View Full Version : Designing An Ultralight Coax Helico
08-25-2004, 02:40 PM
hello every one, i m an helicopter enthusiast from France and this if my first post here.
i apologize for my bad english ;)
like a lot of people i wish to build one day my flying machine and i look for serious tips and help in my design.
I found helpful comments on www.eng-tips.com , very nice people.
i also recommend the work done on UNICOPTER, its worth have a look.
i look for people wo began or tried to build rotors/blades/helicos and if possible and consider their experience as it may save lives.
i began some early drawings you can see at
a complete site will follow this first kick off.
i read some posts here (from Spaced ) about coax rotor design and yaw control problems in autorotation, i m curious about your experience.
friendly thanks for any remark/comment
08-25-2004, 02:44 PM
Welcome Victor & good luck on the chopper!
08-25-2004, 04:10 PM
thanks for welcoming me chris, and good flights on your "dominator" (i think) ;)
as said an old helico french pilot "there is no best pilot , there are only alive ones"
08-25-2004, 10:58 PM
why not a synchropter?
08-26-2004, 12:10 AM
Hey zeeoo, thats me. I changed my name to match my new company name. Whats your question?
08-26-2004, 06:34 AM
to Quadrirotor >>
Andre, perhaps "intermesher" will succed to convince me about go for a syncropter ;)
i must admit i am attracted by the coax design, not for fun but also for maneouvrability, compactness and ovel all, the rotors are just like "classical" rotors, and in an intermeshing config i dont understant well enough the rotor scheme, blade design and specially how to control them, yaw control is a little more mushy than in a coax specially in autorot .
maybe i ll change my mind.... i progress, i progress ;)
to helidev >>
hi Helidev !! as you see i m crawling by there ;)
you got a company ? didnt know , hope success for it.. is it a (future) helico development company? would be glad to read more .. particularly in the future.
in fact im "fishing" information about the debate "how to control yaw in a scalar way in a coax" , i mean safely with no autorot problems, easy to build etc ... quite a "chimère" .
i m particularly looking for precise drawings of existing systems (kamov) , but impossible to find..
helidev, in fact i must write a precise work-sheet for my investigations and/or builds,
then i will classiffy data in the good concerns.
What i plan, first is to build a single rotor and test it, i think this is the first part (execpted fuselage) i can build, i can have access to good modern tooling, and affordable materials ,
so i ll test the rotor head, without blades, just to evaluate fatigue problems, centrigfugal capabilities and validate/modify the scheme, then ill build a blade, validate the molding, and probably make destructive tests on it. then i ll build a set of 3 and mount them on the rotor and .. test and test.
note that i can test the blade independantly of the rotor head.
with the data collected, i will know if i go a good way or not, i think the fuselage will not be a big problem if the rotor is working good.
some informations :
- i consider using a HIRTH engine (2 stroke - 65 hp), rotax enthusiasts say its not a so good engine, but i think it is...
- i consider using for fuselage a kind of home-made honeycomb panels consisting of a foam flat panel between 2 roving+epoxy skins, i have to test a sample for weight and stress. some drawing will be soon on my site http://zeeoo.free.fr/helico/
my main questions are about the design of the rotor as you can see it on my site :
- do you see mechanical problems
- teetering rotors have a "K-link" that lowers pitch on advancing blade and increases it on retreating , is such a system useful for 3 bladed rotors ? my fear is that all the blades could loose pitch (so lift ) at high G ...
- i plan to use an horizontal tail fin to add some control to the helico , i think it could be useful ah high speed to relieve rotor work, i think it also coul be usefull in gyrocopters to prevent negative G as the fuselage so the thrust line will be oriented at the same time as the rotor and will not act as a pendulum. never seen this on a gyro or helico, i wonder if some one tested it.
well well , you see i m hungry about information ...
thanks to you all
08-26-2004, 07:25 AM
helidev ( can i call you christian ? )
i read you re from sidney in australia, is it right? , maybe we should meet one day as my girfriend and i look for migrate to canada or australia, depends on work opportunities ;)
if youre an Aussie, you ve got a good engine manufacturer there > Jabiru, isnt it ?
08-26-2004, 09:33 AM
My concern about coaxial helico is the swash-plates, which are critial parts and riding twice the speed than those of a one main rotor!...
08-26-2004, 10:07 AM
my concern is also about that ...
i joined a drawing to explain the way i see the controls, in a simple manner.
concerning the bearing, yes it may rotate about 1000 RPM, then generate a lot of heat and endure a lot of fatigue.
about RPM capabiliies, the french manufacturer SKF has what they call "fixed section bearing", ball bearings that can have a big inner and outer diameter but keep small balls dimensions, ideal for swashplates (check their online catalogue in the section "other bearings") , they mention these bearing are suitable for high RPM, so i think we can trust them.
about heat, the lower swash plate should rotate at only 500 or 400 RPM, the upper one, the double, but i think the metal around it could act as a dissipator, helped by the moving air around...
perhaps we sould have the comment from a skilled engineer...
