Rotor design in progress ...

Victor Duarte

troublemaker
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hello...work in progress for my design...

this rotor is ready for tip jet, and even can be used in a classical helico, a coax and why not a gyro..

i have the mast , the mast holders and the controls to do... maybe next week..

all opinions, even negative wellcome

thank you
 

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It's pretty, but it looks rigid in blade pitch. How are pitch changes accomplished? From what I could make out in the graphics, the blade yokes are fixed vertically to a drag hinge of sorts (the items in the image that the blade yoke ends mount to). Does this part rotate on the blade's lingitudinal (pitch) axis as well?
 
articulation detail

articulation detail

thanks for your interest Brian.

heres the details :
the part rotates, as you see i use a ball in a housing as articulation.
and thats the point i must improve. perhaps i sould make it one element (ball+holder) actually i plan to use a bearing ball but it may be hard to drill and may also break as glass, btw i plan to add a bushing between the ball and the metal, to make it renewable. you may ask what happens if the blade goes back : the axis in the blade root will act as a retainer.

the pitch allows almost +/-18 degrees horiz (with drag damper) and more vertically due to the flex plates.. actually the mount misses the drag damper that will be made of elastomer, but i still undecided about the shape etc..

thank you
 

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Victor, sorry, I don't get it. What are the goals? What are the avantages over a more convential rotor head? It looks nice. Thank you Vance

Edit; Your new post answers some of the question. I was wondering how you assemble the balls and how you transfer the control imput without confusing the linkage. Thank you, Vance
 
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vance, thanks for your interest.

well the advantages are a little simplification and, i think, the most parts can be tooled in every good toolshop.

other advantages :
- its ready for use in a tip jet (the ducts are made)
- you can adjust the flapping stiffness just by changing the shape of the plates
- the rubber core you can see acts also like a damper, that can avoid eigenmodes.
- the blade root is much more reliable if made of one piece, the root works in traction, the blades attachement to the horn are critical (there was a thread here about vortech blades on a mini 500).
- there is no bearing

thanks vance and more questions wellcome, it makes me think straight

edit : the imput is not mounted yet, i must drax the swashplate before, but they ill fixed on the holder, by under, with a delta3 angle

the balls have a housing, the centrifugal force may be sufficient, but they can be mounted "hot" on a cooled holder with a veri short tolerance (may be hazardous), or simply bounded, inside tha housing you see i plan ti fill it with graphite grease
 
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Victor, do you know how to calculate the centripital force on you bearings? Based on what I have seen they may be a little weak. Most helicopter design books have the formulas.

I also am not understanding you blade dampening scheme. There are some very complex harmonics that can be upset by something as simple as landing gear harmonics being lined up in an unfortunate way. If the blades get very far out of phase it can literaly tear your helicopter apart in seconds.

Don't get discouraged, just get confused on a higher level. I hope your translation works with that. Thank You, Vance
 
be shure your comments are useful

i calculated the centrifugal force with a blade weight of 4 kg and a tip speed of 900 kmh, i found a result about 8 tons, i will take 10-12 tons as data.

yes there are a lot of harmonics, and i have no skills to study them, so i try to damp where i can, i actually study elastomeric dampers and alot have a very low frequency.. should be ok for lag damping.. for the blades, i plan to place the weights in an odd place (not the middle for example) to "cut" the inner resonnance freq

about ground resonance, the ideal should be rigid skids or fully dampened wheels,
i actually focus on rotor, i will show the airframe soon,

solidworks allows me to perform simulations, the blade should be ok, the blade holder also (the rod is 2 cm diameter), my concern is about the cissors effect on the nuts..

i agree with you the ball (3 cm diam) may be weak, and honestly i miss some data on this point.

the plates you see are titanium ( i checked the prices, i can have a sheet of 3 mm thickness for about 40 $) between them is a core of elastomer (the air ducts made of reinforced air hoses are drowned in it)

dont worry, i dont discourage, i m sketching paper foor about 10 years, stopped, continued.. now i ll go until i succeed ot loose ;)

just go on, throw the stones ;) i ll try to catch them

thanks
 
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Victor, I am not throwing stones. For me that would mean being negitive about your work. I'm trying to share information and learn.

