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Speed,Combat,Scale,Racing => Speed Talk => Topic started by: Bob Reeves on December 13, 2009, 06:35:47 AM

Title: Jet questions..
Post by: Bob Reeves on December 13, 2009, 06:35:47 AM

Hi,

We are putting this thing together just for fun and to make noise. Kinda a club project that I inherited. None of us have any recent experience with building pulse jet airplanes and I have a couple questions..

 Will a plastic control horn be OK or will it get melted by the heat of the tail pipe? Hard to tell in the photo but it's going to be about 1/2 inch away from the tail pipe. If necessary I can make a metal one and use a metal clevis. Just would be easier to be able to use what I have.

2nd do you put any rt/lt offset or down/up thrust on the engine or set it so it's 0-0 with the wing?

Thanks for any info..

Title: Re: Jet questions..
Post by: Bob Reeves on December 13, 2009, 03:02:56 PM

Have decided to go ahead and make a metel horn, not worth taking the chance..

Still wondering about engine alingment..

Title: Re: Jet questions..
Post by: Joey Mathison 9806 on December 13, 2009, 05:49:12 PM

going to a metal belcrank is a good choice i think the 100 pound pull test that you guys will preform before you fly would fail.

Title: Re: Jet questions..
Post by: Bob Heywood on December 13, 2009, 06:37:53 PM

Bob,

Zero - zero will work just fine. You're probably looking at a 120 - 130 mph model. Line inertia and drag evidence themselves at take-off which requires a slight lead by the pilot.

You may find that there is a trim change when the engine quits. I have a bit of experience with a friend's Hoyt CatJet trainer. It always tends to zoom when the thrust stops.

One last point. Without prop blast, elevator authority is mushy until some reasonable airspeed is attained.

Looks like a blast.

Bob

Title: Re: Jet questions..
Post by: Patrick Hempel on December 13, 2009, 07:24:27 PM

Hi
I use a plastic horns on some of mine, the pipe will get red hot, if you don't want it to come in on take off, put some out thrust in it, a little, not too much. be ready to back up on takeoff, it may tend to come in on you some.
I am interested in how fast it goes keep us posted on the flight.
Patrick

Title: Re: Jet questions..
Post by: Bob Reeves on December 14, 2009, 07:29:06 AM

Thanks for the info guys,

Made a brass control horn this morning so that's a done deal. Know I had another question but now can't remember what it was, getting old sucks. Anyway it's ready for paint, the white stuff is sandable primer just to fill some of the grain in the hard wood. Looks like I'll be making a heat shield to protect the paint but that can be done anytime..

Thanks again,
Bob