Crescendo Build

Doug Riley

Platinum Member
What J-John said. Watch that gear geometry.

Bensen's original landing gear configuration (the "tail sitter") is very right, IMHO. The aircraft sits on its nosewheel and mains with the pilot in the seat, with about 30-40 lb. weight on the nosewheel. As the rotor spools up early in the takeoff roll, the aircraft soon rocks back, increasing the disk AOA and assisting with rotor spinup. The rock-back, IIR, is about 5-6 degrees, or around 6" at the tailwheel.

Some people find that the fact that a Bensen gyro sits on its tailwheel when parked to be undignified (much as they find the plywood scrub brake, overhead stick, or "lawnchair" seat undignified).

Those who have varied the Bensen design have sometimes altered its landing-gear formula in a way that discards its advantages. For example, the stock Gyrobee has very limited rock-back -- only some 3"-- perhaps because of the "stacked' 2x2 keel/tail tubes. This reduces the available disk AOA during the early part of the takeoff roll, when you could use more to bring up RRPM.

Others have placed the main axle back so far that rock-back is delayed or eliminated. If you happen to have a full- RPM prerotator (as the McCulloch J-2 and Air & Space 18A do) then it doesn't matter. With the typical partial-RPM (or zero!) prerotator found on homebuilt gyros, however, eliminating rock-back is not helpful.
 

Brian Jackson

Platinum Member
No Title

Hi John, and thanks for the review. Yes, increasing nosewheel loading was the purpose of locating the mains further aft. It's a bit more like the Sport Copter arrangement in that regard.

I did manage to finish the radiused slot in one of the couplings last night (in previous photos). Still much more work to be done on it but happy with how that operation turned out. The bottom gets sawn off/milled down parallel with the angle of the slot, and there's 3 more holes to drill and counterbore. For such a small, lightweight part it sure is a lot of work. Learning a lot though.
 

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Brian Jackson

Platinum Member
Doug Riley;n1143126 said:
What J-John said. Watch that gear geometry.

Bensen's original landing gear configuration (the "tail sitter") is very right, IMHO. The aircraft sits on its nosewheel and mains with the pilot in the seat, with about 30-40 lb. weight on the nosewheel. As the rotor spools up early in the takeoff roll, the aircraft soon rocks back, increasing the disk AOA and assisting with rotor spinup. The rock-back, IIR, is about 5-6 degrees, or around 6" at the tailwheel.

Some people find that the fact that a Bensen gyro sits on its tailwheel when parked to be undignified (much as they find the plywood scrub brake, overhead stick, or "lawnchair" seat undignified).

Those who have varied the Bensen design have sometimes altered its landing-gear formula in a way that discards its advantages. For example, the stock Gyrobee has very limited rock-back -- only some 3"-- perhaps because of the "stacked' 2x2 keel/tail tubes. This reduces the available disk AOA during the early part of the takeoff roll, when you could use more to bring up RRPM.

Others have placed the main axle back so far that rock-back is delayed or eliminated. If you happen to have a full- RPM prerotator (as the McCulloch J-2 and Air & Space 18A do) then it doesn't matter. With the typical partial-RPM (or zero!) prerotator found on homebuilt gyros, however, eliminating rock-back is not helpful.
Thank you, Doug. Always a great learning opportunity when you chime in. To clarify, the main gear rake back distance has not been determined yet; the model plan view shows the max range available before there's mechanical interference. The final gear location will be somewhere forward of where shown. I have not cut the drag struts to length yet, nor put toe into the axles until the geometry and w/b is nailed down.
 

Brian Jackson

Platinum Member
After much consideration and a recent Q&A thread on the subject, I have decided to return the landing gear mains back to their stock fore/aft distance instead of raking them back to increase nosewheel weight. I had made a false assumption that this weight increase was desirable, but failed to consider that the only benefit would be for ground steering, whereas mine is to be free castering and would realize no benefit from that mod. In fact Doug illustrated how it may adversely impact take-off distance. A lesson I'd rather not learn the hard way after years of building.

