Take off and landing performance

[TractorBoy]

I've only recently (about 4 weeks ago) passed my PPL after a hectic 6 months, and am beginning to look round for places to go. However, I have a question which I hope the more knowledgeable amoungst you may be able to help me with.

I'm currently flying a Cessna 152, and if I look in the POH at the short field landing figures (for example) for SL and 20 degrees C, I see that the landing distance from 50 feet is 1215 ft. This translates to 370.3 metres. If I apply the factor for dry grass of 1.15, this gives 425.8 metres. If I then apply the safety factor of 1.43, this gives 609 metres (for wet grass it goes up to 714 metres). If I look through Pooleys, there are numerous airfields where the quoted LDA is a lot less than this e.g Clacton (502 / 542 metres), Stapleford ( 500 m on the crosswind runway ). These are the ones nearest me, although I'm sure there are lots more.

Technically, if I go by the calculated figures, then a 152 should not be able to land on them at all - now I know that the Stapleford runway is regularily used, as I learnt there and have landed on it myself, and 152s are operated from Clacton. The same thing can also be done for the TODA figures. In some cases, the quoted values are exceeded BEFORE applying the safety factors.

Shouldn't we be basing our decisions on the values calculated this way - and if so, how come anyone operates from Clacton at all ? ( I'm not picking on Clacton, it's just near me and I want to use it !!! ) - the discrepancies in values aren't small, either.

So what's going on?

[Gertrude the Wombat]

Well, of course you can theoretically deduct a few percent for a headwind, but personally I never do, just to be on the safe side and after all this sort of field might not be able to give you a reliable wind report just before you touch down and they probably don't publish a TAF and the forecast wind for the airfield fifteen miles down the road might not turn out to be applicable.

Net result: I go somewhere that's just on the margin according to these calculations and use just under half the runway. (Having practised short field landings on a proper runway first.)

What happens to people who ignore the results of these calculations? Well, there must be some explanation for the several people who go into the hedge at the far end each year.

I haven't yet tried to fly anywhere that

(1) is well outside the calculated requirements, and:
(2) has several based aircraft of the same type regually engaged in ab initio training

but I guess I'll want to one of these days (popping into Clacton in a 172 to take the kids to the beach was something I was maybe thinking of wanting to do this year but I never actually planned it as the weather was never good enough the right day).

[Flyin'Dutch']

I see that the landing distance from 50 feet is 1215 ft.

You don't have to be at 50ft over the threshold.

If your calculations look 'tight' speak to someone who knows the airfield and the aeroplane and ideally you too and get their advice.

As time goes on and you will gain experience from both flying on your own and with a good instructor you will become better and more comfortable in operating into airports and airfields that are less big.

[Genghis the Engineer]

Yes, experienced pilots the world over use headwind, light weight, experience, etc. to modify the size of runway they need. On the other hand, they also sometimes make the same judgment and increase the amount they use ABOVE the calculated distance.

My advice would be to use the manual to the letter for at-least a year, you recognise yourself that you aren't all that experienced yet (the rest of us just have to keep reminding ourselves that we aren't experienced enough either). Until you are really familiar with your regular flying machine, in and out of a selection of runway types, you'd be best using the strict numbers and safety factors - that's what they're there for.

If it's a runway you trained on, then carry on as before, but I'd just quietly regard any "unknowns" as out of bounds if the sums don't work out for now.

Also, download the GASCo performance calculator from here. It should make doing the sums relatively easy without having to get your calculator out.

G

[IO540]

The problem with all these generic calculators is that they are just that... generic.

Every pilot should obtain the proper takeoff performance chart for the specific type. The figures in that are usually right, for a max performance (i.e. rotate at just above Vs) takeoff. That will be for a hard runway.

What the CAA flyers tell you is to add 30% for grass, another 30% for wet grass, etc, which is probably excessive for short grass.

I can't make the links work, BTW.

[Chimbu chuckles]

Tractorboy the point you, and others, are missing is that about half that 1215' you quote from 50' is air distance.....i.e distance travelled BEFORE you get to the threshold.

On short grass strips of the type you are referring to you would typically be touching down around 30-50m in from the actual threshold. Just past the first cone marker. 50' would be easily 200m before that point...over the field before the one you're landing in...and that's why we always SEEM to stop in 'half' the distance reqd by the graphs. Having pulled the figures and buffered them up hill and down dale and decided the strip is 'marginal' we white knuckle our way down and then stop mid field..and wonder why?

The same applies on takeoff...you can, and often do, climb out to that 'magical' 50' past the far end.

In neither case is the 50' point within the confines of the 'flight strip' ...nor does it have to be....in airliners/transport category aircraft we call it Clearway.

