Home made rotor blades

Monte55

Member
Joined
Jul 13, 2008
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112
Location
Raymore, Missouri
Although I value ideas and suggestions I get on another form, I thought I'd pick more brains here.
I have a micro lite heli project with counter rotating rotors that I have made of laminated marine plywoood with a top cap of 1/4" solid oak combined with the 3/4" marine ply to come up with 1" thick. The rotors are 48", 8" constant cord. I feel I need to glass the rotors. Some say to use epoxy resin and some say polyester will be fine and cheaper. Thoughts??
I may have to cut holes aft of the 25% balance to lighten the aft part of the blade for balance. Is it really necessary with a solid 48" rotor blade? If I do cut holes I would probably fill with foam and then glass. I understand polyester resin will eat the foam and the need for epoxy resin. Thoughts???
If polyester will be fine on the wood, is there a special glass I need to get as far as weave and weight of glass fibers etc. The glass actually will only help keep the ply together and protect the wood as I see, not to add strength to the rotor but some. I would appreciate any good input on this. I have an album of my build on another site if anyone is interested. Thanks
Nick:rapture:

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In my opinion, epoxy is the way to go….polyester is not as strong and it has a tendency to allow ply's to extrude, slither or slide-over one another under a bending load…much more than epoxy. There's a glassing term for that….but my brain can't seem to find it now. Polyester will dissolve polystyrene. I think you may need to find some books on glass stress analyses and layup techniques.

You need to balance your blades at ~24 -26%. At a higher % (~30) they could flutter under some conditions…..you don't want to be flying if that happens ;). A solid wood chord will need to be lightened on the aft portion, or it will require a massive nose weight.
 
New pictures..

New pictures..

Ohh.. new nice pictures! I post a few from your album here.
Look like you can produce what someone might recommend.
 

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home made rotor blades

home made rotor blades

I thought I would receive more input on my question. Anyone else have any input.
I was told by one person to use a product called G4 on the wood before using polyester resin. Any sites I searched on the internet and videos on youtube didn't mention this.
Nick
 
I thought I would receive more input on my question. Anyone else have any input.

Have a look at the recdent discussion regading home made rotor blades going on under ROTOR BLADES. Some of the posting appear to be comments from those with no experience in that area to speak of but others clearly suggest actual, first hand, hands-on experience.

While it seems you have already begun building blades, prior to taking flight with these, if you haven't already, you would be well advised to dl past and present applicable patents, not only from the US but Britain and Germany as well and don't forget Japan; there are lessons there, some of which may save you a lot of expense and possibly grief down the line.

As for the jpgs which you've been good enough to ul, from what I know of these things, your laminates are in the wrong direction; they should be vertical, not horizontal to the cord. A solid wood plank is NOT at strong as a similar guage laminated one and when it comes to flight, without been insane about it, over-built is far better a construction factor than under-built. A rotating blade which delaminates in flight is not something you want to experience; by humans reaction standards, it will happen very, very fast and usually results in the destruction of the aircraft and the death of the occupants.

As you are from England, do have a look at the work done there during WWII with regard to wood aircraft construction. If memory serves me correctly, England was clearly the world leader in that regard. As I know and understand these things, aside from availability of clearly advanced adhesives, not much has changed regarding wood aircraft construction since then.

Hope this was of some help.

tyc
 
Monte55,

Since you have a milling machine, would you not be better off making composite blades, using the milling machine to produce the female mold and the foam core?


Dave
 
Thanks for the reply

Thanks for the reply

Actually I'm in the Kansas City Missouri area in the USA. I'll agree with you on the ply arrangement if I was making a spar. I'm following what I have seen others do that have made a rotor of this type from plywood. I call it a rotor but I guess it could be considered a propeller without a taper and twist. All the laminated propellers I've seen are made this way but not from plywood. I have spent many hours seeking info on this and have not got the response I had hoped for. If this was a long rotor I really doubt this would be the way to go. These are 4 foot long and stiff. Moot point. They are made and now I want to glass them in a good manor. Thanks again for your input.
Nick :usa2:
 
Monte55,

Since you have a milling machine, would you not be better off making composite blades, using the milling machine to produce the female mold and the foam core?