08-27-2004, 12:48 AM
Yep in Australia, would like to meet up any time. My girlfriend would love it, she's learning French at the moment :)
HeliDev (Helicopter Delvelopment, not real imaginative I know) is a registered business now. Right now its more a way of offsetting my costs for when I finnally have a product to sell. I was spending alot on books, computer programs ect.... That I needed some way to keep track of it, plus make it easier once I have a flying prototype. And yes I hope its successful too.
Like I said earlier, alot of my work so far has been evaluating a coax helo. I have a NACA paper somewhere, Ill see if I can email it to you, I found it very interesting. One of the things I found interesting is that most texts test a coax against a 2 bladed single rotor, then state the higher induced power of a coax. To me this isnt comparing apples with apples. If you are going to compare them it should be a 4 bladed single rotor against a coax (2*2 blades) then you have a real figure to compare against. When you do it this way the coax comes out way in front (when you account for TR losses).
What i plan, first is to build a single rotor and test it, i think this is the first part (execpted fuselage) i can build, i can have access to good modern tooling, and affordable materials ,
Im very jealous. I will have to either purchase the equipment or subcontract out the work or both. Its a problem which I have to overcome, and one I havent really resolved.
Unfortunately my real job gets in the way right now. Im working in the building industry to get enough money together to get my helicopter licsense. Once thats out of the way I should be able to concentrate more on my designs, and getting some scle stuff flying. One of the benefits to the delay ahs been the opportunity to research more and refine my ideas further. Ive got about 3 viable ones right now, each with their advantages/disadvantages. I still really like the coax, Im just not sure if Im up to the drive train design. Being mostly self taught has some real disadvantages in the time it takes to learn all the reqiured knowledge, you have to pick your battles :)
Yes Jabiru is in Queensland, there is a helicopter under development in europe called the mosquito, according to their web site they were going to use a Jabiru engine, but didnt work out. I have a friend who visited their factory recenty, and apparently they are working on a NOTAR light helo, sounded interesting, but Im not sure that they will have sufficient yaw authority, time will tell I guess.
With reguard to the swash plates, come on guys its a helicopter. as long as you can get a reliable 500hrs to TBO, theres really not a problem. If you keep the replacement, or servicing of these components in mind in the design there shouldnt be much of a problem. There are plenty of certified helos with bits that wont go that long. Plus being in the airflow should help with the cooling. Dont forget the swash for the TR would be doing 1000RPM on a TR helo, and they do it with out much trouble.
On the whole Andre I like you design, and Im really lookin forward to seeing it fly. If there is anything I can help you with please let me know, Ill do my best.
And ofcourse you can call me Christian.
08-28-2004, 11:17 AM
hi christian, as i see , we may be at the opposite positions physically but we are in a kind of symetry for the ideas ;) like you i consider myself as a simple enthusiast with a good curiosity and understanding.
my GF dreams of australia, she is an architect and her archi-heroe is the australian Glenn Murcutt. i m also really fascinated by your country , this is one of 2 possible destinations in my future, i mean for a lifetime perhaps. we always think the grass is greener far away, France is a beautyful country, but we feel a little tightened, missing space (physical and professional).
if you consider a visit in france, just say it we would be glad to wellcome you.
about our common matter :
- the coax layout is the one i actually understand better..
- you think in building a commercial aircraft, i actually dont (at the moment), but still thinking a good machine sells itself..
- the needs for Aussie market may differ from european for example for crop spraying, and may be for you more in cattle works, airmail, coastguard and recreationnal regarding of you wiiide spaces.
- if you consider to invest seriously (in the future) in a R&R lab, i think you should examine first the good structure (who worsks on what with whitch tool)
- you say software, what soft? i actually am a specialist of discreet 3DSMAX so i can jump easily (quite) to AUTOCAD that should fit our needs..
- i actually work in a kind of schedule for development/design , i classify all the parts to be developped by category (airframe, rotor, blades etc..) and in each one , the general idea> precise details>calculus/data>CAD drawing> test results or questions.
this way i think i could collaborate, exchange or take ideas as you could.
- as you imagine i have a LOT of questions, i can design a global principle even a precise detail, but wil need help for very sharp choices like sizing the parts, choosing metal/materials etc etc , that s why i need a schedule
you said you are jalous ;) , actually thefather of my GF works for a world famous pump manufacturer, he has a friend that could tool and treat any part i could draw, even gears etc, you can be jalous ;) but it will end soon as he will be retreated, but he will keep a link (i hope).. i would say to you : dont pay for parts before you are shure of the global design.. i guess we are not both millionnaires and hawe to work for our passion. have you tried to find a college or technical shcool that could manufacture some of your parts in a educational program, in France we can do that, if your idea is good in an educationnal way, the school can do it (most of times wery perfectly), the problem is time, often it takes a year to be done as they must learn... search this way you could have good surprises... ( i remember that in a tech school near my home town, the mech section built a gyro for a particular person, it was exposed in the hall and really well done).
by now, i work on a new, coax rotor, i invented an original design, with less rods, less bearings and maintenance, more precise and powerful control (if it works ;)), i am actually working on sizing the parts correctly, you ll see it soon, just wait..
i probably be very busy next week as my holidays end.. but dont worry i dont forget nor give it up !
