Q. to Mr Math. [CB]

Chopper Reid

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Thats a little too slow Mitch but going from 23's to to 27's is a big jump and you are now over rotored .What pitch are the GG's set at ?
My gyro with Patroneys 27ft 6 in rev at 300 which is only just fast enough in my opinion
 

Chopper Reid

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Flat bottomed rotors with blunt leading edges, such as Rotordynes, will start and autorotate at amazingly high pitch settings.

With Bensen style pitch adjustment blocks, Rotordynes will still start with pitch set at the upper limit of travel and still fly. Top speed will be in the range of 20 mph with the stick on the forward stop; more power and it climbs, still at 20 mph.

This is something I imagine Pete Johnson has experimented with, back in the days when no one knew the answer to “What if….?”

These Gerry Good win rotors [as far as I know] fly at similar speed to other makes of rotors .
 

Greg Mitchell

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26 foot Disc.

26 foot Disc.

Chopper,

They are currently at 26 ft.

They were supposed to be 25 ft.

Goodwin packs the blades, then strapped the new hub bar to the blade box.

Hub Bar got ripped off in transit. Great way to pack a product Eh!

Got hold of a 3ft and 2ft bar.

3ft bar gives 26 ft, which are the figures I supplied.

2ft bar has 800 plus mustering hrs on it an I've been advised by one ASRA Board member not to fly on it.

Another high ranking ASRA official said I could probably do hops and see what I get as far as rrpm etc. If it's good, send it off for eddy current and die penetrant testing. It would give me the 25 ft I originally wanted.

Both Bars are bent just outboard of middle for cone angle and twisted exactly the same at the same place. This it seems would allow for cutting down the 3 ft to a 2 ft bar.

Thinking I'll make a drilling jig, match drill the holes and cut down the 3 ft bar.

I can not give you any details on conning angle and pitch etc, the manufacturer was never forthcomming with any of my questions and we have since had 'words'.

In an ideal world I would get a new bar from the manufacturer but this looks less and less likely. I have had a similar experience to Echo with the purchase of these blades. Not happy.

What is the HUMP, HUMP, HUMP?

Do I shim the block for this?

Chuck,

I can send you the excel rotor performance data if you like for your perusal and advice.

Thanks,

Mitch
 

C. Beaty

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The rpm at which a rotor spins depends upon blade loading and pitch setting.

Any rotor can be made to rotate at almost any rpm imaginable by monkeying with pitch setting.

But there is an optimum. Too fast and the rotor eats too much power from profile drag. Too slow and the stick will be on the forward stop well before top speed can be reached.

Typically, the stick reaches the forward stop when forward speed reaches about 35% of rotor peripheral speed.
 
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C. Beaty

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The hump, hump, hump Mitch is most likely from being out of track. Out of track produces a vertical lope reminiscent of a galloping horse.

2/rev stuff is reminiscent of a trotting horse.

You should be able to see out of track, especially as slow as your blades are turning.

Look at the rotor tips at about the 2 O’clock position and if out of track, you’ll see two tip streaks. Shims will fix it if no more than a couple of inches out.
 

Greg Mitchell

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Chopper,

Yep, to slow and over rotored at 26 ft, agreed.

Chuck,

Thanks for your input.

Mate, I checked the track when I conducted a couple of pre-flight spinups, with the MLS belt drive pre-rotator. From my eyes, they looked good. One blade end is red the other white. They could have been within an inch or two.

I did string the blades and the string went thru the middle of the block.

I have the hub bar centred in the towers, better tolerances than I have with the glass blade set-up. So I believe the thing is geometrically centred(?)

I had to whack on taller towers which Larry Neal had sent me. I had originally decided to buy DW's. Sad but true.

The towers being taller, required a temporary strike plate/teeter stop arrangement to be made.

The interesting thing was THE 2 FOOT HUB BAR HAS A TALLER HUB, THAN THE 3 FOOT HUB BAR, BY .200THOU.

Neither Hub Block suited or worked with my existing Bensen Head/Patroney Blades. ( These are 23 1/2' Blades, weighing 76 lbs and have a 8H12 profile.)

Chuck, I understand what you say about pitch now.

I had to keep forward pressure on the stick and it seemed well forward of it's normal position for straight and level.