I am off to a trade show for my software company so I won't be back till late Sunday night. Thank You, Vance
 
vance, throwing stones was not intended negatively ;) i was joking, i appreciate every comment or critic, it s useful, have a good show, i will be pleased to read more from you.
thanks
 
Im sorry I I have missed something here but a few random thoughts.
- You have a combination flexture hinged system. Seems overly complex to do both. I would suggest going for one or the other to ease the design process. If you go fully articulated the engineering will be easier, but require more maintenance. Go for the ridgid/flextures more complex design, but reduced maintenance.
- you could simplify your torsion retainer by going to strips of titianium/whatever, instead of a machined plate. This would simplify tooling and reduce costs. Machining titiamium is pretty tough, and you could by it in strips to size, again making it simpler.
I find the way you have done the articulation interesting though, Did that one come to you in a flash of inspiration?
If you went for a spherical bearing, but mounted the other way, you could utilise a strap pack to take the centrifugal loads, reducing size of the bearing required, and reducing the part count of the head. This would also reduce the weight of the head.
Not being critical, just a few random thoughts.
 
hi christian

just some details, the plates you see are titanium, there are 2, and between them a molded elastomeric sheet (3 cm thick)
perhaps i misunderstand your question, sorry

"I find the way you have done the articulation interesting though, Did that one come to you in a flash of inspiration?"

yes, lol, no, seriously, this was my main concern and i changed more than 100 time my idea, tried many ways, i dreamed of an elastomeric laminated bearing.. but i called PAULSTRA and.. no way, they only provide this bearings for helicopter manufacturers and are made specially for them, so, finally this solution appeared to me as the best. the initial idea was to have a single point of contact, reducing efforts needed on imputs.

i see what you mean by inverting the bearing.. just like the XV1, well..its just because i think centrifugal forces on such a ball will tend to make it stick, because of the degrees of freedom needed, the contact sirface may be reduced to a cone-like, needing a bigger effort on controls.. btw, the hub would need to be machined in two or more parts, here the hub is one part.

the xv1 doesnt have a big lag damping because its specially designed fo tip jet, i plan to have lag damping to try to make it multi-purpose.
lets say this rotor is a mix of xv1, bell 412, ecureuil and dick degraw

your thoughts are wellcome, helps me to improve it, i dont keep my fork just for me
cheers
 
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Hi Victor,

Near the top of web page OTHER: Mechanical - Bearing - Elastomeric - General are three pictures of rotor hubs, which might be of interest. The pictures can be exploded. Personally, I would be a little concerned about the ability for the homebuilder to be able to successfully develop this style rotorhub for safe flight.

Just a thought for consideration.

You might want to consider the Rotor Concept - Offset Teetering Rotor . This rotor will be simpler to build, and more importantly, it has undersling.

Two thirds of the way down the web page are two links to the Tri-Teetering Hub: (3-blades per rotor). The offset distance for a craft with a single main rotor will be shorter then that which is shown in the intermeshing mockup photos. In addition, there may be no need to implement the provisions for lead-lag since the undersling significantly reduces the main cause of lead-lag.

Dave J
 
thank you for your recommendations, i have to dig deeper your work whitch is of great interest.
my question would be : how dou you manage a tip jet with offset teetering ?
i saw in your site a very interesting article about a 5 bladed tip jet rotor, was it just and idea or did you think in the possibility of building it?

than you dave , and very pleased to read you
 
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Victor,

The five-blade tip jet web page is just the recording of some thoughts on a wild idea. There is no thought of building it.

I do not favor the tip jet, for reasons such as excessive noise, large centripetal forces etc. I'm not saying that there is no future for this idea, it's just that different people have different perspectives.

"how do you manage a tip jet with offset teetering?"

I don't. :) Just joking.

Would you elaborate on what your concern is? The offset teetering rotor is not significantly different from other rotor arraignments.