08-28-2004, 12:05 PM
hello every one, i m an helicopter enthusiast from France and this if my first post here........... I found helpful comments on www.eng-tips.com .......... i began some early drawings you can see at
http://zeeoo.free.fr/helico/............i read some posts here (from Spaced ) about coax rotor design and yaw control problems in autorotation, i m curious about your experience. victor
Considering that the French were the first to master controled flight [along with the Wright brothers], I have utmost admiration for the French imagination. However, it seems here that you might be reinventing the wheel; I mean why not use existing technology? It is going to be greatly expensive to manufacture die castings and machine specs. to redesign a system when existing systems already are proof tested.
The Carter brothers in Utah desgned a system at great cost; but fortunately got a testing contract from the military to complete their research. If you could use existing products it might save you alot of money. Also why do you want a co-axial rotor system? My understanding is that such a system requires a rigid rotor which limits ultimate airspeed do to increased fuselage drag forces inherent in the design. :)
08-28-2004, 12:42 PM
I agree with you Thomas...The best is to simplify and lessen the number of parts...and use as much as possible automobile parts which are cheap compared to aircraft parts; and for that, the synchropter concept is more adapted to homebuilding (i suppose you don't want to make a certified helico...)...let's say, synchropter with only control on the collective of each rotor (climb and roll) and a pusher shrouded propeller giving yaw and pitch authority to a rudder and elevator...what do you think of that? :cool:
08-28-2004, 01:57 PM
hi thomas and andre , thanks for debating..
i carefully eximine your comments as you re both much more experimented in rotor flights than me..respect.
i try to explain my thoughts...
> have you seen some of my drawings? i m curious about your opinion
> overall i have something called passion, a kind of virus hard to eliminate ;)..
> i think : i am not rich, i must design parts i could obtain at a reasonnable cost, use common parts as possible (automotive maybe), affordable materials (i consider to use common foam and epoxy for fuselage)
> when i understand a system, i try to suppress complexity, i mean, i dont think "heavy" or over-engineered, but "shortcut", "tricky".
> the choice of a coax ? efficiency, safety, manoeuvrability, i dont forget Kamov was the very first light coax heli and worked well, most of the UAV are coax there must be a reason.
> i must admit, i dont like the idea of a propeller for a heli, i think gyro is a better concept. a rotor plus a propeller is quite complicated for an aircraft intended to be simple , no? a rudder for yaw ? even in hover? :confused:
> Dave (intermesher) tries to convert me to unicopter, debate is open.. the unicopter project is the one, i like the Dragonfly concept, i just miss a really "how to" in it..
> i do not entend to reinvent the wheel but use the wheel, i would be glad to use existing parts .. but excepted engine, bolts, the others should not fit (blades perhaps, but custom ones so, costy) , i also could by plans, or even a kit machine.
> i dont want to build a certified helico ;)
> the project is in its earlier time, i try to "pack" all the problems, solutions then we will see, perhaps i ll build a gyro ! who knows, i ve been thinking in a gyro 10 years ago, then a helicopter a litte more costy, complicated, but not at all...
> i can (and must) still thinking, yet, it costs me no bucks, if i can, i will build, if not.. will be shure i must give it up then i m shure i will find a way to fly ;) (gyro??)
anyway, glad to hear from you every opinion, it can save my life more than my bucks!
many thanks (you can quote my bad english :D )
"there is no better pilot, only alive ones" AF
08-28-2004, 02:35 PM
Something which could look like this in a simpler form!!!! (tandem seating, shrouded prop, etc...) :) :) don't forget the synchro is the more efficient of all designs, even the coax...Dick Degraw with his homebuilt Syncopter, can lift 1700lb with only 115hp!!!!! :eek: :eek: :eek: :D;
Only the synchro can give you a roll without using a swash-plate!!!! :eek: :D
(and with nothing moving in the blade...) :eek: :D
08-28-2004, 02:40 PM
interesting indeed, a personnal design? a project? who who ?
the propeller is good for high speeds , i just start with a sight-seeing one :D
"there is no "better pilot", only alive ones" AF
08-28-2004, 02:44 PM
That's a project of the University of Maryland, i look for ref, and i'll be back!...
08-28-2004, 02:46 PM
That's the CALVERT!
08-28-2004, 03:08 PM
mmm you have good arguments about roll, .. andré one point.. mm have you interests in cartercopter ? ;)
(didnt you see a "look-like" between my general design and a Kmax? even a slight one?)
the problem is yaw control.. i have not all the understanding yet..
should it work with a semi rigid rotor like mine? i m affraid i have not the optimal rotor layout. in addition, 6 blades intermeshing... mmm.. the composites design must be very optimal...
as i said in other post in a coax you can design and test rotors and blades separately, in a synchro you cant, as the blade design is depending on the angle, the number of blades , i m not shure but it seems to me that you cannot test the parts separately (excepted for inner features) but the whole assembly.
i read about the hummingbird (if it is that one) that there were some problems with yaw under low power and autorot... a matter to reflexion isnt it?
okay..lets see further... (THX for the link !!)
