Tail Configurations?

Hi all,
I was hoping someone here could help explain the pros and cons of the different tail configurations to me.
From what I have been reading here, the consensus seems to be that a tall Dominator style tail works very well with a gyrobee.
I understand the surface area / volume thing for the tail feathers, but what I haven't found much info on is anything relating to the vertical position of the HS.
I also understand the reasons for the negative AOA on the horizontal stab (much the same as for F/W) but in what position would this benefit the Bee the most...
On a Dominator, the HS is at the same elevation as the center of the prop.
A Sparrow has a tall tail, but the HS is on the keel
The HS on a Watson / Starbee tail from what I can tell is half way between the keel and the center of the prop.
Monarch has small VS with the HS at centerline...
I'm assuming its effect in clean air vs prop wash is one consideration, but what would be the best for the Bee??
Thanks in advance.
Denis

OK...here I go into the deep end of the pool.
I'm no expert...but I'll take a stab at these based on what I've gathered from the forum so far...the real experts I'm sure will weigh in with an accurate in depth response.

>>"On a Dominator, the HS is at the same elevation as the center of the prop."
Because of it's smaller surface area, it is far more effective as a control surface in the prop wash.

>>"A Sparrow has a tall tail, but the HS is on the keel"
It's also MUCH larger in surface area- and as such, lends far more to over all dynamic flight stability- power on or off. Better design if Ya' ask me.

>>"The HS on a Watson / Starbee tail from what I can tell is half way between the keel and the center of the prop. Monarch has small VS with the HS at centerline"
Some designs split the difference by mounting the HS in the middle.

An HS IS important for dynamic stability (compared to an old Bensen HTL design without a true functional HS)...larger is better, in the prop wash allows for a smaller surface area, but keel mounted allows for a truely functional flight surface (since it's NOT in the prop wash).

Like I said...these are my simple "newbie" understandings on these issues.

Hi Denis,
Here is the HS on my Bee. It is 9 sq.ft. and gives excellent stability with or without prop wash.
Thomas

And Thomas' gyro can be seen 5 miles away.

Tails

Tails

Denis,

My DesertBee has a tail very similar to Thomas', except it's painted the gold of the New Mexico flag with red markings, and has slightly rounded corners.

There was a thread after Bensen Days '07 relating to this very topic. I was one of the victims of the test (voluntarily). The actual measurement of prop flow from several birds with different weights and prop configurations confirmed the aeronautical theory. Simply that the diameter of the faster moving air from the prop shrinks from the diameter of the prop going back. The percentage it shrinks is directly related to power (thrust). At about three foot back my 60hp shrank to about 65% of the prop diameter, but Mike's 90hp shrank to about 50%.

The relationship to your question is that an HS on the keel is well out of any possible prop flow even though it's close to the tip of the prop. Only the center half of my HS is in the flow, but that seems to be more than adequate since it has an airfoil shape rather than a flat plate.. My HS is also a little wider than the prop diameter so is still reasonably effective without the engine running (with a reasonable forward airspeed of course).

There is a design spreadsheet that includes a calculation for the HS, without including whether or not it's in the prop flow. I think the file is "HP3.xls".

You definitely want the HS in the prop flow if possible. Especially if you have off-set greater than plus-minus a couple of inches between the thrust line and the center of mass. You can set a small incidence in the HS to offset the effect of the non-CLT condition.

The Good & Bad

The Good & Bad

Dennis,

I would like to add some thoughts here. There are advantages and disadvantages of having the Horizontal Stabilizer in any position. The overall most important thing is that you have an "ADEQUATE" sized horizontal stabilizer, to give you a safe and stable machine.

Having the "H.S." at the center of thrust will make sure that it is seeing plenty of air and being effective anytime the prop is turning and you have thrust. This means it will be effective with a smaller overall size while you have prop thrust flowing over it, even at very low or no forward speed. However, in an engine out scenario you will loose that advantage and be at an even bigger disadvantage because the H.S. is being largely shielded from clean air by the rest of the Gyro. So in an engine out scenario, if you don't have a larger H.S. it will likely be less effective.

Having a H. S. set down at the keel will mean that it will see much cleaner airflow at flying speeds and will not have the disadvantage of loosing effectiveness if the engine goes quiet. So at normal cruising speeds this configuration seems to have an advantage. However it will become less effective at slow or no speed conditions (even with the engine running).

Placing the H.S. half way up will give you the advantage of the prop blast air but will also shelter the H.S. from the clean air down by the keel. Everything in flying is a compromise and you get to choose what is most important to you and to build your aircraft so that it meets your goals. However, anytime you make design changes, it will have effects to the stability or safety or integrity of your machine. Unless you totally understand what those effects will be, you are taking big risks with your life to make those changes. I tend to leave the design changes to qualified and experienced designers and I would feel much better about making a change that lots of other people have already done and that has proven to be effective and safe.

