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Thread: Homemade rotor

  1. #1
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    Homemade rotor

    Have any of u made a homemade main rotor out of aluminum?
    If so could you tell me how to do it.
    Also has anyone ever heard of a wooden main rotor. I was curious if a main rotor could be carved up the same way an airplane prop.

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    rotorblade design isnt something to be taken lightly my friend.

    metal blades normally consist of a front spar (shaped kinda like a D) a bunch of honeycomb, and sometimes a rear spar. Alternativly, they can be built kinda like an airplane wing, using "pockets" and whatnot. There are also aircraft that use Nitrogen filled spars (Sikorsky do it (i know for certain the S-61 does, and probably others) and i've read that some soviet designs do it too).
    Over the outside of the spar and honeycomb is a layer of aluminium, usually with a nickel or stainless leading edge plate (picked for their erosion and corrosion properties) and up around the grips there are a big stack of dubblers, and a grip plate setup of some sort.

    Wooden blades do exist, Sikorskys earlier designs (im talking VS300 era) used wooden blades due to the fact that they are easy to manufacture (same technique as a prop) and i have heard that when Kaman was developing the K-Max they reverted to using wooden blades due to problems getting the track and balance sorted with other blades.

    Composite blades im not 100% sure about, as i have only very limited experience with.

    right, now im not sure how much you know, so if im telling you to suck eggs please tell me, but in forward flight there are a battery of oddball forces to contend with (Coriollis effect, Hookes Joint effect, dissymettry of lift, retreating blade stall to name a few) and i have seen video of a Huey or Huey Cobra blade (was old Nasa footage, didnt explain what aircraft type was used) with a pencil camera attached to the leading edge of the blade. well, they took that sucker up and put it through its paces and the footage in slow motion was quite disturbing... the blade tips bend up and then back down almost perpendicular to the plane of rotation, and theres a whole stack of waveform motion there as well thus the blades themselves are subjected to tremendous amounts of fatigue causing stress.

    if you arent in the position to analyse such forces and stress paths etc yourself then please, consult an Engineer like Orion (on this site) or at the least another Technician (im always here, and there are others on this site) we may be able to point you in the right direction on your design.

    Personally, rotorblade design is slightly beyond the scope of my aircraft designs, all of which use established model rotor blades (R-22 etc for the smaller designs, and Huey / 214 / S-61 blades for the larger ones)
    even a small mistake or miscalculation in that area WILL more than likely end in tears.

    sorry about the novel, i hope it helps.

    Leighton.

  3. #3
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    Thank you very much for your reply it was very informative.
    Would these forces that happen in forward flight be very substansial if all that the helicopter was to fly was around 10mph. I Dont know too much about helicopter flight but im trying to learn( i want to be an aerospace engineer) The type of aircraft im trying to build is called a propcopter. Have you heard of it? I believe i will only need to get the rotor spinning at around 400 or so rpm(im not sure of what lift off rpm is on most helicopters) so will the aerodynamic forces play that large of role. Even if you feel you are insulting my intelligence please post your thoughts as i am very new to all of this.

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    http://web.northstate.net/~emdeedee/page1propcopter.htm

    holy crap! i had not heard of a propcopter before, so i used the allknowing Google.com and the link above was the first site on the list. I must say, that looks incredably cool.

    Rotor RPM is dependent on the size of the blades, spin them too fast and the tips stall, spin them too slow and you wont fly. UH-1's rotors spin at 324rpm, something smaller like a Hughes 500 spins at 490Rpm (dont quote me on that one, its been a while since i worked on a 500)
    If you have plans already stick to them, (the site i quoted above sells plans, that machine looks very nice too) if you are building your own machine send me some dimensions and i'll try and calculate lift etc for you.

    okay so, one issue at a time. Retreating blade stall... At 10mph? No. its not going to be a problem. Sitting in a hover your blade tips are doing the same speed relative to the airflow, ie both blade tips are doing 100mph (thats a nice round figure to use for an example) but when your aircraft has a 100mph forward speed, the advancing blade is now doing 200mph, and the retreating blade is effectively moving a 0mph. see how that works? the result is that the rotor disk is only producing lift on one side, so it wants to fall over.

