Crescendo Build

Brian Jackson

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Quick update: Main axle strut attachment point to keel. Keel extends behind mast 2.5" and accepts 2 opposed spherical rod ends. Lathed stand-off cones constrain rod ends at centerline of keel tube. Connection bolts pass through both the keel and tailboom tubes (bolts in photos are temporary consumer grade). Cones are sandwiched between two .188" thick tie plates that unitize the 2 connection bolts. The plates serve as a reinforcement to prevent the keel from absorbing the entirety of impact loads. Very slight compression pulls the entire system tight with zero play. Drag strut connections are identical except the rod end pass-thru holes are shifted .188" aft of connector bolts due to the rotation angle of the strut in plan view.

The axle tube inserts shown earlier in this thread house a shock-dampened bolt that threads into the rod ends. More photos of that later.
 

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eddie

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Hey Brian it looks as if you might have it figured out,guality workmanship,excellent. !
 

Alan_Cheatham

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Brian,

Back in post 27 Doug informed how minimal a 2x2 in cantilever is for a tail boom and stressed that is more critical given the Bees longer tail length.

Drilling the two holes vertically through the tail tube as you have will weaken the tube considerably compared to the single bolt attachment that put holes along the tubes bending neutral axis. Do you plan on having additional triangulation for the tail tube as Doug was suggesting?

I'm also concerned that a rod end may be inappropriate for the axle tube attachment, have you done any calculations on the loads that will be applied?

Do you intend to install main gear mounted brakes?
 

Brian Jackson

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Alan_Cheatham;n1137646 said:
Brian,

Back in post 27 Doug informed how minimal a 2x2 in cantilever is for a tail boom and stressed that is more critical given the Bees longer tail length.

Drilling the two holes vertically through the tail tube as you have will weaken the tube considerably compared to the single bolt attachment that put holes along the tubes bending neutral axis. Do you plan on having additional triangulation for the tail tube as Doug was suggesting?

I'm also concerned that a rod end may be inappropriate for the axle tube attachment, have you done any calculations on the loads that will be applied?

Do you intend to install main gear mounted brakes?
Hi Alan.

Thanks for the review. Yes, it does weaken the tailboom tube this way if left unbraced. There will be triangulated bracing on the tube. Most of the hard loads at this attachment point will be pulling outward in tension, with a lesser bending component. I would not do this type of connection if there were going to be brakes on the mains because it doesn't provide any rotational constraints on the axle strut tube; the rod ends would rotate until they collide with the bolt. There is a rotational constraint on the axle tube near the wheel at the attachment point of the Vertical Strut.
 

Lee

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Hey Brian, new user here popping in to say what a great build thread. It takes dedication to stick with it as long as you have :) Your machine work and cad skills are amazing too. I was wondering about the model you showed, waaaaaaaaaaaaay back on page one, a side view with the dummies head impaled. That looks like an interesting propeller, a q or P tip perhaps?

Is that a model you did/obtained, and if so, is it a working propeller or a DIY approximation? Very interested in it if it is a working model...... :)
 

Brian Jackson

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Lee;n1137853 said:
Hey Brian, new user here popping in to say what a great build thread. It takes dedication to stick with it as long as you have :) Your machine work and cad skills are amazing too. I was wondering about the model you showed, waaaaaaaaaaaaay back on page one, a side view with the dummies head impaled. That looks like an interesting propeller, a q or P tip perhaps?

Is that a model you did/obtained, and if so, is it a working propeller or a DIY approximation? Very interested in it if it is a working model...... :)
Hello Lee.

Thank you for the nice words. Funny how we don't anticipate the time required to cut & bolt a bunch of silly tubes together. Regarding the prop model, unfortunately it's just a place-holder object I grabbed from the internet. The actual prop going on the ship is made by Prince Aircraft Company; its called a P-Tip and looks similar to the model. I saw one at a fly-in many years ago and took note of how quiet it was. They're also very efficient, albeit a bit pricey.