08-28-2004, 03:16 PM
Yaw? not a problem with an independent shrouded prop. giving authority to a rudder and an ellevator: in fact this concept is like a fixe wing airplane... the lifting group produce lift and roll (like the wing of a FW...) and the rudder and elevator (of a fixe wing...) are more efficient (at low speed) with a blowing shrouded prop...but this synchropter can HOVER!!!! CG can be managed as the CG of a fixe wing!!!! one engine for the lifting group and one engine for the shouded prop.; so many redondancies!!!! Autorotation? easy!!!! loss of the engine of the lifting group-> autorotation, gyro gliding!!!
loss of the prop engine-> keep speed to have rudder and elevator efficiency!!!
use elevator to keep rotors helicoptering!!!!
loss of both-> high speed autorotation :D :D :D :D
08-28-2004, 03:29 PM
wow for me it enters a more complex way.. rotors+propeller+rudder+elevetor a lot of parameters to be evaluated and linked.. synchro ok it is a good alternative to coax, but for an ultralight one, i only see 2 rotors and everything must work by them, i think (i dont mean to hurt your opinion :o ) but a dont need hight speed and i feel these amount of solutions like patches on an incomplete one.. :confused:
if i go for a synchro i ll stay as simple as possible : 2 rotors+airframe, light light..
if i can have a lot of examples of coax light aircrafts or UAV, i would like to see some ultralight sunchro fly, i m hungry about that ! i need that !
i fully trust you about the hummingbird features, the K max is a great chopper, an example of perfection to me... but ultralights.. where?
the green light is not yet for synchro (nor coax) but i guess something good will rise from this debate... let s go on !
best regards (et bonjour!)
08-28-2004, 06:24 PM
Well I must say zeeoo if nothing else youve livened up the discussion in a couple of areas. I lived in France for about 3 months back in 96, loved the place, and the ladies.
Anyway back to the dicsussion at hand.
Rotor layouts dont really make that much difference to efficiency, usually what you gain in one area you loose in another. Dave likes the synchrocopter, quadriritor likes tip jets (I think), zeeoo likes coax, graviman likes the intermeshing. It always comes back to which area you are compared to compromise in.
In some of my earlier correspondance with Dave, I had a few questions reguarding the synchrocopter, primarily that of ground clearance and danger to personel. He said that it would be a problem, particularly on the smaller helos. Really to me this is a major draw back. Tail rotors are dangerous enough, without the danger of walking into a main rotor at about head height. On the Kamx this isnt as much of a problem because the majority of people moving around the helo are experienced ground personel, but in a private or club setting this could be leathal. Another area which I think that Dave overlooks is the neccesity of slope landings. While you can do a "toe in" landing in a syncrocopter, you cant land sine on to the slope, which in certain areas of operation is a big problem. This is in now way to disparage Daves designs, just my opinion that these are important areas which need to be adressed. I have had the good fortune to speak with a few Kmax pilots, and they all love the ship for what they do, mainly fires and logging, but I personally dont think that it would make for a good personal ship.
For a long time I have been focussing on a coaxial helo, one of my main problems is that I want to overcome all problems, which means I keep trying to over design everything. If I could accept something that wasnt absolutely perfect I would be alot better off :)
Coax helos have alot of advantages except one, complexity. While I think that you have some good ideas zeeoo, I think you may strike the same wall. My primary interest in the coax was more to do with the high speed flight option. Utilising the ABC concept developed by Sikorsky you can achieve very high speeds without the need for a wing to offload the main rotor. But this comes with peanalties in weight and complexity.
I must say though that I have gone back to the tip jet idea. Desipte its inefficiency, I think it does have some merits particularly in the areas of weight and complexity. The inefficiency really only relates to hovering flight, but most helos spend so little time in the hover that this may not be tha disadvantage which I previously believed it to be.
Ive been pulling out all my old stuff on the gyrodyne concept, because I think that it can be tweaked enough to make it viable. Also it plays to my streghts a little more. My degree is in Space Sciences, and I used to do a fair bit of work with souding rockets, so this may help with the design a little more. One thing I have noticed in a lot of the old tip jet designs, is the use of a very small tip exhaust, utilising a high velocity exhaust to make power. Interestingly the Canard Rotor Wing under development untilises a much larger tip exhaust, moving more air at a lower velocity. Moving more air at slower speed could be an area to improve a tip jets efficiency. Another plus would be the lower velocity producing less noise, but his will be something to see on a prototype rotor.
It is funny though how many of the old designs were dismissed for what ever reason, when the tilt rotor got a run. The XV-3, doesnt seem to have been particularly successful, except for proving the design could work, however it didnt ever reach it intended speed. Infact the XV-1 went faster, but never went into production.
Currently Im looking at doing a small Fairey RotorDyne. Right now it looks like the easiest to build in a shorter period of time, although these things dont always work out.
You are right though zeeoo, were looking at building different things, probably my main goal is speed, with out the cost.
What I would like to be able to offer is something to compete with the STOL fixed wing market. I have spoken with quite a few pilots in this area and most seem to be very positive about it, although it could be different when the time comes to put the money on the table. :cool:
08-29-2004, 12:34 AM
For a gyro, i am for tip-jets; for an helo, i am for the synchro.
The coax is not safer than the synchro (rotor strike); the lower blade of a synchro is very low, and almost the same as the one of a coax if you consider that the heads of a synchro would be at mid-distance of the two rotor-heads of a coax. For a conventional helico, the tail rotor is the danger, too! for an airplane, the prop is a pb too!. For a gyro, blade and prop are a pb, too.
