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Old Feb 12, 2013, 09:54 AM
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Hey all, noob question here. After watching vids of rc flight the autogyro just seems like it can be fun for a person like me. I'm in the process of building a foam type gyro and have one question about the rotor heads. Why do a lot of the plans and videos show heads that tilt? Is this really needed or can a head stay fixed? Besides that I'm trying to decide if I should use rudder and elevator or make the elevator into two parts and do a elevon setup. Thoughts, input.......help
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Old Feb 12, 2013, 11:48 AM
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Daf....

Thanks for calling in. Fixed heads are more commonly found on twin rotor models like the "Grace" . This set up uses the torque cancelling contra rotating Rotors, and such models have a small fixed wing .

IMHO the best "simple" head ,is fixed in pitch and active in roll ,this type of head is very quick and simple to build ,and results in the positive roll authority required for a successful single rotor design.

Fixed head single rotors can be very difficult to get in trim , before getting broken. and best suited to ultra light designs flown indoors.

An example of a simple roll only head can be seen in the PDF posted on the previous page.

Tom.
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Old Feb 12, 2013, 12:19 PM
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Ok I think I get what your saying. I'm using a plan that lead feather designed. It's all foam so it's going to be light. His flys so ill give it a try

Here is the link to his build thread,
http://www.rcgroups.com/forums/showthread.php

Apache Longbow autogyro (4 min 22 sec)
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Old Feb 12, 2013, 03:54 PM
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Paderborn DE
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Wow, it ended up looking like yours Tom.

Well, ready for the maiden and although it took quite a while due to being knocked out with a virus for a week I have enjoyed the build and learned a lot on the way so thanks Tom.

As can be seen from the photos below the finished result looks like yours so I guess I did most of it right but as they say, the proof of the pudding comes just after launching (OK, I made that one up).

I followed the .PDF pretty much straight with the exceptions that I made the blades 1” longer and the boom ½” longer and I moved the aileron servo to the back of the fuselage box. The blades were extended because I wanted curved tips and watching the videos I could see that the motor had loads of power and the extra inch will actually provide nearly 10% more area (3389,51² over 3032,98²), time will tell. The aileron servo was moved just because it gave a straighter run for the push rods and it was easier to cut a rectangle out of the back of the box than to make a frame (OK, lazy at times). Oh yes, I also added a retaining strap for the battery because I still have problems trusting Velcro and the massive C of G shift if the battery comes off would (I think) be fatal.

I was slightly ‘flexible’ regarding the materials which I used because I just looked around my workshop and the LHS to see what I could use. The fuselage box was made of 2 mm birch 5 ply plywood which is a lot harder to work with and heavier but it was what I could get and makes a really tough structure. I could not find ½” X ¼” (6 X 12 mm) spruce so I laminated (using PVA) 2 X ¼” (6 mm). I can’t see this being a problem but I did laminate an extra bit onto the bottom of the main mast so that the bolt hole would not be on a lamination joint. I could only find FR4 glass plate here in Germany so I ordered some (special offer, 2 X A4 sized sheets for around a Fiver!!!) and afterwards Googled FR4 to find out that it is G10 but fire resistant (perfect for a hot model) and it is 0,9 mm. When I got it I was surprised at how stiff it was (worried that the 0,10 mm would make a difference) but now the blades are on the triangle is quite flexible so I am confident that it will make no difference in flight. I added small pieces of 4 mm OD, 3 mm ID aluminium tube to the outside of the control rods to prevent the danger of the carbon splitting under load (happened on a helicopter tail rotor push rod once, never again, belt and braces). I also made the aileron control rod support plates (???) full length as then are then held securely by the whipping and the glued control rod supports which will in turn strengthen the area where the rotor head bolt goes through the wood. 3 mm Solid carbon rods were used for the elevator and rudder (yes, I fitted one from the start) because I did not have enough 3 mm tube and the LHS was out of stock, ends were bent 1 mm piano wire cyno’d with 2 layers of heat shrink, seem pretty solid.
The only area of concern which I will look at when (if) she flies is the rotor head. It is brilliant, simple cheap and totally practical (result Tom), it was one of the reasons that I built the model because as Tom says, this level of simplicity make building an Autogyro a viable option for lazy builders like me!! However, I get concerned when making a radial bearing take an axel load which is what we are doing here. The thrust of the head is trying to pull the model upwards and the rotor head bolt is retaining the fuselage which means that the outside flange is pulling one way and the inner ring the other, not good for a radial bearing. I am sure that it works (seen the Vid) but I will be looking at getting a thrust bearing somewhere in there. Not a criticism by any means, just an observation which I will look at changing and who knows, maybe Tom will like what I come up with.

