Air Cadet Gliding pix in the 80s (pre glass)
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The Tutor single seat and the Cadet Mark 3 (T-31) suffered from compression shakes in the spars,after long service. There was a structural failure of a Tutor circa late fifties which led to modifications.
Do you know at what location the shakes occurred, along the spar length? And do you know what the remedial/preventative modifications were? In my case in 1957, the Mark III's at Halton were probably too new to suffer from long-service defects like that, but it is nevertheless "interesting" news for the many, many who have flown in these types that such a potentially serious flaw could develop!
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Hello 603DX,
My source is "Slingsby Sailpanes" by Martin Simons,Airlife,1996 pages 62/63. To summize the rear edge of the plywood leading edge skin was attached indirectly to the wing spars. This was done on Cadets,Tutors and many other gliders. Between each pair of ribs a narrow packing strip of wood was cut and glued to the top and bottom flanges of the spar,planed and sanded level with the ribs. The plywood skin was wrapped over the leading-edge ribs and glued to them and also to the packing strips.
The packing pieces,ending abruptly at each rib station created an abrupt change of stiffness in the spar. When the wing flexed under load,concentrations of stress occurred in the spar at every rib. With long hard use(winching loads and heavy landings) the stress concentrations caused by the packing strips encouraged compression shakes which are difficult to detect. Once recognised modification schedules were issued ,Mod 80 circa 1962. I have no doubt that all ATC gliders were very well maintained to strict airworthiness requirements.
The small strut was to prevent vibration on aero-towing.
There must be many glider engineers or someone from the Vintage gliding scene who can elaborate further on this ?
My source is "Slingsby Sailpanes" by Martin Simons,Airlife,1996 pages 62/63. To summize the rear edge of the plywood leading edge skin was attached indirectly to the wing spars. This was done on Cadets,Tutors and many other gliders. Between each pair of ribs a narrow packing strip of wood was cut and glued to the top and bottom flanges of the spar,planed and sanded level with the ribs. The plywood skin was wrapped over the leading-edge ribs and glued to them and also to the packing strips.
The packing pieces,ending abruptly at each rib station created an abrupt change of stiffness in the spar. When the wing flexed under load,concentrations of stress occurred in the spar at every rib. With long hard use(winching loads and heavy landings) the stress concentrations caused by the packing strips encouraged compression shakes which are difficult to detect. Once recognised modification schedules were issued ,Mod 80 circa 1962. I have no doubt that all ATC gliders were very well maintained to strict airworthiness requirements.
The small strut was to prevent vibration on aero-towing.
There must be many glider engineers or someone from the Vintage gliding scene who can elaborate further on this ?
Last edited by T-21; 17th Dec 2011 at 14:41.
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Thanks for that clear description, T-21. Seems the locations were at the rib/spar flange junctions, and centred on the lack of continuity of the packing strips across the ribs. It would be interesting if someone who was involved or was aware of the situation could explain how Mod 80 overcame this.
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Hi Mr 603DX
The problem with compression shakes is that they are not actual splits or cracks. They are buckles in the wood cell walls induced by heavy compression overloading along the line of the wood grain. References are the EAA book - "Aircraft building Techniques in Wood" and the Munitions Board Aircraft Committee "Wood Aircraft Inspection and Fabrication" ANC 19. There are also good explanations available by Googling.
If a compression shake is formed, the failure strength of the wood in compression or tension is badly affected and a failure may occur unexpectedly at some future point. I suppose there are some similarities to metal fatigue.
Compression shakes apparently can be very difficult to spot - they may appear as visible lines running across the wood grain but they can also need microscopic examination and would in any case be concealed by the wing structure, paint etc.
Compression shakes mainly occur at points of stress concentration. As previously described, the system of sliding complete wing ribs down along a main spar and then glueing filler strips along the spar between the ribs effectively produced a spar with a series of stress concentrating notches in it.
On the Tutor/Cadets the strut attachment point on the spar would have been another point where stresses are considerably raised and I assume that the point at which the spar would tend to fail would be just outboard of the strut atttachment area.
On the Cadets/Tutors the stress raising points on the spars in combination with a very high number of load cycles (launches) with (probably) quite a few overspeed/oversteep winch launches with (possibly) some over-strength weak links and (almost certainly) some pretty brutal landings did result in the formation of compression shakes in some mainspars.
The remedy according to the blessed Martin Simons was that the whole wing had to be opened up to allow inspection of the spars. The packing pieces had to be removed and the ribs cut away at the point where they crossed the spars. A continuous strip of wood, effectively an auxiliary spar cap was then glued to the spar before the wing was rebuilt. As he says, if done professionally, the cost would have exceeded the value of the aircraft. But I guess that would not have been a problem for the RAF!