I am not for ultra-light helicos: i want a two tandem seats; but an ultralight synchro, why not? :confused:
08-29-2004, 05:41 AM
add bigger rudder and elevator, use a synchropter rotor... :rolleyes:
08-29-2004, 05:42 AM
Actually the synchro is more dangerous for a blade strike.
There are 2 Kmaxes that I know of which have crashed killing the pilot due to blade desynchonisation. Also the Kellet XR8? had 3 bladed rotors in the synchrocopter layout, which under certain situations would make contact, not catastrophically, but would you take the chance?
While blades strikes can occur in a coax, they are no more likely than a tail strike in a conventional. Unfortunately the records on this are quite hard to comeby, unless you can read Russian :)
The problem with the synchro isnt so much the head height, but the tip height due to the angle of the tip path plane.
08-29-2004, 08:22 AM
hi christian and andré, very very hot topic.. a pleasure, brains work, go on..
christian it apprears that you are an expert , specially for french ladies :D :D but not only...
wow as i see you go for a high-speed VTOL as i understand it... a question, why a VTOL, in your country you might have lots of space, so.... why not a STOL ? the Kamov KA 22 reached some records :
"Eight world records for the altitude reached with the payload and for the speed were set on this rotorcraft". the osprey before the osprey.
well, let me "simplify" my wish : an ultralight, tricky, under engineered, or under complicated, light rotorcraft... the picture you send, andre, are interesting, i would compare my wish to hiller, the bensen looks "patched" (back propeller).
like you christian, i try to have a satisfying solution, if not, i would consider my work as null, thats a problem for "perfectionnists"... while some get satisfied with an average compromise, we cant tolerate that and think a system sould be perfect... a long debate.. :rolleyes:
my concern is also ground clearance.. i agree, synchro or intermeshing, particularly small ones are dangerous . the clearance shoud be a man standing hands up at least (2m60 approx) lets say 3 meters ... as i think my aircraft for cheaper crop spray with a payload of approx 50 kg ( a sack of chemicals or a dose of liquid) i definitely drop the intermeshing.. too dangerous for ground crew, engine nor rotor are stopped during operations.
i tried to keep a clearance of 2 meters, as you see my design is quite high and the skids are too, if i didnt consider the problem, the rotor would be in a lower position, and the skids lower too.
you spoke about blade contact : in a coax you can choose a sufficient space between rotors, increases drag, ok. in an tntermeshing the blades still close, like you i cant be shure they wont touch. if in a coax, gear failure goes to autorot, in an intermeshing, gear failure could go more to crash... by the way in a coax, you can limit the rise of a blade mechanically (with pitch loss) . i posted a question on ENGtips about it , no answer, so, i still thinking.
about ram tip jet, christian, my rotor and blade where initially designed in this way, as you can see there is a kind of path possible for air from rotor-mast (tube) to the blade by the pitch axis .. a changed it a little for a coax purpose. but the fuselage was designed for that ..
the ram tip jet sounds the best solution, i love the idea, the main problem for me was the cost .. i tried to find on the net all kind of commercial compressors, blowers etc but none could fit.. i thought in using a piston engine coupled to a large car turbocharger > not enough to produce the needed pressure and air volume.. the only way is a turbine plus a compressor... costy indeed... too much for a homebuilt ultralight.
look at that :
perhaps some good automotive eng could imagine a good affordable blower this way ? .
i agree old jets could be improved by using a large lower speed jet > higher pressure exhaust, still have no precise answers about it. i also think the problem of such a tip blade is that it works near vortex air so, that air spinning a little generates losses in efficiency, perhaps the reaction effect could be improved, placing the jets elsewhere , over the blade ?, far from blade tip, behind a kind of fence ? fit it to the trailing edge perhaps, not too much because of speed difference...
just an idea : birds wings use the tip vortex to generate more lift did you know? some think in exploit that in aircrafts..dont know much about that..
regards to you all
08-29-2004, 08:44 AM
JUST PASSING INFO :
New homebuilt helicopter magazine
I just wanted to pass this along to anyone that might be interested.
Ok, here's how to read/download the trial issue and to also subscribe for the coming year of 6 issues, beginning with the first issue in November. Go to www.vkss.com/eh_index.htm You'll be able to download/read the trial issue and Subscribe via PayPal. If you'd rather checks sent to our address work just as well.
Please pass this along to all/any you think would be interested.
Thanks as usual for all your support and encouragement. We'll see you at El Mirage.