Anyway, ready for the first flight and looking forwards to it (I seem to have an ‘inner confidence’ in this design).

I hope that this rambling helps someone and if not, why did you read it all??

Thanks again Tom.

Paul Bray.
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Old Feb 12, 2013, 04:28 PM
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Hi Paul

Well, I read it and it helps me! Or, more accurately, it will do soon enough......

We're back home now - its a fair bit colder in the Lake District than it was in Malta, though it wasn't exactly hot there either.

I know I've said it already, Paul, but good luck with the maiden.......hope it goes well. Any chance of a vid?

Nice build, by the way! Whats the A.U.W.?

Dave
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Old Feb 12, 2013, 05:26 PM
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It does not look like mine Paul ..it looks better ! Nice job .

As a matter of interest if your weight distribution is similar to my model then provided it remained connected loosing the lipo should not be at all dramatic ,well ! it wasn't when I set it up to fall off in flight.
You are perfectly correct in you comments and observations re the bearings , and it should be a criticism. As you suggest it's a compromise and does rely on the bearing flange, and inner to outer integrity , which has been ok on my models, but could do with a re think .A thrust washer followed by an over size washer under the bolt head could provide a stop, but I will watch with interest if you come up with a solution .
I really like your idea of mounting the servo in the rear former ,why did I not think of that!
If the shims are correct I would be very surprised if you don't get the model away first time, but good luck anyway, it looks to good to crash lol

Regards; and thanks for taking the time to post the information and photos.

Tom.
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Old Feb 12, 2013, 05:52 PM
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Daf...

Thanks for the link and video , I did have a look at the thread a while back and was impressed with Lead Feathers design .
I guess controlling pitch with throttle is not difficult , and rudder only flat turns help prevent avoiding critical bank angles .
A nice example of a single rotor fixed head.

Tom.
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Old Feb 12, 2013, 06:03 PM
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I've got most of my design finished but the rotor part. I combined leadfeathers design with the swappable series the guys on flite test use. Now I have to figure out how to mount and build the rotor and shaft
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Old Feb 13, 2013, 05:14 AM
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Thanks for the encouraging and kind comments.

@ Pardshaw, AUW is 780 grams or 1.74 Pounds in ‘old money’. Just did some number crunching and came up with a disk loading of 1.18 Oz. per Sq Ft, quite light.
I broke one of my own rules by working that out, I normally never weigh a model and work out the disk/ wing loading before the maiden!! The reason (which I think is quite sound) is that models always seem to end up heavier than you want (or in some cases lighter) and the maiden is always a bit of a worrying time. My head is always full of concerns about the C of G, control throws and the mechanical integrity (i.e., will it fall apart in the air) and knowing that my new Baby turned out a bit tubby only adds to the woes. The more nagging doubts that you have in the back of your mind the less concentrated you are on actually flying the thing which reduces your chance of success, catch 22. You can’t take weight out afterwards anyway so you can’t change the situation but you can take away the concern by not knowing about it (just call me Mr Ostrich with my head in the sand)!!

@ Tom, I have several boxes of left over Hely bits and I am sure that I can find some spacers and a 3 mm thrust washer, the problem will keeping the spacer secured in the correct position as it will be located above the top bearing and the ID will have to be greater than the OD of the bearing inner ring so there will be nothing to stop it ‘sliding out’. Many years ago the German helicopter company Schluter sold a ‘combination bearing’ which would have been perfect for this application but I haven’t seen them for years.

