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Old Mar 18, 2003, 02:56 PM
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Scottsdale, AZ
Joined Sep 2000
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Ryan PT-22

For some time now I have had a hankering to build a scale (electric powered) model of a Ryan PT-22. This is a later variant of the ever popular Ryan STA or Sport Trainer that was used by the Army as a trainer. The main differences are that it has a radial 5 cylinder Kinner engine, swept wings and, last but not least, exposed landing gear struts without any fairings. Here is a
link to some pictures of an example.

The idea is to build it in 1/6 scale, giving it a wingspan of 60" and a best guess weight of around 6 lbs. Planned power is 16 Sub-C cells with an Aveox 1412/2Y and gearbox.

It is the landing gear that is giving me a headache. It looks like something built from an Erector set (I have attached a close up picture). I am looking for advice on how to build a working model of this landing gear that can survive touchdowns that are not always picture perfect.

I figure that I can incorporate a Robart Robostrut for the forward strut, but the rest has me stumped, especially the pivoting arm at the bottom. One idea is to make the Robostrut the main support, attaching it to a music wire leg with a torsion bar, as is commonly done in conventional sport planes. The other struts would become cosmetic, but would still have to survive the rearward forces of landings.

Another idea is to replace the hinge-pivot of the bottom arm with a music wire coil spring, as in the nose strut of a sport plane with tricycle landing gear.

Anybody got any ideas on how to approach this, especially for someone who doesn't have any metal working tools other than a drill press, band saw, hack saw and files? Please don't tell me to add fairings and omit all the struts. I know that some variations had fairings, but it is the gangly look of the landing gear that is one of the main features that attracts me to this plane.
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Old Mar 18, 2003, 05:34 PM
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vintage1's Avatar
East Anglia, UK
Joined Sep 2002
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USE CARBON FIBER!!!

Just my 2c worth.

I invested in some CF rod and tube some time back, and used it all up and now have bought some more.

Its PERFECT for undercarts. Its light, stiff and VERY strong. I am sick of bending pianowire back into shape EVERY landing.

You can make sprung struts as well if you get a piece of rod or tube that fits well inside another bit, and either wind your own springs or buy some from a hardware shop.

I join it togeher by using bits of pre-bent piano wire and cyano to tack it together, then epoxy over the joints. I have got myself some CF thread (tow) which I will use next time to bind up the joins: Soaked in epoxy its almost bombproof.

I reckon that you would find it easuer to work than metal, and you can form the complex bits by moulding glass cloth and epoxy into various lumps and bumps, and then use a set of needle files to get everything just right, and spray it all silver afterwards.

The actual wheel bearings can be piano wire or even bolts. My WWI wheels run with CF hubs on CF rod axle, with balsa and ply wheels and a foam rubber tyre glued around the outside. Saves huge amounts of weight.

I have just about thrown away all piano wire now in favour of CF - torque rods, elevator joiners, undercarts, pushrods, struts - you name it, I'll CF it!

Even thinking of using it for leading edges and spars.

Thik CF ands see if it makes sense in that project!!! :-)
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Old Mar 18, 2003, 08:17 PM
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Daren's Avatar
Los Alamos, NM, USofA
Joined Nov 2000
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Re: Ryan PT-22

Quote:
Originally posted by Jeff Bean
The main differences are that it has a radial 5 cylinder Kinner engine, swept wings and, last but not least, exposed landing gear struts without any fairings.
I'm sure this was a slip of the keyboard, but this airplane didn't have swept wings.



