Glider tug design
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Glider tug design
Just watched a tug and glider from Booker which did not seem to be climbing very well and wondered if anyone has designed a glider tug whose aerodynamic characteristics more closely approximate those of a glider, for instance high aspect ratio wings with a profile matching the glider L/D curve?
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Yes, touring motor gliders make excellent tugs if they are powered well. However for heavy gliders just very well powered planes probably beat anything. A tow behind an Extra 300 is something to be experienced .)
You have to remember that once the tug/glider combination has accelerated to climb speed, the only force the tug has to overcome is the drag of the glider. A glider weighing 400kg with a L/D ratio of 1:40 will only provide 10kg of drag to the combination, plus a little bit added for the towrope. This is why even a fairly low powered tug such as a Chipmunk with a Gypsy Major and the standard Fairey Reed prop will still climb at close to 500fpm with a standard class glider on the back.
Getting the combination up to flying speed is a different matter though.
Getting the combination up to flying speed is a different matter though.
Hmmmm...my first solo aerotow (K13) was behind a Condor (Ahhhh Condor !!!),whilst strapping in I was approached by the Tuggie who asked me how good I was at thermalling on tow !!!
Well i said I would give it a go...certainly improved our climb rate!!
Written on the Condor wingtip was 'Half scale Pawnee'
You cannot beat adequate power for any aviation related activity
Well i said I would give it a go...certainly improved our climb rate!!
Written on the Condor wingtip was 'Half scale Pawnee'
You cannot beat adequate power for any aviation related activity
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A tow in a lightweight glider behind a big engined Pawnee was almost as good as a winch launch
Indeed .. however, a tow behind a small Pawnee is not much fun at all .. for either pilot. Many fond memories of the former and, likewise, the odd grey hair from the latter.
Indeed .. however, a tow behind a small Pawnee is not much fun at all .. for either pilot. Many fond memories of the former and, likewise, the odd grey hair from the latter.
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My vote goes to the Pawnee (the 0-540 one). Great visibility, good performance and nice handling all at glider speeds. I still have nightmares watching a Pawnee 160 towing open class gliders with water....
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As a tuggy, flown a few different type's over the years - chipmunk(with converted lycoming 180 horse power), pawnee, super cub and robin DR400. By far the best tool for the job was the pawnee. The nicest to fly however certainly go's to the chippie. Such a fun aeroplane.
I would suspect the turboprop Porter or perhaps the big radial Wilga may be a force to reckon with though.
As a slight aside, the 'beefed up' grob 109 motor glider is no slouch either. We trialled one recently and it would certainly give the chippie a run for its money.
As for thermalling on tow - making use of any extra energy is always a boost...especially if the club charges 'per minute on tow' rather than by 'height'. If the glider pilot is willing to crank the bank...then all the better!!
I would suspect the turboprop Porter or perhaps the big radial Wilga may be a force to reckon with though.
As a slight aside, the 'beefed up' grob 109 motor glider is no slouch either. We trialled one recently and it would certainly give the chippie a run for its money.
As for thermalling on tow - making use of any extra energy is always a boost...especially if the club charges 'per minute on tow' rather than by 'height'. If the glider pilot is willing to crank the bank...then all the better!!
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You have to remember that once the tug/glider combination has accelerated to climb speed, the only force the tug has to overcome is the drag of the glider.
When gliding, this is a negative term which when added to the glider drag equals zero for a still air glide. When climbing the Tan(theta) is positive and adds to the tension in the tow-line. 500 ft/min at 60 knots is about 12:1 gradient which would add another 33.3 KgF to the drag experienced by the tug.
I'd rate the ability to climb efficiently at glider speeds and plenty of surplus power as the main desirable qualities in a tug. I've seen the super-falke towing, and that doesn't do bad on 100hp(?).
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Depends whether your the pilot or an "accountant". In terms of operating cost, visibilty and ease to fly leaving you free for other things, the Robin 400 is hard to beat.
The Wilga is good but not as good as it could be because of the need to throttle back (ideally) aftr take off to conserve life an the big radial.
The Wilga is good but not as good as it could be because of the need to throttle back (ideally) aftr take off to conserve life an the big radial.
I'd second the Robin 300/400 series as being close to the ideal. You have to factor in the fuel burn as well as the 'ooomph' and in that I think they are very efficient. The DR400 with a VP prop is an excellent performer in this respect and the undercarriage is far more sturdy than it looks.
If you can ignore the initial investment, the best tug I've ever experienced was the Turbo Bravo at Schaenis in Switzerland. It's a mil-spec two-seater with an 'experimental' 360shp Allison turbine in the front instead of the normal 4-cylinder Lycoming... The first launch was in an ASH-25 and the acceleration was so rapid we got airborne in negative flap! I've had 1,500fpm+ behind it in a single seater; the best thing is that it was actually cheaper to launch to height as a) it ran on turbine fuel and b) the cost/min. was high but you needed very few min. on tow. It could also fine off the prop, pull the dive brakes and be ready to go again on the ground from a 7,000' launch in about a minute. Class.
If you can ignore the initial investment, the best tug I've ever experienced was the Turbo Bravo at Schaenis in Switzerland. It's a mil-spec two-seater with an 'experimental' 360shp Allison turbine in the front instead of the normal 4-cylinder Lycoming... The first launch was in an ASH-25 and the acceleration was so rapid we got airborne in negative flap! I've had 1,500fpm+ behind it in a single seater; the best thing is that it was actually cheaper to launch to height as a) it ran on turbine fuel and b) the cost/min. was high but you needed very few min. on tow. It could also fine off the prop, pull the dive brakes and be ready to go again on the ground from a 7,000' launch in about a minute. Class.
