Stump the chumps, Bonanza style

[jpower]

I was bored in my aircraft dynamics and controls class today, and I was trying to figure out the V-tail Bonanza's control mixing system. I figure the ruddervators (is that the word they use?) are interconnected, but I couldn't figure out how you could get pure yaw out of them without involving the ailerons. I asked my professor at the end of class, but he had no idea what a v-tail was or even what a Bonanza was. That's a rant for another time right there--he's an aero professor in the controls department and he doesn't know what a v-tail is. Seriously? Not knowing what a Bonanza is is a little more reasonable...but still. It goes to show how theoretical everything is in college.

ANYway, how do v-tails work? Can you get pure yaw out of them? I don't think so...but how do they work then? Are the ailerons interconnected too? What exactly happens when you stop on the left rudder? How does this sorcery work?

 

[jasc15]

I had an rc airplane with a v-tail, though all the mixing was done electronically. I dont see why you couldnt get pure yaw from it. If both surfaces deflect oppositely an equal distance, and pitching moment induced would be cancelled out by the other, and what you are left with is yaw.

 

[alfadog]

I was bored in my aircraft dynamics and controls class today, and I was trying to figure out the V-tail Bonanza's control mixing system. I figure the ruddervators (is that the word they use?) are interconnected, but I couldn't figure out how you could get pure yaw out of them without involving the ailerons. I asked my professor at the end of class, but he had no idea what a v-tail was or even what a Bonanza was. That's a rant for another time right there--he's an aero professor in the controls department and he doesn't know what a v-tail is. Seriously? Not knowing what a Bonanza is is a little more reasonable...but still. It goes to show how theoretical everything is in college.

ANYway, how do v-tails work? Can you get pure yaw out of them? I don't think so...but how do they work then? Are the ailerons interconnected too? What exactly happens when you stop on the left rudder? How does this sorcery work?

Guess you are thinking that when both deflect say left (one up and one down) that will introduce a rolling couple in the opposite direction? Kinda like the inverse of adverse yaw - "adverse roll". LOL.

Of course, that couple will be operating over a very short moment arm so???

Edit, just realized that "elevators" produce lift in the negative direction so the roll would be in the direction of the yaw but still negligible due to the short moment arm??

 

[docmirror]

There is an intermixing bellcrank just forward of the aft bulkhead where the ruddervators are controlled by the rudders. This translates into a combination of yaw, plus the elevators of the yoke. 'Pure' yaw is accomplished by up plus in deflection on one ruddervator and down plus out deflection on the other one. The rudder travel is limited when the elevator is increased, and you can feel the rudder travel decreased if you hold it down and pull back on the elevator.

The mixing bellcrank combines the forces of the rudder pedals and the elevator. The roll is accomplished entirely separate, and is conventional.

 

[alfadog]

Here is a discussion of the issue.

http://www.charlesriverrc.org/articles/design/donstackhouse_vtailadverseyaw.htm

He has the induced roll direction opposite to what I put them as in my edited response but the rest is as I figured. I think he is correct and I had it right the first time. Yaw left, left ruddervator down, less downforce on left, roll right. Adverse roll.

 

[Skylane81E]

You don't get pure yaw out of a conventional tail either,

 

[alfadog]

You don't get pure yaw out of a conventional tail either,

Because yaw induces a proverse roll? But the tail feathers are not producing the roll couple in that case, right?

 

[tonycondon]

Because yaw induces a proverse roll? But the tail feathers are not producing the roll couple in that case, right?

sure they are. in most normal tail planes i've seen the center of the rudder is certainly above the CG of the plane. but the arm is so short you don't notice it.

i've flown v tail bonanza once or twice and a couple v tail gliders and have never noticed a yaw/roll coupling.

 

[alfadog]

sure they are. in most normal tail planes i've seen the center of the rudder is certainly above the CG of the plane. but the arm is so short you don't notice it.

There ya go. You are correct, sir. LOL.

 

[Skylane81E]

sure they are. in most normal tail planes i've seen the center of the rudder is certainly above the CG of the plane. but the arm is so short you don't notice it.

i've flown v tail bonanza once or twice and a couple v tail gliders and have never noticed a yaw/roll coupling.

Bingo, for proof try and turn the plane while keeping the wings level, the effect is there, just not very big.

 

[N801BH]

I..... I asked my professor at the end of class, but he had no idea what a v-tail was or even what a Bonanza was. That's a rant for another time right there--

Hmmmm..

A professor, teaching aircraft dynamics and controls class to students in a aviation related class, does not know about V tails and or V tail Bonanzas should be given his walking papers and the students should be given refunds for that class.....

