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John Farley's thoughts on forced approaches

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John Farley's thoughts on forced approaches

Old 15th Nov 2019, 07:55
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John Farley's thoughts on forced approaches

I was looking through some files yesterday, and happened across a passage written by our respected past member John Farley. John was a highly experienced test pilot, who was a wealth of wisdom, and an asset to our knowledge here during his time. After reading his book "A View from the Hover", I made the trip to spend a day with John, and was rewarded with many gems of wisdom. Among them, were John's thoughts on forced approaches. Though this wisdom is of moderate applicability to most well mannered, low drag GA planes, I can say that I have applied the technique in rather draggy types, and with some moderation, it works, and keeps you safe. During flight testing of a higher gross weight, Cessna 182 amphibian, forced landing precision benefited from this technique. Certainly an attempt to land power off from a "best glide speed" approach would have ended in pain. Hence my fight manual supplement for the modified plane specified a much faster glide speed, with corresponding reduced expectations in gliding distance.

In any case, here is a passage written in John's book (which I highly recommend):“A View from the Hover” page 354:
“…. A few years later, I found myself on Aero Flight at Bedford where we operated several very valuable single engine prototype research aircraft. The boffins were naturally very keen not to lose one of these just because the engine stopped. Without exception, the aircraft were all the aerodynamic opposite of a good glider. In the jargon they were low lift over drag devices (low L/D) which meant that they all had very steep glide angles.

We have now arrived at one of the most enduring myths of aviation. Aircraft that glide down a 30 or 40 [degree] angle must be awful to land. Wrong. Totally wrong. They are the easiest of them all so far as the final approach and landing goes. Only when I started practising glide approach and landings for aircraft of that type did I start to get a 100% success rate with smooth touchdowns, just after the runway numbers, and at the correct speed. Because of the steep glide angles, it is necessary to be pretty close to a suitable runway when the engine stops. The difficulty that had previously dogged me of looking out the window in order to judge the shallow glidepath and so how to fly around the circuit, just vanished. With the nose apparently pointing straight down at the ground you can see exactly where you will impact if you do nothing. Wind is not an issue and there is nothing to judge. All you do is to throw down the gear and flaps, dive at the flap limit speed, and point the thing at the beginning of the lead in lights (or just short of the runway if there are no lead in lights). Then pull out of the dive at the last moment and fly level, as low as you dare, until the speed bleeds to the one you want for touchdown. This way you impress those who do not realize how easy it all is by plopping it on the numbers. If there are any Hunter pilots out there who read this, try gliding it with gear and full flap at 250 kt and you will see how well it handles – except in manual. Handling is excellent during the flare because of all the speed. What you must not do is to try to land a low L/D device from a descent at its best glide speed, as you will be very disappointed when you try to flare from the steep approach. In 1982, doing AV-8B engine work at Edwards over the lake bed, I had over two hours of gliding in 40-odd episodes with never a concern, should a relight fail. I started each sortie with a practice engine chop climbing through 15,000 ft or so, and then, with the wheels and flaps down, did the practice ‘dirty dart and flare’ over the lake bed as a bit of very enjoyable legalized hooliganism. High risk stuff so far as some onlookers were concerned. But you know better. Of course glider pilots know all about the use of drag to make approach and landing easier. That is why they set up the approach with airbrakes out, and pop them in at the first sign that they are going to land a bit short.

If you are a power pilot who has trouble with doing the occasional glide approach you may (secretly) wonder how glider pilots have the skill and judgement necessary to do it every time. May I suggest a reason for their success? Currency.”

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Old 15th Nov 2019, 12:35
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You could listen to JF talk/write flying forever! (Except for an occasional pee.)

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Old 15th Nov 2019, 12:54
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With the rare and fantastic ability to make anything sound simple and to understandably explain the most complex of subjects as if it was just the two of you sharing a secret..
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Old 15th Nov 2019, 16:02
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Old 15th Nov 2019, 16:22
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And a thoroughly nice bloke too.
Oh, so much so! He picked me up at the train station, and we spent the day chatting (well, me learning lots from him!). For a person who had accomplished so much in really advanced aviation, and to hear about his testing, and training was fascinating! Beyond the comradery, and learning I shared, was one other thinking point for me. John, who seemed to be very bravely managing some health challenges, told me that he was a bit at loose ends as a senior person, as he had not planned for old age - with his profession, he just did not plan to live to old age! But, I witnessed him enjoying life in the golden years, and certainly sharing lots of wisdom here.

