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?
Perhaps the tug you watched had forgotten to raise flaps after t/o or had left carb. heat on... It may also have been 2-up if a tug pilot training flight - or any combination of the above!
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The bigger, the better!!
I used to tow using a 235hp Pawnee at Lleweni Parc (North Wales) in the early 90's in some very Interesting (Turbulent!) conditions and can honestly say that although the Pawnee is not the most comfortable aircraft to fly (being male and this is assumption only - like sitting in a birthing chair?!?) on more than one occasion the brute power and controllability ensured that I remained a member of the human race!! Give me a big throbbing powerplant and a short field take off ability anyday!! - a chippy with 235hp Mmmmmmmmmmm!!!
Expat Dave, Perth WA
Expat Dave, Perth WA
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Cessna 150 with 180HP mod and uprated landing gear has almost the same performance as Pawnee 235 but more economical, especially for ferrying. Initial ground roll is slightly slower but can still handle ASH25s etc.
The Pik27 looks good but perhaps an o360 instead of the Rotax may be better.
The Pik27 looks good but perhaps an o360 instead of the Rotax may be better.
john_tullamarine
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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.
an3_bolt
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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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.
an3_bolt
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....
Soaring Club of Tasmania's 160 hp Pawnee hauls the Blanik with two 100 kgs in it on 25 degree day and density altitude 1000 feet with ROC 300-400 FPM
Same conditions, nil wind, the combination needs about 600 metres to clear 50 feet. Capital cost, maintenance costs, operating costs way down on the bigger PA-25s. Though not suited to lower latitudes and higher elevations, the PA25-160 doesn't deserve severe bagging. (Only rebagging after many years TLC.)
From the Gliding Federation of Australia's website -
Pawnee
This aircraft meets the requirements of the specifications list if the Lycoming engine is replaced with a high-powered automotive engine. In all other respects it fulfils the requirements.
The Pawnee is an ag-strip cropduster. It was designed to carry up to a tonne of fertiliser into the air off rough farm strips. It is enormously strong. It is a very easy aircraft to fly. There are currently over 70 of them on the register in Australia with an unknown number in sheds and hangars as a spare parts source. The type is still in production via the holder of the Type Certificate in South America.
One major advantage is that Pawnees are cheap. This is because they are being supplanted in agriculture by larger, turbine-driven aircraft and so have ceased to be generally viable as cropdusters. Our experience suggests that they are all for sale, and at reasonable prices.
The Pawnee is also, however, the tug of choice of many of the gliding clubs in Australia, New Zealand and UK. (In NZ and UK, despite exposure to "lighties" as tugs, the clubs we have contacted are reverting to Pawnees).
The Pawnee's capabilities in achieving high numbers of tows per hour is noteworthy. On one occasion at Lake Keepit, a Pawnee flown by Ian McPhee performed 84 aerotow launches in a single day.
Its paddock-retrieve capability is outstanding, because it was designed with rough, short landing areas in mind and it was built to withstand the stresses that these operations generate.
In its existing form, though, the Pawnee does have shortcomings. All of them are engine-related.
The Lycoming aircraft engine is expensive to buy, fuel, maintain, repair and fly. It's also noisy (European clubs don't use this sort of engine in tugs because of increasingly onerous noise legislation).
In glider towing, the Lycoming has to operate close to its performance limits, constantly. The result is that almost no Lycoming engine reaches its 2000-hour overhaul level without first needing new cylinders or a top overhaul. Shock cooling on descent is a permanent problem that increases turnaround time and, if not handled well by the pilot, results in cylinder and cylinder head cracking. All of these problems and processes are costly. A top overhaul can run to $18,000. The 2000-hour overhaul costs between $45,000 and $55,000. Spare parts are expensive, as is avgas and the result of all of these expenses is that an aerotow launch is more costly than it should be.
The solution to all these problems is to dispense with the Lycoming, and install a proven, inexpensive, powerful, modern, extensively tested, readily available, easily maintained automotive engine that is also cheap to run to drive the Pawnee. This conversion process must be approved by the authorities, but there is a specific program to be followed which will provide certification of the modifications.
The perfect candidate for this job is the General Motors LS1 Chevrolet V8 alloy engine (better known in Australia as the Generation 3). GM have produced hundreds of thousands of these engines over the past 5 years. The company has spent billions of dollars developing, testing, refining and manufacturing it. The engine capacity is 5.7 litres. It develops 340hp at 5700rpm. It is fitted to a range of high-powered GM vehicles including the SS Monaro. Outside of motor cars, it powers a remarkable selection of utilities, trucks, dragsters, airboats and aircraft. Complete with prop-drive unit (PSRU) it weighs in within a few kilograms of the 235 Lycoming engine.
