Hobby King Dyna jet

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gerre
Posts: 10
Joined: Sat Jul 25, 2015 5:15 pm
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Re: Hobby King Dyna jet

Post by gerre » Thu Aug 20, 2015 6:34 pm

It's not a fuel pump. It's a solenoid valve, acting as an emergency valve.
Anyways, I don't think the solenoid valve is the problem because the
engine is drawing fuel from the tank very good. The petal valve is aligned
and intact. And I would be surprised if the metering jet is clogged,
because of the fuel getting drawn in very good.

Anyways, monday I'm going to try again. :)

Mark
Posts: 10727
Joined: Sat Oct 11, 2003 10:14 pm

Re: Hobby King Dyna jet

Post by Mark » Fri Aug 21, 2015 2:18 am

On my Dyna-jet I accidentally broke the starting air blow pipe off the metering jet by trying to unscrew the part when the jet was still hot. Anyway I just took to starting it without the part puffing air in over the holes. It's a bit fussy if the angle isn't just right. On the left you can see the broken piece I just positioned for the photo. My Bailey jet has 10 little fuel holes instead of 2 like the Dyna-jet.

Good luck starting your jet and all. Maybe your Chinese version has the blowpipe at slightly less than an ideal angle or something. It helps to have the fuel level right up to where it's nearly going in the metering jet. I used to start some homemade pulsejets without starting air by merely misting the insides with some fuel and then lighting the tail end with a flame, but I had to have the fuel right up to the intake for it to sustain when starting like that. Also a hot spark is more forgiving than a feeble spark in some cases. On your one photo you have some clear tubing that is labeled neoprene. I didn't know they made a clear kind. If it's silicone tubing it will swell in gasoline.
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gerre
Posts: 10
Joined: Sat Jul 25, 2015 5:15 pm
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Re: Hobby King Dyna jet

Post by gerre » Fri Aug 21, 2015 11:37 am

I already measured the angle of the blowpipe and I think there's nothing wrong with it (35 degrees).
Anyways, I'm going to try running it without the solenoid valve and by putting the fuel tank closer to the metering jet.
And you are right, it is silicon tubing. My bad :)

Thanks for helping, will keep you informed!

gerre
Posts: 10
Joined: Sat Jul 25, 2015 5:15 pm
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Re: Hobby King Dyna jet

Post by gerre » Mon Aug 24, 2015 10:24 pm

The pulse jet worked! :)

But I still have a lot of questions regarding the engine parameters.
The biggest one is the specific impulse: I found that pulse jets normally have
a specific impulse of around 1000-1500s, but the specific impulse for the dynajet/HK pulse jet is
only 58s, according to my calculations. This can't be true, right? I'm afraid I made a wrong calculation
for my mass flow rate...

Anyway, fun to have a working pulse jet. Not that funny for the neighbours though x)

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