Daren
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Old Mar 18, 2003, 10:50 PM
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Scottsdale, AZ
Joined Sep 2000
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Re: Ryan PT-22

Quote:
Originally posted by Daren
I'm sure this was a slip of the keyboard, but this airplane didn't have swept wings.
No, no mistake there. I have a lot of documentation that says that the PT-22 did have swept wings. 4 degrees and 10 seconds on each panel, to be precise. A 3-view of the PT-21/22 is attached. I have a more detailed one, but it is too big to post here. The PT-21 is the same airframe as the PT-22, difference being that it had a 132 hp Kinner engine instead of a 160 hp engine and had fairings on the landing gear.
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Old Mar 19, 2003, 08:40 AM
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Daren's Avatar
Los Alamos, NM, USofA
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Interesting. You learn something new every day. Here's a picture I found.

Daren
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Old Mar 19, 2003, 09:14 AM
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Scottsdale, AZ
Joined Sep 2000
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Re: USE CARBON FIBER!!!

Well carbon fiber is an interesting thought that I had not considered. Probably because I have never used it, so I would have some learning to do.

I wonder if I could make the bearings of the lower arm out of wheel collars and somehow wrap some carbon tow or fiberglass around them to attach them to the pivot arm. I figure that the pivot arm would be about 1/2 inch thick at 1/6 scale and the struts would be about 5/16 inches.

Vintage1, what is the heaviest plane you have built with a carbon fibre undercarriage? I know it is stiff, but I am worried that it is also brittle and won't flex like music wire does.

Jeff
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Old Mar 20, 2003, 06:06 AM
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East Anglia, UK
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Jeff. Personally I build small stuff, so I can offer no direct experience.



HOWEVER, consider that formula 1 cars are made of the stuff, so strength is enormous. You can afford to use much bigger tube sections than you would with e.g. metal for the same weight.

Also consider that kites and fishing rods - and indoor planes - regularly bend rods a huge amount without them breaking...and it springs back to where it was. Well almost. I do not think the carbon would break in a situation like yours - I would expect it rather to rip out the mountings if it was not sprung in some way.

Hence my remarks on using sliding tubes to make sprung struts.

I am certain you could attach wheel collars using the method you describe. You could use bent pieces of wire epoxied in tube ends to make the oher part of any bearing surfaces although I prefer a loaded polyester for real strength - the stuff sold for car body repairs - chemical metal?

Compared with metal. all you need tools wise is a hacksaw, some small files, some kevlar or carbon tow, and a way of holding it all togther whilst the glue sets. Suits me, cos I have no lathes and drill presses. A selection of bass bearings and some steel rod (silver steel is good, for straight runs - its unbendable almost) should allow you to duplicate just about anything.

As far as making a spring strut goes, I'd do it like this....Oh **** my PC has run out of memory and the CAD program won't load. I'll post this, and reboot and post a drawing in a minute
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Old Mar 20, 2003, 06:41 AM
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East Anglia, UK
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Ok, this ought to be a dead simple way to make a sprung strut. I have found tubes and rods that will fit well enough to do this. The spring? Well you can wind that from piano wire around the CF rod, stretch and cut to size.

I think I have rod at 2mm and tube at 3.5mm and 5mm all of which fit one inside the other.
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Old Mar 20, 2003, 08:27 PM
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Scottsdale, AZ
Joined Sep 2000
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Quote:
Originally posted by vintage1
Ok, this ought to be a dead simple way to make a sprung strut. I have found tubes and rods that will fit well enough to do this. The spring? Well you can wind that from piano wire around the CF rod, stretch and cut to size.
Thanks for the drawing -- very impressive. But what keeps the inner tube from falling out?

Jeff

P.S. I've been drawing plans for the PT-22 with TurboCad and been having lots of fun learning how to use it. I think I've got the hang of the two dimensional stuff, but a three dimensional cutaway drawing like that is beyond me.
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Old Mar 22, 2003, 11:07 AM
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Norfolk, England
Joined Sep 2001
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Jeff,
Sorry to interupt, but Vintage made me think of something.

Vintage,
You do, I assume, use tube for torque rods? I ask because when I tried a carbon rod elevator joiner, the elevators could be twisted to 180 degrees without breaking the glue joint. That amount of twist could severely limit it's use for torque rods.

