SJ50 with a Magnum muffler  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       

All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> SJ50 with a Magnum muffler
Page: [1]

Login
Message << Older Topic   Newer Topic >>
SJ50 with a Magnum muffler - 3/13/2007 12:37:26 AM   
still4given



Posts: 410
Joined: 1/27/2006
From: Victorville, CA, USA
Status: offline 		Hi Bob,

I just received my new SJ50 and what a beautiful piece a machinery it is. Here in lies my problem. Our club is having a pylon race and the rules state that no tuned pipes may be used. I know you call the exhaust that comes with the motor a muffler, but I doubt they will see it that way. So here is my question. I have a Magnum 52 muffler that will bolt right on to the SJ50. Do you think I will lose too much power using the SJ50 with the Magnum muffler over just using the Magnum 52? Would it help to remove the baffle in the Magnum muffler?

Thanks, Terry

_____________________________

Live simply. Love generously. Care deeply.
Speak kindly. Leave the rest to God
       Post #: 1

RE: SJ50 with a Magnum muffler - 3/13/2007 3:53:26 PM   
bob27s



Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Hi Terry.....

Thanks for writing.

Technically ( per the origina 428 racing rules) it is a muffler ... since it is one piece, fixed geometry, not tunable, and is OEM stock with the engine. (the Rossi and MVVS black mufflers are the same type of exhaust system, except those are actually 2-piece units - just in case that comes up)

But that aside...

If it is a new engine, break it in properly, per instructions - with the jett muffler on it. Again, follow the Jett break-in instructions, and get at least 20 minutes on the engine, on the test stand.

You can use a standard cast-type muffler, but you will indeed lose performance. The engine will outperform an OS46, TT46 in this configuration, if you allow the rpm to stay up a bit.

We do run the engines with the lite-jett untuned mufflers, but mainly for sport/3D/aerobatic/control line applications where lower rpm and slightly bigger diamter props are what we are after.

The 38mm muffler bolt pattern on the SJ-50 will match a Webra .40-.50 or ST 40-50 size engine. You would be better off finding a muffler from one of those engines. The Mag 52 uses the narrower 37mm OS46/TT46 muffler bolt pattern, and will not match up properly. Also worth noting, the old K&B61 had a 38mm bolt spread too.

The Jett engine requires a proper balance of backpressure and muffler tank pressure to operate and draw fuel properly. The stock jett-stream, turbo-jett and lite-jett mufflers provides that condition. If you use something like the Mag 52 muffler, this consideration must not be ignored. Id leave the bafflle in place.

What type of aircraft are you flying ?

If it is a Q-500 aircraft, and you use a "can" muffler, continue to target 17,000 rpm ground peak for the engine. You will want to use something like an APC 9x6, 9x7, or APC 8.5x7.25, 8.75x7, 8.5x7.5 D1 series prop. Continue to launch the engine down 300-400 rpm off of peak.

Let me know some more detail, and I can suggest a starting setup

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to still4given)
       Post #: 2

RE: SJ50 with a Magnum muffler - 3/13/2007 5:07:16 PM   
still4given



Posts: 410
Joined: 1/27/2006
From: Victorville, CA, USA
Status: offline 		Hi Bob,

Thanks so much for responding. Here are the rules as they have been posted.


I am planning to use this Spitfire 40 for my plane. A bunch of the guys are using the Hanger 9 PTS Mustang and I want to have something different. I plan to take the plane to the monthly meeting tonight to see if they will allow it. I'm not sure it meets the "Reno Unlimited Class" spec but then neither does the T-6. Anyway, I hopeful that it will be accepted because I love the way a Spit looks in the air. One draw back to the Jett muffler is that it doesn't quite clear the side of the plane so even if they allow it, I would need some type of extension to make it work.

I hope this is enough info for you. I would love some more suggestions.