This caused me some concern in flight at the time, as we use a stick forward rotor brake set-up and noting the position of the stick, I was worried that the brake was close to being engaged. I know auto-rotative forces can overcome the brake, though at a very low minimum rrpm, I wasn't so sure.

It occurred to me to slacken off the trim spring but did not. I was more interested in noting the differences, than fixing anything at the time. Further the trim spring is already bunched up with full back stick. Someone else on this forum mentioned previously how little trim spring tension is required on the Monarch MLS setup.

Definitely heavier stick forces and the blades seemed to resist or were a lot slower to move to their new position. I was very much a different beast alltogether.

The blades hung on during the flare, though I am not sure if that is simply because I had more wing or the tip weighted addition.

There was a lot going on during those two flights. Lots of thought processes rushing through my head. I understand now just because these 26 footers are spinning so slow, it relates to pitch more so and far less to the mean lift coefficient of the blade....in general as the load is also factored.

So Chuck, do you think these blades are pitched up to much, that's why they are spinning so slow, not withstanding being over-rotored at 26 ft? How much faster do you estimate they will spin at 25 ft disc?

Perhaps if I had the 'new bar' I would find it has less pitch and perhaps then my new 25 ft tip weighted fence picketts would be the Ducks Nuts. Perhaps!:D

Appreciate the advice from all.

Mitch
 
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Aussie_Paul

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Mitch said...

Mitch said...

Mate, I checked the track when I conducted a couple of pre-flight spinups, with the MLS belt drive pre-rotator. From my eyes, they looked good. One blade end is red the other white. They could have been within an inch or two.

Mitch, you really need to have the rotors loaded to check track, shake etc.

Aussie Paul. :)
 

birdy

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Sum peoples doings ever cease to amaze me.
They buy a product, change it, then bitch n blame the manufacture that they dont fly rite.
Well no sh1t sherlock, wot your flyn aint wot he sent you.
gota blame everyone but yourself.


What is the hump hump hump? Does this recquire shimming the block?
Every blade that iv had that makes the machine hump were off center.
Shimm the block in the head lateraly.
Sumtimes itll only be a poofteenth, but it makes all the difference.

Iv never been able to throw the ferel around as effectivly as i can now with these blade.
Wot am i do'n rong?
Noone else seems to be able to fly them.
 

Greg Mitchell

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With all due respect 'Watson' where did I blame the manufacturer for the way the blades fly?

Who else am I blaming?

I suspect the blades fly the way the do because they are being strapped to other hub bars. If they flew like that straight out of the box on their original hub bar, then my posts would have been different you can be sure.

I'm trying to do the best here with what I've been left with.

The product came to me minus a hub bar, which was apparently strapped to the outside of the blade box. The manufacturer gave me dimensions for one blade box, not one blade box plus hub bar attached. If he had of told me this, I could have red flagged the freight forwarder. Everyone I have spoken to about how the product is packed and packaged, lacking any form of documentation or instructions, simply shake their collective heads or can not believe it.

The manufacturer has refused to work with me from day one. I shared with you some of my frustration by phone prior to the blades arriving.

I couldn't even get him to send me a picture of his blade profile....had to have an Austrian/German or Russian guy post it here on this forum.

None of my inquirys to the manufacture led to any solid info.

I have talked with as many folk as possible (with a background of experience using these blades) to work through this problem.

I am not on the Aussie forums bagging the manufacturer or his product....I am here asking questions trying to find a solution.

As to your last comment, "Noone else seems to be able to fly them.", your words, not mine. I fly them just fine and I feel once I have a safe 2 ft bar strapped on creating the 25 ft disc and the rotor rpm is up over 310-320 rrpm, shim the 'hump' out, I'll be happier....this is what I'm working towards.

What is the hump hump hump? Does this recquire shimming the block?
Every blade that iv had that makes the machine hump were off center.
Shimm the block in the head lateraly.
Sumtimes itll only be a poofteenth, but it makes all the difference.


That's helpfull. Thanks.

Perhaps you could ask your mate if he is using the same coning angle and pitch on his tip weighted blades hub bars.

Mitch.
 
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Resasi

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Mich didn't bitch. Just asked for help.

Guess he's dealing with what he's got seems to me.
 

Fl90

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By the way.....your stick position will be 15% less with the rotors set up the way you have them.

So, if your trim was 60 with the former blades, then your trimmed speed (same setting on the spring) will be 48.

The shorter hub bar will give you your stick response back.