Pete
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Old Sep 12, 2007, 04:26 PM
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Quote:
Originally Posted by Jeff Bean
For some time now I have had a hankering to build a scale (electric powered) model of a Ryan PT-22. This is a later variant of the ever popular Ryan STA or Sport Trainer that was used by the Army as a trainer. The main differences are that it has a radial 5 cylinder Kinner engine, swept wings and, last but not least, exposed landing gear struts without any fairings. Here is a
link to some pictures of an example.
<snip>
What a neat project! If you need any further pictures, etc., let me know. I have a friend with the real deal, which I have flown in a few times. The klatter of the Mighty Kinner is a sound I will forevermore recognize instantly.

It's still hand prop it to start it, and no radios or other modern accoutrements, and boy is it a ball to fly! The guy has about 1,030 hours flying, of which 1,020 are in that airplane!

I was also taken aback by the "swept wings," but as your three-views show, it's not much.

Gerry
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Old Sep 12, 2007, 06:13 PM
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Albuquerque, NM USA
Joined Sep 2003
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I too am exploring CF rod for LG for the same reason as Vint, flexibility.

You could also use a brass tube as a pivot point and attach to the rod with CF tow wraps. But, how do you make a U shape with CF rod? Or a Y shape? Is there a way to form the stuff so that is still flexible? Do you use resin for binding (like FG) or something like thick/thin CA?

My only problem with C is the expense, but, that is coming down in price. I am also finding that tooling for machining CF is getting obtainable too (wear a good dust mask!).

charlie (cf newbie)
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Old Sep 12, 2007, 07:36 PM
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Kissimmee, FL
Joined Mar 2001
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Jeff,

Some years ago I kit-bashed a GP Super Sportster (the 40 size ARF) into a PT-22. It is in my Fathers hangar in Colorado so I can not post any pictures of how I did the landing gear, but I will try to describe it.

The rear triangle was made as you would with a standard type torsion wire gear. They were mounted in the wing with groved hardwood blocks. The aft one met the forward one at the bottom and then it continued forward to the wheel axle. This gave very nice spring action. The shock strut was simulated with nothing more than two pieces of brass telescoping tubing. I used 90 deg axles that are designed to be silver soldered to the ends of music wire to join the front and rear struts (by not using the wheel axle part) and also to make the axle for the wheel. It has worked very well for my plane. It started out with an old brushed motor and 19 cell NiCad pack so it was rather heavy. It now has a brushless system on a 4 cell LiPo pack and is nice and light.
I did not add the sweep to the wings, just reshaped the tail, wing tips, added the turtle deck, and used williams bro's cyl's to replicate the Kinner. Makes for a nice flying stand (way) off scale plane.
If I can get it out here I'll post some pictures. If I can answer any questions let me know. I have a PT-22 that I fly here at the Warbird Adventures museum in Kissimmee, FL so I can also give you pictures if needed.

Sean
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Old Sep 13, 2007, 03:07 AM
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Sydney Australia
Joined Mar 2005
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Hi Jeff, I'm also a fan of the PT-22 but the one I've started is 1/4 scale so the U/C will be totally scale.

For a 60 inch 6 pound model why not just fit a standard sport model type torsion bar system with the wire legs down as the front strut, the one that telescopes.

All the rest could then be decorative, make it as scale as you want from bits of carbon tube, dowel, plastic tube, whatever. Make the rear strut telescope but don't bother with a spring inside. It will move in & out as the actual leg flexes back.

Make the wire bracing non functional too, just hide some springs somewhere at the top so the wire legs can flex all directions without pulling the baracing out.

Dress it all up & paint it & it will look plenty gangly enough. - John.
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Old Sep 13, 2007, 09:33 AM
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San Diego, California
Joined Dec 2004
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Hey, Sean: With the Kinner engine, and NO sweep back to the wings, what you really had was a PT-20. It did really exist.

Les
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