|Aug 13, 2012, 10:47 PM|
Old heli becomes gyro
Hi, I am a new flyer to gyros. I have a PT25 trainer and absolutely love the idea of gyros. I fly planes and helicopters.
I have had an old helicopter hanging around in the shed for a while so without much research I decided to make it into an auto gyro. During the build I realized I had a lack of knowledge as I needed to make decisions on different aerodynamics. I had no idea what blade loading to work within, nor power requirements or even head design.
I copied a number of aspects from my PT 25. In looking for more info I was lucky enough to find this forum. Now I know there is a lot I didn't know.
Please have a look at the craft so far and comment as you wish. It has not had a maiden flight yet as I fly at a very difficult field that is short with trees at each end and the conditions just have not been suitable for a maiden flight.
Specs Aerobalsa blades 600mm, .25 OS 2 stroke, weight 2.1kg, set blade pitch 3.5 deg negative, hang angle 12 deg, swash control head (original heli).
Thanks in advance for your help
|Aug 14, 2012, 01:28 PM|
Nice conversion keep us up to date with any progress
A few have tried similar conversion including myself with limited success but it is worth trying this is the Wot 4E I have been trying at the moment but no flight yet
|Aug 14, 2012, 03:26 PM|
Hi Joe. I am very pleased that I have caught your interest. I will be in Canada and then the states for the next three weeks so all will be quiet until my return.
I will post on performance once I get it on the runway.
I like the idea of your conversion. I have a spare trainer fuse that I may convert after I have gone to the end of this current project. Maybe I could shoe horn the remains of my old heli into the trainer fuse as you have done. I would be grateful if you could also post how your project goes.
I do have a couple of questions so far. What collective pitch do you intend to begin with? What cyclic throw angles have you set up on the fly bar? What will be your target hang angle? What is your mast angle relative to the thrust line? What is your mast angle relative to the ground during taxi?
Once again thank you in advance for your interest. Kind regards Robin
|Aug 15, 2012, 10:07 AM|
Nice work so far. You're being modest, because looking at the pictures, you've done your homework. The numbers you've given sound good. I don't think you'll want 3 1/2 deg neg. Most of my stuff is about 1 deg or less. The heli head would allow you to determine what the best pitch is with test flights, and put the pitch on a switch; one setting for spin up, and another for flight. As far as roll and pitch settings, I'd start around 10deg on the swashplate, and maybe set a couple of rates on your radio until you see how much you're comfortable with. There are many advantages to a swashplate head. If you fly heli's you shouldn't have any issues. I'll be watching your progress from Afghanistan. Keep up the good work.
|Aug 15, 2012, 01:47 PM|
I agree with mike....3.5 degrees will be too much. This reminds me so much of the whopper so I'll give my advice that David Ramsey gave me.
Make sure your swash is level when setting it up. make sure your paddles are also level, even if your blades are in negative. When you take off, don't give an input in your swash, but use your rudder. When you get up to speed you can then use the other inputs.
The whopper itself used zero hang angle, no down thrust on the motor and was shimmed up on the trailing edge of the elevator. I'm not sure if I agreed with everything the whopper was, but it does fly on good days!
Good luck and keep posting!
Lots of interest in your findings...
|Aug 15, 2012, 10:03 PM|
Hi Mike and Joe. Thanks for the great ideas. I suspected I would loose some head speed with cyclic input. This problem had made me a little nervous as I did not want to kill the head speed with control inputs on take off. The models I have seen so far have all had powered heads. I will remember to use rudder and throttle until airborne.
Up until now I was just going to run a fixed collective pitch but I love the idea of running separate flight modes for take off and normal flight. I will run the collective back to 1 deg after take off.
I have set down thrust on the motor. This is easy to rectify and return back to straight thrust. I have measured the fly bar throws at 8 deg so that should be OK for now. I thought I would run a lot of expo so as not to loose the full deflection if needed.
I will get one of the club guys to video my maiden flight for later dissection.
