Bensen rotor blade question

[giro5]

I have a question for some of the older more experienced rotorheads out there. I have an original set of Bensen metal blades. The hub bar has an aluminum block with a 3/8 hole for the teeter bolt. What if any lubricant should be used here. ie wheel bearing grease, Anti seize compound, white grease like lubriplate, thin oil like 3 in 1, or maybe a brake in oil with a high zinc content. I have a hard time believing this bolt and aluminum block should be run dry. Does any one know what Bensen or Ken Brock would recommend. The rotor head is a Neal Carnes with bearings in the towers but I am not sure if the hub bar will rotate on the bolt or remain fixed and the bolt rotate in the bearings???

 

[Doug Riley]

Giro: it's best to post a photo of your teeter towers. Setups vary.

The classic Bensen arrangement was that the teeter bolt did NOT turn in that central aluminum block. Two bushings, one in each tower turned on sleeve bearings in the towers. These bushings were shaped like little top hats, hence their nickname, hat bushings. The horizontal "stack," made up of the bolt with bushings on each side and the block sandwiched in the middle, was tightened down hard. The block and the bushings swung around as a unit.

But I don't know how Neal Carnes did it. Non-Bensen suppliers sometimes got creative.

Doug (maybe older; maybe experienced)

 

[giro5]

Here is some pics.

 

[giro5]

With my Neal Carnes blades the teeter block has an adjustable arrangement built in I presume to one center the teeter block and to make it so that the assembly pivots on the tower bearings. With the Bensen hub bar teeter block I shimmed the block to center it but I am not sure it is tight enough to rotate on the bearings. May just need more shimming. My goal here is to compare rotor rpm with the bensen blades vs the Carnes blades. 20 ft vs 27 ft with my all up weight. When I bought the blades from Neal I thought he sent 25 footers but it turns out to be 27 footers. And now I have to go measure the bensen blades assembled again to see if they are 20 or 22 feet in diameter.. Been a long while since I messed with gyros but my interest has somewhat rekindled. I have only flown the Carnes blades in a towed configuration since my mac took a dump right away when I had it on my kb2. The large blades are because my elevation is just over 5K feet. Now I also have what looks like a factory gyrobee that I want to try both sets of blades on but also in a towed configuration.

It makes a lot more sense that the teeter block does not turn on the teeter bolt. I would think this would lead to galling pretty quickly.

 

[Doug Riley]

Classic Bensen 81FM metal blades with 2-foot hub had a 22-foot diameter. Bensen eventually offered a hub with (IIR) another foot or so of length.

Your head looks to have the same arrangement as a Bensen (and many others). Assemble it, tighten the teeter bolt snug and see if it teeters freely. If not (if tightening it locks the teeter hinge), then you need either to put shims between the inside faces of the hat bushings and the central block, or make new hat bushings with longer necks. When assembled, the teeter hinge should have a couple thousandths chordwise play, to leave space for the grease under the shoulders of the hat bushings -- but excess play will allow the rotor to shift chordwise and cause random vibrations.

No, you wouldn't want a steel-on-aluminum teeter "bearing." It would become a mess in no time, if it didn't seize outright.

Bensen blades ran at over 400 RPM, even at sea level, when set at their scribe-marked pitch (1.5 deg. I believe). I would think they'd be poor performers at high density altitude. You can squeeze a little more performance out of them by pitching them up by about half of one scribe mark's width. Don't overdo this trick, though. They get harder and harder to start as you pitch them up but, more importantly, Bensen blades are light and don't store much energy. With lower RRPM, they store even less energy. They slow down quickly if you unload them.

 

[Gyro28866]

1st,
You have the hat Bushings with the bolt in the Tower. The Bolt the Bushings and the Hub Block make up a solid unit when tightened down.
You shim the Bushings to give you 4-6 thousands play between the towers and Hub. The hat bushings are lubricated to the Towers bearing/bushing.