Blessings, Terry

_____________________________

Live simply. Love generously. Care deeply.
Speak kindly. Leave the rest to God

(in reply to bob27s)
       Post #: 3

RE: SJ50 with a Magnum muffler - 3/13/2007 6:04:14 PM   
bob27s



Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Well, looks like fun, but ya have you work cut out for ya there

Keep the speed up in the turns - I have a feeling the spitfire is a snap-roll waiting to happen if you pull real hard around pylon #1 Looks a bit heavy, and although it should be quick its not going to accelerate out of turns real well. The wheels are a lot of drag - if the gear is down, consider using some narrow profile lite-flite type wheels, or even disk racing wheels for the event.

Fly smooth. Take time to practice. That is what ultimately makes you competitive and gives you ability to win a race.

Of note....

A Spit Mk XVI appeared at Reno in 1981, and particpated in demonstration laps. Did not actually qualify, but it flew the race course. Spits are very rare, and few use them for racing. However.... There was one campaigned Spit racer back in the late 40s and early 50s. Canadian Mk.XIV #80 flown by J.H.G McArthur. Flew in the 1949 Cleveland national air races. It placed third in the Tinnerman Trophy Race.

Some more info at this link
http://www.warbirdregistry.org/spitregistry/spitfire-tz138.html

That bit of info might get ya in with the Spit

As for the engine... Give it your best shot. Try a regular 10x6 APC and a 9x7 APC. Also look at the Master Air Screw 9.5x6. Nothing bigger. The Q-500 props will not work well with that big of an airplane. The 10x6 will get you off of the ground quicker, but the 9x7 will be faster in flight. Again, let the engine turn up. With a basic muffler, you should be able to see over 15K with the 10x6. Will be well above that with the 9x7. Experiement. Use patience on take-off - let it gain speed.

Let me know which muffler you choose.

Jett has extensions available for this type of installation - .25" increments. The P-51 here has one extension on it.

Also, here is my P-51 - SJ-46, turbo-jett incowl muffler. It is one of the VQ ARFS





I set this up with the big prop to slow it down - tail surfaces structure is not up to going 110mph with a 10x6 on the front


Attachments
Click to see fullsize image.
Click for fullsize


< Message edited by bob27s -- 3/13/2007 6:10:33 PM >


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to still4given)
       Post #: 4

RE: SJ50 with a Magnum muffler - 3/13/2007 6:41:41 PM   
still4given



Posts: 410
Joined: 1/27/2006
From: Victorville, CA, USA
Status: offline 		Hi Bob,

Thanks for the info. I hope you're wrong about the snap rolls but only time will tell. I built a P47 last week and it wasn't bad with a Mag 52 in it but I lost it when my flight pack battery went dead. This spit weighs 4.6 oz dry which is almost 2 lbs lighter than the P-47 was.

Do you carry the extensions in stock? Part #? The race in on the 24th. Not sure it would get here on time.
I thought about using racing tires since there are no retracts. I'm not sure our rock encrusted run-way will be friendly to the narrow tires though.

I should be a full pound lighter than the PTS mustangs that most of the other guys are using. A few of them are using the OS AX55 hence the .55 max rule. I've heard that the AX55 is not much of a race engine so I'm hoping to make up for the lack of tight turning with some speed in the down-stretch. In this day of ARFs, if the Spit doesn't pan out, I should have time to put something else together.
I can alway stick a Mag 52 in there if the SJ50 doesn't work well.

I'll pick up some of the props you suggested, (I already have some of them). I also have some old Topflite 9*8 wood props I want to try on this motor. Been saving them for something like this.

Blessings, Terry

_____________________________

Live simply. Love generously. Care deeply.
Speak kindly. Leave the rest to God

(in reply to bob27s)
       Post #: 5

RE: SJ50 with a Magnum muffler - 3/13/2007 7:03:26 PM   
bob27s



Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Good luck...

I think Dub keeps the extensions in stock if you need them.

the light plane will help a bunch.

Id suggest skipping the old topflites ---- the blades are thick, and remember, rpm is your friend here. APC 9x8 or MA 9x8 may be ok .... but with the SJ-50 porting, getting the engine to 15K rpm or higher on the ground (peak) is what you are shooting for.