Cheers,
Brian
 

Lee

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Is that placeholder a really, working prop in general? or just someones approiximation. I need a model of a good propeller, and hopefully a working rotor blade :p
 

Brian Jackson

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It was a weekend of finishing another critical detail. This time the seat bottom mounting. As mentioned in an earlier post, the seat is a re-purposed high quality office chair I have grown quite fond of over the years. The plywood substrate is extremely rigid and I like the idea of having something this solid under my ass. Upon taking it apart for inspection for consideration for use on the gyro, I was impressed by the steel gauge used for the threaded inserts. However... for an aircraft it would be wrong to trust them no matter how strong they are. If the threads fail there is no redundancy. So it was necessary to strip and de-foam the entire substrate such that bolting direction could be reversed, with the bolt heads "trapped" from above, preventing them from coming out if the treads fail.

I face-lathed all 4 bolt heads to a lower profile to prevent chafing through the foam and leather (the leather was completely cleaned and re-conditioned while off..) Having added register marks where the leather met the substrate proved very helpful when re-installing.

I did add 2 holes through the plywood substrate to clear the bolt heads that fasten the 1/4" thick seat support bars. The photo of the mounted seat (viewed from front) was taken earlier on and shows the old, now-discarded hardware. By the way, the perspective in the photo makes the bar mounts appear shorter, but they are around 8" center to center. The threaded inserts are a coarse thread and way oversized for the load (5/16" diameter). Thus, I used Grade 8 fasteners in lieu of AN to match the threading.

The seat is raised ~3" higher than the stock GyroBee to counter the 1" HTL. Though I didn't snap photos of the completed mounted seat and back last night, it was a smooth install and felt great to sit in. It's rock solid with no play or flexing in any direction. It was a fair bit of work for detail items that will never be seen, but I'm happy with the results.

Edit to add: the under-seat treatment is being covered with a trapped material, not left exposed like the photo.
 

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Doug Riley

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A router in each hand (and arms like Popeye)? Arrgh!

IMHO, those gyro crashes in which the safety of the seat structure (as contrasted with the pilot restraints) may matter are (i) pancake landings and (ii) sideways arrivals. The belts do all the work in nose-first crashes; the seat structure only matters if the belts are attached to it.

In the pancake case, some protection of the pilot's spine might be obtained by putting a block of rigid styrofoam between the seat cushion and the hard stuff below. (Foam rubber, though comfortable, is too soft to help much with shock absorption.)

Bensen used to criticize gyro designs other than his by pointing out that their seats offered no "progressive absorption of G loads." He called out bungee cords (or a homemade version made of truck-tire inner tubes) as seat springs. He may have been extra-sensitive to this issue because he had had a serious back injury in a helo crash in the days before Bensen Aircraft.

Lateral protection is really a tough one in a craft as open as a Bensen-style gyro.
 

Brian Jackson

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Thank you, Doug. Serious things to consider and I thank you for the insight. Not an easy problem for sure. I'm not aware of any progressive absorption in the stock 'Bee other than perhaps deformation of the seat support angles, so I'm curious how others may have addressed this issue. I do like the idea of styrofoam or some form of air bladder. Open cell foam would be useless. I'm almost thinking of a heavy duty Whoopie Cushion... minus the whole fart noise thing, although that might be kinda fun.

On a serious note, it is possible to place a pancake size pneumatic element at the area under the spine/cheeks. I'm suddenly imagining a small bicycle innertube spiraled to cover a solid circular area without overlapping, and partially inflated to a low PSI. Part of the foam could be removed to create a like-sized cavity. Taken a step further, the valve could extend through the seat bottom for access to inflate/deflate as needed for best protection, or adjusted for the weight of the pilot. I'd be surprised if such things didn't already exist in some industry. Racing or trucking maybe?
 

Doug Riley

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Hmm. One imagines something that looks like a big coil of kielbasa cooking on a grill.

Seriously, IMHO, to accomplish any useful G-reduction, the crushable stuff in the seat bottom would have to be surprisingly rigid. I'm not sure that bike inner tube would be stiff enough.

