still4given

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

bob27s

My Feedback: (19)

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

still4given

Hi Bob,

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


I am planning to use this [link=http://ak-models.com/mm5/merchant.mvc?Screen=PROD&Store_Code=AKM&Product_Code=RM-6&Category_Code=RichModel_GasPower]Spitfire 40[/link] 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

bob27s

My Feedback: (19)

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/spitr...ire-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

still4given

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

bob27s

My Feedback: (19)

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

rmenke

My Feedback: (13)

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

still4given

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

bob27s

My Feedback: (19)

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 !

still4given

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

bob27s

My Feedback: (19)

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

still4given

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

bob27s

My Feedback: (19)

nah... its hard to hurt it. only thing that really hurts the engines is a lean/hot run

Bob

still4given

Hi Guys,

Well, I took the Spitfire to the field on Saturday. Maiden flight takeoff was straight and short. Needed two clicks of down and one click of right aileron to have her flying straight and level. I'm excited! I make a couple of passes at about 3/4 throttle to make sure she holds trim and opened her up. Wow, really fast, great through the turns, not even a hint of stalling a wing tip. I'm about half way through the third pass when I hear something. I ask my spotter if he heard it an he says no. Sounded like a low roar to me so I slow her down and bring her around for a closer look-see. Yup, I see a little flicker off the horizontal stab so I land. Broke the stab on both sides about half-way out from the fuse. Bummer.

So I spent the better part of Sunday building a new stab. I did away with the counter-balances on the ends of the elevator and reduced the size of the elevator as well. I had the throws reduced in the transmitter rather than using the inner holes for the control horn at the servo. I'm going to change that to give the servo a little more leverage. Any other ideas of how to reduce the chance of flutter?

Thanks, Terry

bob27s

My Feedback: (19)

Blew the doors off it huh?? (well, stab anyway)

Im pleased to hear the bird flys well, and the engine is running well too !!

recommendation - seal the hinge gaps on all of the control surfaces. That will reduce aero induced flutter. Flutter occurs when you get a rapid variation in pressure at the control surface. Most of the time that is caused by cross-flow through a hinge gap. Sorta like holding a playing card in front of a floor fan. And the same principle a saxaphone reed works on. Getting rid of that cross-flow path solves the problem 95% of the time.

Checking the mechanical linkage is good too. Always sound practice. Its very important for way-too-oversized control surfaces like on 3d planes where airloads can really trash linkages. Interesting thing is some guys rely on the servos to 'survive' flutter, rather than sealing up the surfaces to avoid or get rid of it in the first place.

You can use packing tape, monokote, what ever you wish. Ive also used blenderm (medical tape, the wife is a nurse) Deflect the surface full up, put the tape on the bottom surface of the hinge gap - and work it down into the hinge line. It should not affect deflection. But, you will not require as much throw next time - be aware of that. Sealing the gap increases the control authority and effectiveness.

Stab --- reminds me of my Mustang. I had three viable options when I saw the stab buzzing (entire stab, like yours). One was to un-cover it and sheet it (its made from sticks) ..... one was to rip it out and replace it ...... other was to slow the plane down so it didnt buzz anymore.

Least work - for lazy me --- I switch from the 10x6 prop to a 12x4. Slowed the plane down. flys scale like to boot, really slows down to land. Stab will still buzz if going full power in a dive. So throttle management is important. I only fly it wide open in upward vertical.

For you.... clearly fast is good..... build a solid stab

Send me a photo or three when you have a chance... Id like to see the plane and the engine installation.

Bob

still4given

Hi Bob,

Thanks for the ideas. I am sealing the hinge lines. I built the stab out of two pieces of 3/16" X 4" balsa. I glued a piece of 3/16" X 1/16" carbon fiber into the joint between the two pieces and then sheeted it with 1/32 balsa each side for smoothness. The hinge line ended up about 1" behind the carbon which gave me good bite for the CA hinges. It feels very stiff now. I only had to move the battery forward slightly for balance.

You are right, slowing down is not an option here.

