Rotor length

[BeefBear]

Apart from calculating the length of the rotor required to lift the MTOW of your aircraft, is it possible to be over lengthed ( Russ - I'm talking about your rotor)?

Ted

[Birdy2]

Yes.

[russ]

To be honest..........I don't know

Do know that this was not a problem years ago [ breaking hub bars etc]

I think that we are getting too heavy with machines, maybe the materials used are not genuine spec stuff
maybe the metal urgist guys are changing the ingredients etc, altho their books say it will be OK

Do know that a lot of alloy is made in china.........that's a worry
Do know that blade profiles are changing
Do know that blade building techniques are changing
Do know that gyro designs are changing

Maybe we all change hub bars every 500hrs........but why,give us a reason, whats causeing the prob. Don't throw the baby out with the bath water, so to speak.

Maybe we ALL pay a levy to go to a genuine expert to find the answers here.

Too many Do knows........no answers......sorry

[BeefBear]

Okay...... Let me put it another way.

Light years ago, when gyro's were first becoming popular her in Australia, what was the ratio of rotor length to weight as compared to these days?

I, personally believe that we have created a harmonic reaction which is trying to destroy the currently used hub bars.

Have the rotor head assemblies increased in structural size proportionally to the increase in performance values of the rotors we now use?

Russell makes the point that some metals are produced in China. Do you are the owner of the gyro know where your metal was manufacturered and what does it consist of?

Can the metal that is used in your gyro be traced back to manufacture?

Ted

[russ]

Back in the old days........all gyros were single seat, weighing all up about 190kg, useing 24'.......26' length blades.
By the way....that weight included your fuel

One machine I had back then was perhaps the first turboed soob, direct drive 56" wooden prop. Was giving 360lb of thrust..........went like hell.* *That was in 1985 according to my 25yr old diary [ trusty things them diary's.......aye]

:focus:* * *Never heard of any hub bar breakages then................never

I personally know 3....4 older guys, that go back 30 odd years with gyros, really know their shit, but decline to get onboard with forums, really pissis me off as they have so much to share......love talking with em.

Forgot this bit........gyros were mustering back then, one guy in particular "Rusty Fergusson" was getting huge hrs flying, never busted bars,never.......except when he pranged a machine. I reckon by now he would have 20 thousand hrs up in these things.........what him and some others could tell us would be awsome.

[BeefBear]

Wot???? :bat: YOU never wrote it all down in ya diary?? :girl: What sort of a mate are you

[Bob]

I'm guessing here , but it seams to me the answer is fairly simple, corse I may be all wet too...
sense the gyros of today are alot heavier there is more stress on the hub bars, that havn't realy changed in design from the onset back in the 1980's ... now we're runnin 2 place units ,biger engines and longer rotors on the same or relitively the same rotor heads... in my book thats gott'a be a major flaw !
Granted the benson head is so over built it can and has been used for years on 2 place units ...
BUT is it big enough for a 2 place craft... I don't think it is
instead of using a 1" thick hub bar on a 2 place unit we should be useing a 1.5" thick hubbar at LEAST !
if you increase the weight the craft carries you must increase the striength of the pertanant pieces that keep the thing togather ! its only resonable!
Now I know I made some statements here that for the most part may be way off... the benson head being the same , and the same rotor head being used by a 2 place machine .... I havn't got my calapers on one yet so I realy don't know , but it looks to me their identical or so very close to it its not funny
if you can look at it from a distance and tell its bigger than the norm then its probly fine !
but on the other hand if it looks just like the head on a single place gyro and its on a 2 place gyro maybe its time to make a new one ???? eh ?
I mean come on guys , my rotor is held on with a 3/8" bolt !!!!!! don't it seam a bit wizer to hold it on with something a bit stronger ? the teter bolt is also 3/8" why so darn flemzy for hevons sake ??? weight ? Fooie on the weight make it STRONG !
I realise the holding striength of a 3/8" AN bolt is alot but I for one would sleep better at night if I knew the bolt holding my rotor on was 1/2" or 5/8" instead of 3/8" I would KNOW its not going to shear off in rough conditions .... or anything else for that matter !
from what I've been able to gather on the hub bar failure thing is that it has happened to High -time 2 place machines only and they were running hub bars that are designed to extend the blades on single place machines ( 4 foot hub bars ) 1"x3"x48" .... the same dimentions of the hub bar I made for my machine ... but mine is a single place machine not a 2 place craft.
I don't see what all the fuss is about realy .... if it failed it was too weak in the first place !
it should be a sign to the rest of us to change it RIGHT NOW !
make it stronger or suffer the same fate !
nuttin' hard about that !
...
thats my 2 coppers on the subject !

C ya !
Bob........

[BeefBear]

Bob, you could well be right here. I have noticed that Magni rotor heads consist of 2 parallel plates rather than a solid hub bar. Question here is, does this mean its stronger or simply more flexible? Does having parallel plate have more give in the unit and thus reduces the impact of the harmonic signal being generated by the blade movements?

Ted

[Bob]

I have no idea there Ted .... never have laid eyes on one of those so I'ed be liein' if I said anything else !