The problem with compression shakes is that they are not actual splits or cracks. They are buckles in the wood cell walls induced by heavy compression overloading along the line of the wood grain. References are the EAA book - "Aircraft building Techniques in Wood" and the Munitions Board Aircraft Committee "Wood Aircraft Inspection and Fabrication" ANC 19. There are also good explanations available by Googling.
If a compression shake is formed, the failure strength of the wood in compression or tension is badly affected and a failure may occur unexpectedly at some future point. I suppose there are some similarities to metal fatigue.
Compression shakes apparently can be very difficult to spot - they may appear as visible lines running across the wood grain but they can also need microscopic examination and would in any case be concealed by the wing structure, paint etc.
Compression shakes mainly occur at points of stress concentration. As previously described, the system of sliding complete wing ribs down along a main spar and then glueing filler strips along the spar between the ribs effectively produced a spar with a series of stress concentrating notches in it.
On the Tutor/Cadets the strut attachment point on the spar would have been another point where stresses are considerably raised and I assume that the point at which the spar would tend to fail would be just outboard of the strut atttachment area.
On the Cadets/Tutors the stress raising points on the spars in combination with a very high number of load cycles (launches) with (probably) quite a few overspeed/oversteep winch launches with (possibly) some over-strength weak links and (almost certainly) some pretty brutal landings did result in the formation of compression shakes in some mainspars.
The remedy according to the blessed Martin Simons was that the whole wing had to be opened up to allow inspection of the spars. The packing pieces had to be removed and the ribs cut away at the point where they crossed the spars. A continuous strip of wood, effectively an auxiliary spar cap was then glued to the spar before the wing was rebuilt. As he says, if done professionally, the cost would have exceeded the value of the aircraft. But I guess that would not have been a problem for the RAF!
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A very clear and helpful explanation, astir 8. I would imagine that the extensive wing structure modification described was only undertaken in cases where close inspection of the spars had not revealed signs of significant compression shakes.
In other words, was it more likely to be carried out as a precautionary procedure to extend the safe service life, rather than as an attempt at "repairing" already damaged wing spars?
In other words, was it more likely to be carried out as a precautionary procedure to extend the safe service life, rather than as an attempt at "repairing" already damaged wing spars?
The Ghost In The Machine
Place Kirton in Lindsey, Date Feb 1964 2 solos down 1 to go and held by showers of wintry rain and sleet crossing the airfield. 643 GS are as eager to get rid of me as I am to finish the course. Duty Inst detects a break in the weather. Wings level cable on and off we go, the KK MK3 rockets into the air! Both cdt and glider rapidly vanish into cloud..bugger.
There are tendrils of lower stuff scudding along below the main cloud base and I've just blundered into it. Now my experience level. Min No of launches and 2 solos should have spelt trouble but oddly it was almost as if I was accompanied by a particularly patient calm voiced instructor.
Voice from back seat. 'Don't panic. Drop nose, Dump cable and pop spoilers, don't turn until we drop out of this muck' It is obvious we are actually flying btween 2 layers of cloud. Thankfully the stuff below us is scattered enough to give glimpses of the ground (broken snow patches, incidentally the best camouflage ever invented, airfields just vanish into the general landscape)
OK flown out of it now, but the winch is a good way behind us. Voice. 'Altitude check turn cross wind and watch for any cloud, barely out of turn when. 'Ok lad now pop spoilers a second or two and turn downwind. Overcook the turn slightly I want us placed well inside the airfield boundary. Got that' 'Yes sir' You've got enough altidue for a short downwind led and quick base leg but there isn't going to be a lot of airfield to land in so don't let it float on finals. 'Yes sir'
We duly fangle round the shortened circuit and he's right of course. There isn't much airfield in front of me and by the time Mk3 and cdt finally slither to a halt the boundary hedge is a lot closer than I've ever seen it before.
The rescue posse duly pile out of the Landrover with a relieved DI asking nonchalantly. 'Go all right did it? Just for a moment there I thought you vanished into cloud. 'I did' Oh! Better not mention it too often it's not supposed to happen' I know.........
Happy days but my guardian angel worked bloody hard that day. He's popped up twice since both times after near fatal cardiac troubles. I often fly that circuit many times in my minds eye and just know I couldn't have done it on my own. Discuss....
There are tendrils of lower stuff scudding along below the main cloud base and I've just blundered into it. Now my experience level. Min No of launches and 2 solos should have spelt trouble but oddly it was almost as if I was accompanied by a particularly patient calm voiced instructor.
