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Old 10-24-2007, 07:35 AM
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MJD
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Default RE: And now for something entirely different!


ORIGINAL: Julian537

MJD,

18lb thrust pulse jet?? WOW that is serious. Dont be to close to the border flying that.
The U.S. may shoot it out of the sky.

Are pulse jets legal to fly in the U.S.??
Sure they are legal to fly, they are used in C/L speed in the Jet category. They are limited to the dimensions of the Dynajet, i.e. 1-1/4" tailpipe, and while in the past people used fuels containing large amounts of nitromethane, the speed event is now, AFAIK, regulated to a fuel consisting of methanol and MEK. As far as R/C pulsejets under AMA.. hmm.. not entirely sure, but I think that I saw a rule stating they could not be enclosed. Why is beyond me, as turbines run pretty darn hot too, but perhaps when that rule was written it was in the early to pre-commercial turbine days. In Canada, the MAAC regards turbines and pulsejets equally and, sensibly, they are governed by the same regs, i.e. rigid tanks versus IV bag bladders for example (bladders in rigid outer cases are fine). Bladders are the ultimate tank for these (surprise they also rock for glow engines) as yes, a bubble can cause it to die. I believ eturbines are a bit particular in that sense though how much so in relation I don't know. Pulsejets can start fires, turbines can start fires, so can other things. Noise.. well, heh heh.. you better find a remote flying site becuase brother they are freakin' LOUD! A Dynajet sounds like a bike with open pipes backfiring at 13,200 rpm. The resonant frequency is of course determined by chamber length and design, the Dynajet resonating at about 220Hz. The big guy is correspondingly lower.

CP: Yeah, the C/L speed guys often run larger venturis and intake designs optimized (in their opinion sometimes.. experimenting abounds) for high speed, and they as a result can be more finicky on startup and launch. The specific fuel consumption of a Dynajet size model on gasoline is pushing 3 ounces per minute. On nitromethane/methanol fuel, AFAIK they go through 6-7 ounces on startup, quick launch and a speed run of run up plus 10 laps. I think that equates to around 12 ounces a minute. On methanol/MEK I preszume the mixture is less fuel rich and the specific consumption is lower. These numbers may not be bang on, I don;t fly C/L speed, but from the figures I have read/seen and bearing in mind the stoichiometry of those fuels they seem about right.

The 18lb guy is really cool - it is very light for it's size, at about 900 grams, and uses a turbine fuel pump and speed control for a semblance of controllability. Fuel is a gasoline/kerosene blend. In the Netherlands they fly pulsejets this size on deltas about 1.2 m or so in span (42-44") and hit speeds up to about 400 kph. Google "Team Helmond" for some pics. There is another site that has some CL speed video and RC video, but at home here I am dialup until I go DSL this week or next, and when I do I can find it again.

As to the airplane project, yeah you bet I will post some stuff when it gets under way, likely in 4-8 weeks when I finish some reno work and fixing up my workshop. Canada = depending on latitude 4-6 months of hopefully good flying weather plus 6-8 months of repair and build time. Likely the same for the upper states too

MJD