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Engine Question SJ 50 or SJ60LX

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Old 10-05-2009, 11:46 PM
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tes21966
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Default Engine Question SJ 50 or SJ60LX

Bob,

I have an SJ 50 on a Great Planes Viper and it is quick but I want to add a little more to a sport plane.

Several of the guys in my club fly Hangar 9 40 size Ultra Sticks. Engines range from Webra 55 GT/Speed, Rossi's, YS 45, and a few Magnum 52s. So far the Webra engine rule the roost and I want to change that. Everyone says their engines are as fast as a Dubb Jett at half the price (Webras are $179.00). I don't want to spend $179.00 just to keep up. I had a friend and hero of sorts that said, "Finishing Second Meant You Were The First To Loose". His name was Ralph Dale Earnhardt and even though he made his living racing and my racing is nothing more than bragging rights, I don't like to loose.

Here are our rules: ARF has to assemble by the Manual and with the parts sent with the plane, Operate on 2.4 Spektrum, ENGINE HAS TO FIT IN FACTORY SUPPLIED MOUNT, all planes must be built with flaps, an aftermarket "factory manufactured" muffler is allowed including tuned pipes (noise is not an issue), and all of the planes must be the same color.

My questions begin with what engine? 50 or 60? For the muffler to clear the fusalage I would need to add spacers. How would the In Cowl Muffler work? I am not certain I can change the fuel tank but I am going to ask. If I can what would work in the place of the factory 11oz tank supplied from Hangar 9, what is the difference in the slightly more expensive BSE engines? Is it worth the cost?

I hope you can help. I want the fastest Ultra Stick around. I have started on the plane by reenforcing some areas that look a little week with CA and Epoxy. Tell me what I need to kick their tails.

TS
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Old 10-07-2009, 11:11 AM
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Default RE: Engine Question SJ 50 or SJ60LX

Thanks for writing......

It is hard to really offer up competitive solutions. I can make suggstions, but there are WAY too many variables involved.

Main thing is the Ultrastick, by design and nature, is a draggy airframe. It takes a ton more power to make it go just a little bit faster. Draggy planes need bigger diameter props. So the trick is, can you get the speed from the airframe with a 9x7 prop up front. (also, be CERTAIN to seal all of the control surface gaps or it will flutter a surface if it gets going very fast - and you may not "hear" it buzz.... but it will buzz and can eventually fail)

Your best bet is to install the SJ50 you currently have on the Ultrastick. With a 9x7 APC prop it should turn well over 17,000 peak ground rpm, and will unload well in flight. See how it performs on your Ultrastick. That would be your first choice. If you like the performance from that test, but want just a little bit more, then sure - the 60LX will be that next step.

Nothing at all wrong with a Webra 55. One heck of a good engine. Good torque, decent top end rpm. And yes, about $180. Performs ok on a stock muffler. Then you add a $30 header and $70 full size pipe combination to it, and it really performs - but its now a $280 engine. People tend to lose sight of that. Same goes for the OS55AX great engines, with a jett-stream muffler on it and a 10x8 or 11x6 prop the combination can really produce excellent power for a "40" size engine. A few folks flying that combination on older pattern designs and a few prop-jets. But when prepard that way, the cost between it and a jett engine is minimal.

Also, fast is relative, unless it is measured using a repeatable and consistant method. A Viper with a SJ50, regular jett-stream muffler and the right prop should be flying well over 130 mph. An ultrastick pushed to 100 mph would be considered mighty fast for that design.

Either the SJ50 or SJ60LX will provide excellent performance. It takes playing with the prop selection to come up with the best top end speed. With either engine, start with a 9x7 prop, and then work from there. Some folks flying warbirds with the SJ50 have found that the APC 10x7 works very well (unloads great, and pulls the draggy plane better). No advantage going with the higher rpm muffler choices because the plane will not allow the engine to unload enough in flight. Best possible power would come from adding a full-size pipe to either engine.

Skip the turbo-jett. It is a great muffler, but not as much rpm boost, more of a torque boost. Great for scale planes and warbirds, but for your needs not the right choice.

Muffler extensions - should be avoided. No more than 1/4" extention - or you will see a change in the power curve. Side mount the engine (cylinder horizontal), muffler hung down below, or rotated to another angle that allows the muffler to clear properly. You can also move the engine mount toward the bottom of the firewall a bit, it is a big firewall, and ground clearance will not be an issue. Also consider other engine mounting positions - mount the engine at 30deg or 45deg if the muffler clears better, and also consider modifying the nose of the fuselage slighly to accomodate the muffler. You can use the stock mount, just mount it so it fits better and will get the best fuel flow. Also - airframe mount the needle valve assembly.

Fuel tank - the bubble-jett 8oz, or a Tetra bubble tank (central hobbies) would be a good investment. Not absolutely required, but if you use the stock tank, be sure that NO part of it touches the airframe - well padded (also remember you get to use about 2/3 usable fuel, so the 11oz tank is really a 9 oz tank). Who ever invented that tank-stopper-thru-the-firewall stuff should be drawn and quartered

BSE-vs-Cast. For your application, no real difference in performance. Comes down to your prefernce on appearance, and your budget.

Lastly..... are you racing, or just buring fast holes in the sky???

If racing (on a course or pylon setup) ........ the #1 way to go fast is PRACTICE. A fast plane does not win the race alone, the pilot is the most critical component. Every time you touch the sticks and move a control surface, the plane slows down. Smooth flying (pilot), reliable equipment (pilot, it is a choice and setup), no mental errors (pilot) wins races.

Keep me up to date on the project. Should be fun to follow.

Bob
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