Gyro-Tech US dealer and Modified Airfoil blades

eddie;n1136230 said:
Hey Brian glad you confirmed that the blades are no longer available from GT,I thought that perhaps I was getting goofy,or goofer.

Not a chance Eddie. Thought maybe I was just missing a button on their site. From my correspondence with GT Poland, they simply didn't have the numbers to support production since most folks want the "faster" blades. Makes business sense since that's where the money is. I'm unsure what the genesis of the Modified airfoil was... perhaps they anticipated a larger market for the low-n-slow ships, but I am only speculating. Nonetheless it seems I grabbed the last set of the Modified style there is. Other pilots are flying these but I've yet to learn who or make contact with them.


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Gyro-Tech wrote back to say they would supply an airfoil plot drawing for the Modified blades, which I will post here when received. Their drafter is on vacation for 2 weeks but they have been really great about being forthcoming with any and all info I've requested. They even supplied me with a SolidWorks model of their rotorhead for coordination with my gyro design. (Please nobody ask me to share that here because I would consider that protected information, and don't feel I have a right to.) It'll be interesting to let the number crunchers here churn the airfoil data and see if prediction matches reality.
 
I received my GT blades and hub bar yesterday and gave a glowing first impression writeup in the Crescendo Build thread. Quick question for those in the know... I understand the hub bar is machined with the coning angle built in, but to my eye the bar and its blade strap facing surfaces appear straight and flat (parallel and coplanar.) I know the teeter bolt is close-coupled to the hub, perhaps a couple inches off the top of the bar. But I would have expected to see a small but pronounced angle. I'm new at this so forgive my ignorance on the subject. Is this consistent with what others here have on their ships? Mine is a typical 23 ft. disc (10' blades w/ 36" bar).
 
Brian the earlier hubs bars were made without any angle built in,the EU gyro manufactures wanted the angle built in for

a smoother running blade,GT said that there really wasn't any difference that they could feel between the hubbars being flat

or with a built in angle,all of the later bars have the angle,I know mine does.There was mention of this in a test that was performed

on one of the EU gyros and they did a comparsion at that time,I know that they had to change the height of the teeter tower because

of the angle change.
 
eddie;n1136496 said:
Brian the earlier hubs bars were made without any angle built in,the EU gyro manufactures wanted the angle built in for

a smoother running blade,GT said that there really wasn't any difference that they could feel between the hubbars being flat

or with a built in angle,all of the later bars have the angle,I know mine does.There was mention of this in a test that was performed

on one of the EU gyros and they did a comparsion at that time,I know that they had to change the height of the teeter tower because

of the angle change.

I wasn't aware of this. I will have to check with Gyro-Tech regarding tower heights (teeter bolt). I am fabricating my own rotor head based on the pivot geometry of the GT head, which I was supplied a SolidWorks file of. I'm assuming their model, which is current, is now incompatible with the old style flat hub bar. Will study this more over the next few days.
 
I don't have any answers for you regarding the GT head.The post about

the different hubbars was mentioned in the report about the Skycruiser SC-200 they said that they did have two teeter heads with

different bolt heights and that the hubbar angle is 2.5 degrees.
 
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I guess when you mentioned a change in the teeter tower height I thought you were referring to those of the head billet. Were you speaking of the bearing block on the hub bar?
 
The article said they tried two different hubbar block heights as well as two hubbars,one straight and one with a 2.5 degree angle,it was never mentioned

about the rotor head also called the (teeter tower) being different. ? go to the gyrotech home page and click on news then gyro blog and then skycrusier
 
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The article also said they tested two rotor diameters as well, this might account for the two hub bar block heights as they were experimenting with undersling.

The cone built into the hub bar is really to relieve the bending stress on the blade roots caused by the blades coning in flight.

The GT hub bar we have mounted on the ELA is bent with a 2.5 degree cone, not much but the GT rotor flies very flat. Undersling is an inch shorter than the ELA.

By comparison the ELA has it's cone machined into the ends of the hub bar and it's rotor flies with maybe a couple more degrees.

At no to low rotor rpm the GT blades take on a drooped look compared to the ELA's.
 

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The GT hubbar has the 2.5 degree angle machine in the whole hubbar,I have heard that a lot of manufactures just put the hubbar

in a hydraulic press and bend the angle.

Really good photos of both bars alan,I like the looks of the other teeter block is that ELA.I don't understand why all gyro makers

don't use that type of tower and teeter block arrangement,one of my vibration problems was because of the out of date bolted

together teeter towers,the one piece tower is really the only way to go,perhaps on the lighter machines the old style tower

works just fine,I wouldn't know. the shorter bolt height may be needed because the GT blades are a lot stiffer and they don't flex

up that much in flight and the machined angle might also make a difference.
 