I'm honoured to have received mentoring from John, and happy to remember him here, and recount a small bit of his wisdom.

So I've drifted the thread more. Accolades to John appropriate, discussion on power off approaches welcomed too!
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Old 15th Nov 2019, 16:40
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Just as a further aside, waiting on the ground while a PPL friend was checked out in a C152 at Princeton in NJ, I was rather startled to see another C152 arrive on the runway dead stick. As it slowed, the engine restarted and the aircraft taxied in. Deliberate? Accidental? Lucky outcome?
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Old 15th Nov 2019, 19:18
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I have so many happy memories of John's opinions and advice. A late bit of support and intervention was one of the reasons I did well in my PhD viva, and for a few years I sat on an inter-university committee with him. Several times we got into some thoroughly enjoyable technical arguments, then when we'd run out of steam, the chairman would rejoin the conversation and say mildly "err, Genghis and John, what did we just decide?". I doubt I'll ever stop missing being able to pick up the phone to him and talk over a problem.

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Old 16th Nov 2019, 00:04
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We have now arrived at one of the most enduring myths of aviation. Aircraft that glide down a 30 or 40 [degree] angle must be awful to land. Wrong. Totally wrong. They are the easiest of them all so far as the final approach and landing goes.[...] Then pull out of the dive at the last moment and fly level, as low as you dare, until the speed bleeds to the one you want for touchdown.
Interesting thoughts. I kind of like it.
Although I haven't thought about the relationship of the best glide speed and the typical approach speeds specified for aircraft. Someone else can look into that.

Though he exaggerates with a 30 or 40 degree dive, as even a horrible 2:1 glide ratio would be only a 26 degree descent.

And with the caveat that one still has to have a suitable landing spot that is reachable. A good glide ratio might be appreciated at the start, when looking for a usable landing area. Only when close, change to a high drag configuration if achievable.

Aiming downwards steeply certainly does make the point of landing/impact more clear, although I think he glossed over a bit the issue of how far one will travel after the flare, bleeding off extra speed. The distance covered while bleeding off speed may be not excessive in a really draggy aircraft, but a problem with high glide ratio slippery aircraft, for those are the type where if someone approaches 15kts too fast, they end up touching down way late and roll past the end of the runway. Maybe it's all OK if one did reach a long runway, but an issue if trying to belly something into a shorter field.

The pulling out of the dive at the last moment also poses a bit of a challenge if the descent rate is high. Yes keeping extra speed on will allow one the energy to pull out, but does take some judgement and perhaps practice as he does mention.

At some extreme level of dragginess, one will still have problems despite diving it down at the ground. The guys doing the NASA wingless body aircraft flights in the 1960's were running into the issue that if the glide ratio were getting too low (down close to 2:1 I think), it got harder to pull out of the dive and maintain speed long enough to level out at ground level. Normally their craft were OK, I seem to recall from books, but in worse glide ratio configurations things got tougher. (But I'm not sure what kind of approach speeds they used, relative to whatever best glide they had. I should read up more.)

As aircraft get bigger and heavier in general, one is less likely to just chop the power on final and float it on in like flying some Piper Cub -- When the engines are working on the heavy wing loading aircraft, some power is kept on, the approach is flat, and the descent rate isn't too high. So I can see that when there's no power, keeping the same moderate approach speed may result in a high descent rate and less ability to flare out.

All this stuff resonates with me as I come from skydiving, where canopies flying at a high wing loading are deliberately trimmed nose low to dive fast, rather than float along at best glide or something like that. Glide ratios are terrible partially due to the full sized draggy human hanging below the small canopy. Having the extra speed actually improves landings, as there is the extra energy available to apply a little g for the flare, pitching the canopy back to achieve level flight at ground level. With the extra speed, there's time to fine tune the landing, to let down inches at a time until one's landing gear (feet) are ready to run or slide out the landing. Skydivers also will do turning dives to increase speed before landing, as that will prolong the level flight over the ground before touchdown. (It is fun & thrilling & potentially dangerous too, but that's another matter). So my canopy for example, which is moderately high performance (but not at a high competition level), has a glide speed of around 43 mph and 1500fpm descent (25fps), and a 2.3 glide ratio. That speed and descent rate will smash someone up who doesn't flare properly. (Student or novice canopies might come in at only 25 mph and 800 fpm before the landing flare.) If skydiver air traffic allows it, the preferred technique for landing my canopy is to do a steep diving turn to get 60+mph which gives lots of energy for the flare and time to set up the landing just right.

