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Short Field Landing Airspeed Conundrum

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Short Field Landing Airspeed Conundrum

Old 13th Jul 2017, 02:37
  #41 (permalink)  
 
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John:---- there are civilian Aircraft designed for their short takeoff and landing ability aren't there? They will have a POH describing correct procedure/technique for landing that Aircraft which is a "normal" landing for that Aircraft. They will have P charts as well detailing LDR etc.

That's all I meant mate.

I didn't mean to infer that there is a special "STOL" technique mentioned in their POH, as all landings in that type are STOL and thus normal to the them.

Ok
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Old 13th Jul 2017, 07:25
  #42 (permalink)  
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I think you might have missed my point .. STOL is a military animal. Can you cite a civil aircraft which has a STOL certification ? Not looking at what one might be able to do with them but some certification data in an approved AFM/POH ?

Just interested to know if any such do actually exist.
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Old 13th Jul 2017, 09:23
  #43 (permalink)  
 
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No John unfortunately I'm not an expert in civilian or military certification standards. But there are quite a few out there are known for their STOL capabilities in their design and performance characteristics.

What about the civvy Pilatus Porters meat bombing around?

What about the Twin Otter it's also known as a STOL Aircraft, renowned for its abilities.

Either way certified with STOL capabilities or not they need to be operated in accordance with their POH and P charts.

We are probably arguing over a term.
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Old 13th Jul 2017, 09:47
  #44 (permalink)  
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We are probably arguing over a term.

Yes ... and, no.

The civil certification standards (eg FAR 23) impose margins above stall to give the operation a reasonable chance of surviving problems .. such as turbulence, engine failure, etc.

The military approach acknowledges that there will be operational requirements which dictate operating to a higher level of risk and mishap probability .. ie lower speeds and lower margins above stall. As would be expected, the usual military certification and release to service protocols spend a lot of time and effort in providing crews with detailed information regarding just where the boundary limits are for such operations.

The uncomfortable risk with many civil operations purporting to be quasi-STOL is that this FT work up work isn't done and the pilot is put closer to real operational limits than the civil design standard protocols envisage.

Civil and military certification .. two very different animals.

I would expect that the operational documentation for civil versus military operations on the two aircraft you cite might be quite different in detail ?

Perhaps others who have access to both sets of data might be able to comment ?

Certainly, the POH approved data can be expected to comply with the nominated standards.
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Old 13th Jul 2017, 20:42
  #45 (permalink)  
 
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Maybe I'm missing something in this discussion, but the Information Manual for the 1980 Cessna C172 N Skyhawk (for example) which I have on my bookshelf, gives tables in Section 5 (Performance) for Take-off and Landing distances based on Short Field Technique as specified in Section 4...??
Section 4 (Normal Procedures) goes on to give the techniques for short field and normal take-offs and landings.
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Old 14th Jul 2017, 00:57
  #46 (permalink)  
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.. the Information Manual for the 1980 Cessna C172 N Skyhawk ... gives tables in Section 5 (Performance) for Take-off and Landing distances based on Short Field Technique as specified in Section 4...??
Section 4 (Normal Procedures) goes on to give the techniques for short field and normal take-offs and landings.


A quick net search came up with a 1980 POH dated July 1979 with no revisions affecting relevant pages.

The point in question, here - what are the take off and landing speed schedules for the two techniques - short field and normal ?

Looking at the POH, above, one gets

for "short field" takeoff Vtoss = 1.12-1.21 Vs
for "short field" landing Vapp = 1.34-1.43 Vs

with the range quoted depending on CG for gross weight. The figures quoted are from my sums .. while I have nominated two decimals, the reality is that one should not read to that sort of apparent precision .. so, looking at the forward CG - which is the more critical - one would have approximate margins of, say, 1.2 and 1.4. The usual 1.3 for approach is a minimum and the OEM is perfectly entitled to run a bit faster .. that probably indicates that the TPs were of the view that coming in over the fence with only the maker's name on the clock might not be a really bright idea. If you are of a mind to check my numbers, do remember to apply PECs so that the calculations are done with KCAS rather than KIAS.

