Skywheel hub bar

gyrojake

Gyro Rehab Candidate
Joined
Jan 1, 2007
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E-City, Florida
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Looking for a good skywheels Mc'cutchen hub bar. The short one.
Total length will be three feet.
 
Jake
A quick question, can you use any Mc cutchen blades with any Mc cutchn hub bar or are they made in matched sets like most blades?
Rick
 
The old ones, which I have NOS, are a matched pair,
according to the old Skywheels website.

But maybe it doesn't matter for the hub bar?

The new series of blades can be mixed.

Cheers
Erik
 
Jake
A quick question, can you use any Mc cutchen blades with any Mc cutchn hub bar or are they made in matched sets like most blades?
Rick

They are usually a matched set.
I'm gonna use the hub bar on a set of Xenon blades that happen to fit perfect in the hub bar.
 
Jake, a comparison between SkyWheels and Xenon blades in the same hub would be interesting.

Identical airfoils and probably the extruded blades, with their thick skins, are equally as tail heavy. Do they have sufficient torsional flexibility to cushion the landing like Skywheels?

Or do they drop you like high inertia blades with correct CG do?

I assume you've flown Hughes blades with 5 lb tip weights.
 
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Yes, the profile is identical.
The extrusion differs from the Fleck type rotor, I will post you a pic of the inside and I will also balance the cord and see were it's at.
I am not sure of the flight dynamics,as I have not flown them yet.
I have flown the 269 blades and they performed very well,just spun the other way.
 
During the landing Jake, as the roundout and flare is performed, the “G” load on a rotor is increased. To accommodate the increased load, the rotor rpm must increase or else some form of collective pitch control is necessary.

Low inertia blades, such as original Rotordynes only needed the stick to be bumped back and the rpm increase was nearly instantaneous. They would catch you quite easily.

On high inertia blades such as Hughes with their 5-lb. tip weights, that technique would drop you since there wasn’t enough time for rotor rpm to catch up.

But of course a good landing can be performed with high inertia blades but they must be given more time to accelerate.

With Hughes 269 and OH-6 blades with intact tip weights, I used to roll into a tight turn just before landing and as I rolled out at a few feet above the runway, I could play helicopter for a few seconds.

Most people sawed off the outer 6” of Hughes blades and got rid of the 5-lb. brass tip weight.

Skywheels had a form of automatic collective pitch by virtue of being tail heavy so they performed quite well with a “pop” flare.
 
I have a collection of McCutchen hub bars, some have the splitting between the top and bottom halves (as do many). I used to sell the hub bars to Rotorhawk extruded blade builders, by trimming a little bit of metal off the trailing edge, hawks fit the hub bar as well.
Helicopter Ed swore by them and bought several hub bars from me.

I only have red hub bars, $75 each plus shipping.
 
Tom, Can the hub bars be repaired if they are split and not to badly split?

I have a spare I got with a set of bad blades and the hub bar is split for like 3 to 4 inches on one side. I had thought to repair it as a backup hub for my blades
which by chance fit my blades exactly like the hub bar that came with my good
rotors. Must of been same production run.
 
Darren, you could super glue them together once you clean the split.
It matters on the drill jig they used if it will be interchangeable.
Check your string with the blades in the spare hub withe the bolts in, that tells the whole story.
 
I have re drilled a sky wheels hub bar for different skywheels blades. We had them perfectly strung, then used a piloted spot face bit to pilot off the holes in the blades, so it re drilled the hub bar, oversize but lined up with the blades holes, then epoxied bushings into the hub bar to bring the hole size back down.

They flew great, really smooth until they crashed into a pole barn and split open like a butter bean.....
No it was not me..
 
I have a white one in excellent condition W/teeterblock...$200 + shipping
 

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here is a pic of the blade profile.
 

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Has anyone tried the Super Glue and Baking soda Trick ??

