90% review of QB tail

[Vance]

Thank you Doug, Vance

 

[Dean_Dolph]

..........In particular, points behind the axis such as "C" will cause the rudder to lock while fully deflected; not a good thing.........

Just to add a little clarification (I hope!) to what Doug is saying; the lockup happens on the rudder horn opposite the rudder actuation side. The cable on the non-actuating side will pass over center if in position 'C' and won't be able to move the rudder back to the natural position or the opposite deflection, a lockup.

I don't know if this is what happened to Doug O'Connor in his early model SnoBird when he spiraled in to a flat crash during a 'falling leaf' spiral maneuver at an air show. They blamed it on 'aerodynamic' lock but in fact this could have been what happened. I do know that he bent the rudder horn and the rudder would not move. He walked away (sorta!) with compressed vertebrae that kept him out of his commercial jet jockey seat for a while.

 

[gyroplanes]

Overcenter, etc.

Overcenter, etc.

Doug O's accident caused me to take a long and hard look at the SnoBird tail design when I bought the company. Doug referred to it as an aerodynamic lockup. That we were unable to fathom.

I understand the principle behind "overcenter" we made a few overcenter throttle quadrant prerotator levers (after watching the Ken Wallis TV show video) It's pretty neat to be able to lock in the prerotator lever and just work the throttle and stick. Ken went one better and overcentered his brakes too AND then topped that by having his brake lever release the prerotator upon brake release. One easy motion and no chance of leaving the prerotator engaged.

 

[Doug Riley]

We might drift off topic a little here, but it's winter, so why not?

I don't see how a rudder can lock up AERODYNAMICALLY unless (1) the area ahead of the hinge line has more volume (area x leverage) than the area behind or (2) you're flying backwards (which creates a situation that's effectively the same as #1). Over-center MECHANICAL lockup is useful and is seen on such lowly items as metal lunchbox latches and old pickup truck emergency brake levers.

Gyros often do slight tail-slides in vertical descents, but usually with a touch of power on so that the flow over the tail is still frontways-first. If you turned the engine OFF and did a tail slide, the rudder might in fact get backwards flow and jam off to one side. In addition to getting stuck in a full-deflected state, the rudder would work backwards in that case; left rudder would cause right yaw and vice versa.

Maybe Doug O'C got into a situation like that, or maybe his Snobird's horn mechanism was a little over-center to start with and the horns bent when he tried to force them out of their over-center locked position...

 

[Dale Young]

Sno-bird tail

Sno-bird tail

I put a Sno-bird tail on my Gyrobee, and being a newbie, made the mistake that Doug spoke of previously. I did'nt think to align the horns through the hinge as Doug insisted... And SURE ENOUGH, It locked completely to one direction when I added full throw to that side. After Doug told me of the alignment problem, I corrected it, and all is well now. Fortunately I was just sitting in it at the time.The fact that the Snowbird tail has such large area forward of the hinge ,probably would have made the problem worse due to prop wash holding it to that side. Keep in mind that there is NOTHING WRONG with the Sno-bird tail. This could be a problem for ANY tail (of this design)that has the control horn mis-aligned.

 

[Brian Jackson]

Brian, one of the best ways to get a functionally good tail design is to steal from the Bensen plans. As with other Bensen parts, people are turned off by the homebuilt tail because (with its straight cuts, plywood material and attachment to the SIDE of the keel) it looks uncool. Aesthetics aside, Bensen's tail has all the suble aerodynamic features that go into a good tail. They include:

(1) a counterweight -- 1 to 1.5 lb. seems to be the right amount to prevent flutter. The weight should be set at least 8-12" ahead of the hinge line;

(2) servo area -- adding some area ahead of the hinge line reduces control pressures;

(3) a bendable trim tab -- you'll need to have the rudder set itself off about ten degrees to compensate for P-factor.