 

[tonycondon]

there are exceptions of course though, like the british sigma. they were worried about torsional loads in the tail boom so they centered the rudder on the boom, which required a ridiculously tall landing gear.

 

[alfadog]

Bingo, for proof try and turn the plane while keeping the wings level, the effect is there, just not very big.

But that effect is, I believe, an induced effect of one wing being pushed forward into the airstream while the other become partially blocked by the fuselage with resultant loss of lift. It is an induced effect, not a direct effect of lift changing on the tail feathers.

 

[JHW]

It's simple. To yaw right, step on the right pedal. The exercise is left to the student to determine the effect of stepping on the left pedal.

 

[jpower]

Here is a discussion of the issue.

http://www.charlesriverrc.org/articles/design/donstackhouse_vtailadverseyaw.htm

He has the induced roll direction opposite to what I put them as in my edited response but the rest is as I figured. I think he is correct and I had it right the first time. Yaw left, left ruddervator down, less downforce on left, roll right. Adverse roll.

You don't get pure yaw out of a conventional tail either,

sure they are. in most normal tail planes i've seen the center of the rudder is certainly above the CG of the plane. but the arm is so short you don't notice it.

i've flown v tail bonanza once or twice and a couple v tail gliders and have never noticed a yaw/roll coupling.

Aha! That all makes sense. Basically, you don't get pure yaw out of it, but who gives a hoot, because the roll induced isn't enough to cause problems. Same with conventional tails--this hadn't occurred to me.

It's simple. To yaw right, step on the right pedal. The exercise is left to the student to determine the effect of stepping on the left pedal.

Well I figured it worked more or less like that, but I wasn't sure if you could get pure yaw out of it. Though I was enlightened above to the fact that you can't even get pure yaw out of a traditional rudder, which makes the entire question moot.

I'm still really curious how that bell crank works. I'd love to see a picture of it. Or even a video of it in action. I'll go consult Google once I'm done with midterms.

Hmmmm..

A professor, teaching aircraft dynamics and controls class to students in a aviation related class, does not know about V tails and or V tail Bonanzas should be given his walking papers and the students should be given refunds for that class.....

This is how so much of college is these days. In our class "introduction to aerospace engineering," we were taught a bunch of logic and discrete math, set theory, and state machines. We didn't get to anything remotely aerospace related until the last three weeks of the semester, but instead of learning how airplanes work, our professor threw a bunch of equations on the board and had us use them. Her background isn't in aerospace--it's in computer science. She's involved in a huge research project now for the Air Force running some combination air/naval battle simulations, which is basically all state machines. And I'm supposed to be learning how to build an airplane. Psh.

 

[Pilawt]

ANYway, how do v-tails work? Can you get pure yaw out of them? I don't think so...but how do they work then? Are the ailerons interconnected too? What exactly happens when you stop on the left rudder? How does this sorcery work?

Basic explanation here: http://www.beechcraft.org/vtail/eckalbar/rudder.html

 

[docmirror]

Basic explanation here: http://www.beechcraft.org/vtail/eckalbar/rudder.html

Cheater.

 

[hindsight2020]

This is how so much of college is these days. In our class "introduction to aerospace engineering," we were taught a bunch of logic and discrete math, set theory, and state machines. We didn't get to anything remotely aerospace related until the last three weeks of the semester, but instead of learning how airplanes work, our professor threw a bunch of equations on the board and had us use them. Her background isn't in aerospace--it's in computer science. She's involved in a huge research project now for the Air Force running some combination air/naval battle simulations, which is basically all state machines. And I'm supposed to be learning how to build an airplane. Psh.

I graduated aerospace engineering in '03. Sorry to tell you, it's always been this way. Your major is de facto computer science. Nobody is "building airplanes" from scratch anymore, or at all for that matter and generally neither will you in any meaningful position in industry coded as "aerospace engineering level X".

I don't know how far along you are in the program but I would seriously consider you shadow an aerospace engineer for a couple weeks, because if you think it's gonna get better I think you're in for a disappointment. I never worked my formal field for precisely that reason. It's all CFD, FEM computer coding and watching a screen spit out iterations. Meh. I could make a lot more money on IT if I was truly interested in computers and forego the 3 years of engineering math drudgery, which is painful and merely a haze (you won't be doing much classic math drudgery at work either). Doing engineering curricula to end up doing CS was a big vocational disappointment for me.

