[RotarySMP]

Using a mciro gas turbine as a Turboshaft or turbo prop is again very very cool, but extremely inefficient. The power extraction turbine and gear box are reducing your system efficiency. This is balanced against the improved propulsive efficiency of the large diameter helicopter rotor, meaning you can now lift the engine, it's fuel and it's payload vertically. In a model helicopter, the gain in coolness offsets the terrible efficiency of having to land every three minutes to refuel. This is a niche market.

You really can't get around the fact that turbo machinery doesn't become competitive for flight until you get to continous power of about 400-600HP. By that power output, your recips are getting so heavy, that the mission weight of a the turbine plus fuel is less than the weight of the heavy but efficient recip plus fuel.

Reliablity, and cheaper, lower quality fuel are further reasons why gas turbines have come to dominate from about this power range and above.

Below there, you can not (with current materials and process technology) beat a intermittant combustion engine.

A gas turbine is a continuous combustion device, so as it gets smaller, the combustion chamber has to shrink. The CC volume reduces at the cube of linear dimensions, while the surface area is only reducing at the square. As you ratio of surface area to volume increases with reducing size, your heat losses through conduction increase (minus efficiency) and your skin friction losses increase (minus efficiency). In the turbine and comprossor, your tip clearances reach a practical minimum, but you are using small blades, to the relative tip losses increase as well.

An intermittant combustion engine is also affected by these effects, but to a lessor degree, as you can reduce the number of cylinders, and still keep the CC volume resonably high. The Cylinder is sealed, so your tip losses aren't an issue, meaning you can keep pressure ratios up even as size reduces. As efficiency remains high even down to very small engines, while the weight drops dramatically, your small recip plus fuel load, can be far lighter than your small gas turbine plus fuel load.

There was a NASA study in the late 70's which idendified the Wankel as the most promising technology for low power GA aicraft. It's combination of high power to mass, high power to frontal area, soft failure modes, and low vibration are all favourable for A/C. It is a shame that the bottom fell out for the GA market just as Curtiss Wright etc were prototyping new wankels.

The power level where gas turbines become the most attractive solution will creep down as breakthroughs occur in blade coatings and small turbomachinery design, and trickle down.

A real revolution can probably only occur if monolithic ceramic rotating assemblies become feasible. The hotter you can run your turbine inlet temps, the higher your efficiency. At present, once you get below the about 10000 HP, your turbine blades are too small to support internal blade cooling like the bigger engine have. Therefore your material becomes the limiting factor for efficiency (a big commercial engine can run turbine inlet temps above the melting point of the blade material, as the blade is internally cooled, shrouding in a cooling film of cooler air, and has a ceramic coating).

Metals are already pretty much at the physical limits today, to make a signicant jump in temp, ceramics are the holy grail (this has been know since the war - RR, GE and P&W have investing millions in trying to reach the goal of a ceramic which can survive the heat cycles of repeated starts without shattering as they cool).

The laws of physics shall be strictly inforced!

[epineh]

its expected to be around the $50,000US mark. (I was out by a measly 35k ! )

At that price you should buy two !!!

Funny vid Neatman, nothing like strapping a couple of hot water bottles full of fuel to your belly, a model gas turbine to each foot then jumping from a hot air balloon !!!
It put a smile on my face.

Russell.

[diarmaid]

Hi. Cool video. I, like epineh, was slightly concerned about the location of the fuel bottles. However, I thought they were stuffed slightly lower than his belly.....bit disturbing whatever way you look at it!

I would like to do something like he did in the video. I just have two 'simple' extra requirements.

1) I need to be able to fly like that without the requirement of getting to 3000ft first. Maybe adding larger more solid flying surfaces is an idea. Im willing to sacrifice the vertical takeoff capability for a short takeoff run. Maybe 100ft. Possibly by strapping wheels to knees and elbows and taking off in a hunched position on the ground....(Just an idea) Possibly using a small catapult to get to flying speed instead of a takeoff run(I know kinda dangerous and funky but if it worked then it wouldn't be dangerous because you wouldnt come crashing to the ground!)

2) I need to be able to strap a fuel tank to the persons back holding enough for.....60mins flight....even 30mins would be a starting point....Sounds like the easy part....

Yeah the wankel rotary is pretty cool. I'll have to consider it as an option and look into it more. We studied it last year and I did a short paper on it.

[RotarySMP]

Diarmaid, you are working on a Darwin award!

[diarmaid]

lol....I'll take that as an encouraging compliment!

Link for general info if anyones curious.
http://www.darwinawards.com/

[diarmaid]

FIRSTLY AND MOST IMPORTANT:
This diagram was done VERY quickly and is NOT very detailed. (I think this is obvious! )
I can do much better 3D creations. I have many other ideas which I haven't had time to draw up yet and Im on my way to America this weekend for two weeks so wont be on the zone for a while.