Certainly, these ideas are very testable. Make some weights of the right size and shape and start crushing stuff. It would be useful to review the human skeletal structure down there; the hip bone "wings" and the end of the spine are what matter, not the natural padding (however generous that may be; see above re kielbasa.)

I swiped the styrofoam idea from an old Sport Aviation article about seat safety. I believe the author pictured a military-style metal bucket seat (where there's room below yer cheeks for a fanny-pack parachute), filled in with rigid styrofoam.

There's a narrow range of crashes in which seat design will actually matter. In a freefall from a thousand feet, for example, the seat is irrelevant. In fact, any crash protection that's light enough to get off the ground will be irrelevant at 120 mph straight down.

OTOH, some people have had back injuries, but recovered, from vertically-descending a gyro right into the ground. Styrofoam or some such thing might help there.

You're right that 'Bee builders have largely ignored this topic -- as, in fact, have gyro builders in general. Lots and lots of us sit in plastic or fiberglass seats, maybe with a bit of upholstery merely for looks and comfort. Mighty few still employ the Bensen bungee-cord setup; it looks like a stupid lawn chair, but in fact is much more.

Dennis Fetters touted the familiar polyethylene seat tank as creating a "crush zone" for pancake landings. I have not heard that anyone has ever tested this thought, though...? An empty tank will behave differently than a full one. I dunno if I'd rather descend into ten gallon of gas or ten gallons of air.
 

Brian Jackson

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Thank you again, Doug. Once again you've given me much to consider. The thought of employing a pneumatic element probably stems from another unrelated endeavor I was involved in... how to de-couple a drum set from the floor over old people's bedrooms (attached docs.) Granted we're talking about sudden deceleration rather than impact noise control, but I could see many of the same principals applying. I will design a series of G-metered drop tests over the next few weeks to measure how effective a pneumatic bladder system might be for aircraft application. Having experienced a pancake crash in a Piper Cherokee and broken my back in an auto accident, I can understand why Bensen would be sensitive to that issue.
 

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PW_Plack

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Brian Jackson;n1138053 said:
...it is possible to place a pancake size pneumatic element at the area under the spine/cheeks. I'm suddenly imagining a small bicycle innertube spiraled to cover a solid circular area without overlapping, and partially inflated to a low PSI.
Brian, I think the best answer would be something closer to the whoopee cushion, which absorbs shock with no rebound.

A similar discussion on another forum included an interesting idea - rows of aluminum beverage cans standing upright under a rigid seat. They'd be cheap, predictable in their crushing, configurable for varying loads based on the number of cans, and easily sourced. They could also be partially filled with foam to solve the issue of crushing too easily once their initial shape is deformed
 

Brian Jackson

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PW_Plack;n1138148 said:
Brian, I think the best answer would be something closer to the whoopee cushion, which absorbs shock with no rebound.
I agree. I purchased 2 small wheelbarrow-type innertubes with mean diameter sized for hip joint width. One is for destructive testing and the other for installation, pending test results. I would like to install a small check valve at the tube's valve end that would release pressure above a certain PSI, say 2.5 Gs pilot weight. The problem I could foresee is valve stem diameter. I can't imagine how enough air could escape quickly enough through such a small-ish port to produce the desired results. Will be fun to experiment with, and who knows... might even lead to a decent design.
 

AirCommandPilot

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Brian Jackson;n1138207 said:
I agree. I purchased 2 small wheelbarrow-type innertubes with mean diameter sized for hip joint width. One is for destructive testing and the other for installation, pending test results. I would like to install a small check valve at the tube's valve end that would release pressure above a certain PSI, say 2.5 Gs pilot weight. The problem I could foresee is valve stem diameter. I can't imagine how enough air could escape quickly enough through such a small-ish port to produce the desired results. Will be fun to experiment with, and who knows... might even lead to a decent design.
The rubber will stretch. I don't see a need to release the air.
 

Brian Jackson

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AirCommandPilot;n1138209 said:
The rubber will stretch. I don't see a need to release the air.
It's to prevent rebound. Worst case scenario would return much of the stored energy back to the spine. Some is lost as heat, and perhaps that's enough to rob the system of to be effective.
 