One of the factors that determines the efficiency or otherwise of a glider tug is the rate at which it can get down again after dropping the tow - the quicker down, the more launches it can carry out during the day. Unfortunately, closing the throttle and hurtling earthwards causes rapid cooling of an air-cooled engine, and if carried out as a matter of routine will give rise to a high rate of cracked cylinders. We found that out at Dunstable; the solution was to keep plenty of power on during the descent, although this delayed the return for the next launch.
A turboprop or water-cooled engine doesn't have the same problem. The Wilga has, I believe, an arrangement of shutters in front of the engine that can reduce the air flow through the engine during the descent.
A turboprop or water-cooled engine doesn't have the same problem. The Wilga has, I believe, an arrangement of shutters in front of the engine that can reduce the air flow through the engine during the descent.
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Wilga needed a good tug pilot - it was easy to climb faster than the space shuttle but it gave a speed of 45-50kts down the back end. Which isn't fun in a heavy open class machine - somewhat akin to a fat bloke walking a tightrope.
Pawnee is hard to beat - a good mix of speed and climb rate, and nigh on indestructable.
Worst tow ever was an ASH behind an original chipmunk. Walking would have been quicker.
Pawnee is hard to beat - a good mix of speed and climb rate, and nigh on indestructable.
Worst tow ever was an ASH behind an original chipmunk. Walking would have been quicker.
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A very good compromise was the one-off Swedish conversion of a Pawnee with a Volvo car engine (6 cylinder in line), 3:1 reduction gear, big prop, very quiet, very economical, but not repeatable without huge certification issues.
Chris N.
Chris N.
During the 1995 World Gliding Champs in NZ we had a number of different towplanes. Wilga, 260hp Pawnee, 235hp Pawnee, Cessna Agwagon, Cessna 180 and 182, Cessna Bird Dog and a Gippsland GA200 Fatman.
The best was the Bird Dog, by far, even though it had the lowest power (210hp?). Nest best was the GA200. Looks like a Pawnee, but performs much better. You can also get dual controls, great for towpilot training. Engine never got above 212F CHT due to great cowling design.
Next was the 260 Pawnee, 235 Pawnee, then the Wilga (I thought it would be better), and then a race for last between the Agwagon and the Cessna 180. I can't remember how well the 182 did, but I do remember helping to lift it out of a large rabbit hole it got stuck in!!
The Bird Dog however was a sight to behold. Good speed for the ASW22's/Nimbus 4's, and fantastic climb rate. With a power on spiral dive it also got down pretty quick. I hear the electric flaps can give trouble, but they really do tow well.
Most of my early towing was behind a 180hp Super Cub. That also towed really well, but Cubs are getting too expensive to buy nowadays and you also have the extra hassle of fabric.
For a new tug, I'd go with the GA200. For a second hand, I'd go with a second hand GA200
or a Bird Dog.
Turbines are great for the no shock cooling thing, but a lot of the components (turbine discs for instance) are lifed on cycles (landings). The more landings you do, the quicker you use up the life of the component. Not good if you do lots of short flights, like say, with glider towing!!
I thought Pik were working on a liquid cooled diesel powered single seat tug but I can't find a link to it at the moment. Now that would be a good way to go.
The best was the Bird Dog, by far, even though it had the lowest power (210hp?). Nest best was the GA200. Looks like a Pawnee, but performs much better. You can also get dual controls, great for towpilot training. Engine never got above 212F CHT due to great cowling design.
Next was the 260 Pawnee, 235 Pawnee, then the Wilga (I thought it would be better), and then a race for last between the Agwagon and the Cessna 180. I can't remember how well the 182 did, but I do remember helping to lift it out of a large rabbit hole it got stuck in!!
The Bird Dog however was a sight to behold. Good speed for the ASW22's/Nimbus 4's, and fantastic climb rate. With a power on spiral dive it also got down pretty quick. I hear the electric flaps can give trouble, but they really do tow well.
Most of my early towing was behind a 180hp Super Cub. That also towed really well, but Cubs are getting too expensive to buy nowadays and you also have the extra hassle of fabric.
For a new tug, I'd go with the GA200. For a second hand, I'd go with a second hand GA200
or a Bird Dog.Turbines are great for the no shock cooling thing, but a lot of the components (turbine discs for instance) are lifed on cycles (landings). The more landings you do, the quicker you use up the life of the component. Not good if you do lots of short flights, like say, with glider towing!!
I thought Pik were working on a liquid cooled diesel powered single seat tug but I can't find a link to it at the moment. Now that would be a good way to go.
Pik 27. Rotax 914 power. Not sure if it will be powerful enough for the open class guys.
Windcraft Oy PIK-27
Windcraft Oy PIK-27
Been towed by Bird Dog, SuperCub, Wilga, Citabria 200Hp. and Pawnee (235 and 260). Behind a Pawnee is like being in a slingshot and yes, it goes up and down quick
We seem to have a considerable number of people who fail to lock spoilers before takeoff and it once took me a while to realise the spoilers had popped after a bounce on takeoff
No problem behind a Pawnee
We seem to have a considerable number of people who fail to lock spoilers before takeoff and it once took me a while to realise the spoilers had popped after a bounce on takeoff
No problem behind a Pawnee