I went out flying this morning. Had a very good flight with my own design .15 powered autogyro. Landed at my feet. With the motor now running OK it has plenty of power, even though it is not exactly a small machine. However half way through the flight I could hear the rotors flutter, so eased back on the throttle. No harm done! BUT, I am wondering if rotor flutter is common, - do others experience it? Has it led to broken hinges or blades? (I am using code 5 plastic hinges,- fairly thin).
Any comments or advice?
Colin Duthie (a lone gyro flier from New Zealand)

I have never experienced blade flutter on my gyro but have been warned about strongly. It has to do with the chordwise blade mounting point (should be 25% I think) and the blade CG which shouldbe around 25% as well, I think. Hopefully, one of the experts will check in with a more technical answer for you.

Hi Tintrax,

Boy. all the way from New Zealand, wow!
Warning> do not fly with evidence of flutter. It can instantly
destroy! With no warning.
Flutter is caused by improper balance, can be aerodynamic or
mechanical.
Rotor blade fluutter is very unusual and would suggest improper
structure more than anything else.
Blades are to weak,
Dickybird told the basics of blade attachment which should be.
Will be interesting to learn your findings!
Good luck,

Hal [email protected]

Thanks Dickeybird & Hal. Maybe my hinges are too weak. I have changed to delta hinges of quite thin code 5 plastic, maybe about 25thou thick. I am a bit concerned about heavier plastic hinges as surely they will resist the necessary flexing (?) With the thin hinges & the delta angle the plane flies fine, but the flutter is a nuisance. The rotors are 2 inches chord and 1/4 thick, made of balsa with no other stiffening. Mounting is about 1/3 of chord. The plane can be seen at http://www.geocities.com/tintrax/page6.html (& subsequent page) - the photo shows it before it had the delta polyprop hinges. It is the plane with the red fuselage. I have never seen any autogiros fly, only my own! My own design.
Colin

Hello Tintrax

I fly only small autogyros very similar to yours. Mine all use code 5 polypropylene for hinging on both straight and delta hubs. I have never had the problem of flutter however, I do use a much wider hinge than seen on most small poly hinged gyros. It does make hinging slightly more rigid but this has had no effect on stability or performance. Its surprising just how rigid the hinges can be, I have in the past used thin titanium for the flex material which is considerably more rigid than poly and it has worked equally as well. In fact it was rigid enough to not require down stops on the hub !
This may be why I have not experienced any flutter as the more sturdy hinge prevents spanwise twisting effects. The rotors on my .10 size models have a chord of around 1.5 inches and are solid balsa with a hardwood leading edge.

The picture is of a few of my hubs with the widened hinge material. They are basically very similar to Jim Baxters excellent designs. I couldn't resist also throwing in an image of the carbon fibre hub I made, the thin flexible resin flapping hinge was later replaced by the thin titanium previously mentioned.

One question, did you put your blades directly on the to the tangs of your delta hub or did you still slightly negative shim them like you perhaps would on a normal straight hinged hub ?

Cheerio

Sean

Thanks Sean - Your hubs are very neat~ I like the hinge being wide. Your comments about stiffness of hinges is interesting, I think I have been overconcered about hinge flexibilty, and should use stronger (thicker) code 5 plastic.
Incidence - When I had non-delta hinges i needed negative incidence to get satisfactory spinup. However with 15 degrees angled hinges the blades are at zero. When sitting on the ground in a breeze the rotors spin the wrong way, pick up the plane, hold it nose high, and the rotors stop and start spinning the proper way.
Colin

Hi Tintrax,
You are probably correct, it was (is) your blade hanger fluttering,
not the blades themselves.
You do cover or seal in some way the balsa blades?
Speaking of blades you might find of interest a presentation on
the Model Airplane News web site, the text of it tells all.
Web>www. modelairplanenews.com "Quick and Dirty Rotary wings"
Your mention of how your Delta setting reacts raises curosity.
Would seem> when craft is level the breeze does not cone the
blades?
When held at an angle the blades cone, the conning allows the
Delta effect and thus the negative incidence required to windmill?
For Spindizzy> believe you said you have or do use Delta. Also
that you use only a single attachment to the blade hanger.
If only a single how can there be a Delta effect?
Back to Tintax> when there are several Gyronuts collaberation
is a great help, you would like more Gyro people?
There are model meets, gatherings? If one demonstrates Gyros
at such the amount of interest is surprising!
A final thought> if you should go to more powerful craft.
All full scale blade hangers are from metal.
You have the ability to work with aluminum sheet?
If so an excellent blade hanger can be assembled in one evening
and they last forever with no problems.
I produced two about 5 years ago and like a "Timex" they just
keep on ticking through all sorts of numerous disasters and of
course flights
Good luck,

Hal [email protected]

