The timing of your April article on vacuum pumps was fortuitous as I realized it was about time that I replaced mine. Now I am completely confused on what the wholesaler has sent my mechanic.

The base of the housing says Airborne, but the box says it is from Aero Accessories and it has the inspection port like the Tempest in your article, which would be Aero Accessories. Does this make any sense?

Bill Bittner
Via e-mail

Yes, it makes sense. What youve got is a rebuild of an Airborne pump by Aero Accessories, with the wear port added. The overhauls are part of Aero Accessories product line.

Swampy Fan

I am a long-time user of the Swampy products including the IM30 that you reviewed and the IM20 all-in-one unit that you did not. In the seven years that I have used their products, I have been very satisfied and have had good results from both units-far better than your review showed. Out of curiosity, I did a temperature and CFM test on a 12-volt IM20 that I currently own.

I tested the unit in two areas: in the hangar and in a car that had been parked in the sun for several hours. Unfortunately, my airplane is currently in for annual and several mods so I could not test the unit in the airplane. I also measured the air temperature of the cars air-conditioning unit for comparison. The chart below lists the outlet air temperature at high and low fan speeds and the cubic feet per minute of air moved. I used the excellent portable Mannix DCFM-8906 CFM Master II to do the measurements.

As you can see, the Swampy IM20 ranged from 59.2 to 64.3 degrees for an average of 61.75 degrees, which is a good deal cooler than your tests showed. One possible explanation is this: It is important in the IM30 to position the intake pump as far away from the outlet hose as possible.

If you put the two in close proximity, then I can see the increased temperature of your test as the warm water being returned to the unit was being sucked directly into the intake pump.

I had an elegant and efficient installation of two IM30s in my Beech 18. I positioned one unit next to the cockpit to blow cool air into the cockpit and the front seats. I had another positioned on the refreshment stand near the back, blowing on the back and middle seats. Both were secured by seat and cargo belts. I plumbed both units to a stainless steel Coleman ice chest in the potty area.

I used the units for more than two years while flying that wonderful aircraft. As I could turn the coolers on at the beginning of the preflight, the cabin was nice and cool by the time the passengers loaded. They loved that feature. For about $750, I had a usable and efficient cooling system. A far better bargain than the $25,000 quote from an air-conditioner company. Swampy had enough foresight to offer two great units: The IM30 for large and/or long term cooling using your own design and ice chest and the compact and portable IM20 all-in-one unit that cools a typical four-place cabin nicely and holds two bags of ice, which is plenty for the typical start/taxi/climb-to-cool-air portion of the flight. The swamp cooler portion of the unit then keeps the airplane cool for the approach/taxi/shutdown, even after the ice has melted. Every aircraft that I sold with a Swampy installed flew away with the unit-the new owners insisted. I have had extremely good luck with the units and with the company and owner behind the units. I recommend either highly.

Kevin Lockhart
via e-mail

See page 15 for a detailed follow-up. We tested the small M200 three times and could not duplicate these temperatures. The disparity may be in the volume of ice. Our tests suggest it takes at least 40 pounds to cool efficiently. The M200 holds less than half that. The IM30 relies on a user-provided ice chest, which can be of any size. In our view, the larger it is, the better.

I enjoyed the article on portable GPS in your July issue and agree that these Garmin units are marvelous. I have a GPSmap 296 in my Light Sport aircraft and it performs beyond my expectations except in one area. That is in direct sunlight, which is most of the time in my low-wing environment. Unless its a gloomy day or night, the display is very difficult to read, even on full bright. I have a makeshift shield that helps somewhat, but this one deficiency seriously detracts from an otherwise superb device.

Dudley H. Johnston
Via e-mail