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profqwerty - n/a
25-Nov-06, 09:48 PM
I'm looking for a project, so though I might make another hovercraft! The experience gained in making the Eagle 1 should make this one much easier, and hopefully more advanced.

So I got thinking... what about a turboshaft powered craft?

There are all the probs with jets, e.g. lag, noise; but with some time I think this could work.



Can anyone input some advice for different design aspects?



The prop/fan could be variable pitch to account for the lag; If it's turboshaft the ouput could have some sort of brake on it whilst the turbine spools up (e.g at the start line) (pressure would have to be released (some sort of dump valve)). There could be a governer on the turbine which would make it easier to drive?



Just thinking that this would be a really interesting project.



It would also have to be large enough for 2+ people confortably. A turbine would provide a decent power/weight ratio (i'm thinking a small one btw http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif .)



Could I put the exhaust straight into the hull to provide lift, reduce noise, and supply underfloor heating?



Which hull designs have been proven to be adaptable with a lot of room? And also which is recommended: foam composite or fibreglass please?



Sorry about all the questions!

Toby

Don83000 - n/a
26-Nov-06, 01:42 AM
It's a idea I have thought about doing for the last couple of years in a cruiser but never seem to get round to it I was going to use a Rover APU and it would be possible to use a brake as you sugest but the big problem is going to be noise and as for outputing the exhaust underneath is a non starter unless you are going to use a asbestos skirt. One of the Sevtec hulls would be a good starting point if you wanted something simple but practical and with plenty of room and you would be sitting the turbine up on the rear deck out in the open so exhaust would not be a problem and it would be out of harms way to passengers. You could just use a centrifugal clutch on the output shaft for driving the prop then you could spool up to just over idle and from there on up I don't think power up time would be a problem from tests we did with a load on. The other way we considered was to use the turbine to drive a hydraulic pump (there are some lightweight ally ones about)and fit a motor to the prop and another to lift passing the oil through a large multi row oil cooler in the lift fans air stream you can then run full power but have total control from 0 to max rpm of the lift and thrust.

There have been some turbines on ebay and they seem to make between £500 - £1000.

hovmart - n/a
26-Nov-06, 11:43 AM
just forget it, its been done before and just is not worth the agro http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif

srn4 - n/a
26-Nov-06, 04:31 PM
Im intreagued hovmart...You say its been done before, who did it and what did they do?.... http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif



I have always fancied building a very large sev type hovercraft using ali powered by a turbine/hydraulic system...Prop at the back and a centrefugal fan in the middle...enclosed cockpit..6 seats...hmmmm http://hovercraft.org.uk/images/icons/smiley_icons/icon_rolleyes.gif



Dunc

profqwerty - n/a
27-Nov-06, 04:59 PM
This hydraulic idea is interesting - kind of like a hydrostatic drive system?

It would certainly solve many of the problems, and provide onboard hydraulic systems (cos all hovercraft need that).



Another idea I had was to possibly build a jet engine from turbocharger etc, then feed the exhaust through something similar to a jetski jet, then power the fan directly from the drive shaft.

I guess it would be integrated or have separate lift engine.



Can hydraulics survive fan RPMs, or do you need to gear down from the jet, and up to the fan (weight issues here)



I guess I could find a jet powered hydraulic pump (or with that, a normal engined one!)



The main advantage of the jets is the power/weight - JFS100, common surplus, 90SHP, 38kg, with integral clutch, self contained unit...(I liiike)

srn4 - n/a
27-Nov-06, 05:46 PM
There is a craft which was commercially availble in NZ or Oz..cant remeber which...that used a petrol/diesel engine and hydraulic drive to the lift fan... Maybe someone can remeber which craft that was?



I dont think you would be able to get enough power from a homebuilt DIY turbocharger style turbine....Given the weight of a turbo it wouldnt be very light either...



Take a look at this guys turbo turbines...he managed to get about 7Hp out of a turbo with a free power turbine... www.rcdon.com





I suspect you will find that most turboshaft engines have an inbuilt reduction drive gearbox to somewhere around 7000RPM max so driving a standard hydraulic pump wont be a problem... But as you said, keeping the weight down could be tricky...but by using hydraulics you could quite easily add various other control surfaces/skirt lift etc and control it using a computer to get more stability...



Another thought is what you plan to run your tubine on....It is possible to run a turbine on diesel but an aviation turbine would need some fiddling to make it perform well....



