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bob27s -> RE: Mounting pipes with O-ring header (3/19/2007 3:11:59 PM)
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Hi Walt......
You will love those engines ----- they are running very well.
The engines are still new. The break-in process must be completed, per the instructions.
For those engines, put them on a test stand, and utilize a 9x6 or 9x7 prop. Sounds like you utilized the Bolley 9.5x7 - that is a bit higher load, appears to have allowed the correct operating conditions. If you were able to run at 17,000, while rich, that would have been ok.
You want to run the engines, slightly rich, but running at the rpm target. Start the engines, take them up to 17,000-17,200 rpm and run them there (again, this will be a slightly rich mixture) with the lighter prop for about 15 minutes.
Once the initial break-in process is complete, the engines will run anywhere from 16,500 to 17,500 at peak with an APC 10x6 once installed - this is perfect. Sometimes rpm will vary 200-300 rpm just from location, humidity, temperature, fuel - phase of moon.... stuff like that. So do not worry. Using a bit lighter prop for the first few flights will help. RPM is your friend. The engines will gain in rpm as they get more time on them too. One thing you will notice, is that the pipes will cause the engines to run at the tuned point - so they may actually synch up very well in flight when at full throttle.
Just avoid getting the engines lean. That is about the only thing that can hurt them. Find the peak rpm (briefly) and back off 400-500 rpm from that peak. If it gets past peak and gets hot, shut it off. ..... let it cool down completely before trying again.
For first flights on the plane, if you have a pair of those 9.5x7 Bolley props ..... use those. They pull very well, and really let the engine unload. You can also use the 10x5 prop if you wish.
As for the pipe mount, usually a nylon tie works ok, but alone it does not cut it. There must be some sort of saddle to rest in, usually with a rubber or silicone pad on it that can get a slight grip on the pipe.
This one here is a good example. This is a dave brown pipe mount. Notice where it is located - just aft of the pressure fitting :) This way the pipe can not slide aft - pressure fitting prevents that. Also, the rubber pad located on the mounting saddle keeps the pipe secure and prevents rotation.
[image]http://www.jettengineering.com/hall/ddfulks1.jpg[/image]
One other way that does sometimes help with the o-ring mounts is to capture the pipe aft of the diverant section ... something like this
[image]http://www.jettengineering.com/hall/erik-dave-delta-big.jpg[/image]
And it is possible to mount off of the pipe exhaust tube end, it is just the least prefered.... some of the whiplash and diamond dust guys prefer this, mainly since it is a convenient place to mount it. Just tends to provide the least stability. If it works out for the Duellist installation
[image]http://www.jettengineering.com/hall/deckerv-whiplash-big.jpg[/image]
Example pipe mounts
http://www.dbproducts.com/store/tpmt.htm
Personally, I prefer to use isolator mounts for the pipes when possible.
http://www.dbproducts.com/store/hclp.htm
Another trick Ive learned - when using the tie-wraps, sometimes you can use a piece of fuel tubing over the tie wrap - Ive done this to avoid scratching the pipe up, and sometimes it can help get a bit better grip on things.
I hope this is helpful...
Bob Brassell
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