God grief as a young fella with 300 hrs I used to operate C185s and Islanders in and out of 385m/3000-5000 elevation and ISA+20...500m in a Cessna 152/172 is a doddle

[FlyingForFun]

Just as a point of interest, see if you can find yourself an airport with an instrument approach, and a full set of PAPIs. The PAPIs are, near enough, where an aircraft "should" touch down if it is 50' over the runway threshold. You will notice that, as per the comments above, this is a long way into the field.

However, as Genghis suggests, I'd stick to either what the manual says, or else runways which you're familiar with, until you have a little more experience. If you particularly want to go into a field which the manual seems to suggest shouldn't be possible but which you think would be, then discuss it with an instructor first (preferably one who knows your abilities, the aircraft's abilities, and the field in question), and if you're still in any doubt get the instructor to go with you the first time.

Bear in mind that in most "spam-can" types of aircraft, the landing distance will be much shorter than the take-off distance, so it is your short-field take-offs which you need to be practicing.

FFF
---------------

[Genghis the Engineer]

Bear in mind that in most "spam-can" types of aircraft, the landing distance will be much shorter than the take-off distance, so it is your short-field take-offs which you need to be practicing.

However, also bear in mind that whilst we all can accurately predict where we'll start the take-off, the start of the landing can be a bit less predictable.

G

[john_tullamarine]

Three observations ..

(a) factor me this ... after one attempts a take off/landing at a strip which is significantly less than whatever the relevant airworthiness authority dictates and fails to complete the exercise with a huge level of success .... (history shows many examples of such events) .... at the enquiry/court case/insurance claim/whatever ... how does one explain away the situation without leaving oneself a tad open to censure ?

Not suggesting that I have never done anything stupid in an aeroplane (I flew SuperCubs for quite a few hundred hours and that Type is a blatant temptation for a young chap to be innovative when it comes to paddocks and other off aerodrome operations) ... but one ought to have a few brain cells thinking about the enquiry which might ensue from one's more cavalier actions ...

This is not to suggest that one cannot fit the bird into the field by doing appropriate things .. but that is a bit short of showing compliance with the design and operating Standards relevant to the operating environment within which the fitting might be done...

(b) if I may echo Genghis' helpful observations from time to time ... one is at risk if one assigns a VERY high level of accuracy to whatever numbers come out of a performance chart .. they ought to be used in a somewhat rubbery, conservative manner lest one be embarrassed by the scatter inherent in such animals.

(c) while I will not waste my time checking Genghis' reference corrections (I know his technical competence to be somewhat more than necessary for his assessment of the charts' validity) they look to be fairly typical and consistent with normal models. If one is operating to the typical POH with unfactored data then their use ought to be mandatory at the personal level.

[Chimbu chuckles]

Ghengis I don't quite understand what that graph is for...it has no specific aircraft type on it that I can discern?

JT are you suggesting no difference between TODA and TORA and the same for the landing case?

That we shouldn't apply a bit of common sense to the book figures?

Can't quite figure out your post otherwise.

Brgds

Chuck

[Genghis the Engineer]

Exactly!

The graph has general scales on both the left and the right hand side. Using any units that suit you (feet, metres, leagues, furlongs...) mark the standardised take-off or landing distance on the left hand side.

Then, the various lines allow you to apply, accurately the standard safety factors for tailwind, slope, wet grass, variability, etc. as published and used pretty much worldwide (but I happen to know that this chart used the specific figures published by the British CAA in AIC Pink something_or_other).

This leads you to a value on the right hand side which you can read-off for the safe planning figure for the runway you choose to use.


You'll notice that it does not show proverse factors - that is anything in your favour (high pressure, headwind, lightweight aircraft) is ignored. Whilst you might disagree with this approach (I do!) it is safe, and is the approach promulgated by most national authorities for light aircraft planning.

Where "common sense" comes in (and we all apply it) is where we allow for a lightweight aircraft, downwind take-off, headwind - things that are taken account of in big aeroplane manuals but not usually little aeroplane manuals (the obvious exception being the PA28 for some reason). But, I'd be reluctant to suggest that somebody recently qualified should try to make those judgements.

G

[S-Works]

perhaps it is the ground roll that needs explaining here rather than going into great discussions about clearways etc.

The actual landing roll on a 152 if flown to the correct speeds and not the 70kts that seem tobe taught by most instructors is actually very short indeed. The take off role is also short in a 152 again if flown correctly.

I own a 152 and over the last thousand or so hours have put it into a lot of very short strips. I look for the landing role distance available as being from the point the wheels touch the ground on t he way in and from the point the wheels leave the ground on the way out. On a normal day I can get in and out of 300m without breaking sweat.