    which brings us right on into the next problem, dissymetry of lift. again, in a hover, all forces are equal and everyones having a good time (except for the maintainer in the left seat trying to hover the damn thing. have you ever tried to hover a helicopter?) but when you start moving forward you run into this whole relative airspeed thing again and one side of the disk wants to produce more lift. so, we get around this by putting in a flapping hinge.

    that produces yet another problem... the coriollis effect kicks in.
    that is when the advancing blade tries to accelerate because its flapping upwards, bringing its CofG closer to the axis of rotation. the retreating blade is flapping down, so its CofG is moving further away from the axis of rotation and it wants to slow down. If you ignore this it will cause a geometric imbalance of the rotor system (which means more vibes for you). solution? put in a lead/lag hinge.

    now you've got yourself a fully articulated rotor system. and heres the next issue to deal with... Hookes joint effect. (only applies in a rotor system with more than two blades)
    looking down on the aircraft from above, in a hover, all the blades in the rotor system are an equal distance apart, but in forward flight the tip plane path etc all change, so the rotors trie to move about laterally to organise themselves equally about the centre again.

    got all that?

    short answer, i wouldnt think you have to worry too much about these issues at 10mph. however, i do still stress that you dont skimp on research before you build a rotor. It will probably be the among the first things to kill you.

    Just as a matter of point, a huges 300 rotor system has approx 40 TONS (this is just something i have heard, not to be taken as gospel) of centrifugal pull on each blade. thats somewhere in the vicinity of 90,000lbs sportsfans. now, the hughes 300 is a very small helicopter in my books. if there is a linear relationship in that centrifugal pull issue, then trie to imagine the forces on the rotor system on a S-64 skycrane, or the Mil Mi-26 Halo. now theres something to fry the noodle.



    stay tuned for the next exciting episode when we cover such possible issues as:-
    -control systems (swashplates etc)
    -CofG issues
    -track and balaning
    -the complexities of trying to fly an aircraft and eat a pie at the same time.

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    i havent ordered the plans yet, but i plan on doin so in the next week or two. The propcopter on that website is still a prototype. It doesnt actually have enough power to lift a pilot. The designer told me he can get it to hover and manuever without a pilot in the seat. It only has two 8hp engines on it so it is a little underpowered. Once we figure out all of our rotor stuff we are probably gonna use bigger propellers with more pitch and more powerfull engines. hopefully that will get the thing airborne. I believe it should be able to yaw from side to side( i think that is the word for it) because of the rotor downwash on the tail rudder.(wow i wish i had that engineering degree)

    Does tip stall happen because the airfoil on the tips are disturbed due to the rotor being bent out of shape or what is the cause?
    Last edited by Goody34; February 3rd, 2005 at 04:17 PM.

  6. #6
    Registered User Bob Kelly's Avatar
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    GRIN !

    YES you can make Rotors from wood ...
    are they the best ... No.... will they Work ? YES !

    i have made a set of rotors out of a tree i cut down on my property here .. plane o'l pine trees !
    i took the chain Saw and made the board .
    took that to my table saw... took the Router to the pieces... and then did a few hours of hand planeing and sanding and i had a set of
    9 foot rotorblades.... i ballanced them
    filled any imprefections and will put a coateing
    of fiberglass cloth over each before i use them.
    and ofcorse re-ballance again.

    ........

    You don't have to be rolling in Doe to fly
    all you need to do is Do it yourself !
    .... The Prop-Copter does work... it will lift a man .... though the flight duration is very short, due to the limited amount of fuel above the mast...