So yes I agree that for a low glide ratio aerial vehicle, carrying extra speed into the flare may make the approach and landing easier in many circumstances.










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Old 16th Nov 2019, 04:56
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Seconded, I was most surprised to receive the following email from John, most chuffed, especially asking this peon for his thoughts.
Slender delta airflowDear XXXX

Many thanks for your two 'reading' references on the superstall thread.

I had not seen either.

When they were discussing the various types of vortex instability that could cause wing rock at high alpha I was struck by no mention of the possibility of the vortex attachment point sliding up and down the the leading edge a little. Certainly back in 1964 the RAE boffins at Bedford led me to believe this was the cause of the HP115 divergent dutch roll that followed a rudder tap at a suitable alpha.

In 1990 Valery Menitski (CTP on MiG-29) told me that when he flew the first prototype it was rubbish at high alpha until they nailed the vortex attachment points with a pair if VGs at the base of the pitot. This seemed to me to support the idea of the attachment point wandering up and down the LE as a trigger of wing rock.

Wot think you Sire?

Do you have a reference for where you found the docs in your links?

Happy New Year!

Yours

John

[email protected]
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Old 16th Nov 2019, 05:32
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He was one of a very few individuals that posted using his real name on this forum


A few years ago I asked an obscure question about the Harrier which he answered in great detail, he never patronized or talked down to anyone

John Farley was a true gentleman and a pilots pilot
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Old 16th Nov 2019, 11:33
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I met John at my very first Farnborough Airshow in '74; I happened to be in the SATCOs office when John walked in and SATCO introduced me.
A couple of days later, I was told that John was downstairs and had asked to see me. He had been asked to fly Raymond Baxter in the display next day live on air and wanted to arrange a special 'slot' beforehand to take him up and see if he could make him puke - didn't want him barfing into the microphone for all those watching on TV to hear!
Me, the most junior controller at Farnborough at the tme and John remembered my name our brief meeting!

Years later, I experienced gliding in a Hunter T7.
I was up with the late lightningmate, (not to be confused with Lightning Mate who is still with is on this forum) one of Farnborough's ace test pilots. He pulled the throttle at about 16,000ft just south west of Greenham Common and asked Boscombe for a '1 in 1' to their main runway. Pullng the speed back to 250 kt indicated gave rod of 500ft/mile. Boscombe vectored us towards their centreline giving us range from touchdown checks and when our height numerically equalled range eg 11,000ft at 11nm, he dropped flaps and gear and increased rod to 1,000ft/mile (1 in 1, get it?) and we continued at this rate of descent until it was time to flare for a touch and go.
Most exhilerating!
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Old 16th Nov 2019, 11:51
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Originally Posted by treadigraph View Post
Just as a further aside, waiting on the ground while a PPL friend was checked out in a C152 at Princeton in NJ, I was rather startled to see another C152 arrive on the runway dead stick. As it slowed, the engine restarted and the aircraft taxied in. Deliberate? Accidental? Lucky outcome?
An instructor I flew with at Ipswich in my pre-PPL days asked me to do a PFL over the airfield, in a C152. On finals he asked me if I was sure of making the runway. I said I was. He reached over, switched off the mags and put the key in the top pocket of his jacket.

