Follow up information, reproduced from GCV's Speing 2011 "Airflow" newsletter.

THE SEARCH FOR THE IDEAL GLIDER TUG

(The development and testing of the eTug) __________________________________________________ ____________________

Introduction

In 2005 a syndicate was formed to see if something practical could be done to create an automotive-engined aircraft that would reduce the rising costs of aerotowing and be able to be certified by CASA and replicated for a number of clubs.

Knowing of the history of Autotug in Queensland, we approached Dave Sharples and asked him to join and oversee the project with us.

We named the project eTug (short for “enviro-Tug”) because we intended that it should have a “friendlier” footprint than current tugs – apart from being a lot cheaper to operate, it must be quieter, more efficient in terms of tows-per-engine-hour, more fuel-efficient, cause less impact and erosion damage to grass strips and deposit no lead into the atmosphere.

We have had questions from many people about the project, so this document aims to summarise how we arrived at the specifications for eTug, to answer questions about the other possibilities we examined and to report on the progress and cost benefits of the prototype.

The aircraft we examined which are described here are all well-known, certified and competent as GA aircraft. However, our interest was to evaluate them against the special set of requirements that we developed for our “ideal glider tug”.

As well as applying our own experience, we have talked to a lot of people in the gliding movement with experience in pretty well every method of aerotowing.

The conclusions we reached as a result are set out here, in the progress of the development of eTug.

Specifications and Performance

Towing a glider into the air behind a tug aircraft appears to be a relatively simple process to define and specify. In reality, it is. In the discussion of the theory, however, it attracts all sorts of methods that often reflect the personal interests of the theorists rather than the dispassionate evaluation of the available possibilities. And it should be noted that the original automotive-engined glider tug, Autotug, after flying for 17 years with a Ford Javelin V6 engine, has now been modified to run a GM LS1 5.7 litre V8 engine.

As a syndicate interested in finding the most effective way of reducing aerotow costs, we set out to specify the requirements as objectively as possible, as well as to apply advances in engine technology that have emerged since.

We looked at Eastern Australia, and the rather particular needs we have for aerotowing, and at Lake Keepit specifically as a good example of the requirements of the gliding movement. Here they a

We need an aircraft which is:  Proven to be robust and simple to fly  Powerful enough to tow at high climb rates and suitable speeds for glider pilots  Has sufficient power to easily tow heavy two-seat and heavily-ballasted Open Class gliders  Capable of rapid turnaround for highest possible number of tows per hour (more than ten) both to satisfy demand as well as to reduce the costs of towing  Robust and powerful enough to paddock-retrieve at the height of summer, without any doubt of its capacity to do this  Fuel-efficient

 Quiet  Simply maintained  Cheaply maintained  Affordable for a gliding club to buy

So, knowing what we needed, here is what we looked at:

 Jabiru

A syndicate was formed in Lismore a couple of years back to evaluate the suitability of this type for aerotowing. This project had significant factory backing, with the factory delivering a specifically-modified 6-cylinder 115hp Jabiru.

The evaluation revealed that the aircraft was difficult to control on tow at anything less than 70 kts, making things more difficult for the glider pilot. At this speed, its rate of climb was too low for it to operate as a useful glider tug in terms of time-to-release, producing an unacceptably low rate of tows per hour. Fuel consumption appeared to be encouragingly low, but when considered against a greatly reduced tows-per-hour rate, the advantage was nullified. Further disadvantages were doubts about its ability to paddock retrieve, and its light weight and construction.

The factory acknowledged that for safety, the tricycle undercarriage would need to be converted to tail-dragger configuration because of concerns about possible failure of the nose wheel assembly particularly in operations from rough grass strips.

Other modifications suggested and subsequently produced by the factory included increasing the length of the wings and the surface area of the ailerons, and strengthening the tail assembly to better withstand towing stresses. Whether these modifications will render the aircraft suitable to tow to our specifications remains to be seen. Subsequent test flights conducted at Kingaroy indicated that climb rates were inadequate, and in any case, the cost of the modifications appear to increase the total price of the package to well above $120,000. We understand the modification has not remained in production.

 Tecnam – P 92 Echo Super and P 96 Golf

Initially, this looked quite hopeful in that the factory was offering purpose-built aerotow adaptations. Two models were evaluated in NZ, and as far as smooth-strip towing was concerned appeared to perform adequately. However, with no capacity to paddock retrieve (on cold days, let alone hot) and a price tag exceeding A$140,000 for what is a lightweight and arguably not notably robust airframe, we eliminated it from our contenders list. (Interestingly, the two Tecnams which started towing in NZ appear now to be operating on a very limited basis, and our contact with a number of NZ clubs suggests that no new orders have or are likely to be placed.)