Phil.
 

Greg Mitchell

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Thanks for your observations Leigh.

Hey Phil, I use Chucks rotor performance spread sheet extensively.
I cant remember now, so much going on but the blades are 7 3/8" or 7 5/8"
I think I have been using 7.45 as the chord figure in the program.

True enough Phil, on climb out my forward speed seemed slow, yet climb was still good, great really. I was trimmed for about 45 knots prior and I saw 30-35 knots a lot on these two flights, all the while having forward pressure on the stick and looking to increase the forward speed.

I agree, I believe with a 25 foot disc and shorter towers (these are tall, to suit a 24-25 ft set of DW's Larry Neal uses on USA Monarchs.) will give me far better stick forces.

Appreciate your advice and help.

Mitch.
 

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Fl90

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No problem. I haven't seen Chuck's spreadsheets, but the formula is the same.

I wouldn't spend too much time chasing the humps and pitch on the 3 foot bar, unless you have plenty of time to try different settings. The slow turning blades have all sorts of issues that seem to wander thru the flight envelope.

Phil.
 

birdy

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Rito Mitch, ill accept i mite have jumped the gun and jumped on your head without cause.
Sorry, im taken it back.
Just cant understand the hassle with GG.
Iv never hada problem with him, his blades, or the way he sends them.

But, Back to my origional question.
I didnt get a streight answer outa CB, but i did get reminded of the obvious.
As you know Birdy, a rotor blade carrying a load is operating at a positive angle of attack.
A rotor blade not carrying a load can be made to operate at a negative angle of attack by proper stick motion.

So im readn this as a "yes", a rotor can be commanded to reorientate at a rate that has the decending blade 'fly down'.
If this is happening, then as the blade passes through the decending section of the disc, the drag would, assumidly, be much greater, in that section of the disc.
In a left peddle stomp, the disc would have greater drag between @7 and 11 oclock, which would pull the stick AND the head forward.

Ill have to pay extra attention next time, to see if thats the 'uneasy feeln' im getn.
 

C. Beaty

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Mitch, if you had DWs, you’d throw rocks at anything else.

I suppose shipping costs from the US make them non-competitive but if you needed 100 sets, an ocean freight container would get them to you for minimum freight cost. Probably would also get you a good volume discount.

What is the Oz duty on such items?
 

Fl90

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Birdy, you did get answered....If only one side is flying down, it's called flapping.

Having the rotor pull you bacwards after a landig has the whole rotation with negative AOA.

If you're light enough the rotor can see negative, but one side negative and one positive, at very slow or no speed, would flap the blades.
 

birdy

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Birdy, you did get answered....If only one side is flying down, it's called flapping.
???????????
Not sure youd call this flappn.
Wot your calln 'flyn down' is just the cyclic balancing of the different AS on either side. Teetering IOW.
But wen the retreating blade goes down, its not flyn down, its decending under a pos AOA.
Wen i say 'flyn down', i mean Neg AOA on the blade, air over the top of the blade, opposite to normal air from under.......

Having the rotor pull you bacwards after a landing has the whole rotation with negative AOA.
Not Negative AOA, neg flow [ air in from top]. The blades are still see'n positive AOA. Big difference.
If the blades were see'n neg AOA on landing, theyd be pumpn air up, not down.

If you're light enough the rotor can see negative,
The only time the rotor sees neg AOA is wen your in serious -Gs. Lite in the seat is only lower than 1G.
In an inertia hover, the disc is see'n air in from the top, but the blades still have a positive AOA.

Is it just me, or am i alone ere????
 
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Fl90

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Since a rotor blade is flown into position and not shoved, the only way to have a negative AOA on a blade is to have air come in from the top. Negative or weight being supported by something else (Earth) while the rotor is spinning and the gyro is moving rotor first into the air.

You're talking about two different forces in the rotation of a teetering rotor. You would have hit the teeter stops and probably flipped.

You're talking about overspeeding the rotor, then slow speed high power rudder turn after a pullup. So, that would have you with stick forward from the pullup and as you get somewhere near frame level, kicking the machine arround at high power. In that case the rotor axis would have to change 10 to 15 degrees in the amount of time it takes to spin around. Oversped rotor, no problem, however the gyroscopic forces on the prop and gearbox at high rpm....well we've lost aerobatic pilots from the prop and crank taking out the wing.

Phil
 
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