Returning to stock distance also lessens the angle bend in the axles (which I have consulted Azusa the manufacturer about and is OK). This puts less twist into the system with changes in up/down force.

More to follow in the coming days.
 

Brian Jackson

Platinum Member
No Title

A few more progress photos. Don't have time to go into great detail explaining but that's the beauty of photos. First is the vertical site alignment of the landing gear main strut and drag strut. I have decided to keep the original GyroBee main wheel rear distance, so the main axle strut will be running perpendicular to the keel in plan view. Getting the exact angle measurement of the diagonal proved more difficult than expected so I took this downward shot from true vertical at a ladder distance to verify the geometry photographically, pulling it into CAD to draw over. The bright red dot is the vertical self-leveling laser to align the camera. Struts are rotated upward and supported horizontal for the photo.

2nd photo is of the paper templates contact-cemented to the aluminum stock. These are for the landing gear upper and lower plates that will unitize the main axle struts to the drag struts to form an A-frame.

3rd photo is the mostly finished clevis (on right) minus deburring and mounting hole.

Last photo is the rough blanks cut to size of the LG strut plates. They will be band saw cut to approx. curvature then slightly edge beveled to match that of the engine mounts and other components. I used thicker plates than needed, but will be losing some of that thickness by machining radiused channels to match where they meet the two struts. They essentially become their own full-span saddle blocks. Depth of milled channels is sized to allow sufficient width for tube capture.

More to follow...
 

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Brian Jackson

Platinum Member
Thank you, Vance.

Yes, quite a bit of de-burring, along with ten-thousand other remaining operations. Psychologically the project duration has been tedious and taxing, but what has been helpful is telling myself at the completion of every part that I never have to make this piece again... and of course hoping that is true. One day it will be finished and ready for test flight. I have quit setting target dates. My family is very tolerant of the ridiculous hours I spend laboring over the tiniest details. But this may end up being the single greatest project I'll ever do, who knows, so I really want it to be outstanding to fly and to gaze at. There's a certain romance in having an intimate relationship with every piece and part. This project has changed me for the better, and I wonder sometimes if I'm working on the plane or the plane is working on me. Patience and temperament have certainly improved.

Sorry to get all heady, just helps to take a step back for perspective sometimes.
 

Vance

Gyroplane CFI
In my experience a project like yours is never finished.

There is always joy to be found in making little improvements.

I have watched you grow during your build and feel you have a lot to be proud of.
 

Brian Jackson

Platinum Member
This weekend was about details. The landing gear strut plates and bracket needed one additional feature: a shear pin. I didn't want to rely on clamping force alone to prevent the bracket from rotating about the main thru-bolt at its outer extremity. Otherwise if it ever came loose the bracket would be free to rotate and bind the spherical rod end bearing that is situated between the bracket walls. The pins were tight-tolerance lathed and end-milled to be captured between the axle strut tube OD (that the plate sits on) and the bottom of the bracket's pin bore, with a tiny bit of vertical clearance so the bracket doesn't bottom out on the pin first instead of its foot.

The plate edge will be final ground so that its top surface perfectly matches the elliptical shape of the bracket foot. The photo currently shows it about 1/32" proud. I didn't want to chance damaging the edges during a milling operation that is going on now. The underside of the plates are receiving two radiused grooves that come together in a V shape to nest around the axle strut and drag strut where they come together at the wheel. They become their own saddle blocks that run the full length of the plates rather than 2 points. Depth of saddle groove has been coordinated to leave approximately 3/16" of material at its thinnest section.

Will post photos of the finished assemblies when milling and final edging are complete.
 

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Brian Jackson

Platinum Member
Thank you gentlemen for the kind words.

This weekend was more about design/modeling work than fabrication, though I did begin lathing the lower inserts for the vertical shock strut tubes. Similar curve-tapered form to the other inserts I've posted photos of here but different internal design since there's no compressible elements (would have been redundant with a shock on same centerline.) Also using a 5/16" bolt with these inserts whereas the others use 1/4".