It was this combination of airframe and engine the eTug syndicate decided to proceed with. In taking this course, we recognised at once that eTug would become the direct lineal descendant of Autotug.
It is also of the utmost importance to note here that the project to convert numbers of Pawnees in this way can only work if we, hopefully with GFA support and participation, can gain relief from the CASA regulations by achieving a new class of certification for the aircraft, in the area of operation of glider towing.
More on this subject - The Gliding Federation of Australia Inc. - Tug engine developments
Last edited by Fantome; 24th Feb 2009 at 04:32.
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Let it not be said that I didn't love driving any of the Pawnees .. all great fun. However, the little one didn't leave much to spare on a gusty, bumpy day with a two-seater on tow. At one field, where I was wont to tow many decades ago, I recall that only a couple of us were interested in towing in the little Pawnee .. the others preferred the Super Cubs... mind you that all changed when the little Pawnee was exchanged for a bigger brother.
I'm surprised that no-one has mentioned the Callair .. similar to the Pawnee and, stripped down, a really good tug .. especially when operating from a military aerodrome where one was not quite so constrained in respect of circuit procedures during the recovery. However, I always found the near total absence of aileron control a tad disconcerting during manoeuvring onto short final.
Shock cooling has always been a worry with tugs (and on parachute operations). While I have no recent knowledge of what is done, going back to the 60s/70s it was very apparent that those clubs which used fewer pilots and exercised reasonable control had fewer problems .. largely due to the better training and operational controls which could be exercised.
84 aerotow launches
Good Heavens .. I had a few excellent days but I don't recall ever getting over the 60-odd mark. Ian must have had one unbelievable boomer of a day with a majority of quite low releases ? He would have been one very tired little teddy bear that night ...
I'm surprised that no-one has mentioned the Callair .. similar to the Pawnee and, stripped down, a really good tug .. especially when operating from a military aerodrome where one was not quite so constrained in respect of circuit procedures during the recovery. However, I always found the near total absence of aileron control a tad disconcerting during manoeuvring onto short final.
Shock cooling has always been a worry with tugs (and on parachute operations). While I have no recent knowledge of what is done, going back to the 60s/70s it was very apparent that those clubs which used fewer pilots and exercised reasonable control had fewer problems .. largely due to the better training and operational controls which could be exercised.
84 aerotow launches
Good Heavens .. I had a few excellent days but I don't recall ever getting over the 60-odd mark. Ian must have had one unbelievable boomer of a day with a majority of quite low releases ? He would have been one very tired little teddy bear that night ...
Forgot to add before...one of the good things about being towed by a powerful tug is that you dont have to worry so much about that tiresome 'bowing' (drooping) of the tow rope !!Being towed by (say) an Auster or other low power/highish drag tugs one always had the feeling you would overtake the towplane,especially if you encountered sink !!
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My vote is still for the REAL mans Pawnee. But you are right - the sissy 160 is useful and does not need to be bagged..... (just winding you up - can not resist it!
)
The Supercub is a different story - so sweet, so lovely - love at first flight!!!
)The Supercub is a different story - so sweet, so lovely - love at first flight!!!
Been towed by many types of tug but without doubt most memorable was Morane Saulnier 503 Criquet (Fiesler Storch) which was always airborne before the glider and stayed well above the horizon until release - it was more like being underslung than towed!
Best tow I've ever had was in a Ka6 behind a 260 Pawnee 
Worst I ever had was 2 up in an ASH25, behind a 172 with the old O-300 Continental (was it an O-300 or GO-300??). Man that was a long takeoff and tow!!
Worst I ever had was 2 up in an ASH25, behind a 172 with the old O-300 Continental (was it an O-300 or GO-300??). Man that was a long takeoff and tow!!
The Pawnee's capabilities in achieving high numbers of tows per hour is noteworthy. On one occasion at Lake Keepit, a Pawnee flown by Ian McPhee performed 84 aerotow launches in a single day.
Yes it was and it was a Friday in May '87 I think. After a wet week and was a Friday catch up. The previous week was 78. Those were the old days of 6 students a week.
The Cessna Bird Dog is great to fly but they're getting expensive. All the War Bug crowd who cann't afford a P-51 or Spitfire have driven the price up. And we started having to do a lot of work where the landing gear meets the frame in the belly.
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