Personal Air Vehicle?

[diarmaid]

Hi,
Im wondering if anyone can help me here. Is there such a thing as either:

1) A model jet engine that could lift 100kg vertically off the ground?

2) A model jet engine that could lift 50kg vertically off the ground and a system to link two of these so that they will open/close throttle in perfect harmony?

3) A " " " " " " 35kg vertically " " " and a system to link three of these so that they will open/close throttle in perfect harmony?

Also:

1) Is there a formula relating to jet thrust and force that can be used to calculate the above for specific engines?

2) How much fuel is required for...lets say...a 90min flight using a model jet engine (Approximately will do, I just need to figure out roughly how much space 90min worth of fuel for 1 engine will take up) ?

[vulcom1]

I won't say it can't be done but lifting 100 kg straight up would probably put you into a full scale turbine. Also you would be better with turboprop as your airflow would be spread better and more even. As for fuel load for 90 min. it would be lots. The more power required the more fuel and the model turbines burn about 1/2 lt a min or more.
The only place I know that may be able to give you a bit of info is the GTBA association which is on the web. I would check there.
John

[diarmaid]

Thanks I'll look there but even from what you've just said I think my idea is probably dust. Oh well. L8rs.

[fyffe555]

how high do they have to lift 'it' ?

[diarmaid]

I think 100 to 150ft would be enough initially for a prototype.

[fyffe555]

I'd look at some sort of rotor craft, or if it doesn't have to be vtol a small fixed wing. Is the 100kg load breathing? at 220lbs load plus fuel you're very close to ultralight specs.

You can get 'model' jets to 150lbs thrust and above, the AMA limit rc jets to 35lbs thrust, but to use multiple jets to list 100kg you're on diminishing returns when you factor in engine weight, controls, and fuel system and fuel weight. Like a rocket, there comes a point where adding engines and accessories actually decreases the available payload. That ignores problems of controlling multiple motors.

Also note most jets are rated at lbs thrust in motion, if your vehicle isn't doing 100mph with the appropriate compression benefit then your actual available thrust will be somewhat less.

interesting question tho'..

Andrew

[diarmaid]

Originally Posted by fyffe555 Is the 100kg load breathing?

Please explain what you mean by this in more detail. If you mean physically breathing as in 'alive'.....then yes (At a later stage).

Originally Posted by fyffe555 The AMA limit rc jets to 35lbs thrust

Not sure what the limits are over here, if I ever got to the stage where I needed to find out I will. But 'technically' it wouldn't be radio controlled, it'd be controlled electronically by an operator so prob come under general aviation regulations. What dead weight would a 35lb jet lift vertically before getting significant velocity to feed the engine?

Originally Posted by fyffe555 But to use multiple jets to lift 100kg you're on diminishing returns when you factor in engine weight, controls, and fuel system and fuel weight.

Yeah I was worried about that but I dont think that point would be reached with 4 or less small engines....what do you think?

Originally Posted by fyffe555 Also note most jets are rated at lbs thrust in motion, if your vehicle isn't doing 100mph with the appropriate compression benefit then your actual available thrust will be somewhat less.

So how much thrust would I need to lift 100kg dead weight 100ft above ground level before transitioning to horizontal flight? I imagine I'd need a significant reserve of thrust to remain airborne during the transition phase? (I have all the formulas for lbs thrust vs weight vs resistance but Im not going to route them out right now and I can't remember if there are differences for jet vs prop generated....although I dont think so! )

Going into 3rd year of a 4 year Transportation Engineering Degree course in Sept and Im toying with the idea of designing/building an experimental personal air vehicle for my final thesis/project over the next two years.
Thanks for your advice Andrew, keep it up! I know that the springtail in the USA ( http://www.trekaero.com/
http://science.howstuffworks.com/pav2.htm
http://www.technovelgy.com/ct/Scienc...sp?NewsNum=167 ) is gone beyond the initial development stage, and uses turboprops probably for the reasons mentioned above among others, but Im trying to figure out if the alternative of rc jet engines would be viable. If it is I may be able to get some funding from the university to help with a prototype.
Thanks.

[diarmaid]

hmmmm...It seems about 20lts of kerosene will provide about 60mins of flight dependant on the various obvious factors. This presents a problem. Does anyone ever use alternative fuel sources for these engines which will allow a more efficient burn and thus either less fuel to be carried and/or longer flight?

[diarmaid]

Does anyone know approximately how much an engine such as this (http://www.heward-microjets.co.uk/en...tairh400.shtml) would cost. Its not physically very large (Although possibly too large ). Im thinking around the 15k mark. Would that be about right?
Obviously I'd have to build a small scale model over the next year out of my own money before there would be any possibility of getting funding for somthing like this.
Thanks.

