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Jett 50 Heli questions - 8/11/2003 10:24:23 PM   
noname-RCU


 

Posts: 151
Joined: 5/17/2002
From: Houston, TX, USA
Status: offline 		Hi!

I have a Raptor 50 V2 heli and I fly at 9000 feet MSL. At this altitude, engine performance leaves MUCH to be desired. With this in mind, I would like to know some first hand information regarding the Jett 50 heli engine and hopefully you guys can help me out by answering some questions.

a) Will the Jett 50 fit the Raptor 50 V2 ? ... the Raptor 50 v2 can take
engines such as OS 46/50, TT 50, Webra 52 with out problems ... can I expect
the same with a Jett 50 ?

b) Please be sincere ... is the Jett 50 more powerful than the OS 50, Webra 52 and/or the Rossi 53 (all in heli versions) ?

c) Approximately, how many RPM's can I get with the Jett 50 using an APC
13X6 prop (this is for power reference only) ?

d) Does the Jett 50 share the same mounting dimensions as the OS 50 ?

e) Apparently, the Jett 50 Heli engine includes a 90 degree muffler ... is
the included muffler one of Jett-Stream mufflers ?

f) And last but not least, how reliable is this engine ? ... is it easy to
setup ? ... I have never seen a Jett engine before and I don't know if
there's something I should be aware of before buying this engine!
       Post #: 1

Jett 50 Heli questions - 8/11/2003 11:26:16 PM   
bob27s



Posts: 4733
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: online 		Hi, thanks for writing....

Jett makes the SJ-46 in a helicopter version. The SJ-50 or BSE-50 are not available in helicopter configuration. The SJ-76 is also available in a heli version.

I have attached an image of a SJ-46 powered chopper taken a few years ago.

The engine is the same as the SJ-46 aircraft engine, with the exception of a different crankshaft end to permit collet/flywheel installation.

Mounting dimensions are the same as for an OS46. I am pretty sure the OS50 is the same mounting pattern.

It is a high rpm engine. It will not turn a 13-6 -- too much prop. All of our baseline testing and performance rating is done with an 10x6 APC. It is design to run above 15,000 rpm (preferably 16,000 and higher), so your pitch and throttle curves must be set up to keep it up there.

(for reference, the SJ-46 and turbo-jett muffler combo that I fly in my mustang turns a 12x4 comfortably at about 14,500 rpm. You can only get away with the lower RPM with the lower timed muffler).

Some that have used the engine in the past have chosen a smaller pinion size to allow the engine to run at higher rpm, while keeping the blade speed down to where they are use to.

This rpm info is for max power. The engine is quite happy running in midrange, smooth throttle response, idles great, and transitions smoothly. You will get a bit of a 'pipe step' jumping between 14,500 and 15,000 as the engine gets on the muffler. It is not difficult to set up pitch and throttle curves to stay above or below this most of the time.

You can run the the engine on one of the Hatori (or similar) tuned exhausts, and the performance will be noticeably higher than with an OS46. You will get the most boost from the supplied Jett-Stream muffler.

My personal experience with the SJ-46 in a heli was 5 years ago when I tested it in a Schluter Junior 50. The power was amazing, and far surpassed the OS46 I had in there. My only issue was that I stripped the main gear twice jumping on the power out of a goofed autorotion. You have to let it turn up. Most helicopter pilots today like a "fat" midrange mixture. With a 3 or 4 needle carb, you can do that. Not with a tradtional carb. I had the Jr. flying more like it had a turbine in it. Constant rotor head speed thoughout the pitch range, and the engine RPM never got below 15,000.

That being said, the engine is VERY user friendly, and one of the most reliable products you will find anywhere. All Jett engines come standard with their Red-Jett carbs. This is a 2 needle carb similar to a super tiger carb, and it is unmatched for transition and reliablity. The high end and low end needles are easy to set for smooth transition and consistant power.

The SJ-46 outperforms all other engines in it's class. I have not compared it against an OS50H, but the performance of the SJ46 is only about 500 rpm lower than the SJ50. The SJ-50 will outperform Rossi 45, 50, and other engines in its size catagory.

Sport Jett engins are high compression engines. Although very easy to start, it will requrie a ball drive or socket drive starter connection. A cone start will often slip. A standard starter will turn it over quite nicely.

Having said all of that, flying at 9000 feet ASL is a big challenge for any engine. Its a challenge for even full size piston powered (and some turbine) helicopters. The lift of your rotor blades is limited there as well.

Jett engines are the most powerful production engines available on the market today. With that and all other considerations in mind, I will leave it to you to decide if the SJ-46H is the correct choice for the application.