Another option on the muffler I completely forgot - if its an option - the MACS black one-piece muffler. This is not a tuned exhaust, just a light-weight aftermarket muffler... so it should be legal for your use. Not sure if it will fit any better, but worth considering. #6620 is the part you want. http://www.macspro.com/onepiece.asp
The 55AX is a decent engine, but has to be propped differently ---- needs to run below 15K rpm to perform best. It is not going to unload much in the air. If the pilots match the engine/prop/airframe properly, it can work well .

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to still4given)
       Post #: 6

RE: SJ50 with a Magnum muffler - 3/13/2007 7:23:51 PM   
rmenke


 

Posts: 1684
Joined: 6/25/2004
From: Merced, Ca., CA, USA
Status: offline 		Still4given:

I had the same hastle with our club and its "Open class". In general ignorance, they thought that all "Jett" engines were racing engines. I copied the Jett site with specs on the and comments on the Jett Sport engine, took it to the guys gryping and made them read it. Same guys don't know the difference in pipes (mufflers) either). In general, their purpose in life was to get me out of the winners circle. Lost last year by one point, the gryping stopped, but the general sniveling was at each race. In our T-34 class, I have a standing offer to sell the engne out of the airplane for $100.00 after the race. No takers yet and the thing keeps on winning with no grinding, unlike one or two others. Age is taking the edge from reactions and eyesight. Only death will remove the desire to win, but that is how it should be. ENJOY

(in reply to still4given)
       Post #: 7

RE: SJ50 with a Magnum muffler - 3/14/2007 12:53:31 PM   
still4given



Posts: 410
Joined: 1/27/2006
From: Victorville, CA, USA
Status: offline 		Hi Guys,

Well I took the Spitfire to the meeting last night and got a few double takes and questions, but all agreed that if that is the muffler that comes with the motor I can use it. Very cool!

There were three or four guys who knew about the Jett engines, and they all said if I fly right I should win. I'm thinking I might should add some strengthening to the airframe so it will live through the turns. Can't wait to get this baby in the air.

It seems that only me and two other guys are using something other than the Hanger 9 PTS Mustang. Quite a few of them are using the new OS AX55.

I'm going to pull the engine back out of the plane first and do a proper engine stand break-in before I try and fly it. Thanks for all your help and I'll let you know how we do in the race.

Blessings, Terry

_____________________________

Live simply. Love generously. Care deeply.
Speak kindly. Leave the rest to God

(in reply to rmenke)
       Post #: 8

RE: SJ50 with a Magnum muffler - 3/14/2007 2:23:31 PM   
bob27s



Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		That is great Terry......

As long as you can use the stock muffler (with perhaps no more than a small extension) fly that thing with a 9x8, 10x6 on the front. After engine break in and a few flights on the plane, you can try a 10x7 too. For some reason the APC 10x7 unloads in the air nearly as well as the 10x6.

Also worth looking at ..... if you can get one ..... APC 9.5x7.5N or 9.5x8N these are older design Q-500 prop from about 10 years ago. Each has more blade than some of the newer D-1 props. Either might work well.

Id not worry too much about reinforcing the plane. Just make sure the usual stuff is solid. Make sure the engine mounting it solid. And be sure to balance the prop. Most APCs are pretty good right from the bag, but at the rpm the SJ-50 is capable of, you will want to be sure. It is sometimes more common to shake apart some of the ARFS than to actually see a structure fail.

Of course, fly smooth. You only want small control movements, and preferably no corrections. Every time you move the ailerons, have to hunt to get oun the course or correct a heading, it is like putting on the brakes (really amazing to see how dramatic that is on a radar gun).

Above all else ..... make sure the fuel tank is 100% foam isolated from the airframe - wrap it in foam rubber, do not let it touch structure. Otherwise you risk getting fuel foam in flight, the engine will go lean (no matter how you set it on the ground) and that can potentially toast the engine.

Let me know how things work out !

