Glass Rotors?

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

Sonnyj

Well-Known Member
Joined
Feb 13, 2005
Messages
135
Location
Rosman NC USA
Hi All
A year or so ago I bought some plains for making plywood rotors for a gyro copter. Well it seems I caint find any plywood that suits my needs. Aircraft plywood only comes in 5'x5' and am unwilling to use that many scarf joint's.
So my question is, do you think it possable to lay up fiberglass or corbin fiber to make the rotors from? I would need 2 10'x 7.5"x 1\4" and 2 10'x 7"x 1\8" boards. The spare is also made up of plywood with a
1\8"x1" 10' steel flat bar in the middle of it. Would it be feasable to layup the spare in the fiber glass or corbin fiber with the steel in it. Or could I or should I leave out the steel? I have little to no experance working firer glass but am willing to learn.
Any suggestion?
Thanx Sonny
 

HeliDev

Well-Known Member
Joined
Jul 7, 2003
Messages
108
You will need to be pretty careful here mate, blade failure is pretty unrecoverable.
Could be worth you while to check out some aluminium rotors.
Rotors experience some pretty high forces, and bend in some pretty funky ways. If they arent laminated properly, or designed correctly they will break in short order.
 

Sonnyj

Well-Known Member
Joined
Feb 13, 2005
Messages
135
Location
Rosman NC USA
G'Day Hiledev
Thanx for the advice.
Weren't there a couple of laninateded blade failuers down in Oz? They were the bomded aluminum ones if I remember right. I think the extruded aluminum blades are probably the best bang for the buck and not to expencive, and am saving toward that end.
I have built a set of plywood blades and they "looked" prety good.I never tryed to fly them becouse they were made from cabinet grade plywood, I just wanted to see if I could do it. They turned out very nice and they were easy to ballance and track, I took them out to El Darado dry lake and spun them up and they were guit smooth at 300 rrpm. Now that was 10 years ago and plywwod has changed. All of the supplyers are haveing delamination problems so I will not be useing plywood. Thus the resson I would be thinking about making fiberglass or corbin fiber blades. I cut the plywood blades up and got rid of them when I got done with them and will probably do the same to the first set of glass bldes if I don't like them in any way. The blades will need to be near perfect for me to want to use them.
What I need now is advice on constrution techniques and materals to use.
All sugestions are welcome
Cheers Cobba
Sonny
 

HeliDev

Well-Known Member
Joined
Jul 7, 2003
Messages
108
Without checking the only blade failures that I can think of in Aus are the Robonson failures we had. I would need to check though to be sure.
Pretty sure the robbie blades are honeycomb sandwich, with an aluminium spar. The older blades were an aluminium skin, the newer ones are a stainless skin.
Most of the gyro guys I speak to seem to like the dragon wings, but the vortec ones have a good rep too.
The thing with making your own blades is the number of ways that you have to test for strength. Because rotor blades flex in so many ways it can be hard to pin down the forces that will be seen by the blades in flight.
The other problem is the figuring out the life of the blades. With composites figuring out the fatigue life is difficult without alot of experience and data.
The easiest method would probably to use foam cores, and wrap. That is the methos I have used for alot of RC stuf, and will probably do the same for a larger scale on that Im working on.
However research will be your friend here, theres alot of info on composites around.
 

Sonnyj

Well-Known Member
Joined
Feb 13, 2005
Messages
135
Location
Rosman NC USA
I think the brand name was Gyro tech, that had the falure. There was another but I can't remember their name, anyway it's all in the ASRA forum. The vortec blades are the ones I'm drooling over, They are a very hearty blade and will suffer a lot of misuse. The DW's are a good blade but Earnie say's they are next to imposable to hand start, becouse of the airfoil section he uses. If I were to install a prerotator the DWs would be my first choise if I chose to just buy a set of blades. Mainly becouse I like Earnie and Mike, their just good folks and good at what they do.
I'm still looking around for info on working fiberglass but as yet have not come up with anything solid. It's one of those learning things and like most folks here on the board I enjoy working with my hands and can appriciate a job well done. I luv it when a plan comes together!
Cheers Mate
Sonny
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,343
Location
Saline Michigan
Sonnyj,

I can give all kinds of advice on how to fabricate the rotors, but fabrication and structural design of these things go together, and design is where it is going to be tougher.

When you built in plywood, I imagine that you took a material that is pretty flexible and bent it to your purposes, curving the plywood over ribs, but if you layup fiberglass to the same thickness, it will not conform with anywhere near the ease that the plywood did. Then fiberglass is about twice as dense too, so you would not want the same thicknesses either.

