A Home Made Preheater - no electricity required! Last updated
February 3, 2001: The stove wouldn't keep working. My best guess is that the 30-year old rubber seal in the fuel-tank cap has given up since the unit won't stay pressurized long. Could say the the stove has reached TBO and needs a complete overhaul. So, either I'll get the stove fixed or I'll give up on this (therapy) project and buy a (no electricity required) Northern Companion preheater. http://store.yahoo.com/ultimategear/airpreh.html http://www.stoddardairparts.com/northcompheater.JPG http://www.flyboyed.com/preheat.jpg http://www.burlsaircraft.com/Preheaters.html March 4, 2001: OK, now for some good news. After cleaning up the cap seat seal, and remembering not to overfill the fuel compartment, the stove works fine. See new performance data below...
Making the Preheater...
The first step was finding my old hiking & camping stove system, a Sigg Tourist. The stove and fuel are well encased in the nesting aluminum pots and pan (lid).
The stove is a Svea-123 and supposedly runs on any reasonable fuel. For now I'm using Coleman Fuel (naphtha ???).
The stove mounts into an aluminum base which holds it steady and provides openings for combustion air. The eyedropper (off to the right) is used as part of the starting process (no pump). Use the eyedropper to put a little bit of fuel in the depression that surrounds the "stalk." Light it and the stove gets preheated and lights easily. The other device to the right of the stove is the orifice cleaner (a wire in a folding holder.) The cleaning wire is seldom used with naphtha as the fuel - all bets are off if 100LL is used.
A flame basket mounts on top of the stove base and is intended to support a pot or pan.
Thanks to Lowes (or was it Home Depot - whatever) a short piece of 6" steel duct was fitted with a steel 6" to 4" reducer and a handle bolted on so that the duct and reducer are locked together. This assembly simply sits in the flame basket as shown.
Again, thanks to the home improvement store, I added a 4" steel adjustable-angle elbow. That was followed by a 1-foot piece of high-temp (500-degree) scat tube purchased from my FBO for about eight bucks. The nice thing about this scat tube is that you can bend its internal wire and the tube stays bent. The resulting flattened shape is just right for fitting into the air outlet at the bottom of the cowl just in front of the pilot's rudder peddles. I thought 'bout sending the hot air up and around the engine's exhaust pipe, but decided not to do so. The combustion product contains lots of water vapor. Not a good thing to send into the engine, even backwards.
Set up on the plane...
Performance Data
In an unheated hangar with the outside air temperature at 25° F, the temperature of the air coming out of the scat tube was about 210° F. The air-flow rate was modest but sufficient. The Tiger's cowl was covered by a moving-company padded blanket and the air inlets plugged (hot air escaped around the spinner-cowl gap). Using a thermocouple tucked deeply between the fins on cylinder No. 2, I recorded a temperature change of from 25° F to about 55° F in about a 1/2 hour. My oil temperature gauge showed a temperature increase of from about 35° F to 40° F in the same time.