< Message edited by bob27s -- 3/14/2007 2:28:19 PM >


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to still4given)
       Post #: 9

RE: SJ50 with a Magnum muffler - 3/15/2007 2:38:57 AM   
still4given



Posts: 410
Joined: 1/27/2006
From: Victorville, CA, USA
Status: offline 		I got a chance to run the SJ50 on the bench today. I followed the instructions and ran it rich at 15500 on an APC 10*5. It has a very smooth idle for a brand new engine. I only had a 6oz tank on my engine mount so I had to run several tanks through it to get close to 30 minutes on it. Once I finished with the break-in I switched the prop to an APC 9*8 and leaned it out a bit to see what it would do. I didn't take it till it got too lean but till it stopped gaining RPMs. It tached out at about 17000 rpm. Next I mounted one of my Magnum 52XLS engines and with the 9*8 it spun 16900rpm. I must admit I was expecting the Jett to clean house on the Magnum but it didn't. So, should I expect the Jett to unload better than the Magnum once in the air? I must admit, that until this thread, I never thought of mounting a small diameter prop on the 52. I'm actually looking forward to trying the 52 on an airframe with a 9" prop.

Blessings, Terry

_____________________________

Live simply. Love generously. Care deeply.
Speak kindly. Leave the rest to God

(in reply to bob27s)
       Post #: 10

RE: SJ50 with a Magnum muffler - 3/15/2007 2:39:20 PM   
bob27s



Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Hi Terry,

Thanks for the follow up.

You didnt follow the instructions properly. Do not break it in that rich or at that low of an rpm. Engine is likely still very tight.
http://www.jettengineering.com/tech/breakin.html At 15,500 the engine is bearly running on the muffler.

Engine must break in at operating rpm - which is 17,000 or higher for the SJ-50. You want a light load, and to get the engine up to rpm. Install a 9x6, lean the engine out to briefly find peak rpm, and back it off about 800 from there. Should be running above 17000 rpm while just slightly rich. (you can also use an old 10x6 or 10x5 prop, just clip it to 8.5" diameter and balance it).

Following that break-in sequence, install an APC 10x6. That is the baseline prop. Let me know what peak rpm you find with this prop.

When in flight, yes, the engine will unload quite a bit. The engine will contiune to gain in rpm with flight time. Again, for flight - find peak rpm, back the engine down about 500-600 rpm from that point for launch.

As for the Mag 52, it is intended as an rpm engine. Its a pretty good engine. If you are seeing it turn 16.9K on a 9x8 with the stock muffler - ya have a real good one - take good care of it. The versions I had an opportunity to run ran just under 17K with a 9x7, and just over 16K with a 9x8. Turns right around 15.5K-16 with a 10x6 too. Pretty good in any book. Any size larger prop above a 10x7 was as waste. Didnt unload much beyond that in the air, but ran well. The engine does respond great to a tuned exhaust too.

There were lots of folks trashing this engine a while back saying it didnt run well, and the were swapping carbs. Problem was, they were trying to run 11" and 12" props on it... the engine has a huge carb, big shaft intake, and has to run over 14,000 a full throttle to have any chance of drawing fuel properly. Down side to the design, is that a few folks have reported that the thin-wall crankshaft failed after a while - cracked. Keep an eye out.

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to still4given)
       Post #: 11

RE: SJ50 with a Magnum muffler - 3/15/2007 6:33:01 PM   
still4given



Posts: 410
Joined: 1/27/2006
From: Victorville, CA, USA
Status: offline 		Hi Bob,

Thanks again for straightening things out. I am at work right now so I can't check, but I would swear that the instructions that came with the motor said to drop one inch in pitch for the break-in prop and to open the needle 5 full turns, start the engine, go full throttle and then lean out the motor until it reached 15,500 and run it there for 15-30 minutes. I will check that as soon as I get home. I'm sure I haven't hurt anything so far so I will try what you suggest and slap on a 9*6 and and turn it up to 17K and run some fuel through it.


Thanks for taking the time to explain things so clearly. I'm sure others will benefit from it as well.

Blessings, Terry

_____________________________

Live simply. Love generously. Care deeply.
Speak kindly. Leave the rest to God

(in reply to bob27s)
       Post #: 12

RE: SJ50 with a Magnum muffler - 3/15/2007 7:35:50 PM   
bob27s



Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		nah... its hard to hurt it. only thing that really hurts the engines is a lean/hot run

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to still4given)
       Post #: 13