These figures are pretty close to the normally seen civil certification margins so, it follows, these "short field" operations are what most of us with a certification background would consider normal operations and, certainly, not STOL.

That the OEM elects to refer to the techniques as short field and normal is neither here nor there .. we are talking about certification operations (short field) and a more comfortable higher speed operation recommended by the OEM (normal) .. but not STOL in any sense of the term.

Unfortunately, the Industry is beset by lazy terminology ... (and, I have to admit, I'm just as lax and lazy at times, myself).

If you want a feel for STOL, you could go not much further than carrier operations .. I note that Centaurus, in the first post, makes reference to his experiences in the Sea Fury .. hairy stuff. As a sideline point of interest, another PPRuNe poster (Milt) was the chap who sent Centaurus off for his first Sea Fury jolly all those years ago ...
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Old 14th Jul 2017, 06:01
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STOL a military animal....que..?

Old Sybl..VH-SIB was a TU-206 with a Robertson STOL conversion. Modified leading edge, droopy ailerons with the flaps, extended wings. Had been operated with SIL / Summer Institute of Linguistics in the highlands of PNG. STOL capabilities being the go for the "airstips" there. Could certainly do the tight spots ok.
A Higher Authority trod on it in the BNE super cell storm Jan 1986. Vale SIBL.

There is a Wren Cessna 180 about, also a STOL conversion.
I guess they were certified as per the mods for STOL ops.

These days there are 'flying ' gadgets about for off field landings like the LSA Highlander STOL. Bit of a breeze and its landing run = length of the aeroplane !!
I want one .
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Old 14th Jul 2017, 07:24
  #48 (permalink)  
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STOL a military animal....que..?

That's the general story.

Robertson STOL conversion

I have no specific familiarity with the Robertson mods. However, I suggest that what they do is reduce the stall speeds which, in turn, reduce takeoff and approach speeds while maintaining the usual certification margins above stall. This then reduces runway requirements. Fine to market that as STOL but it is not what STOL design is, per se.

I am happy to be proved wrong in respect of the certification .. but that will require a copy of the relevant approved POH which will tell the story in some detail.

Real STOL, as the military do things, is a different animal which operates much closer to stall and accepts a considerably higher probability of mishap in the event of something going awry. The benefit is a shorter distance requirement. Acceptable for some operations in the military but not for routine civil operations.

in the highlands of PNG

Now, I don't have any information regarding the specifics for the aircraft Type in PNG ... but do keep in mind that the old DCA rules were a tad different for developmental operations in PNG ... so it may be a case of comparing apples and oranges. It's so long since I had a look at the old rules .. the poor old memory is not up to recalling the details now.
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Old 14th Jul 2017, 07:55
  #49 (permalink)  
 
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Originally Posted by cooperplace View Post
of course; I use all 3 as required when I'm in the Grob.
And a very nice little MG it is, too!
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Old 15th Jul 2017, 00:14
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Re my comment earlier about Milt and Centaurus .. the memory played tricks .. Milt sent C off on his first Mustang jolly ...
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Old 15th Jul 2017, 00:55
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AAAAH!! The Wren.
Mate of mine has a lovely Wren 182 (they have their own Type Certificate, as I recall, more than just a bolt -or glue on mod.) and he has even screwed a few more horses in the front by way of an IO-550 -- what a seriously fun aeroplane to fly.

As for the whole discussion, there is what you "can do", what is wise to do.

If it all goes wrong, it will be between you, your god, your insurance company, and CASA's rather variable (depending on their desired "policy" outcome) application of CAR 138.

Bloggsie,
Your interpretation of the venerable US Naval publication and how to fly an approach in larger turbine aircraft (but it works for any aircraft) certainly explains a lot??

Tootle pip!!
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Old 15th Jul 2017, 07:58
  #52 (permalink)  
 
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Had the pleasure of flying a C172 with a Robertson kit fitted to it.

The owner bought it new, picked it up from the factory and then flew it to a maintenance organistation to get the Robertson stol kit fitted.

