New Pulse Jet Go-Kart !

[Chadly33]

Have decided to build a new chassis from the ground up to take the twin engines, as the other one is very restrictive to get in and out of and not a lot of room for anything else. I have also decided to move it here instead of the valveless forum so as not to clutter it up. Already have the chassis rails cut to length and laid out and I aquired these today for the ass end! Nice and fat but round so they only run on the centres complete with drum brakes! Larry would probably have flash backs at these as they come off of a Super Cub that just had a disc brake conversion! God I love working in the aviation industry! I will post more pics. as the work progresses, at the moment I am thinking something like a LowBoy with one of my engines on each side! But still undecided, Any Ideas??

[larry cottrill]

That's excellent! On the wheels, you might need improved hubs for better wear. If they're like the J-3 ones, the bearing is pretty crude.

I will post more pics. as the work progresses, at the moment I am thinking something like a LowBoy with one of my engines on each side! But still undecided, Any Ideas??

Yes! Keep the thrust line low. Same with the overall CG. You're probably never going to run on rough terrain, anyway.

L Cottrill

[GRIM]

Hey Chad, Ever considered a Kneeler,? I used to watch these race,
Very low centre of gravity, good aerodynamics, slippery suckers,

The driver actually rests his chest on top of the engine, in your case maybe the propane tank?
The cub wheels would be fine out back, maybe a small motorcycle wheel up front,

Great stuff either way , keep it up

[Chadly33]

That's excellent! On the wheels, you might need improved hubs for better wear. If they're like the J-3 ones, the bearing is pretty crude.

These hubs are fitted with Timken bearings, one each side so they should work fine. Maybe someone already had them modded? less work for me anyway!

[larry cottrill]

These hubs are fitted with Timken bearings, one each side so they should work fine. Maybe someone already had them modded? less work for me anyway!

No, they're probably stock. The Super Cub had many, many design improvements over the J-3, and better wheels is probably among them. The PA-18 (the real designation of the Super Cub) benefitted from two decades (including a World War) of development, even though the basic design is the same. They were a real workhorse back in the 1950s and 60s, when they were the champions of short field / soft field operations. I wish I had one. There are several modern designs that are actually much better today, designed especially for bush flying and medical missionary work. And of course, there are vastly improved engine designs for them, too.

L Cottrill

[Chadly33]

Got a little bit more done, front and rear crossmembers are welded in. Grill and windscreen sopport hoops are on with braces for the bonnet area. Going for an old roadster,hotrod look to reflect the era that the engines were used!

[larry cottrill]

Man, so far that looks just fabulous. Keep everything pretty low-slung, and you'll have a critter that really moves out and should handle nicely!

L Cottrill

[Chadly33]

Ok, getting a little bit done at a time but its starting to get some shape to it! I should mention that apart from the chassis rails it is all chromemolly and the body will be aviation aluminium. Just need to get my hands on some small motorcycle wheels for up front so I can set up the drop axle and steering! heres a few more pics.

[larry cottrill]

Chadly -

Do you intend to develop the structure as an actual space truss (like the Cub fuselage)? If not, I would strongly encourage you to do so. A thin aluminum skin (essentially, a monocoque fuselage) will streamline things nicely, but won't provide any crash strength to speak of. Even G forces could be problematic with such a lightweight structure, if you don't develop it as an actual truss by carving it up into triangles.

L Cottrill

[Chadly33]

Yeah I did put some thought into that. I was setting out the basic structure before triangulating it out, so I could see if there were going to be any problems with the setup as a whole. I only get two half hour breaks during work so there is only so much I can get done!

[larry cottrill]

Chadly -

Please forgive if I seem too "advisory" -- it seems that you basically know what you're doing. It's just that (as we all know) being a good mechanic and being a good designer are two different things. My last post came from worrying about that little "elbow" near the rear end of each of the side tubes -- a perfect setup for bending failure when the tube is under sudden compression. That point needs to become a "truss node".

One thing that homebuilders often miss is that you can make a complete box of four flat trusses and think that you have a perfectly solid structure -- but not so! Such a fuselage is weak in torsion. You can easily twist it several degrees along its length. Some diagonal bracing is needed inside across the corners of the box. This is a pronounced design weakness in the original J-3 Cub fuselage. One of my flight instructors was an older guy who had been a civilian instructor for the Army in WWII. J-3s were used as Primary Trainers, and the Army version was set up with a long Plexiglas "rear window" and a rear seat that could rotate around to a little "map table". Anyway, he and another pilot got to talking one day about why the Cub shuddered so badly in a spin, which after all is a low speed, low stress maneuver. So, they went up in a Cub, and this guy turned the rear seat around and locked it in place, then had his friend stall the Cub and kick her over into a spin. To his amazement, the fin/rudder, stab/elevators and tail end of the fuselage started oscillating rapidly in a twisting fashion 10 or 15 degrees each side of normal !!! He said after witnessing that, neither he nor his friend ever practiced spins in a J-3 again! Ha. A few chrome-moly tubes (probably even 1/2-inch OD or less) welded diagonally across would have completely eliminated this effect, with only a tiny amount of added weight.

L Cottrill

[Chadly33]

Dont stress Larry, the respect is there. Your comments are always welcomed! Everything is taken onboard.

[Jutte]

Looking good Chadly - envious of you working where you do.
I've seen a few Jetranger wrecks and always thought that they would make
great go cart frames. Years ago over here the place was damn near awash
with Hughes 500C wrecks ( not now ) - mostly people drop R22's now . Brother dropped his R22
and there was stuff all left of it .It was a GREAT landing as he walked away from it!
I was told that the PA -32-112 Tomahawk tail section also performed
some interesting 'swimming' movements when under stress.
I never noticed as I was too busy looking out of the front of the office...LOL!