Be careful and cautious and enjoy flying Gyros for a long time.

Gyro Doug

GyroDoug said:

.......Having the "H.S." at the center of thrust will make sure that it is seeing plenty of air and being effective anytime the prop is turning and you have thrust. This means it will be effective with a smaller overall size while you have prop thrust flowing over it, even at very low or no forward speed. However, in an engine out scenario you will loose that advantage and be at an even bigger disadvantage because the H.S. is being largely shielded from clean air by the rest of the Gyro. So in an engine out scenario, if you don't have a larger H.S. it will likely be less effective...........

Gyro Doug

Click to expand...

What is the primary purpose of the HS? The forces a stab works to dampen during normal flight are not present during an engine out glide. Rudder authority would be important during an engine-out but is stab dampening? If so, what is it dampening?

Two points for Tim...excelent that you brought this up (post #7)...thank you.

My orininal (but possibly flawed) thinking on this issue was that in SLOW flight the Keel mounted would offer an advantage over anything mounted higher since it would catch clean air-flow and DAMPEN for gusts etc. while still in powered flight

ANYONE?...I'm interested in a fuller understanding on this issue too.

Thank You.

RockyMeLad said:

The percentage it shrinks is directly related to power (thrust). At about three foot back my 60hp shrank to about 65% of the prop diameter, but Mike's 90hp shrank to about 50%.

Click to expand...

Thanks for the responses...
I am just trying to understand this further..

So, it seems to me, the fast moving air (prop wash) is being pushed out from the prop in a reducing, conical shape... To me, this would mean the the air blast from the bottom half of the prop would be rising as it approached the tail section and thus, a HS mounted half way between the CL and the keel would have a relatively positive AOA under power... Once the power is cut, (assuming the HS was still seeing a adequate amount of clean air not blocked by the rest of the gyro) the relative positive AOA would be reduced...

Because of this, it seems to me that a HS mounted either on the CL or on the keel would produce the most consistent effects in either power on or power off...??

Not trying to question here....Just a newbie trying to gain understanding.
Thanks
D

Need stability regardless of thrust.

Need stability regardless of thrust.

Timchick said:

What is the primary purpose of the HS? The forces a stab works to dampen during normal flight are not present during an engine out glide. Rudder authority would be important during an engine-out but is stab dampening? If so, what is it dampening?

Click to expand...

Tim,

I certainly have no expertise in this area and am only passing on my thoughts here. I would love to hear Doug's or Chuck's or Greg's thoughts on this subject. However, here are my thoughts:

While it is true that if you have a high thrust line that is contantly trying to push your nose downward, a H. S. can create a downthrust on the tail and counter the force of the high thrust line propeller thrust. However, this configuration is generally believed to be a less than optimal solution to start with. Many (if not most) new Gyroplanes are striving to keep their thrust within a couple inches of being centerline thrust. However all of these Gyroplanes still use a Horizontal Stabilizer, so there must be many advantages to a gyroplanes static and dynamic stability that have nothing to do with the high thrust line of some Gyroplanes. If a Dominator still needs to have a H.S. even though it has a slightly low thrust line, that tells me that the H.S. is used for stability that has nothing to do with a high thrust line.

It seems to me that a H.S. is there to insure that regardless of what forces may act on a Gyrolane while flying through the air that it trys to move in a stabilizing direction. That needs to happen in all possible configurations, at all speeds and through out the complete flying envelope of that aircraft. I would think that one could experiecnce a sudden up draft or down draft, regardless of whether the engine was running and thrust was being produced. One could also fly the aircraft into an orientation that could cause unexpected force to be applied to the aircraft (because of the shape of the aircraft and the aerodynamic forces caused by that shape moving through the air at different angles), regardless of whether it was under full power, partial power or no power.

It just seems to me that those needs could be just as great a zero thrust as they could be at full thrust. I hope someone that understands this better and is much more eloquent than I can jump in here and explaine what I am trying to say in a way that will make logical sene to everyone, or help me see that I am wrong on this issue.

Gyro Doug

I'm not saying a stab is not needed. I firmly believe it is. I just don't understand it when someone says it needs to be down near the keel so it gets clean air during a power off condition. In a power off condition the gyro will be in a nose down glide and I don't see how the stab placement will effect much. It's not trying to counter engine thrustline forces at this point. I also would like to hear Doug's, Chuck's, or Greg's thoughts on this.

I doubt there is any clean air down at the keel. There are shoes, rudder pedals, axles, drag links, braces, etc., all ahead of the keel mounted stab just stirring up the air mass.

Taping some yarn to a keel mounted stab and observing how they react in a power off glide should show one way or another.

