|The Newsletter of Stratford Gliding Club||
Issue 28, September 2004
We have an article from an occasional contributor, George, arguing against one of the myths of why aircraft behave as they do. If you feel inclined to refute (or even support) his arguments in print, please contact The Wire via the pigeonholes, under Q.
From the Chairman
Bank Holiday Monday saw our “Back To The 70’s” day as part of the Club’s 30th Anniversary year. Launches were 65p and club aircraft cost 5p per minute.
Fifty-one of us were on the flying list – almost half the membership – and we all flew despite the challenging conditions, breaks for rain and disruptions caused by the few who made the effort to dig out their 70’s gear and don silly wigs. I don’t wish to cause them too much further embarrassment, but thanks for making the effort go to Ann Pearson, Chris Bingham and Richard Maks. I’m sure the blackmail pictures will be in circulation soon. It’s difficult to believe that I once wore platform boots almost identical to Chris’s.
It was good to meet some past Club members as well. Peter Candy arrived in his hand built 1928 Bugatti which was immediately D.I.’d by quite a few of us. We also managed to add some photographs to our Club archive – Four Club Chairmen (past and present), Four C.F.I.’s (past and present) and a few of members in silly clothing. Incidentally Tony Edlin is currently acting as our Club Historian.
Even with the disruptions and distractions we managed eighty launches on the day, which was rounded off with a barbeque, a few beers and the odd bottle of wine. My thanks go to everyone for making the day a great success, but especially Phil and the other instructors who all worked hard to get everyone flown on a day when only Silver ‘C’ pilots and above were allowed to go solo.
On the subject of our 30th Anniversary, we would like to arrange a celebration dinner, probably at the end of November at a venue yet to be decided. It’s a bit of a ‘chicken and egg’ situation as we need to have some idea of the numbers before we can book anywhere. I’ll be posting a notice in the clubhouse to ask for names and numbers for the event, so please put your name down on the list if you would like to attend.
A firm date to add to your diaries is Thursday October 28th. This is when the A.G.M will be held at Snitterfield Village Hall. You will of course be notified of this by post, but there will be business to done as well as the more informal things we do at these meetings. Please come: it’s your Club, have your say!
Ray (Hoppy) Hopkins 1931-2004
I was shocked, as I’m sure we all were, to hear the news of Ray Hopkins’ sudden death from a heart attack. His funeral was held at All Saints Church, Evesham, on Monday 6th September, and was well attended. I’m pleased to say that that the Club was well represented – gliding played a large part in his life having joined our Club in 1976, as did the Church.
Sue and Ann, his wife and daughter, asked me to convey their appreciation to all members of the Club for essages of support and condolence that they have received.
AD against all ASK Aircraft
As the result of an incident involving a K-7, all of the K series of Schleicher aircraft must have an inspection which must be completed by the end of October. This involves an inspection of the main spar, checking for delamination.
The initial requirement was for a full internal inspection, cutting into the D-boxes to allow endoscope access, However, there are a lot of K-13s, K-7s, and K-8s in action, and at an estimated ten hours work per wing, the likely outcome was that gliding would grind to a halt on October 1st. The requirement has since been relaxed to allow an interim inspection of the back of the spar, with the full invasive inspection deferred until the next CofA.
This makes the problem manageable, and the Technical Officer assures us that we will have a workable fleet available to us in October.
Who’s Done What
Ann Pearson is now a solo pilot. Paul Thornton, Laura Maks, and Richard Ellis have completed their Bronze, and Mike Corfield his Silver.
Jonty Boddington and Nick Jaffray have achieved Part I of the Cross-Country Diploma, and David Searle has Part II.
As a result, Richard is leading the Badge Ladder, Laura is second, and Paul and Mike share third. This can still change, of course, with the rest of the September flying counting towards the scores.
Task and Badge Week
The Task and Badge week was very well supported again this year, with twenty-nine pilots signed up, including four visitors.
The weather worked, but unfortunately it was less than ideal, and the longest successful declared task was 200k. The sky was difficult to read all week, and only the expert pilots were able to take the best advantage of it. Nevertheless, we flew cross-country on eight of the nine days, for a total of 8664km and 248 hours. Thanks are due to the coaches, who organised the week, set the daily tasks, and helped all the pilots who are learning the art of cross-country flying.