    I sujest visiteing your local chainsaw shops to see if you can get 2- 15hrs Still or
    Homelite motors.
    and get a high speed swivel line hookup
    (from a hydrolics supplier ? ) drill a hole all the way through the Rotor spindle and
    feed the engines from a gas can behind your seat.... ( they use a similar set up for jet tip Rotors ) ( if it will hold for 300psi propain i would think it will hold for 20 psi fuel mix. )
    You can save your self alot of money by makeing your own propellers as well ...
    just be sure to use good wood and do a test spin test on everything faster than it will be used..... if it holds its good to use !

    I have made a 60' prop for use on my gyrocopter out of a 2x6" board i had laying arround.
    it worked fine.... infact i think it put out more thrust than my warp drive prop does !.... i have not flight tested it though
    and sense i cannot turn it faster than it will ever be used .... i will just keep it as a spair . with Use with caution in mind !

    So ... Do NOT get the idea everything has to be perfect !
    No doubt its better if its perfect ! but it can be done without it being grade A1 made for that purpose type stuff !

    Just remember .... flying ain't like rideing a bicycle ! if you fall off a bicycle , you may
    get a scratched up Knee.... if you crash your Aircraft you are lible to die !
    .. But if you build it and you trust your life with it .... Go for it ! I Do !

    Bob......

  7. #7
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    Thanks Bob!

    You have given me me much hope
    could you by anychance take some pictures of your rotors and prop?

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    thanx bob

    mr kelly your post about building your own wooden props/rotors has given me and my friend(goody) a renewed boost of confidence
    while we still face many challenges with the propcopter, the fact that we will be able to build the rotor and props ourselves is a big relief,
    what kind of wood do you recomend we use ??

  9. #9
    Registered User Bob Kelly's Avatar
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    The Wood you use should be a hard wood
    but also light ... so Oak is out as its quite heavy.
    Spruce is what they triditionally use because it is Harder than pine and just about as light. No knots for the entire length of the boards ( defects )
    ... I am asumeing you have a table saw at your disposal ... if not you're in for a lot of work ! and alot of blisters on your paws !
    .....
    What i did was look at my rotor on the Gyrocopter and drew out the same shape
    on paper and then transfered it to a piece of plywood as a template / guage . I then carved the plank out to meet the guage is all.
    .... you know.. cut away anything that doesn't look like a rotor blade ! <GRIN>
    I used the table saw to get the major portion of the back top side of the leading edge cutting a sort of triangle out of the plank the length of the board . This is a tricky piece of work
    as any hickups and kiss the blade goodbye !
    ofcorse you must start with a square pice of wood. so trim it down on the saw to be positive it is square ! i made mine out
    of 1"x 7" x 9' each .
    after the first cut the rest was alot easier
    I just more or less rounded the upper half of the leading edge ( took out another triangle the length of the plank) after that was done that left me with a curved top and a flat bottom of the plank. I then trimmed the bottom of the leading edge slightly and then the bottom of the trailing edge. with this Roughed in it was time to move to the hand plane.... rounding all sharp angles .... and in general smotheing it out. with that done you purty much have a rotor blade , it needs sanding and fiberglass reson , then a layer of fiberglass cloth .... smothe that out and then ballance them Well .....

    i took a long board and made a scale by pivoting it in the middle and makeing sure IT was ballanced.... then hung the blades from each end.... Horizonally .... because you want the bladed ballenced to themselves as well ... so mark their center so you can find it easy ... and trim from the lowest hainging end untill you achieve perfect ballance.
    not just close... they have to be right on ...
    at 450 rpm 2 oz. becomes a bunch of weight out there !
    ....

    The prop is alot harder because you have to do half the prop at a time and the board has to be thicker to accomidate the pitch ... draw the airfoil shape on the end of the board at the proper angle ... say 12 to 15 deg. make sure you do the same to
    the other end of the board and GET it faceing in the right direction ! ...
    I made my first prop useing a 2x4 and a drawknife ! it worked great on my 3.5hp Briggs and stratton ! it put out about 80 lbs of thrust !