If you were to build composite blades, they would need to either be laid up over a lightweight core of plastic foam or have skins that are laid up in a mold. There would have to be some sort of spar to carry the tension, torsion, and bending loads generated between the aero loads and rotor head. Then there would have to be some sort of inner end to connect your rotor head to the spar in the rotor. This joint is the one that I would sweat over while designing it - Home workshop bonding of aluminum alloys to epoxy just does not have longevity, so you end up having to design the joints with mechanical interlock instead of just bonding. Other metals are better, but still can be poor.

All of this needs to be designed so that you know it is adequately strong and the materials chosen so that it will hold together reliably. While the struture may not have looked like a big deal in the plywood ones that you built earlier, the design was probably carefully analyzed before you came upon it.

My opinion? Use a proven known design that works in home workshop materials or get a pro knowledgible in both rotor design and composite design involved.

Billski
 

Sonnyj

Well-Known Member
Joined
Feb 13, 2005
Messages
135
Location
Rosman NC USA
wsimpos1
Thank you for the reply.
You have answered at keast one question. The fiberglass will not will not bend the way I would like it to.
Actually there are no ribs in the design, here is a pic of a section of the blades I built. Its a fairly simple method although a lot of carefull sanding to shape is involved.
I have been reading the materal that Jukka Tervamaki has writin and that is part of what makes me think I can do it.
Thanx again for the sound advice and the info
Regards
Sonny
 

Attachments

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,343
Location
Saline Michigan
OK, I mentioned several elements for rotor design, and the section you have contains them all:

The forward section is completely filled, and that is traditionally called the spar in rotor design. It carries bending and torsion loads and some of the tension. The forward aero shape is also in the spar;

The aft section is light and is all aero;

The metal strap is either for tension or for attaching to the hub.

Now to do a reasonably efficient (weightwise) rotor in fiberglass, you start with a rotor foil, chord and span selected (which I think you already have). Then you would determine the loads at several stations along the rotor span. Loads are tension, lift, pitching moments and from that the total tension, torsion, shear and bending loads on the rotor blades at each station. The methods for doing this should be in text books that cover rotor design.

Next is education in composites, which can be weird. I am partial to Tsai and Hahn, but I have another at home that is good too. How is your Matrix Algebra? Everybody works in matrix algebra for structural computations in composites.

You would do a rough sizing for the skin and spar. I would probably make a stout I beam at the 1/4 chord point and forward built up over hotwired blue foam with a skin over the whole thing, just like the Rutan method. Remember, it carries tension from centrifugals, shear and bending from lift, any pitching moments, and internal loads. Then you compute the ABBD matrix for each station, input the loading (include your factor of safety), compute the section strain, then lamina strain, then check the failure criteria. Anywhere that failure is indicated, you have to beef up something and iterate your design until it all passes.

Basic engineering here.

The spar should be designed to carry the tension, bending, shear, and any torsion loads. It will be beefy. The caps will be UNI cloth, UNI tape or some other material where almost all of the fibers run the long way out the spar. The caps will carry bending loads and tension. The shear web will be fibers at plus or minus 45 degrees to carry shear.

The skin will carry aero loads to the spar and what torsion loads you have. These will be pretty thin. Two plies of BID is probably overkill. If your failure criteria say the skins are overloaded, you probably need to beef up the shear web or the caps.

The lift changes as you approach the tips and hub, and the active loads change a bunch as you travel in or out along the rotor, so you might need more spar and maybe more skin thickness in different places. As you approach the hub end, you will need to get the centrifugal and pitching laods form the spar into the hub, and that transition is one to sweat over. Go to the rotor design books for help on this and use BIG factors of safety for this joint.

If all of this sounds big, well it is. Monkey-see monkey-do might actually benefit you here. Are there any fiberglass rotors the size of what you are thiking about on the market? This is called benchmarking. You want to check out how the other guys build their skins, spars, and attach their hub fittings.

Good Luck, Billski
 

Dust

Well-Known Member
Joined
Feb 9, 2004
Messages
302
Location
Troy, Michigan
Great info - really well thought out.

a note - i am looking at props for my cozy and ran into aero composits. they are using very high density foam as the core material and interleaving glass and carbon fiber for the structure. the carbon fiber is for strength in tension and the glass is for strength in both compression and tension.

your description of the airfoil is perfect as i have now done 4 cozy mk 4 wings (two left and two right, and two canards.

the rotor to hub design seems really tricky as epoxy really does not stick to metal well at all.
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,343
Location
Saline Michigan
Hub fitting joints are the tough one. Several methods can be employed.

Direct Bonding - Not usually successful in home workshop methods because aluminum is so active a metal. Skip it...

