Jack Hyde

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I have a new Mojo 60 that wants an engine and am trying to learn which Jett would be best for it. As you know I am not looking for speed with this 3-d plane as it would flutter its brains out if it went very fast. I want a quality engine that is user friendly, reliable, has good mid-range and throttle response, about 10 lbs of static thrust and doesn't weigh a ton. I don't need to overpower it to an extreme. I have been flying 4 lb Burritos for a year. I started with an smooth OS 46 - not quite enouh thrust. Went to an OS 50 that was fine. Put a YS 63 in my latest Burrito and it seems way stronger than I will ever need. The point is I am not a more-power-is-always -better guy. I estimate that an engine that will turn a 15x4 prop at moe than 10,500 will do the job in the Mojo 60. Or a 14x4 at more than 12,000. I don't think any of your engines would be too heavy.
What do you reccomend?

bob27s

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Hey Jack,

Thanks for writing....

Ive actually had a few inquiries from people on the Mojo 60 lately, and a few about the bigger OMP birds.

Jett builds four engines that are specifically built for aerobatics, fun-fly and 3D applications. Big props - lower rpm - light weight - lots of power.

The SJ-60LH (hover version) and the BSE-76L are both "40" size engines. The 60LH turns 12x4 size props around 14,000 (with a lite-jett untuned muffler), and the BSE-76L turns 14x4 and 14x6 props up around 10-11K rpm (with the same muffler). Yes, these are "OS.46" size engines.

For your application, the BSE-100L and BSE-120L engines are ideal. These are the same size/appx weight as the OS61/91FX engine - same bolt pattern - but they are designed for some outstanding top end power at lower rpm with big props.

The BSE-100L would be more at home with the 15x4. It will turn that up around 12,500 rpm. The engine typically turns a 15x8 prop around 10,000. This engine you would want to keep propped between 9500 - 13,000 peak rpm on the top end. Higher rpm is not recommended.

The BSE-120L is a real monster. Same size. This turns a 16x8 at 9500 rpm. Makes its best power between 9000-10,500 rpm. Definately not a high rpm engine - Prop the engine with a peak top end rpm not exceeding 11,500 rpm on the ground. For 3D stuff, folks have found that a 16x6 works very well. A 15x4 is too small. Some folks are running 17x6 and 18x4 props (although Im not sure where they got the 18x4 props from).

The 100L and 120L are supplied with the jett-stream tuned muffler, but pipe-step is not an issue at these lower rpms - the pipe stages smoothly.

All of these engines are prepared with special carbs that give outstanding midrange performance and smooth transition. Break it in, set it up with the flight prop, set the high end needle about 500 rpm down from peak, and enjoy !

I hope this is helpful.

Bob

rmenke

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Jack: Go with Bob's recommendations. Have a BSE Jett 90L, is a wonderful engine, idles well and kicks into higher rpms right now, best carburation I have ever seen on a 2 cycle motor. Well worth the bucks. Let us know what you buy, and post how you like the motor. Be sure to follow the break-in process and fuel recommendations, and you will get years of life out of it. You are about to learn what the term "Monster Power" really means" Enjoy!

Jack Hyde

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I am thrilled with the way my OS 50 hauls around a 4 lb 3d plane. So I am surprised that you advise a 100 for a plane 50% heavier than the 4lb plane. Remember I am not a tear the firewall out flier. Maybe the 76 would be good for me. The 60L at 14000 with a 12x4 APC will produce almost 8 lbs of thrust according to my data. The 76L turning a 14x6 at 10000 should produce 10 lbs. The 100L with a 15x4 at 12,500 gets close to 15 lbs of static thrust. The 76L produces almost exactly the same thrust on the same prop as an OS 91 4stroke I have. It is about 5 ozs lighter.
The reason I am looking at 2 strokes is their simplicity and at Jett in particular is I like the quality. Thanks for the info to digest.

bob27s

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Hi Jack,

yep..... lots to digest.

All depends on what you want from the engine/plane. But do not go by the thrust calulator. They are a good reference, but are not entirely accurate.

The Jett 76L, 90L, 100L and 120L are considered our "60" size engines. Typically used where any other 90 2c or 90/120 4c would be used. All the same size/weight. As you noted, the OS91FS, as well as the YS110, OS91FX and a few others weight about the same. The Saito 100 is an ounce or three lighter.

The 60L and 76L have been used in the smaller burrito, OMP smaller Edge, Katana, Morris Top Cat, H Twist and Pizzaz, - stuff like that. Folks are thrilled

My Aeroworks 60/90 size Edge (9.2 lbs) had the 100L up front. Used a 15x8 with the turbo-jett muffler. Performed extremely well. The smaller 40/50/60 size AW Edge at about 5 lbs has the BSE-76L up front with a 14x4W. Vertical is insaine. Perhaps that is a good reference.




Topcat photo here has a SJ-60L engine with the tuned muffler. 12.25x3.75 over up to 15K rpm peak - flys about 400 rpm down. No issues with an 'pipe' step or anything - smooth as silk. The extra rpms cost an ounce or three more than the Lite-Jett muffler version.

rtrickyjr

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I installed a BSE 120 on a mojo 60. If you cut out for the rear engine bolts and install the engine as far back as it will go (toward the wing) the balance comes out pretty good.

bob27s

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Good information to know.... thanks for the update...

Any photos of the plane/install ?

Bob

rtrickyjr

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Not yet, need someone who has a digital camera (a flying buddy does, and I'll try to 'talk' him into a photo shoot LOL)

No issues out of the ordinary with installing it, and it balanced much better than I expected (I did use a sullivan large tail wheel, and a 6V 2100 pack). I'm using my first hitec digitals with it, and am really pleased with their precision.

I'd give almost anything for a nice lite jett muffler to fit the 120, though, the one on my BSE 76L has me soooo spoiled.

rtrickyjr

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Finally got a photo of the Mojo 60 with the BSE 120L, check my gallery (don't know how to put it here).

bob27s

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There ya go. Looks nice !!
Which prop did you end up running ?

rtrickyjr

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Thanks Bob!

I'm using the 17-6 apc right now. I'd love to get a 18-5 or 18-4, but cannot find anyone who makes one! The engine has great power, but still having a slight transition lag at about 1/2 throttle. I'm using the os 4cyc plug. I think I've still got needle issues (not set quite right yet), but I love the engine so far. The throttle in a hover is very linier, and seems very responsive. Vertical pull out is great, becomes a 'spec' in the sky in a few seconds!

Any more news on what plugs are doing best?

bob27s

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The plug you have there should be ok..... a couple of folks played with the K&B idle bar r/c type plugs.

To chase the transition a bit - go up and down in nitro a bit. Not sure which way is best, probably down to 5% would be my first try.

rtrickyjr

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Bob,
I use 15% in everything, would a 'head shim' do the same thing?

bob27s

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A head shim might help .... not all that much though.

I sent a PM with a few suggestions.

Bob