Thank you for the photos Alan. I noticed that the GT blade straps are also different on mine than yours, as well as the chamfer length on the bar edges. In the unboxing photo i posted you can see the straps end square where the new ones come to more of a point. Ill be aski g GT what the other differences are and how that might affect rotorhead design if at all. I would think using the standard rotor head with the shorter Teeter blocks would have the effect of raising the blades up, which would increase the angle the blades are allowed to Flap before hitting the stops. So I'm predicting they will recommend shorter Towers on the head. I'll keep everyone posted of what I learn from gyro-tech.
 
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Brian,

There are several differences between your hub bar assembly and the one we have, not understandable given the different rotor sizes. Your blade straps use three bolts for attachment to the hub bar vs the four in ours and your teeter block appears to allow for shim-less blade tracking. I think I can see some other differences too but it's hard to tell without more detailed pictures of the teeter block.

When we first got the GT rotor it was touted to be a plug-n-play install on the ELA, in reality we had a few issues, one was tower height. Because the GT rotor is about one inch shorter in undersling than the ELA it stood quite high in the towers and required tall teeter stop spacers (provided by GT) to keep the teeter range within limits. During flight testing we found undesirable control feedback and oscillation.

As an experiment I machined a spacer block that raised the teeter block and increased undersling by one inch, the modification lowered the GT rotor back to a normal position and we could remove the tall teeter stop spacers. The modification also made a marked improvement to control but also increased vibration as the undersling was now incorrect so at this point it was decided to install a GT head with it's appropriately sized shorter towers. Again we had some issues getting the head mounted on the ELA but in the end this was the best solution, stick forces are light and vibration to a minimum now.

So the moral to the story is have your undersling at the correct value and tower height only tall enough to allow the rotor it's proper teeter range.
 

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For our install we had to have the prerotator ring drilled for the RAF ring,and they made a spacer to bring

the ring height back up to RAF spec's,we found GT very pleasing to work with,they were willing to do whatever

it took for a good install,now the RAF package from GT is plug and play for new buyers.

Its interesting to see that your teeter tower is different than mine.I thought it a would be one size fits all tower.
 

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When we ordered the GT head through the US dealer we requested the factory in Poland not mill their name into the side, they were very accommodating with that request. The heads surface finish matches the hub bar, some type of bead blasting maybe, but it's not polished. The ELA like many Euro gyros uses a single bearing head, the RAF looks like a double bearing from what I can tell from the picture.

In ordering the GT head we thought it would be compatible with the ELA teeter bolt but found it was not and later learned GT uses their own specified bolt. Since we really wanted to use the ELA teeter bolt a decision was made to modify the GT head to accommodate it so I machined the additional flats on the sides. Tower wall thickness on the GT head in the machined area now matches the ELA at 15 mm but because the GT head is not tapered like the ELA there is more material surrounding the hole so we believe strength is not compromised.

We also found the GT upper bearing plate wouldn't work as it used socket head bolts that passed through the head and ring gear with nuts on the bottom, there was no clearance for the nuts between the ring gear and steel head plates. ELA uses hex head bolts passing up through the ring gear and head and threading into the upper bearing plate which is tapped, so we just used the ELA plate instead. Gyro-Tech was made aware of our issue and has since provided a revised upper bearing plate that mimics the ELA plate and it looks like it should work fine but we haven't installed it yet.
 

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Alan you worked through it all with quality workmanship, looks real nice.
funny how things can look the same but be completely different.
Its the little things that drive you nuts.
 
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We did encounter an additional problem.

Gyro-Tech uses very large bolts to mount their teeter block to the hub bar, we found the heads of these bolts would make contact with the ELA's upper spindle nut before the rotor could reach full teeter. Given the rotors rotation direction it would likely spin that nut off if contact was made or worse yet, spin both nuts off.

In the end, to get the full teeter range, we found it necessary to thin down the bolt heads, chamfer the hub bar holes so the bolts would sit flush and not install the washers. (you can see the modified bolts in picture four of post #32)

And additionally, GT cuts their bolts shorter so excessive threads don't protrude from beyond the nuts, this exposes un-plated steel so the ends need something to keep them from rusting.
 

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Just curious Alan is the main rotor bearing mounted on a hollow axle attached to the main control arm.
The complete rotor head looks very strong and well made.
 
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eddie;n1136688 said:
Just curious Alan is the main rotor bearing mounted on a hollow axle attached to the main control arm.
The complete rotor head looks very strong and well made.

The spindle is hollow and machined from a single piece of steel, the round part is stepped and threaded for the nuts. Pull two bolts and the head assemble slides right out.
 

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Its built just like a Cessna axle,being hollow makes it incredibly strong and resists flexing
like a single bolt would,thats a really good design. thanks for the picture Alan.
 
I received a reply from Gyro-Tech that included a response about the modified airfoil blades. Here is that portion:

The modified NACA 8H12 airfoil is thickened by ca. 0.5 mm as compared to the original one. The blades have increased lift force but they cannot fly very fast. Also, the modified blades have a smaller chord 203 mm as compared to 216 mm in the original blades.

Their drafter will be providing an airfoil point plot soon.
 
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