Stuart & Kathryn Fields
P. O. Box 1585 / 8075 Seibenthal
Inyokern, CA 93527
(760) 377-4478 ph
(760) 408-9747 publication cell
(760) 608-9747 tech cell
Subaru powered Dominator
08-29-2004, 08:50 AM
Hi Christian, I checked the NTSB reports back to 1990 and I couldn't find any Kaman K-1200 Helicopters that had crashed because of "blade desynchonisation." I beleive that there are more flying here than in other countries and it seems odd that such a design flaw hasn't shown up in this country. When I watch a Kaman fly it looks like the blades should hit and I know early on they had a little trouble, but I thought it had been resolved long before the K-1200 was introduced. Thank You, Vance
08-29-2004, 10:04 AM
where can you have a sprag clutch after the gears? for the synchrocopter, is possible without losing power!!!! :D redondancies are possible!!!! :p
And for height of the helico: :cool:
08-29-2004, 10:26 AM
I have read dissynchronisation of the blades only in the early days of the concept; and what i read is that even if the synch-gear broke, the blade turned almost synchro in straight autorotation; only sometimes, the blades collided gently in their central part (hub), the pilot survived... this hub part can be design for such purpose, even if it is unlikely!!! and the synchro-gear can be designed to be unloaded during normal flight as the drive shaft of the tilt-rotor V22 going from an engine to the other...
There were a contact of a blade with the head of the other rotor, this happened when the testpilot did a very hard roll with slow turning blades...I don't know if he crashed but now we can design for this does not happen!
08-29-2004, 10:50 AM
sprag clutches or centrifugal could be possible with complications, i agree that it is easier in a synchro.
be shure i m very respectfull for Dave's work and told him yet many times ... i m not against dave's work, and read a few pages, believe me, i agree thats actually the best, or the only project of this kind...
andre you must also agree that there are many ways for designing a working helico, from classical ones (proven) to very innovative ones (risky) ... if there would be ONLY one way, the world would be sad sad and freedomless.... one size fits all , not exiting (tribute to zappa).
i ll be clear : my fuselage was designed to be : coax, synchro or even tip jet, my idea is designing parts in order to be re used even if the earlier choices are wrong..
i also think this way for the rotor-head, if a coax is really risky, can it be re used in a synchro, a classical , a jet tip one or even a gyro ?? i try to not loose my work (money) and think every part keeping it in mind.
you must also know that i worked (to help) for the father of a ex-GF whitch owned a helico-company and essentially worked for crop spaying, i helped for 2 seasons, even with bell 47, its dangerous, i cant even imagine with a small synchro, really not... i speak in this very particular way to use an ultralight for crop spraying in france only.
this person was thinking about the replacement of the bells by ultralights or simply stol microlights. modern choppers would be too expensive, r22 not fitting, ultralights like dragonfly, ch7 or others not certified yet, exec maybe but they are all too recreationnal, not "heavyduty" oriented. in fact he tested a microlight airplane the Joker J-300 , seemed it fitted more of the requirements, excepted for take off and landing, required a minimal terrain surface for that, most of the fields, here, do not have.
i dont intend to build a certified helico at the first shot, i must admit i am very very very humble on my skills, i just think that if it works good, it could be a good seed for future developments...
ps : your picture is a tiger, what link with the height of helico?
08-29-2004, 11:22 AM
ps : the helico is a KAZAN russian helicopter. Have you seen the total height of this helico? suitable for synchro... ;)
i don't do philosophy, i want an helico to fly safely at 100 mph, with redondancies... :).
I don't like swash-plate; i don't like the cyclic feathering of the blades, i don't like to deal with torques, i don't like fatigue lifes, etc... :rolleyes:
08-29-2004, 12:01 PM
oops, i m confused, in quick view i saw a Tigre...
andre, yes, yes, height is not a problem with large helicos, i mean 2-4 seat ones, commercial aircrafts etc...
it s more problematic in very small ones, even in K max the blade tips are not out of reach...
well all the aircrafts have to deal with torque and fatigue problems.. not more or less but differently or not at the same location ;) the basic equation being mass + lift + thrust = speed vector ;) what we do well is generate the mass lol the problem is generate the others..
to be continued....
08-30-2004, 01:11 AM
Man being 10hrs out of whack with everyone else sure gives me alot of catching up to do!!!!!!
First up Appologies, I posted that last night right before I went to bed, I didnt mean to sound that agressive with reguards to the KMAX, because I actually like it.
Vance I havent checked the NSTB, however a friend of mine was killed earlier this year in a KMAX, when the blades took each other off. He dropped from 150ft and didnt survive. I believe that Kaman is still working with the Canadian Transport Saftey Beuro to find the cause. And I owe all an appology, the second one was another friend of mine who was killed in may in a Kmax, however he clipped a tree and rolled down an embankment. This one was also in Canada, and the final report isnt out yet. My personal feeling is that it was a similar event to the CH-47 in Korea which clipped the top of a bridge and the rotors desynched causing the crash. While I agree that in a single rotor the same result could have happened, I also know of incedents where a helo clipped an object, and could put down safely.
One of my problems with the synchro copter layout is the absolute dependance on the timing of the rotors.
All of this said, I hold Dave in the highest reguard, I have spoken with im often, and his lateral thinking on many issues alway impresses me. And if someone offered me a fly of a KMAX I would take it in a second. The dangers of rotorcraft are relative, every layout has its drawbacks.
Enough sad stuff, back to the fun stuff.
Why VTOL over STOL, because VTOL is fun!!!!! Man I watch the fixed wing guys trolling along on the ground, taxiing to their runway, flying fixed circuits, straight in approaches, and i feel sorry for them. Ofcoarse they get the last laugh when it comes time for the bill :D
I think to Im a little caught up in the dream of the flying car. Sydney has terrible traffic congestion (not as bad as Paris yet :) ), yet an hour to 2 hours drive away and theres heaps of land. By giving people the ability to live further from their work you can decentralise the population, ruducing the stress placed on the environment, and the people.