I hope this has been helpful

Bob Brassell

Attachments
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< Message edited by bob27s -- Aug 11 2003 6:33PM >

(in reply to noname-RCU)
       Post #: 2

Jett 50 Heli questions - 8/11/2003 11:39:26 PM   
noname-RCU


 

Posts: 151
Joined: 5/17/2002
From: Houston, TX, USA
Status: offline 		Hi Bob,

Thanks for answering.

Ok, so the way I understood things is the Jet 46 will be an excellent choice if a drag-heli is what I want correct ?

Unfortunatley I'm looking for 3D performance which requires high torque through-out the whole range instead of top ultra speed

The Raptor 50 uses an 8.5:1 gear ratio, so as long as I can get the engine running at 15300 rpms or higher I'll be happy with it.

The reason I asked for the 50 instead of the 46 is because I saw this in the "www.jettengineering.com" website:

Sport Jett .50 ABC Helicopter with 90° muffler $310.00

[URL=http://www.jettengineering.com/engines/sj50.html]http://www.jettengineering.com/engines/sj50.html[/URL]

[QUOTE]The SJ-50 or BSE-50 are not available in helicopter configuration.[/QUOTE]

Is this a fact, or can it be some sort of mistake either from your end or from their website ?

(in reply to noname-RCU)
       Post #: 3

Jett 50 Heli questions - 8/12/2003 8:10:05 PM   
bob27s



Posts: 4733
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: online 		Actually, the engine does have a lot of mid range power. The top end power and the tuned exhaust is where the rpm becomes involved. I'm not sure if there is a slightly smaller pinion available for the raptor, but that would give you the best of both worlds.

As for the web page... that is entirely my goof (I am the webmaster)! I posted that data page 3 years ago, and I never noticed it! I will take off the listing.

The crankshaft on the 50 is different than the one used for the 46, and only the 46 shaft is available in a heli configuration.
(just for reference, the standard jett crankshaft and collet are much larger than those found on other engines, thus the need for a specially made crank on the heli engine so it is compatible with OS mounting provisions).

I use to be in the main stream of heli stuff back in the 1980's and through the 90's, but I have not been completely in touch with the heli business the past 5 or 6 years. Quite a bit has changed in the way helis are set up. I use to run an absolutely screaming engine, with moderate rotor head speed for serious aerobatics stuff. From what I have seen recently , now adays people turn bigger blades a little slower.

With your altitude situation, it is hard to say whether simply putting in a more powerful engine will get the performance you want. From my background in aerospace engineernig, you generally need more wing/rotor area to get high altitude performace. Longer blades, sometimes more blades are used. More pitch will compensate up to a point, but extreme high alpha will cause the blades to stall in extream manuevers. The other alternative to added 'wing area' is to turn the existing rotor area faster to create adequate lift. Lots of variables involved.

Anyway... the engine will put out pleanty of power at both mid range and on the top end.

There are are couple of dozen people flying Jett heli engines out there. Some liked them, some had issues.
Usually the complains we got back about the engines were:

1) compression is too high... my starter slips
(make it more like an OS ringed engine)

2) I keep breaking parts in the power train
(cut the power curve back so it runs like an OS)

Bob

(in reply to noname-RCU)
       Post #: 4

Jett 50 Heli questions - 8/30/2003 8:47:31 AM   
dennis



Posts: 1283
Joined: 1/7/2002
From: Minersville, PA, USA
Status: offline 		Interesting. I just happened to look at the whole line of threads.
The picture of the heli is mine at the WRAMS in NY at the Bolar Heli Research Booth. Larry had assembled that X Cell 46 pro with a Jett 46, I also had a 60 size with the Jett 76.
The 76 had to have the P/L replaced as it was so tight the even a 24volt starter wouldn/ turn it over.
Dub took care of that promptly and curtiously,'
Both motors are as described really the most bang for the buck that you'll ever get on a heli. Dependable runners, never had a forced auto on them, good midrange and a top end to die for. Only downside is that they are incredably noisy. Everyone knows when I'm flying

(in reply to noname-RCU)
       Post #: 5

Jett 50 Heli questions - 9/2/2003 7:07:56 PM   
bob27s



Posts: 4733
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: online 		Hi Dennis...

Thanks for the feedback.

Yeah, the jett-stream mufflers are 'average' by airplane standards, but a bit loud by helicopter standards.

I played around with using a Hatori pipe on my .76H a while back, and it actually worked fairly well. I probably lost 500 rpm off the top, but it was quieter.

If you have a chance, email me with your name, city, state, and maybe another photo of the helicopter. I would like to include it in the jett Hall Of Fame page.

Bob Brassell

[email]bob27s@hotmail.com[/email]
[email]webmaster@jettengineering.com[/email]

(in reply to noname-RCU)
       Post #: 6

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