There has been a few Robertson STOL Cessna C206's imported into Australia over the years, good idea to get an experienced operator to show you the finer points of operating with the STOL kit.
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Old 15th Jul 2017, 23:32
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Stationair8
Having flown a number of C-1 or 2XX over the years, believe me, a Wren is a whole different level of "STOL" .Sorry, JT, but I think, in my MNSHO that STOL could long since be regarded as a generic term, certainly based on old brochures for civil aircraft out in the back shed.
At one stage (thanks to Bloggsie) I thought we were going to have a whole new round of "Attitude controls airspeed, power controls rate of climb or descent" versus "attitude controls flightpath (or aim point), power controls speed" but that one seems to have died.
Tootle pip
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Old 15th Jul 2017, 23:37
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Yes LeadSled, I wondered why the owner would actually put a STOL kit on a C172!

The Wren does sound an interesting piece of kit.
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Old 15th Jul 2017, 23:45
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Originally Posted by Leddie Sleddie
Your interpretation of the venerable US Naval publication and how to fly an approach in larger turbine aircraft (but it works for any aircraft) certainly explains a lot??
Those of you who think you know everything are annoying to those of us who do...

Last edited by Capn Bloggs; 15th Jul 2017 at 23:54. Reason: That's better...
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Old 16th Jul 2017, 01:00
  #56 (permalink)  
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STOL could long since be regarded as a generic term

.. of course it is .. but the younger chaps and chapesses, at the very least, ought to have the subtlety brought to their attention ..
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Old 19th Jul 2017, 08:12
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Sure did: power for slope and pitch for speed.
Bloggsie,
Given the rather confused variety of emojis in that post #30, are you suggesting the above is right or wrong??
Please elucidate.

JT,
Having given this some thought, I think a time warp is the problem.

"Back in the day" (before aircraft had an AFM as we know it today, and "handling notes" were rudimentary) a "normal" approach was a glide approach, with "enough" IAS for a short float in the flare before your stalled the aircraft onto the ground.

Indeed, in honour of this "normal" approach, all the RAC/NSW Gipsy Major or Cirrus powered aircraft had the carb.hot air locked on, which did "wonderful" things for performance when you actually needed the power.

A "precautionary approach" as per the syllabus (Pub. 45 and predecessors) was a prelude to an out or forced landing due (usually) weather, and included practicing/demonstrating a low level circuit to determine where you were going to land, followed by a "power on" approach at a somewhat lower IAS than "normal". all aimed at an accurate touchdown at the chosen point.

Seems to me that the present application is to demonstrate an approach at the "right speed" ie; the AFM speed, versus the excessive speed I observe being flown on a "normal" but always now power on, approach.

But, Hey !! Bloggsie, what would I know, compared to Aces of the Bases like your good self, I am happy to admit I am still learning.

Tootle pip!!
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Old 19th Jul 2017, 09:38
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Just fly it like the autopilot does, Leddie, and you won't go too far wrong (ie low or slow)!
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Old 19th Jul 2017, 12:24
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C172 N POH states stalling speed not more than 44kias at MTOW at 30deg bank. recommended short field is flaps 40deg at vref 60 kias. that's at least 1.36 Vs. lighter weight and smoother conditions could see verified at 55 kias flaps 40 and stall say 40kias that's still 1.37 vs. that's a ground roll of about 550ft on pavement. Worst case 44kias stall and 55 Vref is still 1.25 Vs. I guess one could say that the POH is conservative.

However since groundroll on takeoff is probably at least 850 ft then barring emergencies, it's all a bit of a moot point isn't it?
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Old 20th Jul 2017, 00:05
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C172 N POH states stalling speed ...

.. except one doesn't do these sums with IAS .. speed calcs need to be in CAS with PEC corrections as/when appropriate to get to/from IAS.

IAS is a Mickey Mouse number ... very useful for reference as it is all we can see when pushing and pulling .. but it is still a Mickey Mouse number, not relevant for running sums.

More interestingly, once down towards stall, PECs can get a bit average .. run the sums in CAS and then see what the margins might be ...
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