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Thread: Converting a Fan cooled 503 Rotax to free air cooled

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    Converting a Fan cooled 503 Rotax to free air cooled

    As the Title suggests, Does anyone have any experience in this conversion for the 503 to be used in a tractor set up.

    Perhaps some details of the tin ware make up and/or modifications.

    Thanks

    JimG

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    Registered User Head in the clouds's Avatar
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    Re: Converting a Fan cooled 503 Rotax to free air cooled

    Quote Originally Posted by JimG View Post
    As the Title suggests, Does anyone have any experience in this conversion for the 503 to be used in a tractor set up.

    Perhaps some details of the tin ware make up and/or modifications.

    Thanks

    JimG
    Hi Jim,

    I remember that a couple of them were converted down Kooralbyn way in the 1980s, IIRC they were just stripped of the shroud, fan and pulleys.

    Is this for your Karatoo? If so, a couple of things - some folks have found it better to use the fan cooled version even for a tractor application if it is in a cowling unless the airflow can be guaranteed which requires very good baffles. Secondly, 45-50hp might be rather marginal for a Karatoo?

    I do know of an 80hp Rotax 912UL that is about to come on the market because the owner runs a flying school and it is reaching time expiry although it still has 750hrs before overhaul. I think he is wanting around AU$8K no GST. I can put you in touch with him if interested.

    Cheers,

    Alan

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    Re: Converting a Fan cooled 503 Rotax to free air cooled

    Hi Alan, the 503 is for a Tyro MK2 single seat that i recently acquired where the motor sits at the end of the main boom like a Thruster. Therefor the fan has to draw against what i assume would be a negative pressure at the back of the engine when flying. The mod has been done many time before , I was just hoping someone may have some experience on size and ratio of inlet and exit areas etc.
    My Karatoo is on hold and is 80% complete with the f/wall frd already done. It has a EA81 engine with a Hirth G50 box and a adapter kit by Tom Wickers.
    Meanwhile I've just finished sorting out and doing a semi restoration of a Foxcon Terrier that i bought 18 months ago it has a sub4 EA81 suby with an Autoflight box and it fly great.
    Thanks for the tip about the 912UL , I'll spread the word.

    cheers

    JimG

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    Re: Converting a Fan cooled 503 Rotax to free air cooled

    Hi again,

    The (Geoff Eastwood) Tyro is a good little craft built from 1981 and derived from the Winton Cricket and was originally equipped with the 447, so should perform very nicely with a 503. Pics show the Tyro and then Winton Cricket and Jackaroo -



    I have a bit of historical information about them if you don't know it already.

    I have seen free air 503s without any inlet and exit as such, just sitting out there in the propwash, and also seen one or two with a shroud a bit like the fan cooled version but the air enters from a scoop on one side, crosses through the fins and exits on the other side via a reverse scoop. Both seemed to work fine. Just a thought that might save you some work - the Thruster Geminis and TSTs all had a tractor 503 configuration just like your Tyro, and still used the fan system without any problems except when folks didn't replace the fan-belt regularly and it broke. Here are a couple of pics showing an old Gemini that's in our club (Gold Coast Sport Flying Club)

    Converting a Fan cooled 503 Rotax to free air cooled-img_1967.jpgConverting a Fan cooled 503 Rotax to free air cooled-img_1965.jpg

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    Re: Converting a Fan cooled 503 Rotax to free air cooled

    Thanks for the photos and commentary , Alan .
    My aim with the 503 cooling set up is to come up with a simple free air system and not have to worry about servicing a fan belt, plus a slight power gain by not having to drive the fan.
    I have doubts about running in the prop wash with the fan tower and tin off because the head fins run across the engine and would be ineffective. I remember some of my model A/C engines having the fins at 45 deg to the crank line and i always thought that was a good idea to dissipate heat.
    I'll most likely set up a couple of CHT's and do some static testing with a pair of tin snips and a pop riveter.

    Cheers

    Jim ( home base Caboolture )

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    Re: Converting a Fan cooled 503 Rotax to free air cooled

    Quote Originally Posted by JimG View Post
    ....My aim with the 503 cooling set up is to come up with a simple free air system and not have to worry about servicing a fan belt, plus a slight power gain by not having to drive the fan.....
    I quite agree on both points, the fan would consume a fair bit of power I think. In case it helps, I remember a bit about the 'two scoops' version. All made from simply bent aly sheet, about 1.6mm, it had a box that enclosed the cylinders very similar to the fan cooling shroud. Each side of the box had a cutout exposing both cylinders. On one side, the 'downwind' side, there was a tapered scoop, wide at the front reducing to zero at the back, and the front extended forward as well, to catch more air swept into it by the blades of the airscrew. The other side was very similar except in reverse and the back wasn't extended but was larger in cross-section than the front (inlet side), to allow for the expansion of the heated air and also create a 'suction' in the slipstream I imagine.

    The theory - although the inlet side was small in cross-sectional area where it fed the rear cylinder, and so you might expect the rear cylinder to get hotter, the outlet side was much larger at the rear cylinder than at the front cylinder, so that relative restriction of outlet from the front cylinder compensated, and the two cylinders should run at the same temperature. It seemed to work because I never heard of any problems and used to fly with that group often.

    Would love to see some pics of your progress and results.

    See you up at Caboolture one of these days, when I get AussieMozzie finished.

    Cheers,

    Alan

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    Re: Converting a Fan cooled 503 Rotax to free air cooled

    Thanks Alan, what you have described in the shrouding is very similar to what i had in mind with the outlet area being 50% larger than the inlet to allow for the expansion of the heated air with the scoops tapered as you mentioned . Its all very interesting , I'll let you know how it pans out.
    I've been keeping an eye on your AussieMozzie project and look forward to seeing the finished product.

    Cheers

    JimG

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    Re: Converting a Fan cooled 503 Rotax to free air cooled

    I make fiberglass free air rotax cowls, thats what most everybody here is using

    for sale

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    Re: Converting a Fan cooled 503 Rotax to free air cooled

    Hi George, yes I checked them out and they look impressive. I'll send you an email on the address from your we page.

    Thanks

    JimG

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    Re: Converting a Fan cooled 503 Rotax to free air cooled

    Here are some pics I have gathered of a diy set-up. But, it's hard to beat the 'glass one. From personal trials I have found that a simple 180 degree duct feeding the fan intake works wonders.Converting a Fan cooled 503 Rotax to free air cooled-free-air-scoop-1.jpgConverting a Fan cooled 503 Rotax to free air cooled-free-air-scoop-2.jpgConverting a Fan cooled 503 Rotax to free air cooled-free-air-scoop-3.jpgConverting a Fan cooled 503 Rotax to free air cooled-free-air-scoop-4.jpgConverting a Fan cooled 503 Rotax to free air cooled-free-air-scoop-5.jpgConverting a Fan cooled 503 Rotax to free air cooled-free-air-scoop-6.jpg
    Last edited by slevair; October 15th, 2012 at 10:29 AM. Reason: grammer
    Scott

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    Re: Converting a Fan cooled 503 Rotax to free air cooled

    Quote Originally Posted by JimG View Post
    My aim with the 503 cooling set up is to come up with a simple free air system and not have to worry about servicing a fan belt, plus a slight power gain by not having to drive the fan.
    Hard to say, but you might find that the aerodynamic drag from the cooling air intake is more than you gain from eliminating the fan drive power. I would also worry about adequate cooling while taxiing.

    -Dana

    I don't like the idea of term limits for politicians. I think they should get the same sentence as all other criminals.

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