Mechanical Interlock - Make the Al alloy part have shapes that the composites will get a hold of mechanically and then build the metal into the core of the part. Rutan style control hinges use this methods - Many holes are drilled and chamfered, and the holes are filled with thickened epoxy, then the recess where it is to be mounted is also filled, then the metal is jigged into place to cure. Collars, flanges, you name it. But analyze it and understand that most of us use big FoS, like 8 to 20 for these joints.

Bolted Hardpoints - Core material may be changed from foam to plywood or metal at the bolted joint, extra composites may be added to stand the several failure modes that are possible with bolted joints, and crush plates on the outside to spread out the bolt loads.

Books on the subject, Tsai and Hahn "Introduction to Composite Materials" and Jones "Mechanics of Composite Materials"

Want help with the details, come on back here and ask?

Billski
 

Sonnyj

Well-Known Member
Joined
Feb 13, 2005
Messages
135
Location
Rosman NC USA
wsimpso1
Thank you so much, you have givin me a lot to digest. I'll start gathering materals and get a blade bench built.

In as much as I have little to no experance laying up glass or hot wiring foam I, think it would be prudint to get some practice in.

Whitch ever method we use for the hub fitting joints, I will need to be able to break them down for storage and transprot.
I'll attach a pic of the hubbar and one rotor to give you an idea of what I have now.
Thanx again and regards
Sonny
 

Attachments

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,343
Location
Saline Michigan
Sonnyj,

OK, before you go seeking all of the knowledge to design in composites, maybe you should find outif you like working in the medium... which also covers your comment about practice.

The starting point for all of this sort of thing is "Moldless Composite Homebuilt Sandwich Aircraft Construction" written by the Rutan Aircraft Factory. It takes you through the construction methods used in the various Rutan designed homebuilt airplanes by building several sample parts. At Wicks Aircraft, the book is CB ($14.50) and the book plus the materials to do the sample parts is CK (49.50). The book assumes that you know nothing about the topic and takes you through building a bare bones hotwire saw and an equally bare bones epoxy balance. Anyway, they cover the practice of making airfoil shapes, building up a spar, skinning, filling/finishing, etc.

Once you are sure that you want to fabricate in this way, getting either the design help or the knowledge yourself will make more sense.

Billski
 

Dust

Well-Known Member
Joined
Feb 9, 2004
Messages
302
Location
Troy, Michigan
Originally posted by wsimpso1
Sonnyj,

The book assumes that you know nothing about the topic and takes you through building a bare bones hotwire saw and an equally bare bones epoxy balance. Anyway, they cover the practice of making airfoil shapes, building up a spar, skinning, filling/finishing, etc.
Billski
I doubt that you would want to use Styrofoam for a rotor and that is the ONLY foam that can be hot wired, all of the other foams create cancerous fumes when hot wired.

go to
www.iflyez.com

download the aerocanard plans and read the canard/ spar and wing chapters
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,343
Location
Saline Michigan
Hey Dust,

I do not know about cancerous fumes from hot wiring polyureathane and other foams, but all plastic foams that can be hotwired except polystyrene give off materials that are POISONOUS to humans and animals RIGHT NOW when burned, which is a great reason to never burn or hotwire these foams.

Only polystyrene is safe to hot wire. If the foam is tan, it has polureathane and/or polyester in it and will be dangerous if burned, so just do not expose this stuff to heat.

Next comes the challenge: WHY would we NOT want to use styrene foam in a gyro's rotor structure? I can think of no reason why one foam would be better than another here. Perhaps I will learn something here...

Gyro rotors are spun by airflow moving from forward and below the rotor disc, and the airflow is relatively clean, with little in the way of variation in it to drive vibration. No big firing pulse based accels/decels are happening.

Now if we were talking about a propeller on an IC Engine, there are tremendous accel/decell loads from the engine firing cycle. If we were talking about a Rotor on a helicopter, it would have some of those firing pulses, plus the fact that it is driven through the wake of the previous rotor baldes and would have to be beefier than the same gyro blade.

If the propellor is in a pusher configuration, it will also be in the wake off of other structures and aero surfaces of the airplane. These will induce all sorts of vibrations in the prop. Thus the syntactic foam (filler and epoxy) or wooden core used in many composite propellers to help take all resonant modes above the frequency that are available to excite them.

As a comparison, aluminum props are SOLID, while aluminum helo and gyro rotors are hollow structures resembling somewhat beefy metal wings. I suspect that the analog will hold in composites as well.

Now SonnyJ is going to have to find a way to get the flight loads from the spar to the hub fittings, and that will be the hardest part of the process. The problem is solvable, it is just a matter of picking a soluton with adequate safety factor and minimum weight.

Billski
 

Dust

Well-Known Member
Joined
Feb 9, 2004
Messages
302
Location
Troy, Michigan
Originally posted by wsimpso1
Hey Dust,

....polystyrene give off materials that are POISONOUS to humans and animals RIGHT NOW when burned, which is a great reason to never burn or hotwire these foams.