Also received a new material order from Metal Supermarkets including mill certifications. Have kept a paper trail for every part on the ship. Metal arrived in great shape after writing in the online order that certain items must be scratch-free. Glad someone actually reads these.

While landing gear is being finished, there are 2 main areas of design focus currently; Folding mast assembly and rotor control assembly. The upper mast will be redundant 1X2 "floating", flexible both side-to-side and fore/aft. Borrowing a couple design elements from SportCopter. Will go into greater detail in a later post when there's something to show.

In a side note, the company I have been working for in NYC is letting me work in the NJ office much closer to home, so there will be more personal time to build the gyro. This office also happens to be their metalworking factory staffed by some of the finest metal craftsmen in the world. There is much opportunity to learn from them. They are also going to be helping me with a few parts on the plane including the streamlined fuel tanks and the main billet of the rotor head. Progress should be made at a faster rate. Would be nice to fly this thing before I'm too old to do so.
 

All_In

Gold Supporter
What J-John said. Watch that gear geometry.

Bensen's original landing gear configuration (the "tail sitter") is very right, IMHO. The aircraft sits on its nosewheel and mains with the pilot in the seat, with about 30-40 lb. weight on the nosewheel. As the rotor spools up early in the takeoff roll, the aircraft soon rocks back, increasing the disk AOA and assisting with rotor spinup. The rock-back, IIR, is about 5-6 degrees, or around 6" at the tailwheel.

Some people find that the fact that a Bensen gyro sits on its tailwheel when parked to be undignified (much as they find the plywood scrub brake, overhead stick, or "lawnchair" seat undignified).

Those who have varied the Bensen design have sometimes altered its landing-gear formula in a way that discards its advantages. For example, the stock Gyrobee has very limited rock-back -- only some 3"-- perhaps because of the "stacked' 2x2 keel/tail tubes. This reduces the available disk AOA during the early part of the takeoff roll, when you could use more to bring up RRPM.

Others have placed the main axle back so far that rock-back is delayed or eliminated. If you happen to have a full- RPM prerotator (as the McCulloch J-2 and Air & Space 18A do) then it doesn't matter. With the typical partial-RPM (or zero!) prerotator found on homebuilt gyros, however, eliminating rock-back is not helpful.
I love you guys and this forum!!!! U-ROCK!!!!
 

All_In

Gold Supporter
You do excellent work, Brian, you teach & learn and change quickly too. Very impressive qualities!!!!
 

Resasi

Gold Supporter
I spent yesterday observing two single seat gyros with two seater pilots converting to single seat.

Both were being followed at the same time, not my choice, as I would have preferred to concentrate on one at a time. What however was interesting was that Gyro 1 Gyro 2 and Gyro control vehicle were all progressing down the runway at approximately at the same speed.

While Gyro 1 was able to balance without too much trouble, take off and do low hops approx 2-4’ above the ground, in accordance with his brief, Gyro 2 whose brief was only to wheel balance was having trouble balancing.

One was a Cricket, Gyro 2 a Merlin. Both had 582’s both had Dragon wing blades both pilots similar weight and build.

The problem that seemed to be faced by Gyro 2 was he seemed to be having difficulty in raising the nose with back stick at the speed we were going, this dictated by Gyro 1 who was in the lead. Any addition of power and acceleration then allowed the nose to be raised but seemed rapdly to make him very light on the ground with lifting of one or other wheel and at time brief skipping/hopping which he was attempting not to do.

The conclusion I came to was that this was due to main gear geometry in relation to CG?? A point I raise as I am sure that the more educated amongst us will hopefully point me to a calculation in design that addresses this, and a point to be born in mind when in a build where one is trying to get it right.
 

Brian Jackson

Platinum Member
You do excellent work, Brian, you teach & learn and change quickly too. Very impressive qualities!!!!
Well thank you John. Not sure how much teaching I'm actually doing, but learning and adapting is constant. If I ever feel like I know it all, then building & flying gyros shouldn't be on my to-do list.
 
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