(4) Rudder horns that are mechanically neither over-center nor under-center. Many, many people blow this one. A line through the centers of the swivel bolts that attach the cables to the rudder horns must pass through the hinge axis. At worst, this line may be very slightly ahead of the hinge axis; under no circumstances should it be behind.

(5) plenty of stiffness.

More thoughts: A tall tail or wide-span HS centered in the prop wash will help eliminate torque roll. Such roll is otherwise quite noticeable on a light gyro like a 'Bee. Putting negative incidence on only one side of the HS will help with roll compensation, too.

Doug,
I've been working on designing a simple system of combining servo area and counterweight into the design of the rudder control horns themselves. Rigidly mounted via large washers under the glass rudder skin (at 3 points), the stainless control horns extend out and forward of the hinge line by several inches in a forward-swept configuration, and bent up 90 degrees at the ends to form "winglets". The plate area of the winglets can be sized and shaped as necessary to provide the proper servo area. And since the winglet areas are enlarged portions on the blank horns (before bending), and made of stainless, they become their own rudder counterweights.

I'll post some graphics later of what I'm describing. But the beauty is in its simplicity... all 3 functions are served, if sized correctly, with 2 parts that are already required anyway, just elongated, bent and shaped for the aerodynamic tasks. There's no extra parts needed.

It's also an opportunity to shape the control horns in a way that blends with the styling of the QB tail's form, while still allowing the cable eyelets to exist coplanar with the hinge center. Their forward sweep angles are also such that there's no interference with the vertical fin even at full rudder deflection.

I'm picturing the horns being mounted about 1.5~2.5" above the bottom edge of the rudder.

Any thoughts, feedback or insight would be appreciated.

Respectfully,
Brian Jackson

 

[Doug Riley]

Brian, you want the cables to change direction as little as possible, particularly as they reach the horns. The cables have to be low forward of the tail to clear the prop. So, a low placement of the horns is good and high is bad. High involves lost motion as well as a down-bending load on the horn.

Don't forget the sacred principles! Principles like KISS, if-it-ain't-broke and my favorite, "simplicate and add lightness." I might worry about fancying-up the horns to do multiple duties. The usual ones weigh 2-3 ounces, can be made from scraps of 1/8" aluminum and are just dirt-simple. If you start attaching counterweights and servo paddles to them, they're gonna get heavier and more complex.

But show us an' prove me wrong.

 

[Brian Jackson]

One other thing I forgot to mention... The balance of forces between the two horn winglets, being forward of the hinge line, act similar to traditional "centered" servos (single surface), like the Bensen rudder. When the rudder & horns are deflected, the winglet opposite the deflection direction has greater moment authority than that of the opposite side because it starts to approach a right angle in relation to the hinge plane, whereas the opposite winglet approaches more of a head-on moment to the hinge and has less authority. The two acting collectively should replicate the forces imposed by a conventional servo arrangement.

Sorry to be long-winded. I'll shut up now.

Thanks,
Brian Jackson

 

[Brian Jackson]

Brian, you want the cables to change direction as little as possible, particularly as they reach the horns. The cables have to be low forward of the tail to clear the prop. So, a low placement of the horns is good and high is bad. High involves lost motion as well as a down-bending load on the horn.

Don't forget the sacred principles! Principles like KISS, if-it-ain't-broke and my favorite, "simplicate and add lightness." I might worry about fancying-up the horns to do multiple duties. The usual ones weigh 2-3 ounces, can be made from scraps of 1/8" aluminum and are just dirt-simple. If you start attaching counterweights and servo paddles to them, they're gonna get heavier and more complex.

But show us an' prove me wrong.

Thanks, Doug!
Actually I am following the KISS principal; doing more with less, and brainstorming a creative solution to the issues you'd raised in your original post. These are great points, and I'm learning a lot because of them. Your input is valuable and well respected. As an engineering experiment the QB tail could be a complete flop... who knows. But as is true with most failed experiments, it's all part of the learning process.

