A Gas Turbine Cat

By Martin Gibbins

Now for something different, As many out you know the Manchester Club, are known for doing things, there own way, like running mainly petrol powered boats that have been designed and built within the club, instead of just buying what's available, off the shelf, & dropping a glow motor in it.
There is a new addition to the Manchester club range, but as with other things, it has been designed from, a blank sheet, and from a different view point.
As with the petrol and glow hulls, the aim was a hull that would stick to the water, & turn left & right without the need for a rudder
So having got rid of the parasitic drag of the wedges, what else is there, that we can get rid off ?
Anything that has to be dragged through the water, causes parasitic drag, this has been addressed by the FSR-V Racers by reducing the width of the prop shaft / tube, down to where many are using a open 5mm shaft, & a bearing at the end to stop it flopping about, But even this causes drag. I am sure that many of you out there, are saying "so what about surface piercing props"? Yes, but they are still throwing large amount of water high into the air, that requires energy to get it up there.
So lets get rid of the Prop all together, & while we are at it, lets get rid of that other parasite. the rudder. and start with a blank sheet, air is about 1/10th as dense as water so any thing dragged through it. will cause 1/10th of the drag Enter "The DieKatchen", no prop, or rudder, just "lift & shove", with "vectored thrust".

The DieKatchen, is the latest quest, to do something different.
Last year it was a 25 year plus old AMPS catamaran, with a Wren Gas Turbine, sitting where the 10cc glow motor should go.
This left a problem of getting the "AMPS Z drive", to handle the 28000 rpm tick-over of the Wren.
It was the vectored thrust of the "AMPS Z drive", that enabled the AMPS catamaran, to really fly, and to turn so tight, (providing that you got the nose down first)
So the out drive went, but the vectored thrust stayed, as with the Z-drive, thrust is left / right & up & down.

The Wren MW 54, was to much for the AMPS catamaran, when using the vectored thrust, even at 1/3rd power. A larger, more stable platform was required.
A search on the net, revealed a small range of catamarans, but they were all very small, not only in the length department, but lacking in overall square inches (lifting area) and freeboard.

Now I don't know, how many of you have ever built a new mono hull from scratch. (design, build the plugs, then the actual glass moulds, etc etc) believe me, a catamaran is nearer times three, the amount of work than a new mono. but its one way of spending a winter.

While the DieKatchen, was not the first gas turbine powered boat, to make it to the modelling press ( John Barber with his K7 Bluebird) I claim to be the first, to be to operate, a purpose built gas turbine powered, boat, using vectored thrust. based on the tests made using the AMPS catamaran, in Oct. 02

So what's next ?
Water injection, and reheat. multi engines !
The water injection, is coming first, the pump and controls are already installed. (while some full size planes use water when taking off & landing, the plan is to use it "full-time", so the volume / speed, of the jet-flux can be increased, while the internal temperatures can be kept within the engine manufactures. specs.

Reheat, is more of a problem, or should I say problem's)
Any help / comments, in this area, would be very welcome.
The basic pump and control system are already fitted, with view of starting with at reheat fuel factor of, about x4 (four times, the volume of fuel injected in to the jet stream, than into the combustion chamber.) I understand that x10 is the max possible, but that is for the future.
Spraying the fuel in "seems" the easy bit, but its the flame retainers, that are the problem, just scaling them down from full size, makes them near disappear.
This leaves the problem of the area of the jet pipe requiring to be greatly increased when reheat is used.
Has any one got anywhere near a servo / air operated, adjustable jet pipe, out let ??

