End loopy takeoffs with a gyro

Jun 25, 2010 11 Comments by

Like many of you, I have a few different planes, and enjoy flying most of them. However, I do have one or two that are just plain nasty in their ground handling and take offs. You probably have seen these – some Piper Cubs, Beavers, and especially some of the narrow under carriage warbirds. Strangely, not all tail draggers do this. But with one of these “loopy” planes, they are lined up on the runway, power is slowly advanced, and the plane skitters to the left, it skitters to the right, and may loop in a complete circle. Even if it is kept straight for a while, as power is advanced and the tail lifts, it then skewers over to the left from torque. And if insufficient speed has been built up, for example it was heading for the fence and you horsed it up too soon, you are rewarded with a spectacular left wing cartwheel.

I know, when you are relating this story to your mates, you either get a “yup, that’s why I would never get a Beaver, Piper, warbird, whatever …”, or you get a “pilot skill problem, with more flying experience you will be able to handle it.” I understand that more skill may help, but honestly I go flying to have fun, not to work on creating an ulcer worrying whether the plane will get off the ground today. I sure wouldn’t mind some sort of electronic help. And after all, I don’t see people complaining that using exponential on our radios means we are cheating or aren’t skillful flyers.

Now our helicopter brethren long ago found out that even with super human reflexes, it was really difficult to keep the tail straight on their choppers – the least wind, change of engine speed, etc. would make it swing. They discovered gyros. Suddenly, their craft would stay straight, and hovering and flying became a whole lot easier.

The object of a rudder gyro then, is to provide some computer fast electronic help on keeping it straight down the runway on roll out, and fast correction of that torque roll to the left just as it just gets airborne. Once fast enough, the plane generally flies straight without any extra help for sure.

Originally, gyros consisted of a small electric motor spinning two heavy brass disks. These spinning disks resisted movement, just like bicycle wheels or a spinning top. Today, the gyros are solid state and utilize a piezo crystal to detect movement. And specifically, they detect movement only in one rotational direction. Thus a gyro used for rudder control will only detect rotational movement about the yaw axis. Electronics “read” this rotation, and output a correctional signal to the servo, in this case the rudder. Any other movement, i.e. acceleration forward, braking, or pitch and roll are ignored by the gyro.

 There are two kinds of gyros available for model use: rate control (also known as normal mode) and heading hold.

 In Rate Control mode, if anything other than you moving the rudder stick changes the plane’s horizontal direction (yaw), the gyro will give a brief but not sustained correction to help keep it straight.

 In contrast, the heading hold mode is best used just for the take off run. In this mode, when you first line up the plane, you ‘instruct’ the gyro that it is to stay on this exact heading. As you taxi, it will automatically, and lightning fast, make corrections to keep the plane on this heading. After, takeoff, however, unless you want the plane to stay on this course forever, best to switch to normal mode, so that you can turn and do a circuit, etc. Generally on these gyros, you utilize an additional switch on your transmitter to disable the heading hold mode right after takeoff, then defaulting to the rate control mode (normal mode) for the rest of the flight.

 What if we put one of their gyros in our ‘problem’ planes to help with takeoff rudder control? Clearly not all, or even many, of our planes need this, but when you have one of these “ground loopers,” maybe a rudder gyro could help. So, I chose my worst problem planes to try this. The first one is a kit-built electric conversion Mustang, 56” wingspan, about 8 lbs all up battery in. I know, kind of heavy. Never the less, this plane is a lot of fun to fly in the air, and with gear and flaps down, is not so bad to land either. But the take off always makes we wonder if this day is going to end with another trip to the repair bench with it.

 For my first test, I tried a Futaba GY401 heading hold gyro(~$135.00). It mounts next to the receiver with a supplied special double sided foam mounting tape. You plug the one gyro lead into the rudder channel of your receiver, and plug the rudder gyro lead into another lead on the gyro. The third gyro lead plugs into an unused receiver channel to select the gyro mode. I used the Aux 2 switch on my Spektrum DX7 transmitter to switch from ‘heading hold mode’ to ‘normal mode’. The manual describes a few adjustments and selection switch for Futaba digital servo or other analog servo.

