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503 In An Avid


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Posted

Hey Everyone,

It's been a while since I've posted in here, and a while since I've been able to work on my Avid projects. My main project is a model C that I'm pretty much completely rebuilding.

I found a Rotax 503 locally, and I've read that there are a few Avids out there with 503s (Bandit for one). I like the idea of a simple air cooled engine. I understand performance wouldn't be spectacular. I'd be flying out of a 3000' asphault runway. I'm about 160, and plan to mostly haul my kids around for rides. I have a few questions for the 2 stroke Rotax experts though.

1. Could my 582 motor mount be modified to fit the 503?

2. What prop would you recommend. I'd like a ground adjustable, but don't know which brand, what diameter, or how many blades would be best for the 503.

3. Are there any 503 models that I should avoid (I can see that it has 4 plugs in the pictures).

4. Anything else to know before I go look at it?

I plan to get a look in the intake and exhaust ports for scoring. Anything else?

Thanks,

Luke

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Posted (edited)

Well, I guess it doesn't make too much difference now. I went ahead and bought it. Here is a picture from the CL ad. I hope to start working on getting it mounted in the next few weeks. It's a single carb. I think I will probably change to dual carb though.

00101_gVsEciCK21i_0t20lM_1200x900.jpg

Edited by Luked
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Posted (edited)

I have have been running my 503 for 24 years now.  Dual carb, dual ignition. I switched to mixed gas. The oil injection was a pain in the ass. Burning 5 gallons a hour at 5950 rpm. Cruises 69 mph. As light as you are it should do pretty good if your airplane is light. My Bandit started at 456lbs, but now is around 485 or so. I am using a 3 blade ground adjustable 66" ivo prop. I am thinking the 582 is the same mount as the 503. Does anybody else know for sure?

Edited by Bandit
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Posted

I will take pictures of my installation this weekend and post them. I hope that will help you. This has worked good for me.

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Posted

I will take pictures of my installation this weekend and post them. I hope that will help you. This has worked good for me.

Hey Mark, that would be great. Your plane is actually what kept the idea of doing a 503 in the back of my mind over the years. Look forward to seeing how you have your setup.

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Posted (edited)

I flew a couple of times with a guy in Pennsecola Fl. who have a 503 in a Kitfox 4 light squared.  I was amazed how well that plane performed.  Course being at sea level helps as well.  I'm sure the 503 and the 582 bolt pattern is the same, maybe the distance forward is a bit different.....  Just remember, that was in a Kitfox where Mark in Washinton ran into problems.  I'm betting you wont have a problem with an Avid mount.  JImChuk

PS  meant to mention also, I had much better performance with a two blade Warp drive then either a 3 blade 64"  or 68" IVO.  Funny thing is both IVOs were very similar in performance, but the 2 blade blew their doors off.  Wasn't near as smooth though.  This was on a Kitfox 1 with a 582 with a B gear box.  

Edited by 1avidflyer

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Posted

I swaped a 503/Abox single carb out of my KF model 1 and installed a 582/Cbox dual carb, was an easy swap, aluminum mount is same, only difference was i had to modifi one motor mount bar,(went thro the rear carb area) all i did was cut one end loose, moved it down weld it up and now it clears. 

8E558A4F-BB7D-454E-947C-82393443B3D5.png

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Posted

Hey guys,

Thanks for the advice and help. I wasn't really looking for an engine when this one popped up, so I'm still kind of processing what my plan is. This got me excited about the  project again, and is kind of jump starting the completion schedule. When I formulate a good plan, I'll probably be back with more questions.

Jim, thanks for the prop info. That is one of the first things I will want to figure out. It helps to get feedback from people with firsthand experience. A guy out here at the airport has a Power Fin, and really likes it. I just talked to him, and he suggested calling Power Fin to see what they recommend for my engine.

Buckchop, thanks for the picture. The mount on the Avid is "upside down". I think there was at least one Avid where the builder mounted the engine upright though.

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Posted

I would guess that a 66" two blade power fin would take the power from the 503 just fine, especially if you go with the duel carb setup.  JImChuk

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Posted

Powerfin has a pdf on their website that identifies their recommendations for engine/gear ratio/prop combinations. I very much liked the performance of my Powerfin prop that I used on a trike.

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Posted

Thanks guys. I found the pdf Marcus. It's very helpful.

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Posted

The 503 is a plug and play engine.  It's a pretty easy installation. 

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20200802_135215.jpg

20200802_135230.jpg

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Posted

Nice project! I have the original dual carb, single ignition 503 in my Kitfox 1. With full fuel and 200 pounds of people, it climbs at 500 fpm at 57 mph, at 1.5- 2k feet. It cruises 60-65 mph ias at 6,000-6,100 rpm behind a 3 blade 66" Powerfin prop, burning 4 gph. Not a powerhouse, but it feels appropriately powered. No problem flying with 375 pounds of people and full fuel, but I haven't checked the climb rate at gross weight. We probably don't want to know, anyway. I like the simplicity of the air-cooled engine. 

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Posted

Thanks Bandit for the pictures. It's helpful to see a complete installation since there are not many pictures out there. I really like the "Plug and Play" part of this engine. The forced air cooling and built in shrouds make things pretty simple.

Number 29, I'm assuming you are running the B gearbox? what type of Powerfin blades are you using?

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Posted

If you use the 503 you have to use a flat firewall so you will lose some legroom with that installation. 

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Posted

If you use the 503 you have to use a flat firewall so you will lose some legroom with that installation. 

I hadn't really thought of that. It's probably not an issue for me, since I'm not that tall, but I may want to take a passenger once in a while that is a little taller. I'll have to think about that one. I've been spending most of my time shopping for parts to get the engine running. That's my main goal right now.

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Posted

 

If you use the 503 you have to use a flat firewall so you will lose some legroom with that installation 

Just looking at your installation Bandit, and would it be possible to bolt a flat piece of 1/4" aluminum plate to the engine, and have holes in that plate to mount the plate to the motor mount maybe 2" or so further back so you could still have a bump out on the firewall for legroom?  That would move the engine forward, and effect the CG of course, but probably not by to much.  If the 582 has room for a footwell, then that engine must sit further forward as well.  JImChuk

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Posted

Just looking at your installation Bandit, and would it be possible to bolt a flat piece of 1/4" aluminum plate to the engine, and have holes in that plate to mount the plate to the motor mount maybe 2" or so further back so you could still have a bump out on the firewall for legroom?  That would move the engine forward, and effect the CG of course, but probably not by to much.  If the 582 has room for a footwell, then that engine must sit further forward as well.  JImChuk

Jim, I could be wrong, but I don't think the 582 is mounted much differently. Looking at my 503, I think it's the fan shroud that ends up on the left side of the plane that causes the most problem. I need to get mine mounted on the plane to see where it ends up.

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Posted

Yes the fan shroud will hit on the bump out. You might be able to cut out part of the bump out to make it work though. I didn't think the extra inch or two was worth messing with so I went with the flat firewall. 

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