Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Jett Engines?

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Old 10-04-2007, 04:36 AM
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MicroDat
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Default Jett Engines?

Hi,

I'm used to flying YS engines (particularly the YS 110) and I know they're a powerhouse for speed and torque. But I've been seeing a lot of talk about these Jett engines. How do they compare to the YS line? And which Jett motor is comparable to the YS 110 in terms of power and size? I mostly fly 40 to 50 size warbirds and with the YS 110 I can do 120 to 145 MPH, can a jett engine pull the same plane any faster?
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Old 10-04-2007, 09:33 AM
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Default RE: Jett Engines?


ORIGINAL: MicroDat

Hi,

I'm used to flying YS engines (particularly the YS 110) and I know they're a powerhouse for speed and torque. But I've been seeing a lot of talk about these Jett engines. How do they compare to the YS line? And which Jett motor is comparable to the YS 110 in terms of power and size? I mostly fly 40 to 50 size warbirds and with the YS 110 I can do 120 to 145 MPH, can a jett engine pull the same plane any faster?
It is very difficult to directly compair the YS110 4C engine to the Jett product line.
Two very different animals.
The YS 110 is a "10cc" size 4-c engine - it has a pressurized fuel system, and is internally supercharged.
The Jett is 2c, naturally aspirated, with a tuned exhaust (externally supercharged? [&:])

An attempt at an example, A Jett BSE-100 with a turbo-jett muffler -- 15x6 prop --- appx 10,500 rpm That is an aerobatic aircraft setup.

That would equated to a YS with a 15x6 or 15x8 around 10-11K rpm --- the 4c is rev limited, and most users typically you prop it to run below 12,000 rpm. Some do exceed this.

So in that respect, you can see how the torque engines match up.

However, looking to go fast with a speed engine ---- very different engine requirements and prop requirements.
The Jett 90LX turns an 11x8 prop at 15,500 rpm ground peak.
Smaller diameter prop = less frontal area = less drag - if the plane can take advantage of that situation.

On a GP Toni, as an example, Ive seen about the same speed reports from "properly" set up YS installations and Jett powered.

On the Cermark Alley Cat ..... the Jett 90LX appeard to have an edge.

If your application is, for example, a Corsair or RareBear (big cowls, large airframe cross section, lots of inherant drag), you would be wise to chose the YS110 for power, and use something like a 14x10 prop.

Jett can not compair on the big props. Although some have flown the .60 size corsairs with Jett 90L power with some impressive speed and over-all performance results with 12x6 or 13x6 props.

There are a few out here who have mounted the 90L or 90LX in a midget mustang or .40 size warbirds... no doubt they can share the experience the have had. More than a few out here who have run both YS and Jett power that can provide more direct comparisons. In some cases, the smaller planes are much better off with something like the SJ-60LX engine --- saves a great deal of weight, and there is a ton of power to bad had from that little "40" size engine.

If you are flying true-scale warbirds, and are obtaining 140 mph with your YS setup.... you are doing about as well are you are going to do with any engine.

Bob
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Old 10-04-2007, 02:08 PM
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Default RE: Jett Engines?

I just started racing in the RCPRO warbird class. It is set up with brackets so each one has a different break-out time. In the Gold class, which is the fastest, everyone is running the YS. Mostly it's the YS110 because it can go as low as a 513 square inch wing area. I would think the Jett 90 would be just as fast but you would have to have 650 sq. in of wing area so I'm not sure it could compete against the YS in the smaller plane. I would think you would need a pretty sleek plane to keep up running the Jett 60.

The rules were set back when a 120 4c was about equivalent to a 60 2c. Now with the supercharged YS 4c it is no longer true. I don't know of a 55 2c that can come close to the YS 110.

Blessings, Terry
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Old 10-22-2007, 06:46 PM
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Default RE: Jett Engines?

Hi,
I have a question for Bob from jett. I have a BSE .50 and with a apc prob im only getting about 16000 rpms at peak on the ground. The engine was broken in with a 9x6 at 17000 as suggusted. It now have about 10 flights on it. Im using 15% omega fuel and the mcoy 59 glow plug. I talked to Dubb and he says all engines are tested before being shipped. What could it be? I really dont feel like sending it back unless its really necessary. Also what plug do you use for testing?
Thanks alot
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Old 10-22-2007, 07:04 PM
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ORIGINAL: paolino1818

Hi,
I have a BSE .50 and with a apc prob im only getting about 16000 rpms at peak on the ground.
What size APC prop? Are the head bolts tight? Did you take off the muffler at make sure the cyl exhaust ports are lined up?
Those are my thoughts until Bob shows up.
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Old 10-22-2007, 07:41 PM
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Default RE: Jett Engines?

Yeah i realized i forgot to say it is a 10x6 prop. It should get at least 17000. The bolts are tight. What should it look like when i take off the muffler as far as lined up goes. Do you think that it could be the hot plug im using?
Thanks
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Old 10-22-2007, 07:54 PM
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Default RE: Jett Engines?

Check your fuel system, if the fuel foams or the center of the tank is off in relation to the center of the engine, that might be your problem. Dubb will tell you, as he did me, "95% of all engine run problems are in the fuel system. Do you know where the other 5% are? In the fuel system." He real specific about don't let the tank touch ANY part of the airframe, put foam around the tank.
Dubb, Bob, and Dennis have given me so much info that I could write a book, and guess what, it all works.
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Old 10-22-2007, 08:03 PM
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Default RE: Jett Engines?

The amount of liner you see when looking in the exhaust port should look the same on the left and right. If the head comes loose it sometims turns a little but it is easy to see. I would not think the glo plug is causing that much loose.
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Old 10-23-2007, 03:33 AM
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Default RE: Jett Engines?

Also, you might check the needle valve assy. The "neck" nut on the needle valve is sometimes lose from the getgo. I had that problem on my 90LX and know of others that had the same prob.

hope this helps,
V.
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Old 10-23-2007, 10:04 AM
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Default RE: Jett Engines?

Thanks Mike...

those would be my thoughts

If the engine is new and fresh off of the bench runs, you have to ensure the head bolts are tight.

If you change a glow plug, and the bolts are loose (from a hot run, or initial bench running) the liner will rotate when you install the new glow plug. The mis-aligned ports will cause an RPM drop. The head bolts are noted in the engine instructions ..... something we run into every so often, so its the first thign to check. (Happens more with the BSE engines )

The packing nut on the needle does indeed need to be tightened a bit before use. You want it so the needle has some resistance when being turned. That provides the proper seal and needle tension.

First thing beyond all else, is to ensure you are testing/breaking in the engine on a solid test stand. Likely you are, but I mention this for others who read. Useless to get engine baseline info from an aircraft installation.

Also.... it is often useful to remove the needle assembly from the engine, and mount it on the airframe.

Bob
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