Hi Hal - Sealing/covering the blades - They are simply covered in lightweight model aircraft tissue and then given a spray coat of paint (auto laquer). Seems old fashioned but then I I am old fashioned, having first built a model plane 58 years ago, and still mainly using those materials & methods! About 2 years ago I decided to built an autogyro as these machines have always interested me & it was time I did something about it!
The rotor rotation on the ground is when the blades are a bit drooped, hence at positive incidience, coning only occurs after I pick the plane up and hold it nose high, then the rotors spin the proper way, and as you say, the more they cone the more negative incidence to assist `spinup`. Can`t tell how much they cone in flight.
Collaboration - On my own here, no one else into gyros, only me! Good to have this internet contact, all the more important for us loners. I broke the rules I suppose by designing my own plane, but studied Jim`s and Rick`s sites a lot first. First gyro I ever saw in flight was my own with me flying it - a bit of a controlled crash that time! I only found this rcuniverse site after I had flown.
I also have a .35 powered gyro, using same style of ply and code 5 hub, flies well! It is on the web pages I mentioned earlier. This plane is a modified version of Emilio Cabeza`s DC design.
This morning I exchanged the `flutter` hub for another I had as a spare, this has rather heavier code 5 hinges.
Colin

Hi Folks

Firstly for Hal, if you look at the top right grey coloured hub in the image I first posted you will see that the hinge line itself is angled forward . This means there is a delta effect even with the blade fixed parallel to the tang. Using one blade bolt just means that when the rotor strikes the ground it folds up rather than just breaks. On a non delta hub I usually just angle the blades forward so it has its own delta effect then centripetal force takes care of things when it gets going. The bolt has sufficient tension in both the above cases to just remain in position without 'floating'. It works a treat.

Thanks for the incidence info Tintrax. I did the same with my own delta hub, fixing the blades directly to the tangs with no shims. I did notice though that despite having excellent lift the rotor rpm was less than that seen on the straight hinged shim mounted assembly. This gave slightly less roll response. With this in mind I am going to try a small shim on the delta hub to see what effect it has.

I started gyros as you did, all on my own except for the excellent sites you mentioned . I did however get the Simple G plan from Jim as a first model, so you could say I had a small advantage to start !

By the way, the orange blades you can see in the image I posted previously are similar to Tintrax's, doped smooth then sprayed with auto paint. Works ok but tends to crack after time. Next blades I am going to just use polyeurothane lacquer for a 'wood' effect.

Oh dear I do go on don't I

Cheerio

Sean

Hi Colin,
My 1st gyro, a 'DC Gyro' designed by Emilio Cabesas & published in RCModeler in 97 or 98 is an excellent machine.

However i built my blades for it from medium soft balsa with no hard leading edges. It fluttered badly & crashed numerous times.
I had to scrap the blades & make new ones from firmer balsa with 1/4 sq spruce leading edges. The result was no more flutter.

Hope this helps.
Bob Gardner

Thanks Bob, that is most interesting! My .15 powered gyro has simple balsa blades and no stiffening leading edge of harder wood. I have now fitted a new hub with stronger hinges, but the same blades. I will fly it carefully. I only noticed (heard!) the flutter when the plane was not far off, if it had happened at some distance a blade could fly off without it being known that flutter was the cause.
Originially I was using the hub design ( non- delta) design of the plane you mention, I had a failure of a glued join in a blade mounting and lost a blade. Now I always have small nuts & bolts to clamp the parts of my plywood hubs together (as well as glue).
Regards, Colin
ps - made a new hub yesterday- realised today I got the delta angles the wrong way around!!! Now fixing that.

Hi Colin,

Here's a pic of the hub I built for my "Gyrator" 1/2A powered gyro. It looks like alum. in the pic but is just painted with silver dope. It's 2 layers of 1/16" ply with .032" PP plastic between as the hinge material and a cut down Tamiya r/c car front wheel used as a bearing hub. I made the hinge fairly wide 'cuz I was worried about flutter. My blades were made from light balsa with a hard balsa leading edge. No flutter so far (he says with his fingers crossed!)

Hi Spindizzy,
Not trying to be "picky" or anything but believe guys would like
a further look at your "grey hub" mentioned. and me too!
You say centrifugal force causes the blades to go straight from
the rotor post, as I understand.
The grey hub does appear to be of delta character.
The blades are attached with one bolt, free to swivel.
Initially the blades are aligned with the delta tang.
If you would raise them the delta would create negatve incidence
or less than what ever the incidence was before raising.
Now when centrifugal comes into effect the blades no longer
align with with the tang. They are swept back relative to the tang
and supposedly aligned as if there was no delta.
One would have to "play" with the set up to find what results
from this. Would believe there would be some delta effect?
Would that effect be the same as it would be with the blades
aligned to the tang? Or would something weird happen?
Of note> it is possible to have fixed instead of swivel attachment
and get the same action with a strike.
Simply lengthen the tang and add a second PLASTIC screw.
The plastic will shear with a strike while holding the blade solidly
onto the tang otherwise.
Perhaps a better arrangement with heavier more powerful craft.
Good luck and remember> always fly at leasr two mistakes high!

