, though never in a fan assisted aeroplane.

Incidentally, I was lucky enough to spend some time gliding in kiwiland recently (Omarama). Probably one of the prettiest, and scariest places I've flown - hanging in almost silence at 15000ft over mt cook will stay with me for a long time!

Shadowoneau - ah, the old 13. Fond memories :) Crack those brakes open, and it's a LOT worse than a 172. I think the duo on with brakes is almost a better glide than the 172, which is what I was (jokingly?) digging at :)

Excellent point. I've seen very few reports of accidents (particularly UK ones) due to engine failure on final: can anyone supply any examples?

Thanks for all of your replies, some interesting debate.

So from what everyone has said there did not seem to be a sea change from glide to powered approaches at a specific point in time.

Old Not Bold,
Twas my text you were quoting. There are two sides to this, fear of engine failure and so ensuring you can reach the field or just doing glide approaches for good practice. I wasn't dissing good practice, I was trying to home in on what I thought 18G was getting at: that we should do glide approaches just in case like they did on the old days. That is what I was questioning the logic of as I explained in my usual obfuscated manner. If you want to do it for practice then feel free, I don't see any reason why not, it is good fun for a start and I didn't mean to imply otherwise :ok:

With regard to carb ice, I really couldn't be bothered trying cover every possible nitty gritty angle, CH is a relevant to some but not to other pistons in different ways to greater or lesser extents :\

I've always wondered about this, does an idling prob actually produce more drag than a stationary one...especially if its three bladed?

Contacttower, unless there is a massive internal failure (a broken crankshaft for instance), don't expect the prop to be stationary. It will be windmilling, and a windmilling prop will cause more drag than a prop that's running at idle. After all, at idle there's at least a minimum amount of fuel going into the cylinders helping the prop tick over.

What I've heard is that a stationary prop will cause less drag than a windmilling one, but in order to get the prop really stopped you've got to slow down to something very close to stall speed, usually. That's not something you're going to do with an engine failure, unless you've got steel nerves and plenty altitude to spare.

I'm flying aerobatics, including negative g manoeuvres, in an aircraft without an inverted flight system. So far I haven't been in the situation where the prop actually stopped, but one of these days I'm going to take the aircraft up high and deliberately find out at what speed the prop stops windmilling, and what speed is required to get it going again.