[fyffe555]

breathing; I was asking if the 220lbs/100kg was a living breathing pilot. If it is you get into all sorts of caa requirements of course but more importantly (!) the fuel load would then have to be accounted as extra payload and then you are into Ultralight territory.

Bell did a jet powered pack around the time of the more sexy James Bond rocket pack, it was faster and could fly for 20 minutes or more and used a single stage jet engine, no idea of teh specs but google might help.

Dead weight verses jet thrust; It Depends...! mostly on how the engine is rated. There is a nasty equation to calculate the lift due to thrust of a jet but it requires information that isn't readily available for small jets like volumes, speeds, temperatures, eflux shapes and the like. It's pretty much irrelevant anyway since you 're going to need actual static thrust numbers. If an engine is rated as commercial engines are then 35lbs 'Rated maximum continuous thrust', which is a static measure, means if you turned it skyward it should move up to 35lbs weight. The rating for model and smaller engines isn't formal however and some rate 'estimated' which with commpression due to influs speed can be 20% or more higher than static, some rate 35lbs because that's the AMA limit.

For a thesis I'd definitely specify a static thrust test as part of the project, either yours or certified from the vendor and note the operational characteristics, thrust at different spool speeds etc. Note there's all sorts of funny effects on a static or nearly so jet engine operating close to ground, from ground effect, exhaust recycling in proximity to ground to compressor stall problems all of which will affect thrust. You'd need to account for that in the left calc as well as control and safety margin.

To be honest a single stage jet probably isn't the best fit, noisy and thirsty and you appear to need to move large volumes of air relatively slowly, not small volumes fast which is what a single stage jet does. Maybe look at a 2 stage jet such as a bypass turbofan or turboprop.

Or use IC, Moller skycar has eight wankel engines (wankel - oh no!!) turning four ducted fans to the same effect, not realy flying now but the army/vendors are using the same engine in UAV's like the Sikorsky Cypher. You could do it with something other than jets unless jets are too sexy to avoid. I'd even suggest protyping with electric motors on a tether to test the thing.. That's how Bell started doing helicopters after all.

The trek aero proposal does much the same as suggested, shifting high volume, low speed air with ducted rotors to provide higher static thrust. The trick is to balance the available thrust with a useful payload, which in english means will it go up and if so how much fuel do I have left. Modern jets use high bypass fans both for efficiency and static thrust at takeoff.

How much thrust to move 100kg to 100ft Vertical then transition? Depends on the constraints, we've already said that the static thrust of an engine would have to be verified. If it's a back yard project then you could get by with less than a thesis expected to comply with some current flight airworthyness regs or reasonable safty expectations.

There's a bigger issue in that transition to and from flight requires a surplus of power to maintain altitude while propelling the vehicle forward, regardless of whether lift is subsequently available in horizontal flight. An advantage in single stage jets is that as flight speed increases so does their efficiency to some degree.

You might want to cover something a little larger than a bunch of small turbines. As you add engines they get proportionally less efficient, even assuming any of the practicalities can be met. If you can get the weight into the sweet spot then thats fine but for the thesis try comparing to smaller commercial engines like the Rolls Allison 250 turboshaft's are rated at shaft horsepower ~320 and ~135lbs dry, used in small helicopters. For pure thrust Williams has a 1000lbs thrust bypass engine at 300lbs dry. Way to big and expensive possibly, but if you're carrying any kind of fual load witha warm body then your all up weight requirement gets big very fast.

As an aside have a look at the harrier and where the exhausts are located compared to its CoG. It carries its weight mostly on the front 'cold' exhausts. The engine is split with a high bypass fan powering the front exhausts, with the rear hot exhausts powered by the remainder of the bypass and the turbine exhaust.

Is this a vehicle or a strap on?

[epineh]

Diarmaid, maybe you could pursue IC type engines and use some sort of ducted/enclosed fan setup. Myself I toyed with an idea using a hybrid sort of engine (my own idea of course !).

Imagine two counter rotating two bladed props, positioned axially inline. Now towards the center is a combustion chamber of sorts that is closed when the blades cross each other, fuel is injected and ignited pretty much simultaneously and this forces the blades to spin... and so on.

My idea was to use high pitch fan blades, using low rev's blah blah blah...

Now before the flaming begins, I couldn't work out how to get a resultant axial force, instead of just one bang that resulted in scrap metal. I got as far as a port system kinda like a two stroke but there had to be a third part (I figured) to be in the center of the two "pistons" to make them travel away from each other, creating rotational motion.

The advantage of this theory was pure rotational movement, like a jet but with the torque of an IC engine, allowing relatively slow rotational speed and lots of efficient power.

Now that you all think I am crazy, let me just say that if some one uses this idea and builds an engine that:

1 : Works.

and:

2 : Makes them incredibly rich...

Then I expect at least one (1) carton of beer as credit for the idea.



Russell.

[planescott]

AMT Olympus turbines 150lbs of thrust and they are pretty expensive.