Hal

Hal - Like Spindizzy I have my rotor blades held by a single nut & bolt. I am sure they don`t move from their alignment in flight - upon landing they are in the same position as before flight. The blades are clamped sucurely, I have sandpaper on both mating surfaces, quite rigid, but will swivel if the plane tips over on landing, thereby saving the blades etc. On my larger plane I do have additional `pegs` of thin dowel, but on my .15 powered plane the single bolt per blade is fine. I check tightness after a flight, they have never worked loose. The delta angle is maintained at all times.
Colin

Hi Hal,

The outermost hole in my blade carrier is tapped 2-56 (threads hardened with CA) for a nylon screw. I have placed a 1/4" dowel "hardpoint" in the blade that is drilled for the screw. I put the 2-56 nylon screws through the hardpoint and into the hub, leaving about 1/4" sticking out the bottom. When the inevitable occurs, the screws are cut cleanly allowing the blades to fold. I grab the remaining little stubs with pliers and screw them out the bottom. Then I replace the screws and voila, ready to go again!

Whew, much easier to do than to describe in writing.

ps: You are my hero! You're the man that got me started on airfoiled stabs many years ago.

Hi ya'll,
We seem to be getting some excellent info recorded!
Dickybird with a version of what I find to work well, good show!
Tintex with a new approach that makes sense.
We have used sandpaper to keep props from loosening so why not rotor blades?
The basic subject was flutter and it seems appropreate to look into that further.
There is an old axiom which we should consider. "when there is a problem determine the character and then the cause" Don't believe we have considered that as yet.
Another word for flutter would be flexing which would suggest the item is vibrating, moving both ways from it's normal setting.
Would seem causes of flutter could be sympathetic vibration and/or aerodynamic.
An example of vibration.would be Loyal Balyes and the Gee Bee. He pushed the engine above it's upper limit to establish a record. The engine did not like that and vibrated causing a wing panel to flutter and fail.
More common would be aerodynamic and control surfaces for instance.
A common sight is a flag waving (fluttering?) How come it does that? A flag is anchored solidly to the pole leaving passing air to effect what is not anchored.
In contrast if a control surface is hinged at the forward edge and that is all then passing air will effect it as with the flag. Such doings may work fine up to a given air speed. The air force increases as a square of the speed? Then as speed is increases flutter raises it's head.
Control surfaces are properly attached considering two factors.
Hinging>
First at the center of the surface's control force, that is where the force centers when the surface is producung work. (C/L perhaps?)
Secondly, when the first has been done then the surface is balanced about that hinge point,
Good part is when done that way the strength of the surface only has to relate to the force it will create.
It would appear that gyro people have traditionally outfoxed flutter by simply using structure to resist (offset?) any flutter forces. Obviously that has been a useable solution.
However, another consideration has recently raised it's head.
We have seen superior.excellent performance from a rotor
weighing half of the normal. The blades are obviously light ,are not robust but have sufficent strength.
This would appear to offer flutter ability?
No signs of flutter have been seen, how come possability?
The blades are attached to the hanger with one steel screw and
a second plastic screw.
The screws are on the center line of the hanger hinge.
The blades are attached along the airfoils center of lift.
The blades also balance at the attachment point.
Aerodynamically such attachment makes sense?
There is an old adage which says"Lighter flys better"
Reasoning is> weight requires power to move and lift to raise.
A lighter rotor feeds into such reasoning?
Another boring episode? Would hope not!
Good luck.

Hal [email protected]

Well no actually If the tang was simply angled forward from an original straight tang position then you would be correct, however the tang is both angled AND moved forward parallel to the centre of rotation. This ensures everything stays exactly in place be it a single bolted blade or a wet noodle !


Colin, you wouldnt be confusing flutter with flapping would you ?? I only ask as when I make really tight turns or heave back on the stick I always get a lovely 'thrumming' noise from the rotors.............all rotorcraft do it.

You know, I actually went flying with a fi...fix........fixe.....( ahem) fixed wing model yesterday and dispicable though you might think of me I actually enjoyed it ( waits for scornful remarks)

Sean

Hi Spindizzy,
Had a bit of a time understanding your latest jargon about delta.
So studied your photo once more.
Only you know for sure but>
It appears the tangs are as with a non delta hanger.
Delta is attained with the angled hinge?
Stupid question> if you would lay the rotor on a flat surface and
place a 90 deg triangle at the tip L.E. when it is at surface level
Holding that posistion what happens in relation to the triangle
when you cone the blade?
Would expect there is negative incidence, but have you checked? if so how much added negative?
Any other change?
Good show!

Hal

hello Hal

You are looking at the hub in the top right of the hub images arent you ?

The hinge lines are angled and this does give delta as the coning angle increases. I havent measured exactly how much incidence changes with a given angle but I do know it is more than adequate for very rapid spin up and when up to speed the lift is excellent as the coning decreases.

I used delta angle of 15 degree on a two blade hub as an experiment and it was a failure. Blade balance is upset by using delta due to the up flapping also causing the blade to effectively advance forward, this does not seem to be a problem on 3 blade hubs but on 2 blade offset hinged hubs it caused a lot of vibration. I know the whistler model uses delta 3 but this is on a teeter hinge so balance is maintained. Has anyone else used delta on a two blade offset hinged hub ?

Note, Non delta 2 blade hub worked fine.

Cheerio

Sean