On the Wednesday, Barry Kerby and Phil Pickett were at 800′ and preparing to land out at Bicester. A tiny hint of lift at the crucial moment turned into a strong 5000′ climb, enough to let them fly straight home at 180kph and still have 2000′ to spare. Phil took this shot of Barry on the way. It’s in the photo gallery on the Club web site, too. (This picture is clickable, which is hard to achieve in the paper version of The Wire).
The meeting will take place at 19:45 on the 28th October, in Snitterfield Village Hall, as usual.
If you’re the proud holder of one of the Club trophies , please return it to us by the end of September, to give us time to engrave it for the next winner. It would be nice if it was clean, too.
New Ladder Trophies
The Club’s cross-country ladder has now been running for a dozen years, all documented in the Cross-Country Book. With better gliders and instrumentation, more ambitious tasks are being completed, more pilots are taking part, and it now forms a very important part of our club activity.
The requirements to compete on the ladder have become more demanding in time and energy, the difference between 1st and 3rd place can sometimes be only a matter of a few points.
I have donated three new cups for the ladder trophies, to reflect the importance of the Ladder in the Club. Names on the current Ladder trophy, dating back to 1976, will be transferred to the new cup. The cups for 2nd & 3rd places were never engraved, but our records enable us to engrave the cups from the start of the new millennium.
New Winch Trophy
We have also had another new donated to the Club for the Committee to award. It’s the Stratford GC Winch Trophy.
We haven’t yet decided exactly how the winner will be selected, but it will certainly be in recognition of service to a very important part of the Club’s operation.
Often the articles in this section of The Wire contain requests from me to do this or that, or they inform you of unwelcome changes or the like. I am really pleased to be able to write in a different vein in this Issue and share some good news with you.
A little while ago we had a visitor from Birmingham Air Traffic Control who was doing some research into the level of knowledge of different categories of pilots with regard to Airspace. I am delighted to tell you that Stratford Gliding Club members really impressed Birmingham with the results that they obtained from us, so much so that they have let it be known to the BGA Airspace Committee.
I have been told by the BGA that this type of good report helps considerably with their dealings on Airspace and as a consequence, the BGA Airspace Committee are likely to keep our needs particularly in mind, so far as they can, when negotiating over airspace issues in our local area. Of course, we must not be complacent and every Pilot needs to continue to ensure that they keep up to speed on Air Law and Airspace, but I think we should all take pride in the fact that Stratford Gliding Club is being associated with these highly complimentary remarks.
The Diesel Winch
We’ve put a lot of effort into making the Diesel Winch serviceable, and I’d just like to say a huge Thank You to the people who joined in to make it possible: Peter Blair, Martyn Davies, David Ireland, Barry Monslow, Phil Pickett, Fred Price, David Searle, Humphrey Yorke.
Martin Greenwood, Winchmaster
Myths and Legends
If you were at the Club on the 30th Birthday, 30th August, you’ll probably know that we were overflown by four commercial aircraft. These were all observed to be inbound to Birmingham.
The cloudbase was something around 4000ft, and the commercials passed just above the cloud; gliders were below. Now in these circumstances, it’s very easy for us to accuse the airliners of “invading our airspace” but we really have to analyse the situation a little more closely.
First point to note is that, as a gliding site we have no airspace. Licensed aerodromes (such as Wellesbourne) have an Aerodrome Traffic Zone established around and above them. This is a circle based on the (effective) centre of the aerodrome, extending to 2000ft agl and shown in pink on the half mil. Gliding sites have no such luxury: whilst they are also depicted on your map, there is often only an adjacent caption such as “intense gliding activity” or even simply “cables.” So we have no airspace for people to keep out of – and they don’t!
