A View from Broadway
Thing Two (left) and Thing One. Ken Burdick photo.
Apologies to Hanna-Barbera
By Ken Burdick
Yes Folks, it’s true.
Kenny and the jets opened up with Thing Two, a sport jet. Meanwhile, Thing One was still being kitted by Dick Hart. Well, the Blue Thunder kit arrived and is similar to a TARFU, with some differences. The kit itself is complete in every detail and well thought out.
Thing One is a Fast Jet and the primary difference between it and the Thing Two, a Sport Jet, is that it uses monoline, a pressure fuel system and will sport a Fast Jet engine. Materials on Thing One are basswood with no balsa as in Thing Two. Thing One is built for durability, all basswood, a sturdy belly skid and excellent hardware. As of this writing, I still do not have a Fast Jet engine but that’s in the works.
I have learned the difference between a Sport Jet engine and a Fast Jet engine. As you might guess, the Fast engine allows more air in and thus a larger intake. Like in our piston engines, a pressure fuel system must now be used. The pressure tap is on the head and a small hole is vented from the chamber side of the head to a fitting that runs to the tank. This particular head was first designed by “Jet Bill” and is somewhat different from the old Dyna Jet. Similar, but with many many hours of testing and experimenting, it has a different length and shape and port size.
By joining various pulse jet groups on Facebook, I was finally introduced to Al Stone. Al manufactures Fast Jet heads, and they are extremely well made. Dick Hart also sells heads and tailpipes. However, both have no Fast Jet pipes at the time of this writing. (See unobtanium.)
As said, not only does Al manufacture Fast Jet heads, he has the tools and parts required to make tailpipes for the Fast Jet. The pipes are the most difficult part of the engine and require a good understanding of fabrication and jigging fixtures to produce one.
Sure, I could use a Sport Jet pipe, but this is about getting the most out of Thing One, so that means getting the best tailpipe that I possibly can. I asked many what the difference is between a Sport Jet pipe and a Fast Jet pipe. Mostly I got no reply; however, Dick Hart not only answered but sent graphic photos of the two side by side. The fast jet has a divergent cone effect behind the combustion chamber whereas the sport jet does not. Here are Dicks words:
I hope you can see the difference between a Sport Jet and a Fast Jet pipe from this photo. Combustion chamber and first cone are both the same. Sport Jet tailpipe is 1-1/4" inside diameter and the Fast Jet pipe has a divergent cone and a 1-7/16" ID. I guess both engines will run with either pipe and that's certainly how Fast Jets developed; everyone used a Dynajet pipe. These days Sport Jet pipes are regulated and are all more or less the same. Fast Jet pipes are also regulated and have to have a point where the size is the same as a Sport Jet, i.e. 1.25 square inches, which happens to be a diameter of 1.25 inches. Hence the throat where the cones meet.
Sport Jet and Fast Jet tailpipes compared. Dick Hart photo.
So, lil' geezers, it may be a while before I get a really fast tailpipe to go with the fast head I have.
In the meantime, I have completed the thing one (Blue Thunder) from Dick Hart, purchased a fast head, oversized valves and a custom-made valve retainer to go with the head.
I do have a complete Dyna-jet from the one and only ZZ Prop, otherwise known as Mike Hazel. This engine will be the sacrificial goat, so to speak. It will be used as the first flight engine for both Thing One and Thing Two.
This page was upated March 3, 2021