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Help Jet guys - BVM .91R question

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Old 12-31-2002, 04:42 PM
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Blue Skyy
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Default Help Jet guys - BVM .91R question

I would like to use the BVM .91R in combination with a prop. Does anyone have experience using this engine with a prop? I saw one with the fan attached once and it doesn't look like you could put a prop on this engine. Of course I want room to add an aluminum spinner back plate too. An APC 12 pitch prop is pretty thick at the hub. Looking at the shaft, it just doesn't look like it would work.

Lots of questions, but lots of bucks and I don't want to make an error in buying something that you simply can't mount a prop on.

I have attached a photo showing the front of this engine, How could you mount a prop on this? Ducted fan guys, can you help me out?

Bob Holmes
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Old 12-31-2002, 05:03 PM
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ChuckAuger
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Default Fan shafts..

I make an adapter that goes thru the prop hub over the few threads on the shaft. Like a sex bolt, or a Tru Turn spinner adapter that's been turned down.. Look in the thread below "A New Toy" I explain it. In that thread I promised to post a pic, but haven't yet. I can now if you can't understand my rambling explainations.
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Old 12-31-2002, 05:57 PM
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Default Re: Fan shafts..

Originally posted by ChuckAuger
....Like a sex bolt , or a Tru Turn spinner adapter that's been turned down.....Look in the thread below "A New Toy" I explain it. In that thread I promised to post a pic, but haven't yet. I can now if you can't understand my rambling explainations.
What the hell is a sex bolt???
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Old 12-31-2002, 06:32 PM
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Default Sex bolt...

A bolt with the threads on the inside of the shaft instead of the outside...don't ask me how they got the name.
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Old 01-01-2003, 10:50 AM
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Default BVM 91 with prop

To use the BVM 91 with prop is no problem because the tread is inside the shaft. Maybe you need a other screw if your prop is to thick or to thinn.

A little other problem is the tuned pipe from BVM, it is to short for 21 000 U/min on ground and the engine became very hot. It is good for 25 000 rpm. I extended the length by 4 cm and the engine runs much better on the ground with 21000 rpm with a CFK 9x10 Prop. The engine is a monster and not for a beginner.
A few times I lost one blade on the propeller when the engine runs on very high rpm after a long diving down with my speed modell.

Best regards Michael
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Old 01-01-2003, 11:55 PM
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Default BVM .91

Hi Bob,

I have been flying BVM jets for 15 years now. In my opinion, this is one of the finest glow engines ever made. The engine is a design development of Henry Nelson of Nelson pylon racing engine fame and Bob Violett, the king of r/c jets. I have six of these motors and, along with my two sons Paul and William, have put on flights that now number in the thousands with these engines. They idle better than an O.S. 40, transition instantly to full throttle, are designed to turn 24K static, and live forever. As long as you don't run them lean, I don't think you can wear one out. I have never thrown a rod in a BVM engine. We moved on to turbines about 4 years ago, but I still love these engines. If you want to go really fast, build the smallest airframe you can behind one of these and you will be hard to beat.

F3D is correct. You will have to prop the engine for 24K static as Bob Violett does, if you use his pipe, or lengthen the pipe. They unload to about 27K in the air, so it would be best to use a carbon fiber prop so you don't loose a blade.

I saw your plane in another thread, and I am sure it is very fast. I went through 10 OS .91 engines in some non BVM jets I had, and I can tell you that the BVM .91 is twice the motor the OS is.

I hope you get a chance to run your delta design through a good set of traps some time. I would like to know what speed you are getting with it.

You should consider coming to Mississippi this spring when we have the speed event Daryl is putting together. I think you should have a very competitive airplane.

Regards,
Dennis Lott
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Old 01-02-2003, 01:43 AM
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Default Help Jet guys - BVM .91R question

Thanks Dennis,

I first met you at a Jet event held in Shreveport, LA some years ago. You son was working with this wild R/C model that was a real screamer then. It was an expertly built very small .40 size plane that was hand launched. That first flight was absolutely wild!

I would really enjoy coming to Mississippi for the high speed event. Maybe I could get a few extreme speed pilots to come with me from this area as well. Sounds like fun!

So all I need to do is put a threaded shaft into the .91R for a crush plate and spinner nut? It is a removeable just like the Jett interchangeable shafts are and that's it? Watching hundreds of these engines over the years had me intrigued to do this, but Bob Violet always managed talked me out of it when I called him about putting a prop on one of his engines. I would really like to try putting a 12 pitch prop on a .91R. Even at a 7.5" in diameter at 24,000 rpm this engine would have about 5.5 lbs of thrust static. Just enough for an unlimited climb rate at this power level.

Thanks for your help Dennis,

Bob Holmes
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Old 01-02-2003, 04:00 AM
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Default Help Jet guys - BVM .91R question

Hi Bob,

I do remember you at that event. You did get to see the first flights of Paul's Aurora II. He was 15 at that time. He designed and built Aurora I when he was 13. It had a .25 on it. No. II was the smallest airframe he could build around a .40 size Dubro engine mount. He used a K&B Quickee 500 engine on it. It was fast, but not fast enough. He built Aurora III with the same engine, a better airfoil, and a few other aerodynamic improvements. No. III was about 30 mph faster than No. II. He is building Aurora IV right now. It will be much improved over Aurora III with all composite construction and a much better engine. He will have a hot new F3D engine on this one. The biggest problem I see with IV is how to keep it in sight. I guess it is a good thing Paul has eagle vision, because it is hard enough for me to see the last one. If you want to take a look at Aurora III, go to our website at http://home.jam.rr.com/missgang/, click on jethangar, and scroll down to the bottom of the page. It is a lousy photo, but it will give you an idea of what it looks like. We can't post photos of Aurora IV until after the speed event. Can't give away too many speed secrets too early you know!

I sure hope you guys can make it to the event. I think it will be a blast. We are going to do all we can to help Daryl make it a fun and interesting event for everyone. We will most likely have a couple of turbine powered jet demonstrations during the event for those who don't get to the jet rallies.

You can actually use an appropriately sized socket head cap screw for the prop shaft. Drill and tap the socket end for an 8/32 screw (or whatever size you use) to retain the spinner, and you are ready to go.


Best Regards,


Dennis Lott
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