www.pulse-jets.com

Hi,
I designed a kart a while ago, and have just got round to mounting the engine. [Refer to image] I planned to shield the 180 bend with something (possibly stainless or aluminium or both) to help keep the heat away from the driver and fuel, but having mounted it, I am unsure if this will be enough!

I am concerned over how much a heat sheild will help?
- The engine is about 6 inches from the drivers back (lower shoulder blades for me).
- The seat is fibreglass, which will definitely have problems without any sheilding.
- The fuel (propane cylinder) was designed to fit under the PJ, between the seat and rear wheels. A 15kg cylinder will fit, but I plan to use a smaller one, wedged behind the seat to keep it further from the engine.

This part of the design should have been done using TLAR rather than pen & paper!

As a second problem (I am not as worried about this at the moment) is brakes. I do have some small disk brakes mounted, but they wont be very effective for emergency stops at 40mph. Would anyone think it silly to incorporate a simple parachute?


Could people please post their suggestions.
Thank you!
JS.

A thin piece of sheet metal will do the job.
As all the heat is radiation, you'll only have to create "shade", meaning that anything thin enough to not hold the heat will be enough.

My only advice is that if you are even the teeny tiniest bit unsure of your braking system, DON'T DRIVE IT, until you have beefed it up to overkill.

Brakes are the #1 most important component on any vehicle, IMO. This is based on the multiple broken bones I have experienced in the past.

Mr.B wrote:A thin piece of sheet metal will do the job.
As all the heat is radiation, you'll only have to create "shade", meaning that anything thin enough to not hold the heat will be enough.

And shiny is good, really really good. Matt black or dark heat shields are bad really really bad.

If all else fails, use a water soaked 3/4" plywood barrier. Carry a spare full water bottle.

As for an emergency brake, mount a piece of thick plywood on a sturdy hinge in the space between your feet and have it held up by a spring. If you want to stop just put your feet on the plywood board and make it brake against the road.

Since the cart weight won´t be high and because it is thrust-powered that brake will probably stop the cart pretty fast even with the engine running at full power.

marksteamnz wrote:

Mr.B wrote:A thin piece of sheet metal will do the job.
As all the heat is radiation, you'll only have to create "shade", meaning that anything thin enough to not hold the heat will be enough.

And shiny is good, really really good. Matt black or dark heat shields are bad really really bad.

The reflective material is also very important. Don't make the mistake of using something chromium plated! Believe it or not, chrome is a POOR reflector (60 % or some such - think of grabbing an auto door handle on a summer day after the sun has beaten down on it for a while). Aluminum is probably the most practical reflector material, as it is highly reflective (something like 97 percent), cheap, light and easy to form. In terms of pure heat reflectivity, there is no difference between shiny and hazy finish, but that DOES make a difference in terms of dispersion (see below). Aluminum is also capable of very effective heat sinking, because of its high conductivity.

With a shiny surface, you will have to think about how to shape the reflector for good dispersion. Particularly, a concave surface facing the engine will concentrate the reflected heat back toward it, while a convex surface will produce wide dispersion (probably what you want). With a dull "hazy" surface, a lot of the dispersion is taken care of for you, without resorting to careful "optical design" of the overall reflector shape.

L Cottrill