I can't recommend this model for speed. The airfoil is a little thick, which probably accounts for it's good handling in the turns but I'm sure it adds drag. Also, the landing gear broke on the way home from the field, just riding in my trailer. The little blocks they had installed were clued in with either Elmers or CA and not well. It required me to cut open the bottom of the wing and install new larger blocks and glue them in with epoxy.
I hope to get out to the field one or two days this week before the race to try it out again. I have built a CMP Corsair as back-up just in case. Still need to maiden that one as well. I am mounting the Mag 52 in the Corsair. If the Spitfire still flutters, I will swap the SJ50 into to Corsair. It's starting to look like I should have followed suit and built a PTS mustang like the rest of the guys. I haven't seen any of them suffering from flutter.

Blessings, Terry

PS I'll try and get some pic up shortly.

still4given

Here are some pics

bob27s

My Feedback: (19)

Thanks for the photos...

That fit up pretty nicely. Only has a single .25" extension in there ??

So when is the race? Looks like the plane is good to go



Bob

still4given

It's a .50" extension. I actually had the motor mounted with no extension but I had to slide it over too far and then put a lot of right thrust in to get the prop shaft close to center. The extension made things much easier. I'm going to try and get out to the field tonight or tomorrow night to give her another go. Hopefully I've solved the flutter.

Blessings, Terry

still4given

The race is this Saturday. I need to get in some runs this week. Due to my schedule lately I haven't flown any nitro stuff for about three month. Just been flying my foamies in the back yard. Quite a rush flying something going over 100MPH after putting around the back yard for so long.

Blessings, Terry

still4given

Hi guys,

Well, the race went off as scheduled. I got to the field early so I could get in some air time to make sure the new tail feathers would hold up. Much to my surprise, The SJ50 wouldn't fire. I tried replacing the plug. No change. So I pulled the tank, checked it for leaks, replaces all of the fuel lines, still no change. Fortunately I had brought a back-up plane so I was able to race though the plane was possibly the slowest plane on the course. In between heats I worked frantically on the Jett, trying to figure out why it wasn't drawing fuel. Finally, I had pulled off the cowl and inverted the plane so the engine was upright and tried again. Still nothing so I primed it very wet and while spinning it over I could see fuel spraying out of the back of the motor from beneath the head. I had checked some to the head bolds for snugness but not all of them. I pulled the head and could see where exhaust had been escaping. I cleaned it up. replaced the heasd and it fired up like it was brand new. Unfortunately I was too far down in points to go on to the next level so I still haven't flown it with the new tail feathers.

Our club enjoyed it so much that they are talking about having these as a monthly event. So, it won't be long before I fly it again.

Blessings, Terry

bob27s

My Feedback: (19)

Hi Terry....

Well, glad to hear about the event. Hopefully everyone enjoyed themselves!

Sorry to hear you ran into some trouble. Some things to check though before you fly the plane next - read on.....

Getting the engine hot can cause the head bolts to come loose. We have seen this a bunch with the BSE engines for some reason more than with the cast engines (billet aluminum expansion at the threads seems to be greater when very hot)

Something to check, if the bolts come loose, and you noted you DID change a glow plug ---- Note that this engine has a seperate cylinder head button where the glowplug installs (seperate from the finned head/chamber that most production engines use).

For future reference ....What can happen is this:

Bolts get loose (what ever reason) - engine runs like crap or you blow a plug.

You change the plug trying to fix the problem. Didnt notice the head bolts were loose.

In doing so, when you tighten the new plug, the ENTIRE liner assembly rotates while you try to tighten the plug

Next time you go to start the engine, it either runs like crap, or will not run at all. Often fuel flys from the carb and exhaust. This is because the exhaust and inlets are misaligned in the engine.

Now you are really annoyed - engine doesnt run and you have no idea why - you probably goofed up the mixture needle setting trying to chase the problem, and finally you notice the bolts are loose.

Fix for this - simple:

Pull the head - realign the ports (take off the muffler, you can look into the engine exhaust to ensure they align). You will see shadows on the sleeve where it is suppose to have been aligned.

Put the head clamp (finned part) back on. Ensure the head bolts are tight. We only use a hand-screwdrive type wrench to put the bolts in - careful not to over-torque them so you do not strip the head. But they do have to be pretty snug (I like to use a 1.5" allen wrench, but nothing longer). Of course, reinstall the muffler.

After re-assembly I also recommend at least one run with a "smaller" prop, sorta like a mini-breakin run. You may be to re-adjust the high end mixture - ensure the engine runs well. Find peak, back it down 500 rpm or so, shut the engine off with the throttle (quickly) after a 3-4 minute full throttle run. THEN, while the engine is still just a bit warm, double check the head bolts - snug them down. (looks like you have easy access in the plane.