Dave

I've never made molds or worked with composites. This has been a project
that has had a snag at every turn. This is a test to see if all this will come together. If it does, I'll probably try to find some rotors off a R-22 or similar I can modify for my needs. I've called local heli salvage places and no luck.
Nick
 
Hi Nick,

The first step is to decide whether you should produce props or rotors. Determined by disk load.
With a disk diameter of only about 100 inch/ 8ft / 2,5m for your machine, it must be props you should build.
I think the Gen4 and Air Scooter have rotors of more than 4m / 13 ft. in diameter.
Your wide 8" and thick 1" blades need to go quite slow = you need more than 13 ft dia rotor.
Turning your blades as fast as a prop would be an extremely dragy affair.

My thoughts.
 
... I'll agree with you on the ply arrangement if I was making a spar. I'm following what I have seen others do that have made a rotor of this type from plywood. I call it a rotor but I guess it could be considered a propeller without a taper and twist. All the laminated propellers I've seen are made this way but not from plywood. I have spent many hours seeking info on this and have not got the response I had hoped for. If this was a long rotor I really doubt this would be the way to go. These are 4 foot long and stiff. Moot point. They are made and now I want to glass them in a good manor. Thanks again for your input.
Nick :usa2:

That they are made is not necessarily a moot point. The "hands-on" experience gained will not be lost, nor will the experience gained by glassing them. When finished, while they'll make great wall orniments, the experience gained by making them may prove priceless down the line.

If I may suggest, do not rely on what others have said here, rather spend more time dl those patents I made mention of. Look to Bell Aircraft, Hiller, Sikorsky and others who used wooden blades and see how hey did it. The information is out there but it may take time (which will be well spent) and perhaps a dozen or more letters of inquiry from you and the responses may prove to be time and treasure well spent on your part. In the long run you may save a lot of time and money and more if you go this suggested route.

Best of luck with that project.

tyc
 
…. The "hands-on" experience gained will not be lost, nor will the experience gained by glassing them. When finished, while they'll make great wall orniments, the experience gained by making them may prove priceless down the line….
Very well said, and I agree - almost. Sure Nick should complete his blades. But if he extended them with a 48” hub bar, the rotor diameter would be 12ft / 3,66m. In THAT case, I think he would get a good test, and need not at once put them on the wall!

I am not at all the expert on this. So Nick, I hope you will get some more reliable input.
 

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... Sure Nick should complete his blades.

Oh yes, finish them, even if they will end up as wall ornaments but as I'd mentioned, the actual "hands-on" experinece will prove priceless for anyone engaged in this business. Will mistakes be made while finishing them? For Nick's sake I certainly hope so - best way to learn is by making mistakes and some of them will be very obvious, even as he's making them but then again, as experience has repeatedly shown me, it's the best way to learn. The "trick" is, try not to make the same mistake twice - which is not necessarily so easy to do either.

As for that counter-rotating machine which you ul - what make and model is it?

tyc
 
Oh yes, finish them, even if they will end up as wall ornaments but as I'd mentioned, the actual "hands-on" experinece will prove priceless for anyone engaged in this business. Will mistakes be made while finishing them? For Nick's sake I certainly hope so - best way to learn is by making mistakes and some of them will be very obvious, even as he's making them but then again, as experience has repeatedly shown me, it's the best way to learn. The "trick" is, try not to make the same mistake twice - which is not necessarily so easy to do either.

As for that counter-rotating machine which you ul - what make and model is it?

tyc

Who are you asking the question?
 

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12 bladed co-ax..

12 bladed co-ax..

How to do a rotor for just hovering around, low and slow? Can we learn from history?
Look at this – 6 hp – an old Danish 12 bladed coaxial rotor from 1912.
I say AMAZING:

http://aviastar.org/helicopters_eng/ellehammer.php

“The lifting rotors were of an ingenious pattern, consisting of two contra-rotating rings, each of 5.97m diameter, the lower one being covered with fabric to increase the lift. At regular intervals round the perimeter of the wings were six vanes, each about 1.50m long and 0.66m wide and pivoting about its horizontal axis. The rotor system was driven via a hydraulic clutch and gearbox, all designed by Elle-hammer, and the rotor vanes' angle could be altered in flight by the pilot — an early example of cyclic pitch control. After several successful indoor take-off tests, during which the machine was probably tethered, Ellehammer's machine made a free vertical take-off later in 1912, in front of witnesses who included H.R.H. Prince Axel.”
 

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36 hp

36 hp

Yes, 36 hp from this Ellehammer engine :)
 

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