Multi engines, is on its way, the vectored thrust engine mount, to take two engines has already been made, just waiting for a little more overtime to be done, to make the second engine and faced system available.
If you are thinking of getting into gas turbines, there are a number of things that must be understood, that all revolve around safety and noise.
Insurance, at moment the M.P.B.A. do not cover gas turbine powered boats but insurance can be obtained through the British model flying association
For full details of the safety considerations of operating gas turbines, see the G.T.B.A. internet site. http://www.gtba.co.uk/
The amount of noise emitted from the gas turbine, is not quite the same as that emitted from "pulse motors" (reciprocating glow & petrol engines) Gas turbines do not need silencers.
Gas turbines like the Wren MW54, have a very low compression ratio, (0.85 to 1) compared to a pulse motor,(12 to 1), so there is not the sudden peak of low frequency, high energy noise, every time the exhaust port opens. (The exhaust is open 100% of the time) so no need for a "silencer" to get rid of the "high energy peaks".

There is a need for anyone standing "very close" to any gas turbine to ware ear protectors, but if you are standing say 20/25 feet away, the sound levels are down to being able to talk, at normal voice levels with out any problems, as the sound emitted is at a very high frequency, due the high revs of the turbine (160K in the case of the Wren MW54 or 190kK for the Wren MW44) Which, unlike the sound from a pulse motor, does not travel long distances.

Tests have been done with a Wren MW54 and a Irvine 7.5 glow motor, with the Irvine using the normal "Production type tuned pipe & silencer", being run at the same time, standing side by side.
The results were :-
While standing up very close, it was only the Wren that could be heard On walking to the end of the garden, it was only the Irvine that could be heard.
The Wren has been run in the back garden, many times, and even when the neighbours had warned that it would be run some time over the weekend, no negative comment have been received.
The above is my experience, but if you are considering buying a gas turbine, please bear in mind that while there are gas turbines available for the model market, with thrust levels up to 100 lbs. & more, that the noise levels could be very much higher, due to the compression ratios used.

Hence, two Wren MW54's rather than one high thrust motor, with possible very high noise levels.

The first trials were run on the DieKatzchen, starting off with only low % power levels, dialled into the computer control (ECU), & slowly increased over the approximately eight runs.

Steering (using vectored thrust), at very low speed & low thrust levels is much like a multi boat, (not much happens). But as the levels of thrust are increased to 50,000 plus (fast tick over) and the hull gets over walking pace, the boat responds very well, with a turning circle of approximately one &half times it length.

The boat has to be started in the water, as �launching / throwing in� as per a multi boat, is not practical on health and safety grounds (the jet blast, even at tick over is at 480�C. at the jet pipe). This is the cause of a very slow get-away, as would be with a multi boat, if we tried and start from a tick over, in the water.

When started, the boat sits �in� the water, thus has to push itself, up on top of the water (On the Plane) The performance from the starting line, is much like a formula one car, �starting off in top gear�, ( they use 7 plus, gears) Even when using 100% power, the start is slow, compared with a multi boat. But as the speed increases, the rate of acceleration increases, and keeps increasing until the �drag forces, equal the thrust available�. On the face of it, it may be said that is the same as on a multi boat, but on a multi boat, from when just as the engine comes �up on pipe�, to the top of the rev band the amount of �thrust� acutely decreases, as is normal with any pulse engine. This is where the gas turbine scores, as the amount of thrust from the turbine is the same (depending on the RPM) irrespective of the speed of the boat.

How does it go ?, well let us remember that, jet power boats are in there infancy, while glow/petrol powered have had many years development, and have reached near stagnation, with only increases in manufacture engine power, very slowly increasing.

So compared with the above it is, slow, �so far�, BUT with the thrust levels from gas turbine engines, increasing by quite large steps, compared with glow/ petrol, there is a very large potential for Performance.

Craft powered by �pulse engines�, are limited by there need to stay �in the water�, so that the prop. can remain in contact with the water, and with the reduced hull contact with the water to offset the effect of engine torque, (trying to twist the hull around the prop.) thus having to drag the prop tube / prop & rudder etc. through the water, means living with large amounts of patristic drag. As an example of the extents of this drag, there is a article on the net, on the water speed record attempt by Ken Warby, he relates that despite many attempts, he was not able to get even near the existing record, he relates that even after rechecking all the performance figures, based on which a new record was very much �on�. It was only after asking one of the �lower level�, pit crew, �alright, what would you do�, then? The reply was �I�d cut 65mm off the bottom of the rudder�. Ken got the oxy cutter & cut off �75mm�! On the next run, a new record was set!