While I dont believe that my design can do all this, an increase in the number of VTOL aircraft can create demand for facilities, ( we dont even have a heliport in Sydney anymore).
In Sydney alot of our infrastructure has been privitased (thanx John) which is placing restricitons on resouces, particulaly with devlopers salavating at the though of putting a couple of hunderd units on the airport site. Add the citizens who move next to an airport, then bitch about the noise, and land for runways is getting very scarse.
And lastly I guess because its a fairly under developed market. To compete with the multitude of fixed wing companies doesnt seem like much fun.
I have been doning some market research lately, and what I have found is that most peolpe who buy STOL aircraft would switch to VTOL if a couple of conditions could be met. 1, higher cruising speed for cross country flights. 2, reasonable cost. Interestingly most are prepared to pay more for the VTOL option, but not at massively reduced performance. I figure if I can get around the 160mph cruise, Ill be looking good. This is why I have to look at alternative layouts, a traditional helo just requires to much power to get that speed.
A freind of mine put it as "Id pay lancair prices for RV performance in a VTOL"
Andre, please dont get me wrong mate, but have you seen the KAMX in person? It would have to be near 4m to the head, and you can still reach the blades when 90deg to the fuse. Not that theres a problem with this if you are prepared to accept the danger to ground personel as part of your design.
Im going to start a new thread for tip jet discussion, as this seems to have drifted from the topic description.
A good debate is hard to beat :D
08-30-2004, 12:41 PM
There is alot of information here I will have to go back and read more carefully. I do believe that great designs in aviation start small, on paper, in a workshop and finally in production.
I designed an automobile with a school chum back in high school. It was a very simple design made specifically for sand dunes around Lake Michigan. The one factor that saved us a great deal of frustration was that we built a plastic model of the vehicle before we ever started the project.
Plastic is easily molded and durable enough to withstand proportionate stressers. Built to scale, it should be your first project that will be used as reference in building the real thing. Many factors look good on paper, but once you see the 3D model you will recognized the need for this step in building your dream. Plastic was good for a car design since much of a car is molded. Balsa Wood might be more effective in aircraft modeling since most of an airplane is linear in its raw materials.
08-30-2004, 01:08 PM
hi thomas, i think you re right about projects.... pounds of sketched sheets dont cost a lot.. the following costs LOTS of bucks.. :(
your experience is very interesting ... why did you gave up ? what where the problems you could see ?
about plastic for a scaled helico.. an RC model if i understand .. my sister's Bfriend tries and tries to push me to do one !
i am not shure we can test all features in a RC helico...
> the small scale allow tolerances that should be lethal in full scale, i ve seen such RC "air-rats" flying..
> the fatigue tests wont give the same results, specially in composites, they are not linear....
i try to imagine "steps" in the design, testing one before going further or partitionning the design in independent blocks..
in my case i can test the blade-root then the rotorhead then a blade then the bladed rotor... i can test each one independently, excepted for the final mount that will give the real performances.. but i know my blade will hold out on the blade-root that will hold out on the rotor-head, controls are another part of work, finally the whole rotor may not work good or have bad performances, too much vibrations.. thats because the initial design was bad... only real test will tell, may be its the choice of that kind of metal, that kind of elastomeric, i try to make each parameter localized on the parts.
actually it is what i learned.. but i m convinced i will learn more again and again.. specially from experiments like yours..thanks indeed.
please post others
08-30-2004, 02:53 PM
............... > the small scale allow tolerances that should be lethal in full scale, i ve seen such RC "air-rats" flying..
> the fatigue tests wont give the same results, specially in composites, they are not linear....
i try to imagine "steps" in the design, testing one before going further or partitionning the design in independent blocks..
in my case i can test the blade-root then the rotorhead then a blade then the bladed rotor... i can test each one independently, excepted for the final mount that will give the real performances.. but i know my blade will hold out on the blade-root that will hold out on the rotor-head, controls are another part of work, finally the whole rotor may not work good or have bad performances, too much vibrations.. thats because the initial design was bad... only real test will tell, may be its the choice of that kind of metal, that kind of elastomeric, i try to make each parameter localized on the parts........
Yes, you must bench test everything when starting from scratch; not only individual components but also composites at every stage of development. The most difficult, I think, would be estimating the G force factors that convensional regulations rate at six times the normal loading.
Engineering costs run high when multiple test must be run on each component for:
Material tensil strengths, elastic strain and corrosion factors are always a worry.
I and a friend built a "dune buggy" as a summer project after graduating high school. We bought an old sedan from a junk yard and stripped it down to the frame, drive train and engine. The model provided us with good approxination of where we would have to make torch cuts in the frame, where to mount the roll bars, place fuel cells, fashion components necessary to make it street legal, engine modifications etc. The entire project cost less than $50 and we had a babe magnet all summer long.
By modeling we planned each step procuring material and equipment as it was needed on a one time basis: borrowed a acetylene torch for a one time use making preplanned cuts, removed scrap waste in one trip, did all our welding at one time, procured materials (seats, sheet metal, mirrors, engine braces/mounts, iron beams, counter weights, etc. at one time rather than at random.