2nd,
I just run the spreadsheet and with AUW of 500#; the 20' x 7.5" cord will turn at 435RRPM; the 22' x 7.5" cord will turn at 377RRPM; but with a 27' x 7.5" cord it will turn at 277RRPM. That is mighty slow and I don't think you will have sufficient centripetal force within the blades for rigidity.
What do you think a realistic/actual AUW will really be???

My Bensens sweet spot was 375-400 rpm. 1 1/2 degree pitch put them right on the mark for me. A 2* pitch slowed them to 340'ish which incresed the height of the coning angle and I flelt a bump in the seat.

 

[giro5]

Went out and checked the rotor head and hub bar again. Actually, had it shimmed ok and the assembly tightened ok so that the bolt is moving with the bearings but the bolt is not too tight so as to distort the towers.. My all up weight used to be about 510 lbs when I was flying the 27 ft blades. they worked fine when I towed the kb2. Current all up weight is right at 530 lbs when towing with the bensen blades and 550 with the 27 footers. But I am curious as to what the rrpm actually is with the 27 footers vs the 22 footers at my altitude in the summer 80 - 95 deg day.

Last time I towed was nearly a disaster. my driver had no common sense about the process. Mostly my fault for thinking otherwise. We towed for about 20 minuets in a racetrack pattern until he slowed enough so the gyro touched ground again and I released the tow rope. The first driver I had was good from the start after discussing what we were about to do. The second driver I used was like we never talked about what and how to tow.

Anyway thanks to all who responded. If I ever get this done I will post the results. And one last thing the Neal Carnes extruded blades and hub bar weigh in at 78 lbs. It seems to me they have a lot of energy when up to flying speed.

 

[Doug Riley]

My first gyroglider tow driver was a high-school buddy a year younger than me -- meaning age 15, too young to have a driver's license. But you don't need a license to drive on a private runway -- and he'd been driving since he was about 10.

He was excellent and is still a good friend. Ya gotta pick 'em right!

 

[mrmean99]

I have a question for some of the older more experienced rotorheads out there. I have an original set of Bensen metal blades. The hub bar has an aluminum block with a 3/8 hole for the teeter bolt. What if any lubricant should be used here. ie wheel bearing grease, Anti seize compound, white grease like lubriplate, thin oil like 3 in 1, or maybe a brake in oil with a high zinc content. I have a hard time believing this bolt and aluminum block should be run dry. Does anyii one know what Bensen or Ken Brock would recommend. The rotor head is a Neal Carnes with bearings in the towers but I am not sure if the hub bar will rotate on the bolt or remain fixed and the bolt rotate in the bearings???

You mean there is nothing? Not a bushing at least? Well my father was Steve Phaneuf of Rotordyne in Burbank California. His rotor heads were a work of art. I worked with him and my uncle making blades and adjustable hub bars. We used an oil light bronze bushing. Very close tolerance

 

[Doug Riley]

On a Bensen-style head, the central block and the "hat" bushings on each side of it are locked together by tightening the 3/8" teeter bolt. No lube is needed in the central block, because the bolt, the block and the hat bushings teeter as a unit. The bearings that allow this motion are mounted in the towers.

The Rotordyne head (the first kind of gimbal head I flew) was different. The central block contained Oilite bushings. These had about a 1/2" ID. In these bushings turned a steel tube with a 3/8" ID. The 3/8" teeter bolt passed through this tube.

The tube extended out to the inside faces of the towers. When you tightened the teeter bolt, it pinned the tube between the towers. When the rotor teetered, the tower-tube "stack" turned in the bushings in the central block.

Kinda the opposite of Bensen's practice. No "hat" bushings, and no bearings at all in the towers.

It turns out that Oilite is not a great choice for this application. The rapid back-n-forth of the teetering motion, under the full weight of the gyro, is enough to cause the Oilite to stick to the steel. Some Oilite gets torn off the bushing and clings to the steel tube. You really need antifriction bearings (needle, ball,. etc.) in this sort of application.