Ok, so,

This is an approximation of my first idea except that idea was minus the wings shown.

Would this be possible?

1. Between 1 to 4 jet engines on a backpack mount on the persons back.
2. Engines mounted onto a control system (Not shown) to allow tilting for forward/reverse if flight was upright (minus wings) or upwards/downwards if flight was parallel to ground using wings shown.
3. Heat shield over the legs.
4. Orange square is fuel tank.
5. Detachable wings made out of light weight material possibly fiberglass coated kevlar.
6. Small wheels (Not shown) approx 125mm diameter strapped to knees and elbows for takeoff/landing run if using wings and flight parallel to ground. Takeoff/landing in a hunched position. This avoids need for enough thrust to lift dead weight.
7. Wings could be up to 10ft span (5ft each side but the smaller the better) if detachable from unit, and if not too heavy so that they would be portable and could be secured at destination in an upright position (e.g Against a wall or just like a motorbike! )
8. Wings would likely not be swept as speeds would be low.
9. Drag reducing helmet/clothing could be used.
10. Lightweight 2 or 3mm plexiglass screen could entirely surround person to reduce drag.

Surely engine technology has advanced enough to try something like this and have 30mins flight time? Is there any type of solid fuel or compressed gas fuel as opposed to liquid which may help get around the weight to energy generated ratio problems?

I believe that some of the 'rocket packs' used in the 60's were powered with a hydrogen oxygen mixture using H2O in one tank and O2 in the second. However this only gave 30sec flight time which is useless. Im thinking along the lines of solid petroleum fuel, or high-density low volume solid fuel used in todays rockets, or possibly mixing vapourised liquid fuel with high pressure oxygen just before ignition?
Modern solid rocket fuel has a mass fraction of approx 1:10 which would allow my 100kg to be powered by 10kg fuel, however Im not sure of the burn rate of this fuel (Back to my research ...also I dont want to be travelling above 100mph at least initially )
Although some of these may negate the possibility of using current engines, I am willing to attempt to design a new engine as my thesis instead of designing the vehicle which would be powered by it. I probably know more about engine design than aircraft physics anyway.

So....lets hear all possible opinions and any ideas.

Also: I have two years to work on this starting this week, so I want everyone to throw oil on the fire at every opportunity, I want to drain your minds of all your knowledge and experience, THINK BIG, THINK POSSIBLE NOT IMPOSSIBLE, THINK HOW MAN HAS GONE BEYOND THE BOUNDARIES THROUGHOUT HISTORY AND HOW THE FUTURE IS OUR OYSTER......etc etc. :nono: And dont give me any of that crap and bull@%#! about "if it could be done someone would already...."

Im in the enviable position of being in full time employment which is paying a nice wage and putting me through a full time bachelors degree, so I can afford to spend money developing this (Whatever 'this' turns out to be). Because its for my thesis SWMBO will allow limited expense. Im not talking tens of thousands but I just spent €3k on a new laptop so I can do the same to change modern private transport!

[fyffe555]

'rocket' packs used hydrogen peroxide and a catalyser (silver?) to produce high temp steam.. was a chemical reaction 'rocket' rather than a heat combustion rocket. Had about 20 litres or around 20kilos of fuel for a 30 second run with about 160kg thrust in the 60's/ You could probably double the flight time with modern materials - if you really wanted to.

Have a look at the Bell Jet Pack does much what of what you've drawn.

Just found this; http://skywalkerjets.com/

Here's a link to the engines used; http://www.usamt.com/Mel/comm/comm_Specs.html

45lbs thrust ea *8 is 360lbs. Engine are 5.3lbs ea ex support equipment so that's 42.4lbs just on engines. At 45lbs thrust each engine is using 1 gallon US or 6.5lbs weight a minute or *8 52lbs fuel a minute....

[fyffe555]

And this; http://cgi.ebay.com/ebaymotors/Jet-Z...temZ4650946782

[diarmaid]

Damn Richard Hermon! He had the advantage of being born before me and got there first!

Thanks for the links. The 150Lbf engine there uses 1.4kg fuel per min and weighs 17.5lbs. This is not very good....

Ok, so the maths works out. You could fly for approx 10min in dense air using numerous small jet engines. Thats not really good enough for commuters unless you live < 10miles from your work and have quarter of a million dollars to blow. (And are an American, which for a man who wants to save lives with his invention I think is kinda racist. People need saving in Europe too!)