We got an expert opinion (race care designer) to evaluate the modified frame. We both worked at an auto dealership at the time and had access to old salts in the industry. They were delighted to see us revel in issues they valued.
When we were complete we tested it on location and found the ass end was too light to go through the sand. We anticipated a weight problem from the beginning and added crane boom counter weights to the rear axles but it was not enough. We cut too much off the back end to support any more weights so we had to modify a short bed behind the seat to stack more weight. This actually added utility we had not planned. It gave us carrying space for camping gear, beer keg and an extra passenger or two.
It was the best summer I ever had. We both went into the military at the end of the summer. We donated the buggy to the high school auto shop. I went to army flight school and my friend went to submarines in the Navy; I never saw my old friend, Jeff, again but I will never forget him.
You can not anticipate everything, but without a workable model it is difficult to anticipate anything.
08-30-2004, 11:25 PM
Thats the beauty of CAD.
I first started with CAD, because Im a pretty poor artist. However with the power of these programs now, you can see if everything fits, test tolerances, assign weights, even find the CoG.
One of the problems with scale modeling is the scale isnt linear. It takes alot of work to extrapolate performance from a model. Anything below about 1:3, is virtually useless for anything more than a general estimation of handling.
However Im a firm beleiver in the 5P s . Prior Planning Prevents Piss Poor Performance
08-31-2004, 06:31 AM
Heli, I count 6 Ps...
08-31-2004, 08:21 AM
hi christian,brian,andre, thomas and every one here
thomas thanks for your experience.... always the same : cascading "russian dolls" problems...
i agree that CAD allows today a great mass of previsions but nothing better than real..
about scaled models, i agree with christian, hard to interpolate, perhaps harder than to test in real size (talking about homebuilts).
brian, i ve seen a 6X factor, what is this factor, safety factor? it sounds high.. i heard more about 1.5 for aero construction, 2 for cars and... 10 or 15 for building.. could you tell more?
christian and andre check that : www.rotrex.eu.com/ models c15 and sp30
woooo ! seems to be the best manufacturer for superchargers .. uses in high end cars.
98 % efficiency , self oil circuit, no need a pump, just to link to a shaft or a belt, isnt it marvelous.. dont know about pricing but i esimate it to about 2500 or 3000 $ (supercharger kits for cars, with complete hosery etc are about 6500$).. if some one knows..
to be continued for tip-jet...
08-31-2004, 08:31 AM
VORTRON has bigger one!...
08-31-2004, 08:55 AM
i didnt see in Vortron just the "compressor" component, have you a link ?
i just saw a packed system with electrical motor...
i you look at ROTREX you ll see they have really big ones..
the lifetime of their superchargers are about 6000 hrs !!
the fact that they are mounted in ferrari, lotus, bmw and others (search in google)
make me have a good opinion about them.
it is not just for contradiction, andre, ;) tell me more arguments (not i have a bigger one :D) if tomorrow id have to by one, whitch one can fit? whitch one can be fitted with the less cost (ROTREX give a detailed "howto")...
i trust your opinion, just seems to me that there will be a great mount of work to fit Vortron part, if i can by it seperately, so, reliability is problematic, with a proven all-in-one i d be less stressed...
hope you understand.... just go on andre, 2 brains in contradiction are even better than one alone...
08-31-2004, 09:03 AM
That's only a nose-sight! ROTREX goes to 550hp engines, VORTRON which is a division of VORTEX can drive 1200hp engines!!!! but i must have a closer look!!!
08-31-2004, 09:04 AM
i finally found a pricelist :
Price list of superchargers and accessories
With integrated oil pump
Including oil container
100 – 250
1,0 – 2,0 l.
150 – 300
1,6 – 2,5 l.
200 – 350
2,0 – 3,0 l.
250 - 400
2,5 – 4,5 l.
300 - 450
2,8 – 5,0 l.
it looks cheaper than the 5500 $ you told me
08-31-2004, 09:10 AM
allright 1200 hp engine ..we talk about trucks at least.. to be considered for a light or med helico ...
would like to know the size, weight etc..
a question for your skills :
dont you think engine ignition will be problematic, i mean, to rotate the compressor from zero to 10 000 RPM or more should take quite a minute, even more, dont you think theres a problem with recoil starters ? with the torque transmitted ? you must have a really GOOD an full battery,
every opinion wellcome
08-31-2004, 10:54 PM
Hey Guys, didnt we start a tip jet topic for this? :)
Victor, those seem pretty good. One reason I was leaning toward the turbo is because to turn it off during flight all you need is a diverter for the exhaust, no clutching, however you can always use the air for the engine.
I must say though those look pretty good.
Im hoping to get a chance tonight to work out how much air I will need, work is getting a bit mental lately, hard to find the time to do some calcs.
Andre, yours seem good to, but in hte link that you posted they were driven by an electric motor at pretty high RPM, may be a problem to gear it up that high, reliability wise.
09-01-2004, 02:18 AM
All centrifugal blowers are geared up to sometimes 150 000rpm!!! rotrex, vorton, vortex, paxton and other have gears inside etc...
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