Thank you so much for your helpful ideas. I have been a bit of a pioneer within my own club and therefore have had to turn to the internet community for assistance. I hope to return the favor as I gain experience.
I will be sure to post my progress.
Kind regards Robin
|Aug 17, 2012, 09:55 AM|
Joined Nov 2004
Expect more sluggish control than when it was a helicopter because:
1) The RPM will be much lower
2) The fuselage has a lot more inertia to overcome.
I made the flybars on mine about 50% longer than stock to get some control authority back.
I suggest having high rate on tap and/or an expo setup in case you have marginal control.
+1° pitch may be too much, especially with cambered blades. The true zero lift setting is about -3°, so +1° is really about +4°. I'd start with -1° and work up to the highest rotor speed.
Note that the highest rotor speed is also the one that makes the least torque so will suffer from the most speed dropoff due to control input. I found that the optimum collective setting was such that you were below max RPM but you didn't lose much with control. With direct cyclic input and max RPM it is possible to pull down the rotor speed far enough that it takes a LONG time to get rotor speed back, speaking from experience.
|Aug 27, 2012, 11:00 AM|
Thanks so much for the help. As I mentioned in earlier posts I am out of town right now. I will set up the pitch for fastest rotation while holding it in the wind. I have set significant expo rates up already with full cyclic throws available if required.
Although I m on vacation I am now looking forward to getting home to fly. I will definetly be posting maiden flight video along with all settings for comment.
Thanks again for your help, I'm humbled and greatful for your interest.
Robin (Flash) Wallace.
|Sep 30, 2012, 06:53 PM|
I have made the suggested changes to the blade pitch angle and taken the downward thrust off the motor.
I went out to the field for a test fly and it turned out to be one of those days when things just would not go right. Firstly my video camera had a corrupt SD card and then the wind swung to a cross wind making for a very sketchy day for auto gyro flying.
I have taxied the gyro for a few runs and found that the head speed dies. If I hold it up and into the wind it picks up good head speed so I am pleased with he blade pitch. What I am suspicious of is that I don't have enough mast angle. If fact I only have 18 degrees for rotor attack angle. I am aware that 20 degrees is supposed to be the minimum rotor attack angle so I am going to have to make some changes to the model.
I don't have the luxury of being able to change the mast angle so i am going to have a try at lifting the nose with a taller under carriage. Once I have done this I'm confident that I can then get enough head speed to move onto the next issues that normally come up with auto gyros and maiden flights.
Hopefully I can attach some video too once I buy a reliable SD card to replace the current one.
|Oct 01, 2012, 08:04 AM|
I really wouldn't worry about the attack angle. It will just take a little longer to get the blades spinning up. Besides, if I was going to increase the angle of attack on your model I would put bigger wheels in front..it would also help your ground handling. But like I said, I wouldn't change anything.
Well, I hope this machine sorts out for you. With enough determination, you can make anything work...so don't give up!
|Jan 03, 2013, 03:45 PM|
Hi to those that are interested.
It has been some time since I have made any progress in sorting this gyro out. This is mainly due to a combination of weather and seasonal commitments.
I have made some changes after test taxing and holding the craft above my head. No flying at this stage although I am now very close.
I have discovered that the fly bar and associated mechanism, was creating so much drag that the head speed would not come up to full auto rotation. Further more, when cyclic inputs were made the head speed would decay even more. The craft is quite heavy anyway so I need as much lift as I can get. I have removed the flybar along with all associated linkages and converted the gyro to a flybarless unit. I am using a 3 axis control to stabilize it. I currently fly flybarless helicopters and am confident that the gyro has good stability with the electronic control unit on board. Now when I hold it into the wind it feels very stable as the electronic system looks after it. Inputs from the radio seem to control the correct axis and of about the right amount. I was unsure whether swash phasing may be required as the head speed is significantly lower than a driven head.
I have set the blade angles for what feels like maximum torque which is about -1 deg as suggested by MNOWELL129.
I will continue to post for those that are interested. I know I probably seem like a bit of a dabbler, but I have to say that I am thoroughly enjoying the technical aspect to developing a difficult project.
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