Ok, so what about the winged idea. You operate like a current airplane except minus the actual aircraft. You basically become an ULTRA ULTRA ULTRA light aircraft. Small wing, small engines, and only the weight of yourself, your engine/s, and wing. I think this is the way it might have to go. Take off at low speed over a very short distance. Fly for an hour with absolute minimal weight. It would basically be a modern motorbike in the sky minus the 'bike' part. A more apt comparison may be a manned kite! Maybe a small combustion engine is a better idea. Jet technology as mentioned above is fancy and slick but just isn't there yet.

Im sure I (we! ) can figure something out. the question I have to ask is, 'Do I (we ) really need to take off vertically?' Sure it looks nice and may be useful now and again, but is it really needed with the copious amounts of modern paved roads?

PS: I know this thread and all contained therein seems a little crazy, and maybe funny, but I am perfectly serious about this. Im also perfectly sane (I think! )

PPS: If someone follows this thread and in the future uses some info from it to build any end result before me, thats fine, just dont try and patent or publish anything before I hand in my thesis please.

[diarmaid]

Im thinking swamp boat type of design, except only two feet wide and simply a 7 ft long frame with a person lying belly down head first between the two frame sides, with a single engine behind and a wing attached onto the frame only inches above the persons back..

Im also thinking the wing should be some sort of fabric such as used on current ultralights maybe so it can be detached easily and folded up upon landing. Maybe a full V wing, instead of two sides.

A thought just popped into my mind.....if we could go fast enough we wouldnt need a wing. (Seriously, this is probably a REALLY REALLY bad idea! ) How far/long can a cruise missile travel for? And at what speed? I dont think they break the sound barrier. No Im not insane just thinking out loud...

[diarmaid]

Referance the swamp boat comment previously. Something like this maybe with a flying surface above the guys back, or foldable wings at the sides. (Not shown) Please remember the drawings are very quick and basic. This looks MUCH more solid and heavy than the lightweight tubing picture in my mind.
The cage for supporting the prop would be just that, a cage, not solid. Probably necessary for birdstrikes etc. The prop cage should also be hinged onto the carriage area so that after landing it could be tilted flat against the carriage for storage.
Again just throwing ideas out there. Please everyone feel free to contribute. Better diagrams will follow as the idea progresses and I get more time. There would be controls at the front on a console.
I envision a finished product would have to cost less than €10k MAX. Preferably sell for about €6k-10k. Therefor about a €5k to €8k approx production cost all in per unit.

[fyffe555]

if you turn it the other way ...http://www.hiller.org/flying-platform.shtml


or \; http://www.flying-platform.com/future.html

[diarmaid]

Those flying playforms are great but as shown its been done already. Also, its quite large. Im thinking one man transport, liftable by one man, that can be packed away into a cupboard. However it does give food for thought. Thinking outside the box is always good. Thanks fyffe. Looks like we're pretty alone in this thread so far....is there nobody with other ideas...or just nobody willing to comment!! lol

[planescott]

make this radio controlled

[epineh]

[QUOTE=diarmaid]

PS: I know this thread and all contained therein seems a little crazy, and maybe funny, but I am perfectly serious about this. Im also perfectly sane (I think! )
[QUOTE]

Lol Well for what its worth, I think you are sane, although the voices in my head tell me you are crazy

As for the solid rocket as propulsion, I thought that once ignited they burned until the fuel ran out without any way of stopping. If you go that way make sure you are pointing up before lighting the fuse...

Russell.

[diarmaid]

Hmmmm.....not being able to stop the fuel burning may present a slight problem to some potential customers!! lol

planescott.... :cheers: wow, what a fantastic site. I have got to get me one of those helis for commuting to work! Im ordering a set of plans to see if I get any inspiration from them.

I've been thinking that the capability to hover is actually quite important although dependant upon the application. Its actually quite simple really, for the basic commuter market the version above - fixed wing, pilot in a lying position, ultra ultra ultra light aircraft with a short takeoff/landing run would suffice. When you start getting into other markets such as rescue or military that the current PAV prototypes focus on, then you need to be able to hover and takeoff/land vertically.

Assuming that I continue with this for the long haul I need to decide which route Im going to take.

Driving home today I was thinking about the aerotrek vs platform designs. The layout of the rotors above the pilot in the aerotrek gives the design an inherant instability due to the position of the weight in relation to the center of gravity. And this instability, although not really relevant in powered flight would become more pronounced as power decreases on takeoff/landing. Also I think this rotor position makes it difficult for the vehicle to fly in anything other than an angled upright position.

In the platform design you have a low center of gravity but you end up with a large base area and I imagine less manoeuvrability.

If two rotor assemblies were used as in the aerotrek, but they were moved to approximately level with the center of the pilots body mass (instead of above), this would allow a huge increase in stability. It would also allow a transition into horizontal flight. Therefore, the design would have the best attributes of a vertcal takeoff/landing backpack design, but flight surfaces could be attached to allow the vehicle to take off vertically, then transition to fly with the pilot in a lying position.