I hurd talk about rotor heads designed to reduce harmonics , that may well be one of them, i dunno.

in the world of aircraft, especially Rotorcraft.... Solidity is not alwayse a good thing ! this is very true, but if it were my guess I think I'ed go for the over stressed aspect of the use in question.
its kind'a like the Ford carberator , they used the same carberator that they used on the modle t's right up to the 1950's and early 60's they Only changed it because they had to , not because it was the smart thing to do .... anyone that had a ford in those days with a small 4 or 6 cyl engine in it knew that replaceing the carberator alone would realy increase the horse power of the automobile ! but the old carberator did work.... even though it was never designed for the job it was later given...
same goes for the hub bar ... it works, been working great for many years... but now their starting to let go ... it just wasn't designed to handle that kind'a load ...
thats my guess, I may be way off here but it stands to reason the way folks do things there's a fair chance I'm right hehehehehehe
Personally I feel if the rotor system is set up properly in the first place there is no need to have a Mast that isn't too strong, or a hub bar thats too strong and have to worry about the non flexing of these parts .... if the rotor system is RIGHT there will be no harmonics because its ballanced properly in the first place... sure you'll get the motion of the advanceing blade and retreeting blade in there
but by all intents and purposes they cancle each other out (or so it says in fine print) ...
the problem is that setting up a PERFECT rotor system is shooting for the Moon ! its realy hard to get exactly right , so folks have came up with ways arround the problem....
.... but we shouldn't look for an easy way out if you have to design the aircraft arround your short comeings ya know ? do it right the first time and you don't have to make up these ways arround the problems caused by the rotor being out'a whack ! .... like flexable masts too thin of a hub bar...
it just seams kind'a silly if ya stand back and look at it all...
Now I'm no expert on anything ! and I know that is a realy simple way of looking at a complex problem
but its complex..... WHY ? because of the comprimises ?
I've often wondered what a gyro would look like and preform like if all the compromises were thrown out and good solid KNOWN things were used instead of the Compromises ! hehehehehehe
I bet it would be a realy diferent animal than we're used to !
.... then again it just might be the same and weigh a ton ! HAHAHHAHAHA

too many unknowns... too little time to find the answers ! so we're stuck with wondering ! hehehe!

C ya !

Bob......

[BeefBear]

Thanks Bob,* *I've always wondered if the amplitude of the harmonic wave is greater on a rotor which is longer.* As I understand it the rotor head design hasn't changed that much over the years.* People worry about the weight of an aircraft but seem to accept that the same designed head which worked on the 23 footers will also function correctly on a 29 footer.

Ted

[Bob]

EXACTLY Ted ! you got it !

longer usually means lower in frequency....

changeing the length of something that is getting shook to pieces by harmonic vibration can change the shake entirely ....
I had a home made jig saw htat worked great except the darn thing would shake extreamily bad
it'ed almost make ya go blind just trying to use the thing ! ...
I changed the lenth of the support atm for the returning action of the blade ( because the other one broke ) I made it shorter by about 6 to 8 " and walla.... hardly any shake at all !
and the thing had a 1.5" stroke ! and I used a washing machine motor ! heheheheh

Longer Rotor blades would have a lower harmonic frewuency than a shorter rotor blade.

I noticed a dramatic change in shake and stuff when I changed out my 1' hub bar with the 4' hub bar I made.... but that is probly not a fair comparison as i finally ballanced the blades RIGHT before i put them back on with the longer hub bar.(grin) but all the harmonic shakes I had noticed as the rotor spun up were just ....GONE. it would go through 3 stages of minor shakes gatting up to Flight speed before... after the new hubbar and ballanceing there was none of that ...
there is a point at which my gyro resonates with the motor .... and believe me if you leave the rpm right there ic can get nasty .... it happens arround 2800 to 3000 rpm I alwayse go past that airia as fast as I can ...

Harmonics are a fasinateing study ! My Ham radio experience ( KN4ID is my call) has helped me understand it alot ... sense I delt alot with the makeing of antennas !
Amplification by harmonics is a principal used extensively in ham radio stuff.

Catcha later !

Bob......

[BeefBear]

True Bob, but in this case is the harmonics causing the issues with the hubbars coming from a horizontal or vertical source?

[Bob]

Unknown ! ... more than likely both ... or a twisting action which is worse... when you have 2 harmonics that blend togather they come out produceing a vector thrust or a twist to the object
in antennas, this means you make a antenna in a spryl as in some high frequency antennas .
but a harmonic is a harmonic.. weather its at light speed or at slower viberations as in a rotor rev viberation.... when they add up its usually bad news because the product of the 2 harmonics makes a big shake.... like Rouge waves at sea.... same principal here ...
weather its vertical or horizonal or a combonation of both ( which is reasonable to asume )
harmonic spikes are just that SPIKES ...when plotted on a graph... they realy jump to extreamly high amplitudes.... easily weaking a hubbar over time ....

the cure ...get rid of the harmonics.... if you can't ...get rid of the strain... if you cannot reduce the strain..then make the hub bar stronger .... there realy isn't much else you could do
....
for what its worth , thats how I seez it !

See ya !

Bob......