 

 

After installation and testing, I was off to the flying field. Once I had the plane lined up straight on the runway, I rapidly flipped the Aux switch on and off 3 times, leaving it in the Heading Hold position. This instructs the gyro that this is now the desired course of the plane, and the rudder is in a neutral position. I then accelerated down the runway, and if the course was a bit off, I could still manually move the rudder to keep the plane headed down the middle of the runway. But, virtually all that nasty swing one side to the other was gone, and once some speed is built up, no more torque role to the left! As the plane lifted off, I switched off the heading hold mode, and continued with whatever my usual flight routine would be. Interestingly, in flight, and with the gyro in the Rate Control mode (Normal Mode), I could bank, climb, dive, etc. and the plane really didn’t feel much different to me. Landing was straight forward, perhaps even straighter than usual for me!

 For my next test, I tried the GWS PG-03 gyro ($38) in my electric Spitfire. This plane is 56” wing span, 6 lbs all up. Initially I flew with a 4S-5000 battery, and the plane was reasonable on take off, but still requiring a fair amount of finesse to keep straight and not torque over to the left. However, in the air the plane was a bit underpowered and somewhat anemic in normal flight patterns. Since the motor could h
andle it, I then switched to a 5S-5000 pack, and rebalanced the plane. Now takeoff was not so mild mannered at all, but once in the air a whole lot more power and fun. I installed the GWS gyro by merely taping it to the inside of the fuselage wall close to the receiver, using the supplied special foam mounting tape. The gyro plugs into the rudder channel of the receiver, and the rudder servo lead plugs into the gyro. This gyro is always in Rate Control (normal mode), so no other connections or receiver channels are needed. One simple adjustment, described in the gyro manual, is required to ‘center’ the servo output, and a second adjustment to set maximum sensitivity.

 

 

Again at the flying field, I now lined up on the runway and slowly accelerated. But this time I still needed to input some torque correcting right rudder transmitter stick movement, but it was much easier. There was no nasty or sudden swinging left to right, and a very smooth takeoff. Once in the air, again, I was not really aware of any impact on my usual flying routine form the gyro. Landing was uneventful, and even easier to keep straight.

 Overall, the heading hold gyro is superior, but more expensive and requires an unused function on your transmitter to turn the modes on and off. The rate control gyro is considerably cheaper, easier to install, and does not require any other transmitter channels. Thus, if I have any more “ground looper” planes, I probably would try the simpler and cheaper rate control (normal mode) gyro first.

 If you try this, and it works nicely as it has for me, then it will be up to you whether you tell any of your fellow pilots about the gyro, or whether you just bask in their complements about how skillful your takeoffs have suddenly become.

By John Falconer

  

 

 

 

Fixed-Wing Flight School, How-tos

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11 Responses to “End loopy takeoffs with a gyro”

  1. Bob Moore says:

    Thanks for a great article with the full explanations..

    This is what I needed in two of my models.. I am going to try an E Flite.. about $65.00 ea.

  2. Bill says:

    I dont understand the need to sw off Heading Hold as the plane will always accept stick movement to overide any Gyro setting wont it??

    • Debra Cleghorn says:

      Good question; we’re checking on this one!

    • DGH says:

      Bill
      As a helicopter pilot who uses the Futaba gy-401, you are correct. In fact, for us, we put the gyro in heading hold for aerobatic flight. In fact, most heli pilots only turn HH off for final landing, if at all.
      However, you must be comfortable flying with rudder to be able to do this, otherwise the plane will not turn, except with a 90 dgree bank.

  3. DGH says:

    This is a good idea for those really squirrely planes. I have a Top Flight Staggerwing which could use this. I’ve been flying for over 30 yrs and I still have trouble with mine. As long as it doesn’t become a crutch to where you never learn how to control the tail at all.

    Many heli pilots know what happens when the gyro suddenly quits working, so many of us actually practice some flying with the gyro turned off, once we’ve learned to control our aircraft. Just in case.

  4. Harvey Swift says:

    If you leave the heading hold on the gyro will attempt to keep the nose on the same heading. You must use the rudder control when you turn to keep the turn balanced. When you release the rudder you have just reassigned a new heading. You can fly the airplane just fine, you just have to coordinate your turns. It would be easer to use rate mode if you don’t want to use the rudder.

