Flying Magazine Review of DA40 NG

[Rich]

I don't have much trouble at high altitudes because on any long trip where this matters I'm pretty far below MTOW. It's just me and the frau (maybe) and some luggage. And mine is one of the lightest Stars around, so takeoff weight on a trip I will be at about 2300 lb.

The nature of my trips is also such that the 40 gallon tanks have almost never been a factor. Maybe twice in all these years would having the fifty-gallon tanks saved me a fuel stop (at the cost of having what has turned out to be an obnoxious limit on CG - the NG being even more restrictive , BTW).

[Rich]

Rich: My typical DA in the summer months is about 2.5K feet. My aircraft also gets light slower than 59 Kts, but I want the margin above stall (plus, I fly the book speeds as precisely as I can).

Steve

Here's an interesting anomaly. In the DA40-180 POH, you'll note that Diamond publishes speeds for particular operations at various representative weights. For example, note the variation in initial climb speeds for different weights. Uniquely (as far as I can tell), one and only one rotation speed is stated, with no allowance for weight variation. Presumably this was set for the original MTOW of 2535 and had never been revised or refined. The stall "cushion" at that weight with T/O flaps is 8 knots. But at my typical takeoff weight this difference would be more like 12-13 knots, and sometimes even higher, as I can easily be off the stalling speed table on the light side. And I find rotating when it feels right results in a speed about at lift-off pretty much in line with the initial climb speeds.

The NG manual, on the other hand, does give different rotation speeds for different weights. At 2646 lb., rotation is shown as 65 KIAS, and the corresponding stall speed at that weight with T/O flaps is 60 knots, a mere 5 knot "cushion".

[pietromarx]

How high did you get Peter and how heavy? I used to find performance excellent up to 10 K or so. Climb at 90 knots TRUE (not indicated) and lean for best power.

I tend to go as high as I can without oxygen (I get tired of the cannulas) and depending upon the winds. I am generally at 10-12.5K depending upon VFR/IFR and direction.

The plane's weight eastward was around 2,600 lbs at takeoff, though on the way back west I was at around 2,250. Made little difference in climbing ability or cruise speed.

The real issue to me is sinking air masses from mountain waves and thermals, not to mention convective. As a sailplane guy I love rising air (free gas), but maintaining altitude in the Sierras and Rockies is difficult on warm summer days.

I stay upwind of rising terrain and avoid developing cumulus as much as possible. To me this means never traveling on the east side of any mountain ranges in the US.

This last cross-country trip was a lot of avoiding all of the above. Probably added 2-3 hours to the total travel time.

[carym]

I tend to go as high as I can without oxygen (I get tired of the cannulas) and depending upon the winds. I am generally at 10-12.5K depending upon VFR/IFR and direction.

If you don't have one, I suggest you get a pulse oximeter and check your oxygen saturation when you are up at 10-12.5K. My wife and I find that we need to put on the oxygen when we are above 8K for me and 6-7K for her. Admittedly we're old and our heart/lungs don't work as well as they used to, but I have found that many younger individuals also desaturate above 8K. Wearing the cannula can be a pain, but it really reduces stress significantly.

[Colin]

For my long trips (SMO – FHR for instance) I have on O2 at 5k and above. It makes a HUGE difference in how tired I am at the end of the long flights. That means it probably has an impact on cognitive perform and since that's what might keep me alive when something goes wrong, I put up with things stuck up my nose.

Probably added 2-3 hours to the total travel time.

I read that as, "I got to be in my airplane for three extra hours this summer." Sound like a good summer.

[pietromarx]

I tend to go as high as I can without oxygen (I get tired of the cannulas) and depending upon the winds. I am generally at 10-12.5K depending upon VFR/IFR and direction.

If you don't have one, I suggest you get a pulse oximeter and check your oxygen saturation when you are up at 10-12.5K. My wife and I find that we need to put on the oxygen when we are above 8K for me and 6-7K for her. Admittedly we're old and our heart/lungs don't work as well as they used to, but I have found that many younger individuals also desaturate above 8K. Wearing the cannula can be a pain, but it really reduces stress significantly.

I have one. For whatever reason, though probably due to lots of biking up hills, my SPO2 remains at 100%.

[pietromarx]

For my long trips (SMO – FHR for instance) I have on O2 at 5k and above. It makes a HUGE difference in how tired I am at the end of the long flights. That means it probably has an impact on cognitive perform and since that's what might keep me alive when something goes wrong, I put up with things stuck up my nose.

Probably added 2-3 hours to the total travel time.

I read that as, "I got to be in my airplane for three extra hours this summer." Sound like a good summer.

Too funny. True. It has been a good summer.

My issue is that this is nothing compared to the number of hours I spend in airliners. The last three years have been well over 500,000 miles.

[carym]

I have one. For whatever reason, though probably due to lots of biking up hills, my SPO2 remains at 100%.

Peter,
I really don't mean to be argumentative, but I want you to be careful and safe. It is impossible for you to have 100% SPO2 at 12,000 feet. The oxygen saturation dissociation curve of hemoglobin is not influenced by physical activity (biking up hills) and the partial pressure of oxygen at that altitude will not allow for 100% oxygen saturation of hemoglobin. If you are interested you may want to look at this article (it is available on line):

https://amga.com/.../09/LuksSwensonPuls ... titude.pdf

The one thing you may be exposed to in single engine airplanes that can give a false elevation of a finger pulse oximeter is carbon monoxide. If your pulse oximeter is working correctly, and you really read 100% at 12000 feet, I would make sure that your cabin air intake is not letting carbon monoxide into the cabin.

[pietromarx]

Interesting. Agreed. First, though, to be clear I only do above 11k for as little time as possible.

I was curious, too, and have tried two different finger pulse oximeters. Both have generally shown 100% at altitude, though I have had readings in the high 90s %. In reading the AMGA piece it shows in Figure 4 that at 4,000 meters (roughly 11,000 feet) the *mean* readings from the different research studies was 88-95%, so it is entirely possible to have normal higher readings. Who knows? I wish I was a better bicyclist, but at age 54 I am good enough to get up a hill and, having grown up in LA, perhaps have lungs and perfusion abilities to keep my SPO2 at reasonable levels despite past (and now future?) smog and lack of O2.

I haven't gone higher than 12,500 in the DA40 (or any unpressurized airplane), though I am sure my SPO2 readings would drop.

On the CO side, I have a monitor / alarm in the plane. Further, I haven't had the signs of CO poisoning (headaches, nausea, etc.). The cabin intake appears fine, as does the muffler shroud, etc.

Your link was broken (404), but maybe this one is right? http://dev.amga.com/wp-content/uploads/ ... titude.pdf

[carym]

You’re right, the link worked when I tried it at work, but does not work from home. However, your link is the correct one. You are doing everything right and if you stay above 90% saturation you should be ok without oxygen. Since these posts are read by many others, I wanted to be sure that other readers are also aware of the potential issues. Since I am more than 15 years older than you my lungs no longer do as well and I start to desaturate (<90%) above about 8 or 9K.

Stay safe!