dasintex

My Feedback: (10)

When placing a Gyro on an Airplane for Rudder Control on Take Offs, does the Gyro work best if it is mounted on, or as close as possible to the CG, or would it work best if it is mounted in line or slightly aft or fore of the Main Landing gear?

My thought was that the Main Gear act like a pivot point and if the Gyro was close to the Main Gear it would sense Tail rotation quicker than if it was further down the fuselage where the CG may be?

Or; it doesn't matter where it is placed, it will all work the same?

Flypaper 2

Not that critical within reason. Usually ends up close to the CG at any rate as that's where the rcvr usually ends up. Gyro really works well on rudder keeping the plane in line on takeoff. Great for warbirds and such that need a lot of care.

HarryC

My Feedback: (1)

Within a rigid structure, it doesn't matter where the gyro is, it will give the same result. A gyro senses angular rotation and if the structure is rigid then all parts of it MUST rotate at the same rate. If they don't then something is bending. Doesn't matter if it's way out in the wing, in the tail, in the nose, on the CG, all give the exact same result.
Beware those who will insist that it must be on the CG, it's one of those modellers' myths!

BarracudaHockey

My Feedback: (11)

Ahh common sense, we are finally managing to spread correct information

I love it!

Now on to twisted servo extensions....

chuckk2

When you move the Gyro from the CG Punkt (CG Dot) it changes the amount of short term movement the gyro is subjected to.
This does impact the sensitivity and possibly the sensitivity "balance" between gyro channels. (X,Y,Z)
Think "Rate of Change" and "Deflection"

BarracudaHockey

My Feedback: (11)

Wrong.

It measures rotation rate about an axis.

That doesn't change no matter where you mount it. And assuming what you're saying is true, do you think the distance we could change that in a model is significant?

dasintex

My Feedback: (10)

Let me throw something in here for consideration; the purpose of my Gyro use is to control the rudder, keep the plane straight on takeoff; it seems that on takeoffs, with the Plane on the ground the point of pivot would be the main wheels because they are still in contact with the ground; I did an experiment in regards to the best place to mount a Gyro; and I will say that the Gyro will operate no matter where it is mounted, however, what changes is the amount that the Gyro works or the amount that it will affect the rudder and quickness to react.

Here is my experiment; I took a Gyro, un-mounted on a plane, hooked it up to the radio and rudder servo, I rotated the Gyro and the rudder reacted immediately and with enough Rudder throw to have some authority; I then took the Gyro, mounted it on the end of 12" ruler, the other end of the ruler had a hole in it at about the 1/2" mark, using this hole as the pivot point I swung the ruler from side to side and the Gyro/Rudder reacted, not as quickly and with marked reduction in throw; I then mounted the Gyro in the fuselage directly in line with the Main Landing gear and with the plane on the floor and the main wheels in contact with the floor, I swung the tail from side to side, and the Gyro/Rudder reacted immediately and with authority; I then remounted the Gyro approximately 8 inches further down the fuselage towards the Tail, I swung the tail from side to side again using the main wheels as the pivot point and the Gyro/rudder reacted slower and with less rudder throw.

My thought was that it does matter where the Gyro is mounted in regards to rudder use on take off with the main wheels in contact with the ground acting as the planes pivot point, and maybe in the air it doesn't matter where the Gyro is placed!

BarracudaHockey

My Feedback: (11)

It doesn't matter anywhere.

If you turned the gyro 10 degrees per second on your first test, then the rudder would react 'x' amount. That amount is based on the electronic gain, more gain more reaction.

If, on the end of the ruler you again rotate it 10 degrees per second, you will get the same reaction. The gyro doesn't know its moving sideways (or forwards at 200mph in flight), it just knows it turned 10 degrees per second and will react accordingly.

I don't know a better way to explain it.

BarracudaHockey

My Feedback: (11)

Look, I don't want to sound condescending or know-it-all. Everyone has their niche right? My friend used to make sails and sews me up beautiful wing bags, and makes flags for my glider tow lines out of old lawn chair bags. He's a great pilot but he can't enable dual ailerons on his radio without calling me at 10 at night.

You're in my wheelhouse here. I eschew posting resumes but I worked on gyro stabilized surveillance and weapons systems for 20 years on the P-3 Orion. Radar antennas mounted on the nose and tail that had to be perfectly synchronized and level to the earth no matter what attitude the airplane was in. Camera systems that had to remain on a target no matter what the plane was doing, weapons antennas mounted on pods on the wings. You get the idea.

So it is with no small expertise on the subject that I offer what I consider to be a well educated opinion on the subject.

dasintex

My Feedback: (10)

Not condescending at all, appreciate your input and sharing with us your experience; here's my take off from this, I agree with what you have been saying, 100%, no problem; I just know from my humble simplistic experiment, that the Best results or effect that I wanted for me, and that's the key, its the effect I wanted, seems to be when I placed the Gyro in line with the main wheels or close to that line, may not correspond with logic, but it seems to work best for what I want to accomplish and I'm good with it because it works. However, if I got the same results weather the Gyro was placed at the Pivot or further down the fuselage away from this Pivot Point I would have been equally good with, in fact I would have preferred that result because you can't always place the Gyro inline with the main wheels, anyways, appreciate your replies and help.