 Cessna 150

Two Queensland clubs have converted Cessna 150s to Cessna 150/180 tugs. Their experience as recounted to us is that the airframe, particularly the tail assembly, will not stand up over time to glider towing stresses. The Kingaroy club Cessna has had the tail section rivets replaced twice in less than 2000 hours. No further rivet replacement is possible, so the empennage has been bolted, apparently. It is said that the next repair will require complete replacement of the empennage. Its tricycle undercarriage will not allow rough paddock retrieves. While inexpensive to buy, the model is now 45 years old and becoming scarce, and in any case, the shortcomings outlined here took it out of contention for us. Kingaroy has replaced its Autotug with LS1 engined Pawnee.

Cessna 150 – Subaru engine

Boona club investigated this combination and found the engine was so heavy the aircraft could never meet W & B limits. The project was recently abandoned.

 Super Cub - 180

The performance of this aircraft is similar to that of the Aviat Husky (see below) – relatively low rates of climb and low numbers of tows per hour. In addition, it is also becoming a collectors' item, and is consistently increasing in cost, putting it out of consideration.

 Husky

Looked at in the light of our specifications list, the Husky's shortcomings a  Lack of robustness. LKSC had a number of structural failures with their Husky, the last resulting in the aircraft being written off  Tows at low climb rate  Descent rate also low  Hard to achieve high tows-per-hour  Operates at the limits of its capabilities in hot-weather paddock retrieves  Expensive to maintain  No locally available parts

On the positive side, it is relatively quiet and fuel-efficient (although the low number of tows per hour reduces this latter benefit somewhat).

Changing the engine to an automotive type was considered, but rejected as impractical because of the shortcomings listed.

 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 Buenos Aires, Argentina.

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, some clubs we have contacted are reverting to Pawnees).

The Pawnee's capability to achieve 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. However, the Lycoming engine requires time spent gradually cooling after glider release that limits it to about 7.5 launches to 2,000' in one engine hour.

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 $55,000 and $65,000. 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 8 million of these engines over the period to 2006. 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 Commodore and 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. (Current production has replaced the LS1 with the L76 with 6% more capacity and 10% greater power.) 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 be quite different from Autotug. The immediate success of eTug encouraged Autotug to fit the same LS1 V8 engine.

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 continuing 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.

The Prototype – Conversion and Advantages

The conversion of our first aircraft, VH-CUR, commenced at Bundaberg in 2005 with Dave Sharples and Ian Watson performing the work and creating the solutions to the need to accommodate water-cooling and other automotive engine peripherals within the airframe.

In an aircraft application like ours, the LS1 engine runs at about two thirds of its maximum rpm and power output. It operates on climb at 3800 to 4200 rpm, with a power output of about 250hp at the propeller. The LS1 engine is capable of running at this rate indefinitely, and has demonstrated that it can do so in numerous applications – and because our LS1s have been balanced, operation is particularly smooth. (Incidentally, the 235hp Lycoming delivers only 195hp at the propeller on climb, giving the LS1 a significant power advantage).

The engine drives a 3-bladed carbon-fibre propeller through a 2:1 reduction drive, producing propeller rotation up to 2200 rpm. At this speed we have found the engine's consumption of premium unleaded petrol to be about 25% less than a Lycoming engine. And, this is achieved with a considerable increase in launch rate. With finer tuning and propeller experimentation it is hoped to further reduce eTug's fuel consumption.

Quite apart from fuel consumption, cost savings and power advantages, there is another important benefit of a water-cooled engine. At top of climb, the pilot simply closes the throttle and descends to the field as fast as he wishes. This is because there is no shock-cooling effect to manage. In addition, the aircraft is fitted with a Tost retracting rope winch. This pulls the tow rope entirely into the fuselage, which will allow shorter approaches and improved aircraft positioning for the next tow. So with faster climb rates and considerably faster descent rates and better positioning, the turnaround time between tows is significantly reduced, enabling a minimum tows-per-hour rate of more than fourteen. Rates at Gliding Club of Victoria have been as high as fifteen.

In operational terms, the LS1 conversion offers other advantages over the Lycoming. The Pawnee is already an easy aircraft to fly and land. Along with the LS1, we are adding a number of features that will improve safety and efficiency. We are about to fit a closed-circuit TV camera to give the pilot a clear view of the glider's position and performance on tow. Improved visibility of the aircraft in flight will be provided by high-intensity strobe lights positioned above and below. The Tost retracting winch will also help simplify the pilot's landing approaches, and with the line retracted and a separate short tow line on board will make paddock landings and retrieves much simpler. The winch will also simplify the ground crew's work. A further important benefit of this winch is to eliminate the risk of unrecoverable upsets of the tug. This can happen in a conventional installation when pressures on the tow rope make it impossible to release at either end. A guillotine mechanism at the winch allows the tug pilot to cut the rope in an upset or other emergency In terms of costs, too, the statistics are persuasive. For a 6-cylinder Lycoming rebuild – say $55,000 to $65,000. For a complete replacement of an LS1 engine – under $8,000 (short engine $5,000). LS1 maintenance, too, is vastly cheaper than maintaining a Lycoming. No matter what the service intervals, the automotive engine is intrinsically cheaper to service, and has the advantage of considerably lower parts and consumables costs. With the addition of platinum spark plugs, the 100-hourly cost is limited to 6 litres of oil, an oil filter and 3 fuel filters. (With platinum plugs, EFI and no lead in the fuel, there is no plug fouling.) In service we have found oil consumption is negligible.