The problem with most spamcam drivers is they fly the aircraft to fast, either through bad instruction or bad technique.

So here is a question, what is the safe approach speed for a 152 with full flap that will give the shortest landing distance?

Next what is the correct rotate speed that will get you cleanly of the runway in the shortest distance.

Lets compare notes.

[Final 3 Greens]

Bose

Been a while since I flew a 152, but I seem to remember that it worked pretty well at 55kias for both.

However, I'd be interested to hear your views as your 152 experience is an order of magnitude more than mine.

[S-Works]

Pretty close. You are right it will work pretty well at the speeds you quote and on long runways at other speeds as well!

All figures at Max weight.

Short Field: The correct lift off speed is 50kts IAS and accelerate to 54kt IAS by 50ft. At sea level on an unfactored surface this will give you a ground roll at 10c of 210m.

My aircraft has the "sparrow hawk" conversion with Sensenich prop rather than the standard cocktail stick on the front and a gap seal drag reduction kit K&N Filter etc which takes another 15% off the ground roll.

Approach speeds: The straight and level clean stall speed at normal CofG is 36kts IAS (on my aircraft it is 33kts IAS due to the drag reduction kit flapped speeds are also reduced). At 10d flap stall speed is also 36kts IAS and at 30d flap its 31kts IAS

The 50ft speed is 54kts IAS with a threshold speed of 45kts at full flap. On a 10c day on an unfactored surface this gives a ground roll of under 140m. Lowering the threshold speed with currency on type further lowers the ground roll. On a good day I can beat 100m.

[Maxflyer]

Bose-X

When I land your 152 you need to add approx 200M to your figures!

[Genghis the Engineer]

Without doubt you can improve upon the published figures for any aeroplanes - the values are based upon the speeds in the POH, normal handling techniques and include a requirement that the speed at 50ft (both on approach and climb-out) must be no less than 30% above the stalling speed in that flap/gear setting.

BUT, whilst that may be reasonable behaviour on the part of somebody with hundreds of hours on type, it would be unwise of somebody new to a type (or new to a licence) to attempt such practices, and EXTREMELY unwise of an experienced pilot to encourage such a person to try.

G

[S-Works]

Actually Genghis, I WAS quoting book figures! Which makes my point that most people fly the average spam can at the wrong speeds.

I also stated the figures were unfactored and as such it is the responsibility of the pilot to factor as they see fit. The point being that if the aircraft is flown at the correct numbers it will easily go in and out of these places.

In capable hands my plane will go in and out much better than the book figures.

[Genghis the Engineer]

However, you were quoting roll, not distance. Planning is generally done to distance.

G

[S-Works]

Genhis, I say again, I say again....

I WAS quoting the POH, would you like the page and paragraph numbers as well......

My POH gives both sets of figures and I quoted roll to explain why people can and do safely fly into runways that seem to be to short on the face of it.

[Chimbu chuckles]

Ghengis how can one make an informed decision on whether a strip is suitable or not without having a knowledge of the difference between T/O or Landing roll and distance...either available or required?

If you approach to land on a normal 3 degree slope (and single engined light aircraft don't generally but it gives some basis to begin understanding) that equates to 320'/nm. 320' every 6080' or 50' every 1000 odd feet.

Now I think a C152 approaches steeper than that but since it's been 20 + years since I flew them a lot I have no idea of a super accurate figure....to be conservative lets call it half the foregoing...500' before the aiming point you pass 50'...151m. So a minimum of 151m (my first estimate you will recall was 200m which I think is more accurate but still conservative) out of the 370m figure from the first post is before the touchdown point. These rough figures seem to gell with bose x's POH.

The touchdown/aiming point on strips of the type discussed here should be between the first and second cone marker...if not down by the third cone marker good airmanship dictates a go around in my opinion.

The 50' screen hieghts are certification figures...how many airstrips actually have a 50' tree/hill/building/power lines at the bitter end of the TORA? Precious few.

I am all for being conservative with new pilots just starting out but is not 3 times the landing run required being available conservative enough? In my opinion a 30% buffer is completely adequate unless conditions are extreme....far to many pilots buffer their buffers for no good reason and then decide something is not safe, possible or 'legal'.

In PNG for reasons, generally, of DA and slope the vast majority of strips did not fit on the P charts at all and yet we generally took full loads in and out safely and with ease...I am not suggesting bush flying is the realm of newly minted PPLs but some common sense must be taught and applied lest the aircraft's basic utility be ignored and the nanny state/fun police be allowed to take over

Brgds,
Chuck.

editted for poor spooling.