HarryC

My Feedback: (1)

Completely wrong. A gyro can only sense where it is pointing, it can not sense movement.

HarryC

My Feedback: (1)

Then you must have had some other variable in your experiment. The behaviour of a gyro isn't a matter of opinion, it isn't something that is up for debate like politics or which colour scheme is best. Gyros sense only where they are pointing, they do not, they can not, sense movement. If there are a gyros in the nose, over the wheels, on the CG, on the tail, on a wingtip and you swing the plane then unless your model is flexible or cracked all parts of the model will change to point in the same direction at the same time and the gyros in all those places must see the same change in direction of pointing at the same time. Their different movement due to being in different places is irrelevant, a gyro can not sense motion, only the direction of pointing.

dasintex

My Feedback: (10)

All I am going to say, regardless of the Science, is that the Gyro worked better when placed inline with the main gear and not so much when placed further down the fuselage, no other varibale involved, like I said a very simplistic experiemnt, results were the same when Gyro was placed on the ruler out of the plane, it works for me, got the results I wanted, and that's the bottom line; end of story!

Lifer

My Feedback: (1)

After this is over, can we discuss 2-stroke oils?

HarryC

My Feedback: (1)

Which proves that other variables were involved! What you say you saw (a massive variable!) is not how a gyro can behave therefore your experiment was flawed. This is not a topic of debate, it is not a matter of opinion or personal theories. That is how gyros are, and that's that!
If a gyro behaved differently depending on its distance from your arbitrarily chosen CG, it would be impossible for makers of gyro instruments for aircraft, such as the Attitude Indicator, Direction Indicator, because they produce one instrument which you fit to your panel which could be all sorts of random distances from the CG.

Imagine a plane with three freely mounted gyros, the free spinning wheel types, one on the CG and one at each wing tip. The gyro disc is vertical and aligned front to back. All three are parallel and pointing forward. You rotate the plane to point another way. All 3 gyros still point forward the way they were at the start. But not according to you, you say that the ones on the wingtips must now be pointing a different direction! That's not how gyros behave. if you think that then you misunderstand, at a most basic and fundamental level, what a gyro is.

dasintex

My Feedback: (10)

Whatever!

BarracudaHockey

My Feedback: (11)

I think your ruler experiment is flawed because the rate of change is probably different.

dasintex

My Feedback: (10)

Again, another Whatever!

You guys are missing the point, it works for me and I could care less that it doesn't follow your logic and Science based knowledge, so you can place your Gyro where you want and I will place mine where it works best for me and that is inline with the main gear!

HarryC

My Feedback: (1)

Barracuda, we may as well give up, he is denying that 1+1=2

dasintex

My Feedback: (10)

You mean it's not '3'

Appreciate your help and input, I'm just going a different route that works for me, have good day on both sides of the pond!

Rafael23cc

My Feedback: (6)

Dasintex, you are most likely correct. There is a slight difference in mounting location. But here is where understanding the gyro and its programming comes into effect. For the gyro to be 100% percent effective it should be as close as possible to the CG of the aircraft. Anybody that knows anything about aviation knows that at the CG is where the axis of rotation is. But as you also know, the CG may not be the most available place to mount a device. So that's where the programming of the device comes into effect.

All of my experience with gyros comes from helicopters, I have zero experience with airplanes. On a helicopter, there are very few options of mounting the gyro right below the main shaft, (where the CG is, or should be) So we all mount the gyros either just above the tail boom, or inside the canopy, several inches away from the Main Shaft. But we also know that we need to go into the gyro programming at tweak the number to fit the machine.

In my eyes, all of you are talking about the same thing, just in different languages.

Rafael

dasintex

My Feedback: (10)

Correct!

When I mounted the Gyro close to the point of Axis, that being the Main Landing Gear which serves as the Pivot Point or Center of Axis for the Rudder on Take Offs, had the most effect or results I wanted; further down the Fuselage the effect lessened and I had to increase gain which I was running out of; I had more control over the Gyro when it was mounted on or near the Pivot Point.

It works for me!

beepee

dasintex,

One point that has not yet been mentioned, the closer to the CG (or thereabouts) the gyro is, the less vibration it will likely experience. Or, is this point going to start yet another flaming debate.

You are on the right track. I have one for the same purpose and located it in place of the pilot. It works. The only issue I have is that it needs tuning every flying session, but it is an old piezo unit.

Bedford

BarracudaHockey

My Feedback: (11)

Well, you want a gyro in the area of least vibration. Thats not necessarily on the CG.

dirtybird

My Feedback: (5)

I guess my question is it actually a Gyro or is it an accelerometer?