The advantages continue to mount: consider the noise factor. At a prop speed of 2000rpm, and with a properly muffled engine exhaust, the LS1-engined Pawnee is quieter in flight and on the ground than any equivalently powerful GA aircraft.

On the airfield, it creates considerably less erosion and impact damage because its landing rolls can be shorter and more direct, its positioning manoeuvres can be considerably shorter, and the retracted towrope will do no damage at all. The towrope itself will last very much longer than they do now.. Both of these advantages also represent cost savings to the operator – less airfield maintenance, and reduced purchasing of ropes and rings.. It is also worth noting that the winch can be readily adapted, on the spot, to a shorter towrope for use in paddock retrieves.

A final benefit – perhaps not quite as important, but a benefit nonetheless – is that using unleaded mogas will reduce the amount of lead deposited into the atmosphere, so providing a useful environmental effect as well as a 25% saving in fuel cost.

In combination, these benefits and advantages have convinced us that the LS1-engined Pawnee represents the efficient and cost-effective future of glider towing in this part of the world. This view is reinforced by the budgets for the final cost of the converted aircraft, which, once the development and prototype costs are amortised, will not exceed $45-55,000 each. (One critical issue is that this does not include development costs for Type Certification, which could be completely prohibitive unless relief is sought and granted from the Regulations.)

This estimate (minus the TC costs) is based on:

 the conversion being performed by the eTug syndicate for quality control and security of IP

 conversion of a PA-25 235, 250 or 260 minus aero engine and mount.. The PA-25 135 has not been tested for installation of an LS1. It should also be noted that Pawnees fitted with wing tanks require more complex plumbing and pump peripherals which will increase the costs slightly

 the converted aircraft delivered to the purchaser ready-to-fly at Scone, NSW.

 Is limited to engine related costs as all airframe costs are the same for LS1, or Lycoming engines

Having completed the first conversion, we are committed to certifying the aircraft, and are working with GFA to seek a specific glider tug certification category.

We named the project “enviroTug”, or eTug for short, because with its significantly reduced fuel consumption, unleaded fuel, reduced impact and erosion damage, better pilot conditions, quieter operation and considerable cost savings, it does have a friendlier environmental footprint which is worthy of note.

The bottom line advantage, though, should ultimately accrue to the clubs that fly it and the pilots who are towed by it. In aggregate, our budget comparisons and projections indicate that eTug will cut the cost of aerotows to less than half. That means twice the launches for the prices being paid now, or putting half of what pilots are spending now back in their pockets. And all with an aircraft that is built for the job, and which works the way gliding folk need it to work. The higher launch rate means one eTug will nearly do the work of two PA25-235 Lycoming engined tugs.

Financial Benefits Engine: This summary of the estimated cost savings which will result from using eTug as opposed to a Lycoming-engined PA25 is based on a 2,000 hour timeframe – the normal life of a Lycoming engine:

Fuel $ $ PA25 – Avgas at 60l/hr @ $1.75/l 210,000 eTug – Mogas at 45 l/hr @$1.30/l 117,000 Savings 93,000 Maintenance (Engine only) PA25 – Top overhaul @ $20,000 – Rebuild @ $60,000 – Total $80,000 eTug – New engine & peripherals 10,000 Savings $70,000 Extra Tows eTug - +6 tows/hr @ say $45 per tow $540,000

Total Estimated Savings with eTug per 2,000 hours $703,000 (GST excluded) It looks very much to be the right aircraft/engine for the job.

Airframe: While it is true that the costs to maintain the airframe are the same for either Lycoming, or LS1 engines, the higher launch rate of the LS1 distributes the airframe costs over a larger number of launches so creating a substantial saving per launch:

If airframe maintenance cost on average $2,200 per 100 hours the total cost over the 2,000 hours will be $44,000 and this will be distributed over many more launches than was possible with a Lycoming engine.

Progressing the Project

At the time of writing the eTug syndicate has converted our first Pawnee, VH-CUR, which has now completed over 500 engine hours. The conversion is a tribute to the work and experience of Dave Sharples. Dave's original creation and operation of Autotug have had a profound effect on the progress of eTug.

The syndicate's second Pawnee, PIJ, has now been bought. The syndicate also owns a second LS1 engine and three prop drive units. We have had approaches from three clubs in Australia and two in NZ who are interested in talking to us about Pawnee conversions for them. However, until the rules are changed to allow eTug to be certified, these conversions can not proceed.

Gaining GFA's support and active involvement in lobbying CASA to create a new class of restricted certification for the Pawnee/LS1 configuration for glider towing would speed this process immeasurably. In fact, active support from GFA in this effort is probably essential.

The eTug Group Sydney