Anyway.... perhaps you gained a bit of info on what the competition looks like, learned how to fly the course - so you can take better advantge of the Spitfire next time out. And best of all the other guys havent really seen what your plane is capable of yet Are they in for a surprise next time ! [&:]

Bob

still4given

Wow Bob!

It is like you were looking over my shoulder. You nailed it right on the head. I do remember having one lean run-in the previous week when the tail feathers broke. I had decided to run the rest of the tank out instead of emptying it. It started out putting out plenty of smoke but after a few minutes it began to sag a bit and I reached down and richened it up and it started running fine. I'm sure now that it got too hot and that is probably what helped loosen the bolts. I did notice when I had the head off that the liner rotates very easily in the case. I took some care lining it up before replacing the head. It seemed odd to me that there were no alignment marks of any kind. Seems like something that could easily be done at the factory to aid us guys at the field. I can see how the whole liner and button can move if the head is loose. Yup, I had fuel spitting out of the carb when trying to start it and the fuel draw was almost nil. Makes sense now that I know the liner was turned. I'm a whole lot smarter about this engine now than I was last week. Thanks for the detailed instructions. Almost sounds like wisdom born of pain. Hopefully others who may read this thread will see this and save themselves some grief later on.

You're a treasure. Keep up the good work.


About the races, this was our first try at holding a pylon race. For some reason the club came up with the idea that if you cut a pylon you could go around it again and keep going. So, we had guys who had cut, swear that they had lapped the other guys and still came in first. You can imagine how difficult it was keeping track of who was in the lead. The scoring was just a mess. Still, we all had fun and the guy who won, raced clean all day so AFAIAC he win was well deserved. I have since done a search and found the [link=http://www.swraracing.com/]SWRA site[/link] and the racing rules they use should solve the problems we encountered. I'm really looking forward to more of this aspect of the hobby. I just hope they don't somehow rule out engines like my Jett. It would be a shame to only use this fine engine for sport flying.

Blessings, Terry

bob27s

My Feedback: (19)

First time I ran into a rotated liner it about drove me nuts Pretty rare it happens. The BSE90LX engines seem to be most prone to this.

Two images shown here are cases where suddently the engine dropped rpm (a limited slip rotation?). Couldn't be explained by the engine owner, until I told him to take a look. Sure enough he had a lean flight, blew a plug - and ... well... you lived it You can see how the liner rotated a few degrees, and that misaligment dropped the engine nearly 500 rpm (restriction on the inlet side mainly to blame). Note how the "shadows" indicate where the sleeve was initially, and you can see the amount of misaligment by looking at the port opening relative to the crankcase.

Keep in mind, try to avoid running the fuel tank dry. If you are using a conventional fuel tank, consider the last 25% of the capacity as "unusable fuel". If you have an 8 oz tank, consider it a 6oz tank. Below that level, you will (not may, will) start drawing air bubbles into the fuel feed line because the clunk is bouncing around, there will always be a bit of foam in the tank, and after a point part of the clunk inlet will be exposed to air. If you run down toward a dry tank, and suck an air bubble, it doesnt take long for the engine to go lean, temp spike, and overheat.

One sure way around that problem - consider using a bubble-free fuel system. Jett bubble-jett tank, or a Tetra bubble tank. These are not pressurized bladders, they simply isolate the air from the fuel. Muffler pressure acts on the outside of the fuel bag inside of the tank. Absolutely eliminates any fuel foam issues, and you CAN run these tanks until they are dry without much of any risk. So, an 8oz bubble tank is 8oz if usable fuel. Yeah, its an investment, and not 100% required.... and the fueling process requires a special fueling syringe. Again, just something to consider in the future.

The alignment marks are built in --- visually line up the port looking into crankcase exhaust port. [&:] In all honesty, that is the best method. That is all Dub does at the shop.

Putting a scratch/line/mark on the top of the liner would just leave a good space for a headgasket leak. Pinning liners has the same problem, the pin has to go somewhere, and there is not much realestate to install one.

Yes, using some established racing proceedures helps a ton. SWRA, NEPRO, or just going by the AMA 428 Q-500 guidelines will help. Race proceedures are basically the same no matter what aircraft are being flown.