Replacement Sport Rotors installed.

[Smack]

Oh Chuck, I think Vance's response proves the quote by Arthur C. Clarke, "any sufficiently advanced technology is indistinguishable from magic".

 

[Jincamty]

Hi Chuck, Does centrifugal stiffening increase the rotors inplane resonant frequency? Is there a simple formula? (assuming a constant mass beam)
Cheers Cam.

 

[C. Beaty]

Yes, Cam, centrifugal stiffening raises the inplane resonant frequency of a rotor but off the top of my head, I can’t say how much. That’s a topic that came up in the earlier discussion of 2/rev and I think it was Jean Claude DEBREYER who came up the definitive answer.

I measured the static resonant frequency of a 7” DW rotor by using a jig saw clamped to the hub and driven by a variable voltage power supply to find resonance which occurred at about 6Hz. The rotor was suspended by cords from the ceiling beams attached to the nodal points of the rotor; about ¼ rotor diameter in from the tips.

I wish I could find the earlier discussion of this subject but my navigational skills with this new format aren’t very good.

 

[C. Beaty]

Oh Chuck, I think Vance's response proves the quote by Arthur C. Clarke, "any sufficiently advanced technology is indistinguishable from magic".

Yep; to a monkey, a coconut must seem like magic.

 

[Alan_Cheatham]

I wish I could find the earlier discussion of this subject but my navigational skills with this new format aren’t very good.

Chuck,

Would this be the thread?

https://www.rotaryforum.com/forum/rotorcraft/theory-of-flight-aerodynamics/25552-aerodynamic-vibration

 

[C. Beaty]

Thanks, Alan, I believe that’s the thread but it’s not as definitive as I had thought. It does, however, serve to illustrate the complexity of the 2/rev problem of seesaw rotors.
***********
It’s all Bensen’s fault for necking down the rotor to 2½ inches at the hub. I understand there’s never been a 2/rev problem with SkyWheels rotors as a result of the wide hub that straddles the rotorhead.

 

[Doug Riley]

For what it's worth, i found the vibes generated by the 23-foot Skywheels on my Air Command 447 to be unpleasant much above 70 mph, and disturbing at 80. Of course, the machine was supposed to be a 63-mph Part 103 ultralight gyro and, without a HS, the nose tucked so low from HTL at 80 that vibes were the least of my worries. Getting dumped forward like a kid riding in a wheelbarrow was of more immediate concern.

Much later, I found that my tandem Dominator with a fore-aft slider head was quite civilized at 100 mph. However, the 2/rev was not entirely gone, just muted.

In any event, Chuck, I wonder if you agree with me that "cabin hop" from slightly varying rotor thrust through the rotational cycle is part of the 2/rev mix -- in additional to the in-plane 2/rev addressed by Young. The Bell and Robinson mast-engine-tranny mounts allow some up-down movement as well as in-plane movement, IIR.

The Bay State (Mass.) PRA chapter tested some gimbal heads to destruction and wrote up the results in the PRA mag around 1970. One of the failure modes they explored on their test machine was a varying vertical pull. They reported that asked Bensen how much the rotor thrust varied with the rotor's revolution, and the Bensen replied that the variation was about 6 lb. Obviously, that's triple hearsay and old data to boot, but perhaps worth some value as an order of magnitude.

 

[Vance]

No Title

My magic seems to be working because the stick shake and cabin hop never gets to be annoying anywhere from a 140kts indicated air speed to a vertical descent despite my allegedly incorrectly designed hub bar, blades with a negative pitching moment and a stiff mast on The Predator.

Oddly most people who ride in the back seat of the Predator remark about how smooth she is and some people say that it feels like she is going to shake herself apart. I suspect it is about gripping the stick tight and trying to quell the shake but I have not been able to verify this.

She has not been able to shake herself apart in over 1,800 hours of flying.

 

[C. Beaty]

Was the vibration with the Skywheels rotor 2/rev, Doug?