Dunc



Oh, and as an aside to proove your power to weight comment...Rolls Royce produce an engine which weighs 85Kg with auxilary pumps and reduction gearbox and produces 2000Hp....its a pretty brand new engine which they claim will get 4000Hp if its fiddled with...currently there isnt the demand for the power...

profqwerty - n/a
27-Nov-06, 05:55 PM
Ok, well 7HP proooobably isn't enough for a decent sized hover!

Yes - most are reduced to about 7000RPM, and some with inbuilt clutches....This could just go through belt drive to the fan! Then throttle would control the clutch, and the engine's built in governor would take care of the engine speed (if use an APU).



That would be a pretty good setup, and use shaft drive for lift/sep engine?



An apu would have only three settings: idle, no load, full load right? so just before use set it to full load, it spools up, and governor keeps it at its design speed...



Lots to think about http://hovercraft.org.uk/images/icons/smiley_icons/icon_smile.gif !



I saw a setup a while ago (it might have been a concept) where the exhaust went through a tube with holes in that drew in cold air, cooling the jet and increasing volume air flow...this could work to let exhaust go into skirt (EGT is something like 300-600C i think).



Any reason why it couldn't run on propane?? Jet A-1 can't be that hard to come across? maybe an APU would run on diesel, as other people use them also...



I think computer control might be overkill, but it's certainly possible (valves etc would be pretty expensive) http://hovercraft.org.uk/images/icons/smiley_icons/icon_confused.gif



I'm sure I can find a use for this RR engine now though http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif

jon_curtis - n/a
27-Nov-06, 06:18 PM
i once saw a vulcan APU (the guy picked up two, still sealed for a couple of hundred quid each). that ran on 95% saw dust!



the guy developed this thing as a gen set, for use in forest areas, like finland, it had an external combustion chamber, where he burnt the saw dust with a minimal injection of kerosene, and wacked the expanding gases back into the turbine expansion stage.

it was a rather clever thing, ran the expanding gases thru some kinda cyclone filter (he called it) before it went back in the engine.



when i saw it he was still trying to get a patent, when i asked him how he kept the thermal effiecny of the cycle up, which bit is the heat exchanger, he pushed me out the door quick lol.



one thing that would worry me on a small light hover is turbine blade failure! it would take more than a few layers of chopped strand to keep one of them in.

Don83000 - n/a
27-Nov-06, 06:23 PM
On the apu's the output is already geared down and a local hydraulic supplier told me he could match the rpm no problem as for the modified turbo they do not produce enough power look at the ones on the net that have been fitted to go karts etc the performance is not great.You could run on kero if you can't get jet fuel but you should be able to get it ok.As for turbine blade failure you just fit a balistic blanket as they use on the dragsters and these are just layers of carbon fibre cloth.

machineage - n/a
28-Nov-06, 04:08 AM
There is a craft which was commercially availble in NZ or Oz..cant remeber which...that used a petrol/diesel engine and hydraulic drive to the lift fan... Maybe someone can remeber which craft that was?



but by using hydraulics you could quite easily add various other control surfaces/skirt lift etc and control it using a computer to get more stability...






Hi Dunc - that would probably be my Mustang - link below. I'm just about to update the site!



The lift system utilizes a Hydrostatic drive with a positive variable displacement axial piston pump which powers a fixed displacement motor. A charge pump is also incorporated. The fluid power is put to good use elsewhere by way of hydraulic servo powered independant elevators and rudders. It also provides the power for dual cooling fans. Being Hydrostatic - only a small resevoir is required for the Hydraulic oil.



The Mustang is pretty much agreed to be the smallest size craft to successfully employ such a Hydrostatic drive due mainly to cost implications. Weight is also a factor which has to be born in mind.



Chris

simonollman - n/a
28-Nov-06, 07:31 PM
there’s a company up in Scotland on the web that make a turbo jet ducted fan,

carnet remember the name of them now but if you have a look for it you will find it?

well saying that it was maybe 2 or 3 years ago?

profqwerty - n/a
28-Nov-06, 08:28 PM
hmm, can't find this company, but will continue looking.



The hydrostatic looks to be overkill for a smallish craft (that may be used for racing!). Direct drive ftw, if a clutched one can be found.



Surly the turbo ducted fan would be against racing regs (they say no to rearward facing jet exhausts for some reason http://hovercraft.org.uk/images/icons/smiley_icons/icon_biggrin.gif ....)



Will keep looking for a suitable engine though.

simonollman - n/a
2-Dec-06, 05:14 PM
heres a vid of a turbo prop



http://www.nickhaddock.co.uk/turbine_media/PJTurboprop.wmv





can you imagine straping that to a hover

srn4 - n/a
2-Dec-06, 08:26 PM
That is one weird engine...I think its a pulse jet....scary things!!!