The second point seems to be a bit more difficult for folk to grasp. The commercial boys (and girls – yes they have lady pilots too) that overfly us are mostly being controlled i.e. being told where to go what to steer, altitudes to climb/descend to, by Birmingham Approach Radar. These controllers are responsible for sequencing the traffic into Birmingham, and preventing aircraft under their control from colliding with each other. The aircraft they are controlling are for the most part in the Birmingham TMA, but sometimes, especially when busy, commercial aircraft are vectored out of the TMA. This is when they overfly us at Snitterfield. In essence, therefore, the airliners are under positive control, but just outside promulgated controlled airspace. The pilots are very probably unaware that this is happening – they’ve an aeroplane to manage on its initial approach to landing, and they certainly won’t have the half-mils out. They may be told to watch out for gliders, but then again, they may not.
So the airliners that we see over the site are entitled to be where they are – in open airspace – just like us. Whilst our intrepid instructors stress the importance to Stratford glider pilots of not going into controlled airspace, the reverse is not true – the big boys come out!
What, as a gliding club, can we do? Well basically, not a lot. We can caution our pilots to keep a good lookout, and stress the inadvisability of thermalling up into the cloudbase, The only other action we can take is to quietly remind Certain People that we are where we are, and question the wisdom of sending airline traffic into an area of well known gliding activity.
And the CFI’s doing just that.
Bob Horsnell, Airspace Officer
Not One But Two 500km Flights in One Weekend
Most glider pilots dream of completing their 500km flight at some time in their gliding career but to complete two such flights over one weekend has got to be somewhat unique and a good reason to pen a few lines in support of your Club magazine.
After a dismal wet spring, for me the cross country season started this year on the 16th May. Phil Pickett said he could not spare the time to land out, and declared a 200km triangle. I convinced him that the day was worthy of a 300km, Grafham Water and Ledbury but to be difficult he went round the other way, but we both completed with minor difficulties and Phil pipped me on speed, as usual.
The following weekend, 22-23 May, high pressure was building over the country, polar air was moving in with low overnight temperatures, it had to be worth points on the ladder. On the Saturday Phil Pickett tried another 300km triangle, Diana King 400km, and yours truly a 513km triangle, Chard and St. Neots. We all completed. As so often is the case on the longer flights, the day comes to an end and you are left struggling on the homeward leg, always disappointing when things were going so well for a fast time, wishing you had taken off earlier. I learnt a long time ago that when the going gets tough it’s important to keep going: if you’re still flying, you’re in with a chance. These situations seem to bring out the best in me, a few knots and a few feet become important and your standard of flying and decision making takes on a new meaning.
I am now approaching the dreaded Northampton, many a pilot’s downfall, low, with just a little sun on the ground and a bad out-landing area to pile on the pressure, and bingo, a little thermal put me back in business. After three such scenarios I gained enough height for the final glide with nothing to spare. I hate final glides into a setting sun, if the navigation is slightly out you have a big problem. After some seven hours flying it’s nice to be back.
Sunday looks like being another good day. Phil King tells me he is trying 600km, Axminster and Cranwell; a brave choice. It’s very rare that one good day follows another but in fact it turned out slightly better than Saturday, thermals were easier to locate and centre. I settled for a 528km triangle Bury St Edmunds and Abergavenny, a flight that I completed last year with much difficulty at the second turning point. At 11.30 it was still blue but looking promising to the east. Phil King took off about this time and disappeared, clearly under pressure to get started. I made the decision to launch at 11.50, into a blue sky. When the wind is light and you are loaded with water it’s a difficult decision to make. A blue thermal to 3,700ft and I’m on my way. A bit of luck is essential, you can’t always make the right decision on the ground. I arrived low at Gaydon but then settled into a nice pattern of climb and glide, cruising at 80-90kt. The second leg to Abergavenny went well with just a couple of low points, but the wind at 4500ft was from the north west at 16kt and progress was rather slow. Conditions north of the Severn estuary were good, but looking ahead there was evidence of sea air and conditions were dying fast. It was clearly time to change gear, dump water, fly at best glide and conserve height.