Only polystyrene is safe to hot wire. If the foam is tan, it has polureathane and/or polyester in it and will be dangerous if burned, so just do not expose this stuff to heat.

Next comes the challenge: WHY would we NOT want to use styrene foam in a gyro's rotor structure? I can think of no reason why one foam would be better than another here. Perhaps I will learn something here...Billski
yeah- the poison thing not cancer - good catch and worth repeating.

I'm no engineer just a lowly builder, just "seems" like the rotor would be under more stresses than a wing - but hey, what you say makes total sense and i will defer to you.

on the engineering side, don't forget the final part of the engineering - test it. when burt designed and built the spaceshipone, after engineering the best he/they could they found out in test flying it that the control surfaces had to be extended 18" - BIG change.

On the plans availability - they have been removed from the web site. that is not a problem, if you want to review them i know of cozy and long builders all over and we can make arrangements for you to visit one and review the plans

hey Billski - you are doing a great service here, your answers are spot on and on the positive side - no one could ask for better advice, just had to add my .02 worth and learned .25 in return
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,343
Location
Saline Michigan
Dust,

Your comments are good and I welcome them. Please, do not let me stifle anybody's comments... "Challenge" is not meant to be taken as a aggressive term in engineering discussions, just a "make me believe you" point in the discussion.

I just thought that you might have a reason why foam would be unsuitable that we could learn from... Remember, there was a time when foam cores were considered to be too flimsey to be used as anything in aircraft structures... and glue and string was never thought to be suitable for primary structure, but look, we are doing it!

Certified Helos have rotors generally with a honeycomb core in the back half, metal honeycomb under metal skins, and Nomex honeycomb under composite skins, and some of them at densities not a whole lot higher than our foams.

If anyone else does know of reasons not to use foam in gyro rotors, please, jump in.

Billski
 

Bob Kelly

Well-Known Member
Joined
Aug 19, 2004
Messages
373
Location
N.Calif Mountians
Hummm !
I agree and disagree with alot of this
...
I'll try to keep it short and to the point.
Gyro Rotors are not used like Helicopter rotors , therefore they are not subject to the horrable twisting and all that a Helicopter would give them. there for they so not need to be as strong as a Helo rotor. they need to be laterally strong... that is lengthways and have enough resistance to twist so that they don't change pitch on you but that is about all. ( thats still quite alot granted!) blade flap is about the worst thing you can do to a gyro rotor baring strikeing something with the rotor .
....
Personally I think Sonny j's first attempt of a rotor blade was fantastic
...and all he realy needed to do if he was concerned with the plywood comeing appart was simply to lay a coat or 2 of fiberglass cloth on them and thats that !!!!
although the airfoil section that he shows is about 2 times as thick as the rotors on my gyro they still should work fine ...
Seams to me You guys are complicateing something very simple !
the rotors need to be strong enough too.....
1. withstan the RRPM and not come appart
2. not change in pitch any if at all possable.
3. not crack , peel or split with regular use.

with that in mind Fiberglassing plywood blades fills the bill ! their easy to make don't cost an arm and a leg to make and once completed are waterproof and easily cared for
Pluss if you should ever bugger one up you can repair it !

the Alum leading edge and blue foam core with fiberglass skin blades on my rotor are very durrable I have busted them 2 times and have been able to repair them both times with no ill effects the problem I have incountered is the fiberglass I use eats the blue foam up ! ... but there are ways arround that ! . just wish I knew what reson doesn't eat the blue foam !!!!!

there are many ways to form fiberglass (reson and cloth) into the shape of a rotor and you don't have to Engineer a rotor to do it .
just make it stronger than it needs to be ! at the root of the blade where it clamps to the hub bar and along its length as well as the tip where the tip weight resides ....

if However you are trying to make the Rotor as light as possable then You better Engineer it and find out just how little you can get away with !
but in todays Gyros thats not nessarry they can stand alot more abuse than they could when they were first being made a heavier rotor will still fly .... its just well...heavier !
we're not building rocket ships here just a rotor... be it a plank cut to a airfoil shape or a Dragon wing carbon fiber wonder with the twist built into the blade and all that ... its just a stick with a shape cut into it ! treet it like one and you'll be fine ...

thats my 2 coppers anyway !

Bob......
 

Dust

Well-Known Member
Joined
Feb 9, 2004
Messages
302
Location
Troy, Michigan
are you using epoxy or that other stuff mmmm, can't remember the name of it as we do not use it in a cozy, foam and fiberglass construction, as it melts the foam. oh yeah polyester resin ima tinkin
 
Top