    Ofcorse you ballance the prop by drilling a tiny hole in the exact center and lube the nail you put through it to pivit on ...
    tinker arround with it long enough and you'll get it !
    ....
    I have made my rotors and props out of Pine alone ...its what i had on hand !
    they seam strong enough indeed ... but the true acid test is spinning them ! and you MUST give them a good spin test ...
    to check for ballance as well as them comeing appart .... How you do that with a prop copter is easy if you have 2 heads... one for regular pitch setting and the other with NONE.... so the rotors will spin as fast as possable ! ( increasing the pitch will slow them down ) .... so fire it up, and run for cover ... if it survives its good to use ! hehehe !
    ....
    No i don't have any pictures real handy of them sorry but you probly got the idea by now anyway !

    these are some ideas you can use ... but above all use your head and think what the consiquences are if the Rotor should fly appart in mid flight ... so if you make them yourself be darn sure they are Stronger than they need to be !

    i made both of the rotor blades i have here in 2 days .... then the bad weather set in ... and i havn't got them fiberglassed yet
    .... even if i do not put cloth on them i will at the very least give them a good coating of Reason to help striengthen them and smothe out their surface.
    .....
    Also Note ... Most Rotor blades have a weight at the tip of the blade to give it a better chance to autorotate and less chance to slow down real fast ....
    1" x 1/8" x8" mild steel counter sunk
    into the back half of the leading edge and screwed in at 1" intrivals should do the job nicely... then reson them in good !
    i havn't done these to mine yet but will put them about 6" from the tip of each blade . ( if you need more weight make them longer ! )
    .....

    Good luck !

    Bob.....

  10. #10
    Registered User Bob Kelly's Avatar
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    Wood prop

    Here's a quick drawing i did to show how i made my wooden props, keep in mind this picture only shows one end of the board
    the other end is the same ... just make sure
    the leading edge's are pointing in the right
    direction ( i have made more than one piece of firewood by getting the angles confuzed ! )

    in the Picture I plan to attach somehow....
    the red lines are cut on the table-saw ,
    the green lines are where i used the Hand plane , and the blue lines is sanding ,
    though in reality the green and blue are all done with the hand plane, just a finer setting.
    .....
    For the Rotor blades, the proccess is the same
    except that I put the airfoil shape flat on the bottom of the board.... ( no pitch )
    the cutting of the red lines on a 1" thick by
    7" wide and 9 foot long was tough... I extended the fence with a scrap of wood which helped a bunch....but watch your fingers ! (heheheh)
    once the 3 main cuts are made, planeing the airfoil shape into the board is a simple task and it goes suppriseingly fast with sharp tools .
    ....
    the only other thing i can think of is when you aproach the hub with your cuts stop and trim it off with a hand saw ... so you can taper the hub part smothely I stopped about 8" from where the hub plate would set and gave the hub portion of the Prop
    a good smothe long taper up to the hub from the blade. as much as for looks as for striength.
    if your needing square ends on your rotor blades ( like mine ) just don't cut all the way through the length of the board and taper it off by hand like you do on the prop .
    By now i am sure you got the idea ...
    its not hard at all .. and i am frankly supprised at how few of people have ever made a prop ....

    Now no doubt there are better ways out there to do this, and probly makeing a more efecient prop as well, but i do know
    this method works as i have done it myself
    and have spun the prop to 4500rpm with no signs of vibration or comeing appart !
    Anyway, good luck to ya ! I hope you build your Flying toy ! <GRIN>

    Bob....

    Note: the picture shown has an extreamily agressive pitch to it ... the bottom side of the first box to the first red line going up is
    the pitch angle.... if you want a certain pitch use a thinner board so all the cuts are relitively the same .... or just change the angle and whiddle away the extra wood.
    i would think that on a prop-copter you'ed want a steep pitched prop so you could have the shortest props as possable on the engines that turn the rotor.... more head clearance ! ( more head clearance is a good thing ! )

    in any case you'll have to deside on the prop type and pitch after you get the motors ... higher RPM will need lower pitch
    or gear them down !
    good luck !
    Attached Thumbnails Attached Thumbnails Homemade rotor-woodprop-02.png  
    Last edited by Bob Kelly; February 11th, 2005 at 11:07 PM.