Thanks again,
Brian Jackson

 

[Brian Jackson]

For whomever might be interested, here's the tangents of the QB tail. It's 3 perspective views and presents the idea. Missing are the horn-winglets which I'm still drafting. The first post showed sharp corners whereas this one shows the blended radii.

Respectfully submitted,
Brian Jackson

 

[Brian Jackson]

The attached image is just a quickie concept rendering of the servo/rudder horns I was attempting to describe earlier. It's just a sketch and nothing has been sized yet, so the proportions aren't accurate. Just kinda gives the general idea. Though they weigh very little, the majority of their weight is at the outer ends, which should help eliminate any chance for flutter, and the winglets placed forward of the hinge plane should help lessen pedal pressure. The eyelet locations where the rudder cables attach are exactly perpendicular to the hinge. Not shown is the bent flange where they mount to the rudder. Since all the sheet and plate parts are being water-jetted, they can be any shape, curved, etc. The horns shown only require 2 90-degree bends. Pretty simple really. I'm not sure I like it yet though.

Happy New Year!
Brian Jackson

 

[Brian Jackson]

Horray! I've been working all day to restore my broadband connection after a viral/hacker attack. Isn't this "information age" wonderful? Pretty soon we'll get to submit retinal scans, passports and DNA samples to buy a f**king loaf of bread. At what point did somebody think tracking my movements was a good idea? Hello Earth... I'm scratching my balls right now... no, not because of the ionization of the atmosphere or static discharge Science Fiction has us believe is due to your "gravitation defrabulators." It's because my balls itch.

Enough of that.

To everyone whom has been following this thread, it was just an idea. That's all.

It could have been straight lines and flat surfaces. But I doubt even the reverse fork surfaces worked. Consider the QB tail dead. It was an experiment.

 

[Vance]

Hi Brian. I realy liked the way it looked and my understanding is that thick airfoils give a more progressive control and better dampening. Please, someone corect me if i am wrong on this. I hate to see you throw away such a progressive idea. Many tails I have seen on gyroplanes look like Barney Rubble designed them. Thank you, Vance

 

[Brian Jackson]

Hi Brian. I realy liked the way it looked and my understanding is that thick airfoils give a more progressive control and better dampening. Please, someone corect me if i am wrong on this. I hate to see you throw away such a progressive idea. Many tails I have seen on gyroplanes look like Barney Rubble designed them. Thank you, Vance

Hi Vance. It's amazing what a good night's sleep can do! . I was kinda mad at the world last night, and extremely frustrated. Please forgive my outburst. But I appreciate your comments very much.

During a dream last night I was toying with elongating shapes on the tail, kinda like modeling clay. I came up with a way to reconfigure it slightly that would give it greater rudder area without sacrificing strength. So when I woke up I hit the CAD and lofted a model of the revised design, ran some numbers and "Eureka!" Rudder area is now 4 sq. ft., HS is centered on TL, HS sweep is brought in slightly for greater rotor clearance, yet HS area is now 6.1 sq. ft.

Gone are the horn servos, but I was dreaming of an idea regarding flutter control... Have you ever tried to roll a pop can when it was full, versus one that was empty? The full can won't roll far at all because of the dampening effect of the liquid/air mixture inside. Wondering if there's a way to utilize this effect in place of offset counterweights. Maybe not. I'm still nursing my first cup of coffee

Decided to go ahead and have the new "revised" QB cores milled this week and see what happens. Hopefully I can persuade Tim Blackwell & Gang to help me with the kevlar layup. I figure, even if it's a failed experiment, it'll make for a very cool mailbox!

Respectfully,
Brian Jackson

 

[Vance]

Hi Brian, I have not had good luck with structures made from carbon fiber. There seems to be a duribility challange. I have better luck with a combination of E glass and carbon fiber. The E glass seems to help with impact damage and a couple of layyers doesn't seem to add much weight, especialy if you vacume bag it. They both absorbe the resin well. They don't seem to get along with aluminum though, so some care is required in the design to stop galvanic corrosion.