Voice from back seat. 'Don't panic. Drop nose, Dump cable and pop spoilers, don't turn until we drop out of this muck' It is obvious we are actually flying btween 2 layers of cloud. Thankfully the stuff below us is scattered enough to give glimpses of the ground (broken snow patches, incidentally the best camouflage ever invented, airfields just vanish into the general landscape)
OK flown out of it now, but the winch is a good way behind us. Voice. 'Altitude check turn cross wind and watch for any cloud, barely out of turn when. 'Ok lad now pop spoilers a second or two and turn downwind. Overcook the turn slightly I want us placed well inside the airfield boundary. Got that' 'Yes sir' You've got enough altidue for a short downwind led and quick base leg but there isn't going to be a lot of airfield to land in so don't let it float on finals. 'Yes sir'
We duly fangle round the shortened circuit and he's right of course. There isn't much airfield in front of me and by the time Mk3 and cdt finally slither to a halt the boundary hedge is a lot closer than I've ever seen it before.
The rescue posse duly pile out of the Landrover with a relieved DI asking nonchalantly. 'Go all right did it? Just for a moment there I thought you vanished into cloud. 'I did' Oh! Better not mention it too often it's not supposed to happen' I know.........
Happy days but my guardian angel worked bloody hard that day. He's popped up twice since both times after near fatal cardiac troubles. I often fly that circuit many times in my minds eye and just know I couldn't have done it on my own. Discuss....
Last edited by Prangster; 5th Jan 2012 at 15:06.
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First solo's can also be very exciting!!. Winch failure at 300. Dumped cable [possibly a bit under tension] 'S' turned as per book, landed safely. I was amazed I kept so cool about it whilst it was happening, as I always considered myself not particularly capable of being 'cool' under pressure. Only problem was, that later, as a Staff Cadet, [fortunately dual] I lost control on the winch,'!!' got into an overbank situation which was heading rapidly for disaster until my guardian angel in the back dumped the cable and recovered it for me. To this day, I have no idea why I didn't do it myself, I guess I just stuck with it too long. Later, as a PPL, I never failed to overshoot an approach I was unhappy with, so I must have learnt something from it!!! [613Halton]
This 'being cool under pressure' seems to be endemic for 613 Staff cadets. I was a P2 flying air experience in VX275 one evening off what is now runway 02 (compass base to Aston Clinton corner), the OIC line (now a BGA national coach) told me 'if you overshoot the launch point you can drag it back by yourself'. I arrived on base leg with a little too much height even with judicious use of spoilers, so a did a 'beat' only to find the northerly component in the wind took me too far to get back over the hangar next to the old 613 hut, so I decided to go for the field to the south of the airfield (on the right as you approach from the main camp) planning my approach to do a steep turn to miss a tree and some grazing cows and running this all over coolly in my mind whilst adjusting speed and spoilers and briefing my passenger.
Unfortunately a large tree stump got in the way and in trying to miss it I ground looped and tore the skid off.
Unfortunately a large tree stump got in the way and in trying to miss it I ground looped and tore the skid off.
Cool Under Pressure
We were probably trained by the best gliding instructors in the world but were too young and naive to know it. Result was that when things did go pear shaped we were more than able to cope. I did a bit of staffing on 644 and came to appreciate just how brilliant the deliverers of knowledge were. It was almost as if they breathed the essence of flight into their charges by a strange form of gliding osmosis. Taking my cdts for air ex apart I didn't do any serious gliding again until doing a course at Pocklington in the late 1980's. It was almost as if the twenty odd year gap didn't exist. Ducks and water come to mind.
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Apart from Family considerations, I always look back on my time as a Staff cadet at 613 as some of the most enjoyable days of my life. How privileged we were to get all that flying and life experience so young!!!! Prangster, as you say, the knowledge never leaves you. After 17 years of not flying anything at all, I solo'ed in a Cessna 150 after 4hrs 10 mins dual. All power pilots should be glider pilots first. Such happy times!!
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Jem60, Totally agree all private pilots should start gliding first. Would teach better stick and rudder pilots as we fly closer to the stall and they would be better equipped to deal with a dead engine .
Now how do you land this thing.......
Mate of mine mega hours on 747's eventually got into a glider cockpit...Cue chaos. I think the runway perspective was so different he just couldn't sort it
Last edited by Prangster; 11th Jan 2012 at 15:45.
Kenley 19!!
Great image Clive (was it one of Alex's med format one's !!).There are some clues:-
WE 989 (not a Kenley resident) was pranged (written off) in june 71 so that gives us a finish date,and the number of original Airfield buildings standing helps to give us a 'start date'.
Points of interest. Aircraft firing butts stiill there,Fuel Farm looks servicable (gone by early 60's),Airfield dump looks clear of 'lincoln' and later wrecks.