  5. Jay Wiley says:

    Tourqe is only one of factors at play with a conventional gear (tailwheel) aircraft. Torque from the motor is trying to spin the fuselage around the center axis in the opposite direction from the propller (like a helicopter) On the ground this puts more force on the left wheel and therefore more drag which can add to the left yaw tendancy. There are at least three other elements that have more to do with the left turning tendancy which are “P” factor, gyroscopic action and spiral slip stream. “P” factor refers to the asymetrical thrust that the propeller has when sitting in the three wheel stance (tail low) as compared to level flight (tail high). The downward travleling blade is at a higher angle of attack to the relative direction than the upward travelling blade and so creates more thrust on the right side yawing the nose to the left. The propller is a gyroscope and when it changes from angled upwards in the three point position to level as the tail comes up there is a reaction 90 degrees to the right which adds to the left yaw. Lastly there is a spiral shaped slipstream created by the propeller as it “screws” it’s way through the air that circles the fuselage counterclockwise (from the front) and travels along and primarily hits the left side of the vertical stabilizer pushing it the right and the nose to the left.

    Whew! I hope I got that all correct (I’m sure someone will tell me if I didn’t) So, we like to call it torque because we recognize the term but it’s really more that that. The take off transition of a tailweel aircraft is pretty complicated. This is why tricycle gear aircraft are easier for some as the “P’ factor and gyrscopic effect are much less. Not to mention that a tailwheel aircraft is always trying to swap ends since the CG is behind the wheels….but that’s another story.

    Jay

  6. bc says:

    Jay that is a pretty accurate explanation you gave there. The P-factor is one of the biggest factors until airspeed increases. The torque become a big factor at rotation as the aircraft does not have as much airflow over the wings to counteract it. Now combine this with the P-factor that was getting better as we accelerated but now becomes worse again as we increase the angle of attack for climb out. This becomes a big problem with small models with large props producing lots of torque when they are rotated to slow. Unless you get on the rudder quick you will be making a left turnout towards the ground.

    As for the gyro. You can get a decent rate/heading hold gyro from hobbypartz.com for around $12. It is the detrum gy48v gyro. And these are not just for takeoff, they can be used for learning 3d flight as well. Hovering is made easy when the rudder works for you.

  7. Scott Page says:

    Great job explaining gyros — however you limited your examples to yaw only — and didn’t mention the newer MEMS gyros that are more vibration tolerant. (I prefer a $10 MEMS gyro that’s only 8 grams)
    I find that a gyro for roll (aileron) is the ticket to being able to fly in windy conditions. (if you think about it .. yaw and pitch are not the big problems in the wind — roll is fatal)
    Now if the wind is up and everybody else is sidelined I just switch on the roll gyro and I’m good to go. Also wind flying is really fun because you can “play” the the wind.

  8. Ben Lanterman says:

    You need to turn off the Heading Hold before the first turn you make after takeoff. Remember that HH mode always wants to keep the airplane going in the direction that the gyro was initialized. If you try an aileron/elevator turn the rudder will try to fight the turn. If you input rudder while in HH mode in flight all you do is to select a new heading for the rudder to want to correct the airplane to. Then any maneuvering from then will have the rudder fight back. I have forgotten to turn off the HH on one of my pattern ships and suddenly have it wanting to do a knife edge flight during the turn. So definitely turn off the HH after takeoff. As I noted in my Model Aviation article I have had great luck with the gyros – I have over 30 airplanes with them installed and am totally satisfied with the results. I have seen too many great scale ships broken on takeoff due to ground looping, etc. to not recommend using a gyro. Try one, you will like it. —- Ben

  9. Ben Lanterman says:

    I forgot to add – here is the Youtube site for a video of results using a HH gyro for takeoff. It is quite dramatic in many cases. As far as flying in the wind – isn’t that part of the fun? I look at the gyro only as an insurance policy to protect airplanes like the scale WWI airplanes and other loopy machines. Why not spend a few more dollars to protest an airplane that you have put hundreds of hours into building? Here is the web site —

    http://www.youtube.com/watch?v=KOuPeUE0_nQ

    Ben

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