Conceptually it is a very interesting set of topics to an aviation enthusiast. I still keep my books in aerodyamics, aeroelasticity and materials and fatigue. But from a vocational application standpoint, it's a bait and switch. I wish I had gone to dental school and just got me a library card

 

[gismo]

I know I've got pictures and a diagram of the Bonanza mixer but I can't find them. Here's something similar from a different airplane, the Bonanza version looks a lot more rugged and IIRC is machined from solid metal:

 

[NoHeat]

That picture helps a lot!

 

[jpower]

I graduated aerospace engineering in '03. Sorry to tell you, it's always been this way. Your major is de facto computer science. Nobody is "building airplanes" from scratch anymore, or at all for that matter and generally neither will you in any meaningful position in industry coded as "aerospace engineering level X".

I don't know how far along you are in the program but I would seriously consider you shadow an aerospace engineer for a couple weeks, because if you think it's gonna get better I think you're in for a disappointment. I never worked my formal field for precisely that reason. It's all CFD, FEM computer coding and watching a screen spit out iterations. Meh. I could make a lot more money on IT if I was truly interested in computers and forego the 3 years of engineering math drudgery, which is painful and merely a haze (you won't be doing much classic math drudgery at work either). Doing engineering curricula to end up doing CS was a big vocational disappointment for me.

Conceptually it is a very interesting set of topics to an aviation enthusiast. I still keep my books in aerodyamics, aeroelasticity and materials and fatigue. But from a vocational application standpoint, it's a bait and switch. I wish I had gone to dental school and just got me a library card

Yeah, that's pretty much what I've figured. I'm still a sophomore (in terms of how long I've been here...I'm technically a junior by credit but most engineers end up ahead anyway), but this is a course juniors usually take. It's just the way my schedule worked out.

And see, I'm okay with doing these problems that involve lots of linear algebra and whatnot--I just want to see how it applies to airplanes. If you had sat in most of my class today, you would have thought that we were taking linear algebra. We spent no more than ten minutes talking about steady state flight and about 45 minutes learning about using the Taylor expansion to evaluate matrix exponentials. If aerospace engineers sit around all day working out Taylor expansions to raise e to a matrix, then oh boy am I in for it once I'm out of school. I do not get the impression that that's what they do, though. Show me some interesting stuff--CFD would be a big improvement from what I'm doing now. We didn't talk about airplanes for the first three weeks of this class. We did linear algebra. And now that I'm talking in circles I should probably go back to studying. Long story short, I'm happy to do the math. But show me some airplanes too!

 

[tonycondon]

i haven't done anything requiring more than a 4 function calculator since i graduated Aero E in 2008.

 

[us AAirways]

Yeah, that's pretty much what I've figured. I'm still a sophomore (in terms of how long I've been here...I'm technically a junior by credit but most engineers end up ahead anyway), but this is a course juniors usually take. It's just the way my schedule worked out.

And see, I'm okay with doing these problems that involve lots of linear algebra and whatnot--I just want to see how it applies to airplanes. If you had sat in most of my class today, you would have thought that we were taking linear algebra. We spent no more than ten minutes talking about steady state flight and about 45 minutes learning about using the Taylor expansion to evaluate matrix exponentials. If aerospace engineers sit around all day working out Taylor expansions to raise e to a matrix, then oh boy am I in for it once I'm out of school. I do not get the impression that that's what they do, though. Show me some interesting stuff--CFD would be a big improvement from what I'm doing now. We didn't talk about airplanes for the first three weeks of this class. We did linear algebra. And now that I'm talking in circles I should probably go back to studying. Long story short, I'm happy to do the math. But show me some airplanes too!

Just waste the students time/money to keep the Professor employed and make the program drag on for 6yrs making the school more money. IMHO

 

[jpower]

Just waste the students time/money to keep the Professor employed and make the program drag on for 6yrs making the school more money. IMHO

Well, it's only a 4-year program...and some people get out in 3 if they're very lucky (read: come in with 40-ish credits).

 

[Sleepingsquirrel]

I found this v tail mixer on ebay. I understand it now.

 

[gismo]

I found this v tail mixer on ebay. I understand it now.

For anyone trying to visualize the mixer in operation, the outermost pivots attach to the airframe, the elevator cable from the control column attaches to the top (by the spring) and the rudder pedal cables attach to the top of the two arms located between the center and the outer pivots. In the second picture the side facing up on the table faces to the rear of the airplane and the links from the rudervator horns attach to the bolts halfway up the same arms the rudder pedal cables attach to.

When the control column is pulled back the top of the center arm is pulled forward pivoting the entire mechanism on the outer bearings. This pulls equally on both ruddervators forcing both to rise. Pushing on the right rudder pedal pulls the left arm forward and the right arm back causing the right ruddervator to deflect down while the left one goes up.