Having flown 140nm along the second leg, I was not prepared to give up, my priority was to at least round the last turning point. which I eventually did at 1,000ft. agl, over high ground. With 54nm to go, getting back was out of the question. There were however a couple of bonuses, I was now running to lower ground with a slight tail wind, aiming to reduce the retrieve distance. When the time came, I radioed that I was very low and 35nm to go. Ahead was a conveniently mown field, and whilst considering an approach so that my landing would not be across the grass ridges a little luck prevailed in the shape of a weak thermal which I hung onto like grim death, climbing to 2,000ft. The sun had now re-appeared and a small cloud was forming above me, clearly I was back in business. Having now cleared the sea air, conditions remained such that I was able to arrive home, I felt not a bad weekend’s work. Phil King decided to cut short his flight after 460km because he was not happy with his speed and progress.
Gliding, at the end of the day, is really about cross-country flying, you can read the books but the true test is to get out there and do it. To achieve the longer tasks you need a good day, planning is important and an early start is essential, selecting the right turning points and a measure of good luck. Every flight will have its high and low points and a tale to tell at the end of the day. By the way, my first 500km flight was in 1986. This is cross-country flying, this is why we do it, so get out there and put yourself to the test and enjoy it. Good luck!!
Why does the nose drop in a turn?
There’s a common explanation for this, which entirely fails to explain the phenomenon. This article debunks the myth.
If you bank an aircraft, the lift generated by the wings is at an angle to the vertical. There is a vertical component, which is less than when the wings are level, and a horizontal component which causes the aircraft to follow a circular path. This is where the mythical explanation stops: the vertical component of lift on the wings is reduced, so the nose drops. Twaddle.
When you bank the aircraft, the tail plane also banks at the same angle (If it doesn’t, your fuselage is broken, and the nose will drop for other reasons. But I digress.). The reduction in lift from the tail plane is therefore exactly the same as that from the main plane. The moments of these forces about the CG remain equal, and the aircraft has no reason to change its pitch.
So what does happen? Initially, the vertical forces on the aircraft are no longer balanced. The lift from the planes is insufficient to balance the weight of the aircraft, so there is a downward acceleration, and the rate of descent of the aircraft increases. This causes an increase in the angle of attack of the air onto the planes, and angle of attack is a source of lift. The angle of attack increases until the resulting vertical component of lift balances the weight of the aircraft, at which point the rate of descent stabilises.
Assuming the pilot does nothing, we can now see what’s happening to the lift from the planes, and the effect on the pitch of the aircraft. The main plane has two sources of lift: Angle of attack; and Bernoulli lift, which depends only on air speed. However, the tail plane is symmetrical, and doesn’t generate any Bernoulli lift. So, with the aircraft at its increased rate of descent, the lift on the tail plane is increased by a certain proportion, the angle-of-attack component of lift on the main plane is increased by the same proportion, but the Bernoulli component of lift on the main plane doesn’t change. Thus, the change in total lift on the main plane is proportionately less than the change of lift on the tail plane, and there is a moment pitching the tail up, which is what we all know happens.
The aircraft now accelerates forward, because of the pitch down, until the Bernoulli lift increases to balance the weight of the aircraft, at which point the aircraft is flying stably in a new attitude. The extra lift will tend to lift the nose, though, so there will be oscillations before stable flight happens. We know this happens, too.
If an aircraft is flying level, and a gust pitches the nose up, the same changes happen, but for different reasons. The angle of attack increases, because of the change in pitch relative to the direction of flight, rather than the rate of descent. The effect is the same, the corresponding change in the lift on the planes tends to pitch the tail up, and the aircraft is stable in pitch.
It’s perfectly possible to build an aircraft that does not drop its nose when it’s banked. All it needs is for the tail plane to have a profile that generates Bernoulli lift. However, such an aircraft would also have neutral stability in pitch, which is distinctly undesirable.
So the answer is: An aircraft drops its nose in the turn as an inevitable side effect of pitch stability.
(1) At 10°, the vertical component of lift is 99% and the horizontal component is 17%. At 30°, it is 87% and 50%. (2) The lift on the tail plane is often negative. The mathematics of the changes I’ve described explain what happens with a clarity which is difficult to match using English. However, note that the increase in AoA on the planes is an increase towards greater positive values. As the AoA on the tail plane increases, it goes from negative to zero to positive, as does the lift. It is not an increase in negative lift.