I have found it important to think of design as iterative and not be afraid to scrap several designs before the end of the program. Thank you, Vance

 

[Brian Jackson]

I hear ya, Vance. I'm no stranger to scrapped designs, but there's always something positive to be learned from them that can be applied to other projects or revisions. Imagine if Igor Sikorski or Bensen quit after a setback or failed attempt. We wouldn't be having this discussion right now.

I spent most of my youth designing and building perpetual motion machines... talk about an excersise in futility . But I learned a great deal about physics and engineering in the process, so that puts a very positive spin on an endless series of failed designs. It also got me in therapy, but that's another story

The few engineers whom I consider personal heros stressed how important it was to not get emotionally attached to any design in progress, and knowing when to shut up and listen to smarter people. Occationally that's easier said than done. But I do love the experimenting phase of designing something new, and applying things I've learned here in creative ways.

Thank you my friend.
Brian Jackson

 

[Dean_Dolph]

.........To everyone whom has been following this thread, it was just an idea. That's all.

It could have been straight lines and flat surfaces. But I doubt even the reverse fork surfaces worked. Consider the QB tail dead. It was an experiment.

Brian, don't be so quick to abandon this design!

I can assure you that there are others that have thought or are thinking much more off the wall and out of the box than you but don't have the talent to express those thoughts visually or otherwise. I don't believe anyone is trying to rain on your parade but are offering observations and views, which in fact may only be personal preferences. Even if it turns out that this exercise is impractical, it may have value in a synergistic sense, so you, and others, are not wasting anyone's time by your presentations.

You presented your idea here for critique and thankfully (I'm sure you agree!) we have Doug, and others, with knowledge, experience, or both, on this Forum to offer an honest one along with a dose of reality.

There are those who prefer conservative design and see beauty in simplicity and then there are others with a different view of esthetics. The small gyro seems to offer a base for expressing those esthetics. It is my belief that esthetics and creature comfort is what sells just about all consumer items and the purchaser gives very little thought to the engineering behind the items. Personally, I have always had to battle to balance my desire to personalize and make things look a little better (in my eyes!) while recognizing that keeping things simple means less can go wrong.

Esthetics give us pleasure so there is value in creating something like the QB tail as long as it performs the function that a tail is designed for without compromising safety or performance, as in a high weight penalty.

I agree with Vance, the QB tail looks good and others, like J. Landry, seen intrigued enough that it would be a shame to not pursue this until it is obvious that it won't meet mission criteria.

 

[Brian Jackson]

Dean,
What an amazingly insightful post! You are a wise man indeed. Thank you.

I just wanted to reiterate that constructive (or even destructive ) criticizm was the reason for this thread. And everyone's input collectively has taught me greatly about things I may not have even considered on my own. Since there's no "Gyro Design College" I'm aware of, it's logical to toss ideas onto this forum, and whatever aspects of it don't get trampled on might just be the seeds for a workable design. Heck, even "scientific methodology" requires that. Whatever's left you experiment with to learn more. So I've never felt that anyone was "raining on a parade". Quite the opposite; Those whom have chimed in to voice their opinions have taken the time and trouble to educate me, and for that I am grateful.

Lastly, I just wanted to mention that this tail wasn't drafted for aesthetic value, but merely as a way to gain many of the benefits of a tall-tail within the confines of a short form factor. It's "cool" looks were only the result of blending the sweeps and tangents for strength and stress relief. However, when I stand back and look at it, I suppose it is kinda pleasing to the eye.

As of this morning this is design revision #15. So, yeah, it'd be stupid not to at least see what the thing does.

Thanks for the dose of reality, Dean. I admire your articulation. As they say: Some people have a way with words and others... well, um, not hAvE wAy/

God bless,
Brian Jackson