Letters: 10/05

Garmin GPSmap396
As always, I thoroughly enjoyed your latest issue, especially the article on the new Garmin GPSmap396. I have found it to be fabulous and your article was right on the money. It gets my vote for the 2005 product of the year.

However, it appears that there is a surprising flaw in the unit, especially since it was designed for aviation use, that I thought you should be aware of. On my first flight, I noticed that my compass was off several degrees and I started into figuring out why.

The GXM30 antenna is actually quite magnetic and seems to be the source of the error when sitting on the glareshield. I contacted Garmin about this and they indicated that there is a magnet in the antenna, which could be causing the problem.

Certainly, I can relocate the antenna, but it would be much better to not have a magnetized antenna base. Certainly, this will have little bearing on the units popularity and Garmin still has a winner. But its something consumers should probably know, and perhaps something that Garmin should address.

Dave Johnson
Via e-mail

We should have reported the fact that the antenna has a magnet and will disturb the compass if placed too close. The GXM30 manual notes this fact. Frankly, were so accustomed to magnets in other XM antennas that we simply moved it away from the compass and ignored it. But we agree, it would be better if Garmin hadnt included the magnet.


I bought a PDA-based XM weather set-up two weeks before the existence of the GPSmap 396 became know. Damn! Besides the comparisons you listed in the sidebar on PDA solutions, don’t forget that you also get the GPS-driven instrument page with the GPSmap 396 as part of the price. With the PDAs, its another $1000 to get something that might truly save your bacon while youre trying to avoid the weather.

Alan M. Gewirtz
Via e-mail


MIA: Quality
I am a devoted reader of Aviation Consumer. I love the unbiased reports of airplanes and gear, but I think Aviation Consumer has to go a step farther. Our American airplanes are in the same category as our American-engineered automobiles, that is, they are horrible when it comes to reliability. If the engines in our airplanes were as terrible as the systems, there would be a law against flying. As prices continue to increase on these unreliable airplanes, the systems remain as unreliable as ever. If you own an airplane, you know what I am writing about. We need to demand a better product.

I have a 2000 Mooney Ovation 2 and love it, besides its faults. I cant imagine what it would be like if something didnt break every other flight. It just might be the American way to do things, but its horrible, in my view. I have thoughts of buying a new airplane, but quickly come back to my senses. I think these airplane systems are designed to fail. Design the non-critical items to fail, then there is no liability issue.

American automakers have lost the competition battle. They can barely give them away. Each week, there is a new deal to be had in order for them to sell them.

When will there be an import light general aviation airplane? Sign me up for a good one. I will definitely try one, given the unreliability of the American-engineered and made products. Something has to be done to curtail this issue. The common excuse: Oh, there is a lot of vibration in airplanes. We must get real about what the real problem is. I bet if we stop buying these airplanes, the manufacturers will step up and make them better. I know I am not the only owner who is tired of this. I tried buying a late-model airplane; it had 100 hours when I bought it. That did not work. Is there any relief?

Ellis Johnson
Mooney Owner
Aztec Owner


Some Basic Physics
Nice article by Mike Palmer on porting and polishing in the September issue. But there’s a slight misstatement in the third paragraph when Mike says, … it makes more power from the same fuel and air. Actually, the correct statement would be to say that it makes more power from the same displacement by using more fuel and air.

By improving volumetric efficiency, more air gets into the cylinder on every cycle. To remain stoichiometric with the additional air, you then need more fuel to maintain the proper mixture ratio. Because the power generated is based on a thermodynamic process of heating air molecules in a confined space and extracting work from that hot gas, the more air molecules you have, the more work can be extracted in the form of power to the crankshaft.

David Rosing
via e-mail

Youre correct. We missed class the day this topic was discussed in Physics 101.


Three-Blade Props
I just received your August issue and was particularly interested in the article on three-blade props. But I must disagree with this statement:If you have an older Cessna 180 or 182, a Comanche 250 … were wary of recommending three-blade props for these models …

I own a 1961 Comanche 250 and when I decided on a field overhaul, I also went with a three-blade prop from McCauley. There is virtually no vibration at any engine power setting. You can lightly touch the yoke and its as smooth as silk. I have noticed no difference in cruise. Its neither faster nor slower. The time it takes to rotate is improved and the climb rate is much improved. All in all, I think my decision to replace my worn out two-blade Hartzell with a three-blade McCauley was a good decision.

John A. Navarro
Moreno Valley, California