Brian Jackson

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Productive weekend. Axle strut tubes drilled to receive keel connection inserts. It's a little tricky to drill a round tube through the exact center, even with a vice that has its own tiny bit of play. So I left the tubes long, using the sacrificial 1" extra length to test and adjust the vice's clamp-down position a few thousandths fore/aft until centered. To check, I used a 3/8" diameter transfer punch as a feeler gauge between the inside wall of the tube and the cutting edge of the bit, rotating the drill chuck 180 degrees by hand before gauging the other side. When both sides were equal the vice was centered. Then the 'real' holes could be drilled. I then dyed and mic-scribed the true tube end relative to the edge of the hole and finished the cut on the table saw, with the tube clamped to the miter gauge.

I use 2 strips of 1/4" plexiglass on the vice's clamp faces to both protect the workpiece and because it has a surprisingly good grip on the material for a modest amount of clamping pressure.

A couple of things I did beforehand to ensure the perpendicularity of the holes was plumb the drill press as accurately as possible, and level the tube before applying vice pressure. In retrospect I wish I'd used a marble inside the tube instead of a level... just for ease. But all turned out well. A spare cymbal stand from the drum set works great for fine adjustment support at the far end of the tube.
 

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Brian Jackson

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Busy building and haven't updated in a while. From the photos it must look like all I do is lathe but other items have been done as well.

Since Doug Riley's post regarding tailboom reinforcement, I have run a great many design concepts and settled on one that addresses multiple issues. I contacted Lonnie Prince of Prince Aircraft Company; makers of the carbon fiber P-Tip prop going on the ship. The proper setback clearance ahead of the prop at the tailboom was determined, and that will become a critical tie point of the airframe. But I also wanted the system to address torsional rigidity of the tailboom tube, not just upward deflection. The reason being to eliminate the need for a support arm running from the top of the v-stab to the cheek plates, and the complication of adapting it for a folding mast. The composite tail is to be shorter than a Dominator-type tall tail, but because it has separate hinged rudders and V-stab, it can be rigidly attached to the tailboom. That being said...

Hollow (but thick walled) stand-off cones will be installed on opposite sides of the tailboom tube just ahead of the prop as far back as Mr. Prince's clearance allows. The base of the cones are sized to match the 2" square tube. A single threaded rod will run continuous through both cones and the tailboom at the neutral flex point (center of side walls). The threaded rod will be nutted on both outer ends of the standoff cones and be under a great deal of pre-load tension. There is also to be an internal spacer under compression inside the tailboom tube at the thru-hole.

There are 3 airfoil shaped struts that will run to this new tie point; 2 jury struts in tension running from the two outer ends of the standoff cones to a single point at the center of the bolt at the aft end of the engine support angles. The third strut is a larger airfoil profile that runs from the top of the tailboom tube (above the tie point cones) to the center of the rear bolt that clamps the engine diagonals to the mast. This larger profile will take compression loads during tail-first landings. The 2 jury struts form an inverted V that is within a few degrees of vertical when viewed from the side of the plane. The standoff cones become the third leg of the triangle that will tend to keep the tailboom tube from twisting to the degree it would unsupported.

Will go into more detail when build progress gets that far. The standoff cones are similarly shaped to the axle strut inserts shown in the photo, but the outside diameters are significantly larger due to the bending loads that will be imposed on them. Even so, they are surprisingly light weight. I do not like adding weight below the CG, but other modifications mentioned at the beginning of this thread have collectively raised the CG such that there's a little room to work. By the way, I did purchase airfoil struts for use here only because I want the airflow to the prop to be as clean as possible, especially being close to the blades.
 

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Brian Jackson

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Tailboom Standoff cones test fit. Their tips will connect to thin jury struts in tension (via turnbuckles) to the midpoint of the bolt at the aft end of the engine mount. They work opposite of a single compression strut (not shown). More to follow. Some things just take more time than one might anticipate.
 

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