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By Derek Piggott 
During the summer, I had the opportunity to fly the World Class PW-5 and
the Russian Me-7 Mechta in competitions. I had long waited for an
opportunity to try and make a comparison between them. Although I did not
come to any great conclusions about their relative performance, I am able
to give an opinion about the handling and other characteristics which may
be of interest to people trying to make a decision about buying a new glider.
I first flew the PW-5 prototype some years ago and only had a couple of quick winch launches before the first contest day this year to re-familiarize myself with the glider and to check the instruments. However, in this year's Competition Enterprise I had no worries about taking it cross-country from Sutton Bank because it is so easy to fly and has such good approach control. I enjoyed every minute in the PW-5. The PW-5 World Class Glider The design, construction and finish are of the very high standard we expect from Polish gliders. The design competition was intended to encourage a glider for club use as well as for an International Championship, but several features need changing for club use. It is fitted with a nose hook as well as a C of G hook that is further back than on most gliders, making it essential to keep careful control over the early stages of a wire launch. Any surge of power could result in an uncontrollable near vertical climb with disastrous results for an inexperienced or lightweight pilot if the cable breaks. This is unacceptable and should be modified without delay.
The lower attachment of the seat back needs to be more positive. In turbulence or even bumping over rough ground it could become free and move back, which is potentially dangerous. The other worrying feature is that it probably needs three hands to jettison the canopy. I believe that steps are in hand to modify this on future aircraft. The glider comes with a set of Polish instruments that leave much to be desired. In particular the altimeter is confusing as it records 3000ft per turn of the large hand, but the ASI and compass are excellent. The total energy compensation supplied for the variometers is of the capsule type that can work quite well. But it has long been superseded by the Brunswick tube mounted on the fin and more recently by electronic compensation. One alternative of mounting the tube vertically above the fuselage behind the wing cannot be considered a really satisfactory solution. So a tail mounted probe is another item for the manufacturers to fit as a standard.
The PW-5 has very docile stalling characteristics and remarkable stability in circling flight. It seems able to out-climb most heavier glass 15m machines by virtue of its crisp handling. Its ability to turn in small circles makes it easy to use the stronger narrow cores in the thermals. This helps the less experienced pilot to use thermals and achieve high rates of climb and good cross country speeds. The excellent air brakes make field landings a simple matter. Dick Johnson has made tests that confirm the manufacturer's figures for the performance as better than 32:1. If, like me, you have a stiff back from rigging heavy gliders, you will love the PW-5. The wings are light and the rigging easy if you read the instructions. The elevator connection is automatic but the aileron and airbrake rods have to be connected. However, there are no loose parts such as safety pins to get lost. The Polish trailer is excellent and a joy to tow. The Russian Me-7, Mechta This is a remarkable little machine of only 1 2.6m span, ie about a meter less than the PW-5. However, if you fit the wing root fairings and the turbulator tape as suggested by Dick Johnson in Soaring magazine, it seems to have at least the glide ratio of the PW-5. I was loaned the glider for the Northern Regionals at Sutton Bank. Once again the weather did its best to ruin our fun and we only got four days of cross-country flying. I flew in the Sport Class and battled against a number of Discus, LS4s, an ASW-19 and an ASW-24. However, I really did enjoy competing against the better machines, especially when I was the only glider to complete the 212km quadrilateral and so won the day. It is certainly a glider I will want to fly again in a competition. The glider I flew did not have the Russian instruments so I am unable to comment on them. Personally, I would always want to choose my variometers and for this kind of glider, keeping to a low budget, I would choose an electric variometer with averager, plus a Winter mechanical one arranged to be switchable to give airmass (NETTO). Airmass readings are a great help in extending the glides in this class of glider. Good total energy compensation is essential but this is easy as the Me-7 is plumbed for a total energy tube in the fin. The early version has a main and tail wheel and there is an alternative available with the main wheel moved back to provide even more room for very tall pilots. This version has a small nose wheel. I am told that it is not heavy on the nose wheel when the pilot is aboard and that it can be steered easily during the takeoff and landing run. The cockpit is roomy ! On first getting in, it appears that the view ahead is seriously restricted by the joint in the canopy. Most people who have flown it agree that within a few minutes of getting off the ground this is hardly noticeable and the all round view is still very good. The cockpit sides are rather high and getting out with a parachute could be made easier by fitting a strip of wood or glass across the floorboards to prevent your shoes from slipping. If you already own a Me-7, why not do this little mod before you fly it again. You never know, you might be glad to be able to get out in a hurry ! I was amazed to see that the production Me-7 still has no differential in the ailerons but in spite of this the handling is good enough. Surely differential ailerons would make it even better ? Like the PW-5, the Me-7 is a very light glider and inexperienced pilots making their