Tim you are right with the engine out the HS is not needed in clean air. No PPO No PIO I guess you can still PIO but without power to adjust for it is harder to do.

Mike, I suspect you are right but as you've stated the only way to find out is the 'tuft' test. And then the results could be different for different machines.

I happen to like the placement of Rocky's stab with enough in the prop wash that it should provide some damping and then some outside the prop wash in clean air; what ever that is! I'm not sure there is any clean air in back of a pusher.

It would be interesting to see pix of Rocky's machine with tufts on the stab. with prop turning and then with engine off.

Rocky, can you tell us the overall length of your horz stab?

Just trying to point out both sides.

Just trying to point out both sides.

Timchick said:

I'm not saying a stab is not needed. I firmly believe it is. I just don't understand it when someone says it needs to be down near the keel so it gets clean air during a power off condition. In a power off condition the gyro will be in a nose down glide and I don't see how the stab placement will effect much. It's not trying to counter engine thrustline forces at this point. I also would like to hear Doug's, Chuck's, or Greg's thoughts on this.

Click to expand...

Tim,

You are being too sensitive when it comes to anything that is said that could be construed as a negative about your prefered H.S. position, when you interpret what I said to be saying the H.S. needs to be down on the Keel. I did not say the H.S. should be on the Keel, I simply pointed out there are both positives and negatives to either location, and tried to point out what they were (at least to my way of thinking.)

I personally think the Butterfly Line of Gyros is the cream of the crop when it comes to modern designed Gyros. Larry Neal has designed some models that put the H.S. in the middle of the propwash and others that have it down on the keel. He did this because of other factors that had to deal with,. with other aspects of the design. And as I have talked to him about why he designed them differently he explained the differences and why he had to change that particular design as opposed to his other designs.

Designing an aircraft is always a bunch of compromises in order to reach your specific goals for the planned mission of the aircraft being designed. I do not think a H. S. has to be in any given position to create a stable and safe Gyroplane. I can think of several different models of Gyroplanes that have the H.S. in both the middle of the prop wash and down on the keel, and I think they are stable and safe Gyroplanes to fly. But I also think they will have slightly different handling characteristics and their safe flying envelopes may be a little different.

I think it is good to go into any situation with both eyes open and to understand both the advantages your chosen model provides as well as any disadvantages or limitations it may have. Just seems wise to me.

Gyro Doug

I'd REALLY like to THANK everyone here for the superb input...as always, I've learned LOADS from the disscussion here. As a "newbie" this is WHY I whole heartedly support RWF...it get's my brain cells spinning and keeps the gray matter sharp!
Thank You "everyone"!

GyroDoug said:

Tim,

You are being too sensitive when it comes to anything that is said that could be construed as a negative about your prefered H.S. position, when you interpret what I said to be saying the H.S. needs to be down on the Keel. I did not say the H.S. should be on the Keel, I simply pointed out there are both positives and negatives to either location, and tried to point out what they were (at least to my way of thinking.)

I personally think the Butterfly Line of Gyros is the cream of the crop when it comes to modern designed Gyros. Larry Neal has designed some models that put the H.S. in the middle of the propwash and others that have it down on the keel. He did this because of other factors that had to deal with,. with other aspects of the design. And as I have talked to him about why he designed them differently he explained the differences and why he had to change that particular design as opposed to his other designs.

Designing an aircraft is always a bunch of compromises in order to reach your specific goals for the planned mission of the aircraft being designed. I do not think a H. S. has to be in any given position to create a stable and safe Gyroplane. I can think of several different models of Gyroplanes that have the H.S. in both the middle of the prop wash and down on the keel, and I think they are stable and safe Gyroplanes to fly. But I also think they will have slightly different handling characteristics and their safe flying envelopes may be a little different.

I think it is good to go into any situation with both eyes open and to understand both the advantages your chosen model provides as well as any disadvantages or limitations it may have. Just seems wise to me.

Gyro Doug

Click to expand...

Doug, I'm not being sensitive about what you said. I don't have a prefered stab position. I put mine where it's at because it was the easiest way for me to add a stab. You're not the only one who has said the stab needs to be down on the keel to get clean air during an engine out and my comments were not directed at you. I've asked the same question in other threads and no one has anwered it.

My rudder

My rudder

Start last night working on my tail!

What about a canard?

What about a canard?

Just out of curiosity, has a canard ever been employed on a gyro? If not, what are the theoretical advantages or disadvantages? One disadvantage I see on a pusher, is that it would be out of the prop wash. I can also imagine some adverse reactions to up and down drafts. What do the experts say?
doc matt

here is my completed tail feathers for my Hornet. It is a full flying tail the complete V-stab moves as a unit and the H-stab is mounted solid to the keel.

Dan

Happy Holidays all.