Prefect seems to be in original siver/yellow scheme.
Officers new garages in nearest e-pen.
Runway white crosses indicate that the powered flying element has finally departed,(circa 1958-9), they are fairly new and are still being weathered.
Tennis players in 'whites,but not enough resolution to check the cars.
So i am having a shot a 1959-61 ish, and certainly post RFTsky film.
PM me for an interesting image !!
Anyway what a fantastic place and should have been properly preserved as a definative BoB airfield.
Frelon will no doubt be able to help.
WE 989 (not a Kenley resident) was pranged (written off) in june 71 so that gives us a finish date,and the number of original Airfield buildings standing helps to give us a 'start date'.
Points of interest. Aircraft firing butts stiill there,Fuel Farm looks servicable (gone by early 60's),Airfield dump looks clear of 'lincoln' and later wrecks.
Prefect seems to be in original siver/yellow scheme.
Officers new garages in nearest e-pen.
Runway white crosses indicate that the powered flying element has finally departed,(circa 1958-9), they are fairly new and are still being weathered.
Tennis players in 'whites,but not enough resolution to check the cars.
So i am having a shot a 1959-61 ish, and certainly post RFTsky film.
PM me for an interesting image !!
Anyway what a fantastic place and should have been properly preserved as a definative BoB airfield.
Frelon will no doubt be able to help.
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Hi Pobjoy,
The photo was found at KY about a year ago by Keith Chandler, the current boss. We assume it was taken by Alex, but it is not confirmed. Frelon guessed some time ago by email, but I don't recall the date he put on it.
PM on route now, cheers!
The photo was found at KY about a year ago by Keith Chandler, the current boss. We assume it was taken by Alex, but it is not confirmed. Frelon guessed some time ago by email, but I don't recall the date he put on it.
PM on route now, cheers!
Kenley
The image looks very 'med format' to me so rather points to Alex.
Frelon would have been a staff cadet at that time so will remember the Lincoln and Spitfire. Of course if they had been proper staff cadets then they would never have let the Spit get trashed (it should have been hidden in the gliding hangar).To think i spirited away a 3inch rocket with fins and its associated warhead (two trips on a bicycle) before they were 'dozed' into the ground.How anyone managed to fly in those wellington boots amazes me when i think about it.
Frelon would have been a staff cadet at that time so will remember the Lincoln and Spitfire. Of course if they had been proper staff cadets then they would never have let the Spit get trashed (it should have been hidden in the gliding hangar).To think i spirited away a 3inch rocket with fins and its associated warhead (two trips on a bicycle) before they were 'dozed' into the ground.How anyone managed to fly in those wellington boots amazes me when i think about it.
Prefect over Kenley Officers' Mess
Oh, those were the days!
I did my A & B at Hawkinge (all those WRAFs) in summer of 1959 and applied to be a Staff Cadet at Kenley and did my first flight there in April 1960 with Roger Munt.
I can well remember the half of the airfield that we could not use because of the rugby and football goal posts - shows up well in the picture above, so a small airfield made even smaller by this restriction in the early days.
I cannot remember the runway numbers (31) being so white and bright so would suggest that the date is probably just after the airfield was closed to regular flying, but before I joined in 1960, so Pobjoy's guess of around 1958/59 is probably near the mark.
George Nunn was CO, and Johnny Gilbert CFI and we only flew Saturday afternoons and Sundays. When we built up a good team of staff cadets we badgered the hocifers to see whether we could come to Kenley on Friday evenings and get to fly both days every weekend.
In my first year at Kenley I did the staggering sum of 64 flights (only 5 in the T21). I wonder how many flights today's staff cadets get in a year??
I did my A & B at Hawkinge (all those WRAFs) in summer of 1959 and applied to be a Staff Cadet at Kenley and did my first flight there in April 1960 with Roger Munt.
I can well remember the half of the airfield that we could not use because of the rugby and football goal posts - shows up well in the picture above, so a small airfield made even smaller by this restriction in the early days.
I cannot remember the runway numbers (31) being so white and bright so would suggest that the date is probably just after the airfield was closed to regular flying, but before I joined in 1960, so Pobjoy's guess of around 1958/59 is probably near the mark.
George Nunn was CO, and Johnny Gilbert CFI and we only flew Saturday afternoons and Sundays. When we built up a good team of staff cadets we badgered the hocifers to see whether we could come to Kenley on Friday evenings and get to fly both days every weekend.
In my first year at Kenley I did the staggering sum of 64 flights (only 5 in the T21). I wonder how many flights today's staff cadets get in a year??
Last edited by Frelon; 30th Jan 2012 at 11:57.