first flights should choose good conditions. There is only one tow hook on this machine and its position is a compromise. It is satisfactory for aerotowing but perhaps not quite far enough back to get the best out of winch launches. However, because of the light weight, it launches very well and gets a good height on winch or car launches. The tail wheel is a sensible size and makes ground handling reasonably easy. With the tail wheel firmly on the ground at the start of the take-off the glider is scarcely affected by crosswinds. In a strong crosswind a slight backward movement on the stick can be used during the start of the takeoff run to keep the tail wheel in contact until the speed is sufficient for good rudder control. The wheel brake proved very effective and it is possible to end up for a moment with the nose on the ground at the end of the landing run if you brake fiercely at low speed. On rough ground I would recommend allowing the glider to find its own way off the ground rather than making a large movement forward to lift the tail during the take off run. As with the PW-5, care is needed not to over control and set up a PIO (Pilot Induced Oscillation). While it is vital not to get too high above the towplane at anytime, It is quite unnecessary to attempt to keep any glider flying within a foot or so of the ground until the towplane leaves the ground. Trying to keep too close is the most usual cause of starting a dangerous oscillation close to the ground and has resulted in many accidents. To avoid problems, the secret is to move up to about 5-10ft as soon as the glider leaves the ground and to watch the towplane and not the ground ahead. Like the PW-5 the Me-7 is an easy glider for thermalling because it is possible to turn in extremely small circles. Dick Johnson in the USA, found that there was a laminar bubble on the bottom surface of the wing spoiling the performance and recommended a simple wing root fairing to improve the airflow around the wing root at low speed. Fitting the zig-zag tape turbulators eliminates the bubble and enables a lower speed to be used and also seems to prevent any sudden loss occurring if the turn is pulled a little too tightly in an effort to squeeze the best out of the lift. Who can afford not to take advantage of almost 10% improvement in the glide ratio at low speeds? I made both these modifications and found a noticeable improvement in the climbing performance. I used aluminium fairings taped into position and DYMO tape cut down with pinking shears as an inexpensive form of zigzag tape. The stall is a little more definite than on the PW-5 and often results in a mild wing drop, but recovery is instantaneous on relaxing the backward pressure on the stick and there is no reason for anyone to have problems with unintentional spins. Like most other gliders, in thermalling turns of a reasonable angle of bank it is practically impossible to get the glider stalled - you simply run out of elevator power. Rigging and derigging the Me-7 is very easy and can be done by one person without any trestles. I've seen it done although I prefer to have one helper and use a wing trestle. There are no metal fittings on the spars and just the one main pin holds the wings together - a very clever system. The wings simply push into boxes in the fuselage and are pulled together by the cam on the end of the main pin. Turning the handle of the main pin in an anti-clockwise direction pulls the wings in and lines up the parts to make pushing the main pin in the last bit very easy. All the controls are automatically coupled during the rigging making it a joy to rig. Both the PW-5 and Me-7 are great fun to fly and probably only very careful comparison flights would show their relative performances. Their small wing span is quite undetectable apart from their crisp handling and they both climb well in weak conditions. Some people have expressed doubts about such light aircraft surviving in club members' hands. The Me-7 has been flown for several years at the Mynd and has proved rugged enough for club member treatment. It is certainly not a hot houseplant requiring special care. The PW-5 is obviously strongly built and it seems almost certain that it will incorporate small changes in the near future now that the manufacturers have got the message from many other countries. The Edgley EA9 In addition to these small gliders, this year I flew the Edgley EA9 Optimist prototype in the Lasham Regionals. This is similar looking to the K-18 but uses Fibrelam for its construction and is really a completely new design. On the first day that was only a 101km O/R, I was the only glider to get back in very scratchy weather. But the EA9 also performed very well on the real racing day winning on a 316km task and coming only 4th in actual speeds. This time the competition was limited to DG300s. The early teething problems are now fixed and I understand that a small batch of kits will be produced making it the first new British glider since Slingsbys stopped in 1982. Fibrelam is used for ceilings and floor boards of airliners and is a glass sandwich with honeycomb filter. The fuselage is made of flat panels and these are cut out on a tape controlled milling machine leaving tabs on the outer skin which are then used to assist in the joining, in a similar way to a cardboard model plane. Only very simple jigging is needed. The result is a very light and strong structure, much lighter than normal glass-fibre wet lay-ups. The glider has excellent handling and a very good contest record, a 6th place at the Northerns, 3rd place in the 1996 Lasham Regionals and now the 1st place in the Lasham B Regionals (It can't all be the pilot being in practice for a change!) "Derek has flown two of the smaller gliders in competitions this summer with good results and gained a 1st place in the Lasham Regionals in the Edgley EA9" Footnote: The prototype is fitted with an XK1O "Club" variometer system, complete with the dedicated averager option. Reproduced by kind permission from Sailplane & Gliding (Dec 1997 - Jan 1998 issue) |