  11. #11
    Registered User Norman's Avatar
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    Originally posted by Leighton
    http://web.northstate.net/~emdeedee/page1propcopter.htm

    holy crap!
    Can't argue with that!
    That web site says that the Curtiss-Bleeker set the record for lifting the greatest weight per horse power, but it fails to mention that that was in the early '30s, years before a successful helicopter took off. None of the Curtiss-Bleeker models actually flew, there were just some tethered hovers INSIDE A HANGAR. After a few "flights" the drive train broke and Curtiss puled out.

    Think of the forces on the props. The motion of the rotor is creating centrifugal force almost (but not quite) in the plane of the prop disk and gyroscopic precession not to mention the (unplanned for) cyclic momentum reversals on the moving parts of the engines and that's just standing still. Once you start moving forward you can add P-factor which also reverses direction twice per revolution. There are also velocity surges as the propellor moves from the retreating side to the advancing side.

    No wonder something broke! It's just lucky that a gear failed before the props started disintegrating.

    I'm not a big fan of tip jets either but at least they're not as likely to kill somebody. Just deafen them and cost too much to run. I haven't heard anything about using pulse jets but it seems like the centrifugal force would be a problem for those thin reed valves. Ramjets have been used successfully (if you define "success as" flying, not selling) I believe Hiller was the most successful but you don't see too many Hillers around anymore.
    http://www.aerospaceweb.org/question...rs/q0141.shtml
    http://www.fantasyofflight.com/aircraftpages/hornet.htm

    The pressure jet designed by Gluhareff is a neat looking engine but NONE of the drawing sets you see advertised on the internet deliver the rated thrust. Some people, in particular a couple of guys in Canada named Viv and Luc, are working on getting plans out with the correct information.

    http://www.pulse-jets.com/
    http://www.glc-inc.ca./
    http://www.tipjet.com/index.htm

    Keep working on that engineering degree and in the meantime stay safe
    --------.~.
    --------/V\
    ------//----\\
    -----/(------)\--Norm
    ----(^^)-(^^) "For some years I have been afflicted with the belief that flight is possible to man" ~Wilbur Wright 5/13/1900

  12. #12
    Registered User Sonnyj's Avatar
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    Hello Goody
    There are a couple more options for you to consider.
    A feller named Monty sells a set of plans for plywood rotors,he is at montecraig@juno.com.
    They are built from avation grade birch with a layer of fiber glass to finish.
    Also you can visit the PRA site and maybe get plans for the Benson blades.
    About the propcopter auh,the fack that none are flying should say something about it.After all,what happens if one engine fails?
    Intelligence is not a privilege,it is a gift,and should be used for the good of mankind.

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    i believe we are going to go with a jet tip helicopter now, there is just too much that can go wrong with a prop copter

  14. #14
    Registered User Bob Kelly's Avatar
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    Norman !
    thank you very much for the links to the jet places.... ( and to think i paid for the same drawings ! )
    That bit of help is invaluable in my experiments here... thank you .... now i have something to work with..... instead of guess work !
    ............
    I would realy like to see a tiny ram jet engine..... you know....say... one inch in diam.
    to see the changes in the length of the parts
    in order to make it work....
    i have seen the 6" main chamber one many times ... it looks so simple ... but have found that changeing the diamator changes everything !

    I am wondering if smaller ramjets on a short rotor would work as well .... say a 3ft rotor ...tip to tip... ...just a big fan in reality.... but what a fan it would be if you could get it to work right .... perhaps with such a fan the AIR CAR is possable ?

    Or perhaps build a " Manta " like in Unreal 2004 eh ?
    interesting !

    thanks again !

    Bob.......

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    This is what i found in PR China.Actually it's not home made one.Some guys had it made by a plant.The al. series is 6063-T5,of construction grade.Guess it has to be milled on it' trailing edge to make a better balance.But all i concern most is wether it's strong enough.
    Attached Thumbnails Attached Thumbnails Homemade rotor-6063-t5.jpg  

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