Of course this would need quite a bit of power for the transition, and to maintain horizontal flight against the weight of the rotor assemblies, but this would be easier due to the position in the center of the overall flying mass and ability to attach small wings to generate lift. This layout would also be more natural and comfortable for a pilot who would basically be strapping the vehicle to his hips. (I think this is a 'eureka' moment.....although maybe thats a bit premature!)

What do ye think?

[diarmaid]

Ok folks. I now have a relatively solid idea in my mind. Which in my mind I have actually started building!

I have been thinking about the nuances of the rotor assembly construction, but I really think its not a major engineering challenge, although Im going to have to get myself a mill or access to a mill, and also learn how to design and cut metal gears. Any comments?

But thats the least of my worries for now. I am going to have to decide upon a proof of concept design and I think Im going to build this in minature using model aircraft engine/s, or else slightly larger 'minature' using 50cc moped engine/s. The building definately wont start within the next 6 months due to my finances being tied up in other things (Such as buying tools/equipment). It will also probably take a few months of design/refining and research to decide upon a build model. I may cannabilise my proof of concept to build a second miniture which would more approximate the appearance of the final life size model. Comments please?

Im thinking the final life size prototype may be powered by a 125cc or 250cc 2 stroke motorbike engine/s but Im off to google now to get conversions for cc into horsepower, some weights, and other info. And the actual engines dont need to be decided upon just yet. A regular 2 stroke engine would have the advantage that if flight time is limited access to refulling is abundant on the roadside. Any comments?

I figure though that I will start with the engine mounting and build outwards in all directions from that. Also Im going with a prop design (Not nearly finalised...in fact...not drawn!) and hope that when my cnc router is built I can use it to carve out wooden prop blades for me. If not, then I'll carve them by hand with my power planer and some elbow grease. Comments?

The mounting shrouds for the prop/props will probably be thin aluminium sheet. Comments?

As I said Im going to be away for a while, but I will draw up some proper 3D diagrams. I can already picture some of the mechanical parts, and I am going to need advice on the zone here about machining them and what metals to use etc.

Im also thinking about patenting since its not expensive and just for 1 year in case, but gotta get a solid design first!

Thanks. L8rs.

PS: Im NOT tying myself into doing this to the end but Im getting very excited about it and it wont cost anything other than time to see how possible it is.

[diarmaid]

I nearly forgot!

I dont know nuts about propeller physics, and the science of airflow through a propeller etc. Can anyone point me in the right direction to get some info on this please?
I'll be able to do better research when Im back in university next month.

Im thinking three bladed prop/s but dont have a clue if this is a good/bad idea and dont want to spend twelve months carving ten different prop designs to try and end up getting bogged down.

Im also thinking I'll make up a rough wood or clay model before a proof of concept design so that I can actually look at a design and see if any problems appear that I havent forseen.

L8rs.

[diarmaid]

Hi all. I think I may have found an engine type. The springtail uses a rotary engine. Thats how it gets 118hp from such a small size. Im going out on a limb here, but I think I should be able to find a scrapped Mazda Rx7 somewhere that was written off from behind and salvage the engine. But thats if I reach that later stage.

First would be a proof of concept model. I've seen lots of model aircraft engines for around $100 upwards, I also have an old one of my own lying around somewhere so shouldnt be a problem there. Im also thinking a two bladed prop from a model shop should be fine for the proof of concept but a 3 bladed would be better. I've seen two bladed on e-bay ranging up to 26" for only about $9.

Does anyone know where I can order a three bladed r/c propeller online?

Last but not least, Im still going to have problems with propellers. It seems that a ducted fan would actually be advantageous as opposed to a regular prop. I cant find a large enough ducted fan online for sale. They are all only about 3inch max diameter and electrically powered. I need one about 12" diameter initially. Im not worried too much if its supposed to be electrically powered as I can just alter it. Any ideas where I can get one? Thanks. I suppose if I get my cnc router built I might be able to use it to carve a ducted fan blade with just a bit more setup than a 3 bladed prop, but I'll find out when I have it built.

Im also thinking that I wont use variable pitch blades. Although it would be better it would get way too complicated for me, and I want this to be simple and straightforward hence relatively inexpensive to build. What I do envision is that the entire prop/fan along with its shroud would pitch around two axis. This shouldnt bee too hard since the blades themselves would still be fixed in position.

I might have to buy a milling machine for this but my college might have one. Im back there in 3 weeks.

[diarmaid]

In the thread below Im trying to get some info on the connection from the engine/drive shaft to the propellers. Feel free to view it and share any advice. Thanks.

http://www.cnczone.com/forums/showth...915#post190915