I understand it cures faster and it is sand-able
 
I would be very careful of using any CA type glue (super glue ) on any thing that has any flex in opperation as it is very strong but but also has no give before breaks. Some form of aircraft grade epoxie would be much better especially if you could find one that has the same modulus of elasticity as the epoxie(?)(polyester?) the hub bar was built with.
Rick
 
Here’s what Pete Johnson in this thread says about high inertia blades:

http://www.rotaryforum.com/forum/newreply.php?do=newreply&p=361232

Russ, you make some very good points.
Back in the day when I flew Hughes blades, I had one pair with the stock tip weights, and a second pair with the weights removed.
The weighted blades were great for Xcountry flying, but they were dramaticly different manouvering characteristics. The heavier blades were sluggish as compared to the light ones. They responded to control inputs entirely different, giving them an entirely different "feel", making difficult adjusting from one to the other. Most notably landing!
After flying the light blades for a time and switching to the weighted blades, my first few landings were always ..."less than elegant"! The heavy blades required rounding out and loading consideably earlier, or you could just mush thru and smack pretty hard! The "feel" for the heavy blades came pretty quick, but then when switching back to the light blades, I would invariably flair too high a couple of times before my reflexes readjusted.
I have not flown the heavy Dragon wings, but I suspect switching back and forth would yield simular results. Maybe not a good idea.

Lots of people confuse tail heavy with “high inertia.” Tail heaviness provides a form of collective pitch while purely high inertia does not.

Tip weights increase inertia by a factor of 3:1 as compared to uniformly distributed weight; in other words, a 5 lb tip weight has the same effect on inertia as an extra 15 lbs spread uniformly over the length of a rotor blade.

When a rotor blade is tail heavy, aerodynamic force acting on the aerodynamic center during the landing flare twists the blade noseup if the blade CG trails the AC, providing a form of collective pitch.

Tail heaviness also provides a light stick, something like self actuating brakes or power steernig. Real high inertia blades cause a heavy stick.

The AC is nominally at ¼ chord for most conventional airfoils.
 
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This hub-cracking issue terrified me when I first saw it on my McC hub. But...

To confirm that Tom is right, you have only to think about the loads on a hub. Of course, most hubs don't feature a sleeve completely surrounding the blade; just straps top and bottom. The straps (or half-shells in the case of the McC hub) are normally loaded mostly in tension (2-3 tons' worth of it). The hub resists up-down prying loads via the clamping action of the bolts, not the fairly weak glue seam between the upper and lower half-shells.

Chuck B., I think that the McC's do exhibit some of the characteristics of a fairly high-inertia rotor, though tempered by the G-twist effect you describe. I recall my early flights in my McC-equipped Air Command, after only flying Bensen blades before. I was amazed at the almost fixed-wing-ish float that I'd get if I flew gently down into ground effect with little-to-no flare, powered back and just waited. That 70 lb. of spinning mass stored more energy than the 25-lb. Bensens.

The McC's also could be a little slow to get out of the way if you gave them a sharp lateral stick input. You could get some slap-back in the stick as the blades lagged and tapped the teeter stops.

A modest amount of this effect is no bad thing, IMHO. It indicates some rotor damping, which can help to prevent overcontrol. I think that the stock Bensen's propensity for porpoising was attributable to low rotor damping as well as the lack of a meaningful H-stab.
 
Doug, if each blade of a 23’ 70 lb McC weighs 30 lb., then it has the same MOI as a 10 lb rock on a 11.5’ string. (MOI = mass*radius²/3 In the case of a uniform bar)

Exactly the same as a 15 lb DW blade with 5 lb tip weight on a 23’ rotor. But the DW with 5 lb tip weight will drop you during the landing unless you use a procedure that allows the blade time to accelerate during the landing flare. No built in collective with its attendant angle of attack instability.

Where rotorblade MOI really matters is jump takeoff gyros. All of Dick DeGraw’s jumpers have used tip weighted DWs.

Rotor MOI is also important for good transition to autorotation in helicopters.

Here’s a video of John Snider doing hovering autos in his Mosquito using DWs with extra tip weights:

https://www.youtube.com/watch?v=_W_5lo_trDI

The construction of DWs permits the addition of tip weight without upsetting the chordwise CG.
 
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