There was a gyro pilot out West somewhere, perhaps from Arizona whose name escapes me that used to fly with the 8H12 extruded rotorblades that have been sold under several different brand names, made to the same dimensions as Skywheels. He used a Skywheels hub that he lost; -I don’t recall whether he crashed or the hub just came apart- anyhow, he had to go to a standard 2½” Bensen type hub but the 2/rev vibration on his homebuilt “thing” evidently became unbearable. At my suggestion, he stiffened it up with parallel drag links and that solved his 2/rev problem. I think he died of natural causes several years ago.

It’s certainly not my intent to endorse any tail-heavy rotor. Years ago at a Bensen Days flyin, long before I had knowledge of Skywheels’ tail heaviness, I was flying down the main runway at Wauchula ~ 100 yards behind Steve McGowan in his Mazda Rotary powered Parsons Blunderbuss when he did a hammerhead turn directly in front of me, leaving us closing head on. I immediately shoved the stick forward and landed, deciding the sky wasn’t big enough for the two of us.
When confronted, Steve said there was plenty of room and no danger.
Only later did I learn that an uncommanded midair flare was a common occurrence that Steve disguised as a hammerhead when spectators were present.

I have negligible experience with Dreadnought class gyros so have only experienced vertical hop as a result of out of track; feels like a galloping horse as opposed to a 2/rev trotting horse.

 

[Doug Riley]

Chuck: Yes, i know the galloping sensation with bad tracking.

Of course, I'm claiming to have felt vertical hop in an open-frame, bare-bones 40 hp gyro

The high-airspeed vibe in my Air Command was faster than tracking gallop - pretty definitely 2/rev. It came on as I sped up from about 50 toward 60, 70 and on to 80 -- a speed that felt pretty crashy to me. I never flew that fast when out gyroing by myself; I'd push it only to keep up with faster FW craft or more aggressive gyro pilots. Even then, I refused to fly that fast in any turbulence, because of the PPO-ish feel at high throttle and speed settings. Air Command's factory H-stab later solved the PPO-ish feel problem.

For awhile, I thought this sensation might really be pushback through the stick, traceable to the larger cyclic pitch changes forced onto the (slow, heavy) McC rotor at higher airspeeds and hence higher blowback angles. Al Hammer claims that's not so -- that the automatic 2/rev cyclic pitch changes experienced by a blown-back rotor are "kinematic freebies" that consume no energy. At least I think that's what he said....

 

[Jean Claude]

The Bay State (Mass.) PRA chapter tested some gimbal heads to destruction and wrote up the results in the PRA mag around 1970. One of the failure modes they explored on their test machine was a varying vertical pull. They reported that asked Bensen how much the rotor thrust varied with the rotor's revolution, and the Bensen replied that the variation was about 6 lb. Obviously, that's triple hearsay and old data to boot, but perhaps worth some value as an order of magnitude.

Yes, 6 lbs of variation to 2/rev vertically on the mast is also what finds my spreadsheet for the B8M around 55 mph

 

[Doug Riley]

Thank you, sir.

 

[Kolibri]

Besides Sport Rotors, are there any other blades/bar with 1,600 hours on them which could be safely relied upon
for many more hours, much less fetching $2,000 on the used market?

_____
The most astounding aspect of this story remains unmentioned: the freight company that delivered this shipment
from New Mexico to California, and what they accomplished for just $700.

They picked up eddie's "dangerous" and "crap for balance" blades which gave him 100 hours of "vibration" and "miserable flying"
-- and magically made them smooth and safe for the next owner.

What amazing alchemists of aviation.

Regards, Kolibri

 

[All_In]

Besides Sport Rotors, are there any other blades/bar with 1,600 hours on them which could be safely relied upon
for many more hours, much less fetching $2,000 on the used market?

_____
The most astounding aspect of this story remains unmentioned: the freight company that delivered this shipment
from New Mexico to California, and what they accomplished for just $700.

They picked up eddie's "dangerous" and "crap for balance" blades which gave him 100 hours of "vibration" and "miserable flying"
-- and magically made them smooth and safe for the next owner.

What amazing alchemists of aviation.