My battery pack would hang at around the C of G location, but, I am worried about it swinging like a pendulum causing a shift in the C of G backwards and forwards until Terra Firma stops the movement.
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Old Feb 13, 2013, 09:04 AM
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Paul, Tom,

I personally wouldn't worry about the thrust effect on a radial bearing. Bigger Autogyros than the Crane fly use them and have no problems.

The bearings we are using a deep groove bearings and I just looked at the spec of typical ones on a manufacturers website, lots of complicated maths and stats in the data sheet but if I read it right it boiled down to a statement that thrust loads can be upto 1/4 of the spec radial load. 3mm bearings were rated at 300 Newtons!, so we can go to 75N load before worrying. With a 750gram model pulling 10G in an unimmaginable manouver would still leave a factor of safety of 10.

malcolm
(I hope I understood the manufacturers spec)
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Old Feb 13, 2013, 10:11 AM
Flying one day at a time....
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Paul,

Thanks for the info on your build - sounds great! I'm sure the maiden will go well when you get a break in the weather. Good luck! (BTW - I completely understand your rule about the weight, so thank you for doing it anyway!)

I ordered most of my bits and pieces today. Should be able to start the build next week and will post pictures from time to time as I go. I took a decision up front to source enough material to build two complete airframes (including rotor head and rotor blades). Partly this was to reduce the proportion of postage costs, but also to give me flying spares!

I'm holding back on buying the motor, ESC and battery until everything else is complete. I doubt that I'll buy two of each of those as the cost would be too high. We'll see.....

Dave
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Old Feb 13, 2013, 12:00 PM
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Hi Malcolm,
interesting, I was aware of the deep groove thing but never looked at the thrust load that they can take, I am also the person that ignores ABEC ratings because bearing manufacturers are notorious for using different tolerances and for ‘extending’ the truth (I wonder if the same people give LiPo cells their C rating???).
My experience was purely from playing with Helys for a few years where I have had bearings fail when subjected to a side load.
It will not be a chore to take the head off and test the top bearing for ‘notchyness (???)’ every now and then.

Cheers,

Paul Bray.
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Old Feb 13, 2013, 02:39 PM
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Paul and Malcolm.

Thanks to Malcolm for the reassurances that confirms my relatively long experiance with the bearing set up . It's not ideal but keeps things simple ,light ,and low cost . Play will develop after an hour or so use but ,I have not found it effects the way the model performs, or had any failures ...yet!

Just getting back to Paul's concern about lipo security ,can I reiterate that the original design used the under slung lipo retained by Velcro, as a way of reducing crash damage which is not uncommon when newbies have a go with any Autogyro .As you all know this type of product is sold with varying quality depending on the supplier ,and in particular the effectiveness of the glue layer can be a problem with cheaper brands.

The stuff I use is industrial grade and there is no way the lipo will fall off , but believe it or not I have tested to see what happens if it does! and yes you're right I am quite mad lol, but several flights were carried out with a substandard lipo fix and every time despite it swinging around wildly control was maintained followed by successful landings .I hope it would fair to say that this model tends to be tolerant of some extreme abuses .
Paul thanks again for the detailed scan of your build ,just the job and helpful to others.

Tom.
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Old Feb 14, 2013, 02:57 AM
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Wow, Tom, you should be in customer services somewhere!! Risking a model just because someone makes a comment, that’s what I call commitment!!

I know what you mean about Velcro but at the moment all that I have is some ‘reasonable’ stuff from the local DIY store which does hold and stick quite well but not as well as industrial strength, hence the belt and braces.
My first attempt at an Autogyro was Al Foot’s Monotwirl which, as I learn to my cost, was quite sensitive regarding the C of G position so I figured that maybe all AGs are the same. Fitting the strap (which I had lying around) took around 5 minutes to cut the slot with a Dremel which made it low cost/ effort insurance.

I have also found a way to stop the top bearing wearing, I just ordered 4 more, as you know, Murphys law states that what you have you never need so now that I have spares on the bench It will stop the one in use from wearing out, simple :-)
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Old Feb 14, 2013, 10:07 AM
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Paul.

I just like experimenting , and taking up the challenge of finding the structural and flight limitations.
I have a dozen Autogyros , so if one becomes a sacrificial lamb it's not a great loss lol.
Look forward to hearing about your improved bearing .

Tom.
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