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Old 16th Nov 2019, 12:43
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Reading these comments, it makes one realise one's own modest placing in the aviation 'pyramid'. People such as John Farley and Eric Brown were right at the very apex.
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Old 16th Nov 2019, 15:02
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Originally Posted by ShyTorque View Post
An instructor I flew with at Ipswich in my pre-PPL days asked me to do a PFL over the airfield, in a C152. On finals he asked me if I was sure of making the runway. I said I was. He reached over, switched off the mags and put the key in the top pocket of his jacket.
When I was doing my instructor rating, the same happened to me, downwind at White Waltham, in a PA28-160. Way too high on finals, I learnt just how accurately one could control one's flightpath using the passenger door as an impromptu air break. Happy days.
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Old 16th Nov 2019, 15:09
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Back in the day, having flown from Coventry to Valley with Carl Butler in his AOP Auster which was taking part in the Battle of Britain display, I found myself having a sarnie in the Crew Room, & John arrived with his lunch box & sat alongside for a blether. He was flying the Ryan PT-22 that day, also based at CVT, so I had heard the unique sound of the Kinner radial several times, but it was the first time I had heard his wonderfully apt description as “sounding like it was having permanent engine failure”

He also lectured the PFA strut at Coventry one evening on flying the Harrier, & towards the end, there we all were, sitting on our seats with hands on imaginary controls, all being talked through a landing - concentration etched on every face!

Now on topic - some years later I had an engine fail in my Tipsy Nipper, luckily overhead my strip, & although another owner had advised that engine off, it had the glide performance of a toilet seat, it wasn’t that drastic in the event, but in a day with a blustery crosswind, draggy enough to ensure perhaps a slightly modified version of John’s technique worked beautifully.

A total Aviation Gentleman, to be sure.
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Old 17th Nov 2019, 09:22
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Originally Posted by pchapman View Post
Interesting thoughts. I kind of like it.

Though he exaggerates with a 30 or 40 degree dive, as even a horrible 2:1 glide ratio would be only a 26 degree descent.
JF was not normally prone to exaggeration -
Remember he had the 'pleasure' of flying A/C of the calibre of the Short SB5 and other 'one off' designs - other possibilities might have been - Boulton Paul BP111, Avro 707, , Hunting 126, Fairey FD2 and Handley Page HP115 and Short SC1 - although I do not know how many of these A/C he actually did fly.
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Old 17th Nov 2019, 09:38
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He certainly flew the FD2.
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Old 17th Nov 2019, 15:14
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Appreciate the comments about JF but seeing as the thread is about gliding technique after a power loss, I will try to get it back on track and hopefully we can keep it there.

I re recently read an article about power loss in high drag aircraft in the ultralight world where they have relatively small inertia compared to the jets or the C182 on floats. The link is here.....

https://electricmotorglider.com/2018...energy_part-2/

There seems to be difficulty picking up speed and potentially stalling if the flare is too early. Any opinions on this article or related info would be welcome.
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Old 17th Nov 2019, 15:55
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Originally Posted by tcasblue View Post
Appreciate the comments about JF but seeing as the thread is about gliding technique after a power loss, I will try to get it back on track and hopefully we can keep it there.
Most of us actually read the thread title TCAS = John Farley's thoughts on forced approaches
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Old 17th Nov 2019, 17:39
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tcasblue,

At first read, that article looks excellent, and expounds a number of issues I raise during type training. I'm going to read again in great detail. It is one of Dave Thurston's (Design for Flying book) which I own and fly, and it's a very draggy glider!

To further one's understanding a little more, read up on helicopter autorotations. Yes, Helicopters glide, just not far! But they're very controllable, and indeed a lot of fun to glide, you're just not doing it for long! BUT, there is a limiting "height velocity curve" for every helicopter, as there should also be for every airplane. As with helicopters, you can get an airplane into a combination of height, and speed from which a successful glide landing after an engine failure would not be possible - and no one tells pilots this alarming fact. It's up to pilots to figure it out for themselves, and avoid that regime of flight (without being told what it is!). But helicopters have an added advantage in the glide and flare over an airplane. Helicopters store energy for the flare both as airspeed (which may be held faster to store more energy, as a plane), and as extra rotor RPM, as helicopters can be autorotated with rotor RPM greater than that permitted for powered flight, so as to store energy in the extra rotor RPM, to be used during the flare, which airplanes cannot do.

This is why I train, as John's passage later validated for me, to store extra speed in a glide. Unless you need to stretch your glide to make it to the coast, or over the mountains, choose a spot closer, make no attempt to stretch the glide, and get it down well. With the extra speed stored, you can either spend it to prefect your flare, or dump it out at the last minute as a sideslip, or more flap extension. 'Worst is you land long. 'Better than landing short on a forced landing!
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