Dave J
 
dave, i like your wide-thinking, your page about the starfire helped me to confirm that a progressive/non linear twis is efficient.

i must improve my understanding of offset teetering, indeed it picks my curiousity.

my concern is more about a rotor that could be prerotated by tip jets, even powered by tip jets, or more classically, just powered, or at least, autorotate... i like the idea of interchangeability.
i just tried to think it in a way some features like flapping stiffness could be changed just by changing a few parts, (the flex plates )

i know, you may think i begin by building the roof instead of the floor.
the airframe is ready to draw, and again i tried to keep it simple.. and modular, the mast being mounted on an independent pylon, mounted on the airframe with silent blocks, the engine is also independant.

as you can see in the pic (not CAD but 3D) i only use flat and rounded panels(roving/foam/roving the honeycomb for the poor ;)) and a simple 4130 frame drowned in the panels assembly, the engine will be mounted on silent blocks just behind the mast pylon.

i also tried to keep in mind the possibility of using the blade in a 2 bladed rotor.

could also fit for a synchro ;)

thank you dave
 

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Victor,

Some thoughts;

Your fuselage appears to indicate a craft that is intended for high forward speeds; therefore,

~ large twist will be a no-no.

~ 2-blades on a rotor with high controllability (offset flapping hinge or hub spring) will result in a 2/rev vibration during forward flight. Even a 2-blade / 2-rotor coaxial will have this vibration. Heck, if you get up to around 220 knots even the 3-blade rotors will result in 3/rev vibration. Go to 4-blade rotor, like the ABC should have, and your problem is theoretically solved. :eek:

Dave J.

PS. For the fun of it, a novel means of propulsion has just been added to the bottom of the previously mentioned web page five-blade tip jet web page


Thought for the day (or alternatively; for the hell of it):
All the world's animals, on the land, in the water and in the air, are latterly symmetrical.
All the world's vehicles, on the land, in the water and in the air are latterly symmetrical.
The exception being the single rotor helicopter. Perhaps Igor was a little too eager to get something off the ground. :D :D
 
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Rotor Rooter said:
Victor,
Your fuselage appears to indicate a craft that is intended for high forward speeds;

oh i will be contented with a cool 120 kmh, if there is less drag, it s better

Rotor Rooter said:
~ large twist will be a no-no.
i must say i dontget it, what is the expression no-no ?

Rotor Rooter said:
~ 2-blades on a rotor with high controllability (offset flapping hinge or hub spring) will result in a 2/rev vibration during forward flight. Even a 2-blade / 2-rotor coaxial will have this vibration. Heck, if you get up to around 220 knots even the 3-blade rotors will result in 3/rev vibration. Go to 4-blade rotor, like the ABC should have, and your problem is theoretically solved. :eek:

thats why i was for 3 blades, at least, you gonna laugh but its a matter of cost, thinking 1 blade more is 1/3 cost more, but yes 4 blades could be better in the way they can be lighter, thinner..

i forgot to mention that in my design, i intend to make the blade removable by only removing one axle (a quick bolt? dont know), the pitch control being on the articulation, for those with place problems

i see what you mean by symetrical ... synchro forever ;)

i also found a high end mean to propulsion, called "alternative bi-neuronal pitch" :D :D
 

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Allright!
well i must say i v choosen a 10 deg twist olny a the root, coming quickly to 5 and 0 at the end, i must admit i hav no method to determine these numbers, but just an average of the general common twist angles, the common sens whould force me to keep a symetrical airfoil, but i considered the vr7 like you suggested me, my concern about that is, due to the coG being different of the center of thrust, will this difference be very noticeable or can it be bearable in a small scale rotor ... i m shure you have somthing about this

i looked your 3 bladed teetering rotor, couldnt see clearly all the components, just because im used to 3d views, but each time i read your site, i find more to dig, i must clearly check all your formulas, and classify them by theme..

thank you dave,

ps : i forgot to join this pic, yes the blades are a little long
 

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Dave or Victor, do either of you have the dimensions for the VR 7?
Ive looked everywhere and havent been able to find the station co-ordinates.
Victor, you could look at elimianting the Lead/Lag hinge like the XV1 did by having the blade take up those moments.
Whlie the blades and hub woulf be a little heavier you would get around having to have lead lag dampers.
I concur with dave re the elastomeric bearings. I think that they could give you trouble to design correctly.
 
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