Regards, Kolibri

The average FW certified aircraft pilots used to only fly 50 hours a year. With the increase in fuel I've heard but do not know for sure that it is less now.
I would suspect that gyroplane pilots on average fly less than that per year but even it it's 50 hours a year it would take 30 years to put 1,500 hours on a set of blades for the average pilot.
My point is most do not even come close to that so you're asking for statistics which few have ever experienced and may never even reach there would not be many who have even tried. Sad but true.

PS:
Chris may have over 1,500 hours on her previous TAG and not heard her blades were a concern or diminish the sales price as they look almost new.

 

[Vance]

The sixteen hundred hour blades are worth $1,999 to me to have as spares in case I need to send something on the rotor system out for repairs.

Being down for repairs is not good business for a flight school. I have a spare helmet, spare wheels and brakes for the same reason. I have lots of spare parts and even have a core Lycoming IO-320.

No one has offered me $2,000 so that is clearly not the market value.

I had a steep learning curve when I first received my Sport Rotors and I admire Eddie for being willing to experiment. From Eddie’s description he has his RAF smoother than The Predator by a wide margin.

Winds were 19kts gusting to 29kts today so I still have not properly tested my new to me Sport Rotors.

I have maintenance scheduled for tomorrow and winds are expected to be 20kts gusting to 30kts so testing will have to wait. It is not a priority for me.

I expect the winds to continue through Monday with a chance of rain Monday.

I have a new primary student starting March 4 so hopefully the weather will settle down and I will be able to test them properly before then.

My sixteen hundred hour blades are still together just in case.

 

[Kolibri]

The average FW certified aircraft pilots used to only fly 50 hours a year. With the increase in fuel I've heard but do not know for sure that it is less now.
I would suspect that gyroplane pilots on average fly less than that per year but even it it's 50 hours a year it would take 30 years to put 1,500 hours on a set of blades for the average pilot.
My point is most do not even come close to that so you're asking for statistics which few have ever experienced and may never even reach there would not be many who have even tried. Sad but true.

All In, yes, I understand that, but even if I never imagined that I'd time out a set of 2,000+ Sport Rotors,
I'd nonetheless insist on flying them vs. others with less service life.

My point was mostly rhetorical: that I know of no other brand of 1,600 hour used rotors for which the seller could ask $2,000 without gales of laughter.
However, with a set of Sport Rotors, such an asking price is not unreasonable.

Regards, Kolibri

 

[eddie]

Kolibri what do you think the selling price for my RAF blades was?

 

[All_In]

Hi Kolibri
OK seems I need to learn this as I do not know.
What is the time life you have discovered for the other blades manufactures. I did not know any had them.
I've not heard a time life on Dragon Wings.
I've not heard of anyone in 8 years telling us they have to replace their rotorblades because they reached there time life limit. Maybe only because none have reached those limits but what are they for the other manufactures you are comparing?

I just talked to Ernie today and should have ask him but it was before I read you post. I will tomorrow and ask his opinion on the others blades and let us all know what an experts opinion is.

 

[All_In]

Well Ernie is out until Monday so No Joy yet.
However did ask the employee. He said he never heard of a time life on DW but did not know about the others.
He said he has only replaced blades that have hit something since he's been there and one set of DW's was many years old and had over 2000 hours on it so he's not sure should ask Ernie on Monday.

 

[Vance]

I have been told Sky Wheels are on condition.

The earlier AutoGyro products had a listed blade life limit of 700 hours.

The newer AutoGyro products have a listed blade life limit of 2,500 hours.

The RAF blades on The Predator had about 250 hours on them when I replaced them for cracks in the trailing edge that were growing. They were nine years old. I don’t know what the RAF hour limit is as I was not using them on an RAF.

In my opinion the cracks were a time related issue.

On a non-series production experimental gyroplane the aircraft are all different and flown differently so in my opinion a life hour limit would be pointless.

Most parts in aviation have both an hour limit and a time limit.

For Example the time between overhaul on my Lycoming IO-320 is 2,000 hours of 12 years.

As I recall the Titanium Explore are on condition.

I have heard the Magni blade are to be inspected at 2,500 hours and there are lots flying out there with over 3,000.

I will leave it to John to report on Dragon Wings.