Will my DieKatzchen break any records? Well before that, records will have to be set.

Back to the trials, with the density of water, being approximately ten times �thicker�, than air, the amount of power required to get it �out of the water�, is many times that required to get an aeroplane airborne. And that part of any boat must remain in contact with the water, drags the potential for speed down, so what happened then?

As the power levels were increased, the hulls started to lift. This had to be done in stages, as with any prototype, things need adjusting etc. etc. One of those was a need to address the problem of part of the engine mount, flexing. Remember we are using vectored thrust. This involves the whole power unit, on its mount, thus the thrust & turning / twisting moment, as the hulls trim, also has to go through one pin. The problem was not with the pin or with its related thrust bearings, but with the actual mount, that had been made of 3/16^th ply, super glued to gather (no it was not caused by vibration). The jet, even when running at full power (160,000 RPM) is not smooth, it�s super smooth. If you put you finger, on the engine, on the top near the compressor, not only can no vibration be felt, it is near cold, the turbine end of the case only get warm, when running at any speed) the mount was remade using fibreglass, (the next will be in epoxy, to save weight)

With most things working correctly, Full power runs were made. The hull was coming out of the water, but was not up to a speed ware the centre section, was able to give any lift.

It was only after looking at some video tape, of the last run, was part of the reason found. It was noticed that, the boat was rarely driven in a straight line, for more that a few yards, resulting in the hull being pushed sideways. The need of a bigger water, or maybe I should use the lake length ways, instead of cross ways (if only our licence to use the water would allow us).

The video also showed what happens when you do not treat you power unit with care. A few runs earlier, I had refuelled without filtering the fuel, & of cause there �was� some stuff in it. It had worked itself through the pump and had blocked two of the twelve injectors! Resulting in a sudden raise in temperature with a lick of flame out of the jet pipe & a cloud of blue smoke, with greatly reduced thrust, just before a partial seizure.

So what has happened since? The power unit was stripped, and the blocked injectors confirmed and replaced. And the turbine up rated to the full Wren MW54 mk2 spec. (another breakthrough in engine design). I am sure there was something else�. Aah yes! We added another engine, so it�s now a Twin powered, vectored thrust, catamaran!

The new engine is another Wren MW54 mk2, assembled from a kit. I was not feeling up to putting it together, so by 15 yr old son Ben, put it together. I did offer to help, but as with most teenagers I was told to p�s off, sorry, I mean go away. It was a Wren �open day�, & there was others there, (adults) building there engines. And with no more help, than anyone else needed, from the people at Wren, Ben put the unit to gather. Yes it did start first time, & up to the required Specification

It did take him a little longer than most of the others but I did �insist� that he did most of the balancing by hand, as if he was going it at home. Wren will do a �full balance�, on engines built during the open day, free of charge; you could not make things to easy for these teenagers.

The people at Wren, could not be more helpful, & not only, at the open days.

The assistance they give to engine builders, at the open day, is a blend guidance and confidence building. The manual that comes with the kit, covers everything, it�s only the confidence, in ones own ability, that makes it seem difficult.

To tell the truth, he did make a �cock-up�, of one piece (he is not here, so I can tell you). Deep inside the gas turbine, there is an air filter, that requires some holes to be punched through it, for the bolts to go through, (the only holes that have to be made in anything in the kit); he punched a bolt hole, in the wrong place. It cost me 50p for a new filter, but who�s perfect? I took a video of him building the whole engine, just to prove to others that he had done it himself.

The video was shown to the Explorer Scouts that Ben is a member of, it see if he could get a badge ( it�s a scout thing), but they do not do badges for building gas turbines.

The boat is now ready for some more test runs, after many modifications to the lay out of the controls / pumps and fuel tanks. Plus the addition of TWO micro pore fuel filters.

Watch this space for more updates��