SummitPost.org

http://www.lvrj.com/news/breaking_news/ ... 80722.html

"Due to higher density altitude, the helicopter 'thinks' it’s higher than it really is, Lorenz said.

'In layman’s terms, if you’re outside and cutting the grass on a normal day you’re going to be fine, but if you’re outside cutting the grass in 110-degree temperatures, you’re not going to perform at your best,' Lorenz said."

That higher density altitude is dangerous stuff.

MoapaPk wrote:http://www.lvrj.com/news/breaking_news/FAA-probes-Mount-Charleston-copter-crash-62480722.html

"Due to higher density altitude, the helicopter 'thinks' it’s higher than it really is, Lorenz said.

'In layman’s terms, if you’re outside and cutting the grass on a normal day you’re going to be fine, but if you’re outside cutting the grass in 110-degree temperatures, you’re not going to perform at your best,' Lorenz said."

That higher density altitude is dangerous stuff.

Hahaha! Brilliant. I love how his 'technical' explanation, which makes no sense, has nothing whatsoever to do with the 'layman' explanation. WtF?

Wouldn't want that dude flying me around...

Sounds like he knows more about cutting grass than flying helicopters ...

When I jump on my Toro lawn-cutting machine in the 110-degree heat, I

have dreams that I'm piloting a helicopter over the Nevada desert !!!

lcarreau wrote:When I jump on my Toro lawn-cutting machine in the 110-degree heat, I

have dreams that I'm piloting a helicopter over the Nevada desert !!!

That lawnmower is dangerous stuff.

MoapaPk wrote:http://www.lvrj.com/news/breaking_news/FAA-probes-Mount-Charleston-copter-crash-62480722.html

"Due to higher density altitude, the helicopter 'thinks' it’s higher than it really is, Lorenz said.

'In layman’s terms, if you’re outside and cutting the grass on a normal day you’re going to be fine, but if you’re outside cutting the grass in 110-degree temperatures, you’re not going to perform at your best,' Lorenz said."

That higher density altitude is dangerous stuff.

Not sure what you meant, but the guy was quoted as saying that warmer temperatures created a higher density altitude, which is correct.

From http://en.wikipedia.org/wiki/Density_altitude:

Density altitude is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation, or, in other words, the height when measured in terms of the density of the air rather than the distance from the ground. "Density Altitude" is the pressure altitude adjusted for non-standard temperature.

Both an increase in temperature and humidity will cause a reduction in air density. Thus, in hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude.

Also:
"higher density altitude" NOT= "higher-density altitude" (whatever that would mean)

Also:
"the helicopter 'thinks' it’s higher than it really is" == "the helicopter performs as if it’s higher than it really is"

I love how his 'technical' explanation, which makes no sense...

Wouldn't warmer temperatures mean a slightly lower air density, thereby replicate higher elevations?

Well, I didn't think that there was any rational interpretation of the verbiage in the paper, but maybe DH has one.

I think it would have been simpler if he had said: the density of air normally drops with altitude; when the air is warmer than usual at a given altitude, the density is even lower, so the helicopter has less lift than the operator expects... if he is so stupid that he doesn't adjust for that fact, or his helicopter somehow doesn't have an outside T indicator. (And the lower viscosity probably figures in too.)

However, the excuse is still pretty lame. The daytime T swing is much greater than the 12F-above-seasonal-norm we had on that day -- which was also a fairly still day by Charleston standards. If anything, we weren't getting the normal adiabatic exchange, which would be much more of a problem. If you are flying at 11500' over a 11900' peak on a clear day, you should be using visual cues, and you sure shouldn't be cutting the hairy edge depending on 2% more lift.

I've seen helicopters cutting it close, flying right over the 11000' connecting ridge (near Lee Peak), all summer long, on days with approximately the same T. This is a fairly new phenomenon, and maybe the pilots will be a bit less obnoxious now.

It isn't that hard to temperature-compensate a barometric altimeter.

Baarb wrote:Wouldn't warmer temperatures mean a slightly lower air density, thereby replicate higher elevations?

Yes.

The quote was about density altitude, which is a different concept than density.

MoapaPk wrote:you sure shouldn't be cutting the hairy edge depending on 2% more lift.

Exactly. I only explained the quote because I thought you might have misread it. The "density altitude" quote was not from the pilot, by the way.

Like you wrote, these pilots are crazy if they are flying so close that their success or failure can be determined by a 15-degree difference in air temperature. I don't know how much 15F degrees makes in aircraft performance due to the lower air pressure, but it's likely trivial.

MoapaPk wrote:If you are flying at 11500' over a 11900' peak. . . .

The crashes in the upper parts of those mountains have always seemed so absurd to me. Even in fog at night, what is so difficult?

Charleston Peak is the highest point for 135 miles in the closest direction. If you're flying over that range, just fly at a minimum of 13000 feet, and you have nothing to worry about. In 1903, there might have been issues with attaining that elevation, but anything built in the last 70 years shouldn't have a problem and shouldn't need to be aimed through a pass, 1000 feet below the summit, day or night.

And if your plane can't get to 13000 feet, don't try to fly over the Spring Mountains. Fly around them. Especially if it's nighttime!

What the hell are you guys talking about ???

Do people have "density" levels ?

If I were performing at an elevation above 13,000 ft, I'd have TROUBLE keeping it up, too !!!

!!!!!!!

I went by the crash today; I really didn't expect to see it, based on the info in the paper. It's on the NE side, with the impact site about 11825' +/- 8' -- also much higher than I thought from the paper's claim that the pilot was flying at 11500'. The tail broke off and ended up about 200' lower (vertical) down the mountain.

Kudos to the pilot -- nobody died, which seems amazing. They were flying late in the day, but it was still light enough to see the mountain.

I do wonder, though, what flight plans are being filed with the FAA. This summer on two occasions, I saw helicopters flying close to the NE side of the mountain, at about the same elevation, almost the same place. Given the highly variable winds on those slopes, it doesn't seem like a good idea.

I chatted with a local heli expert. That model has a theoretical ceiling of 14000' under good conditions, but with the reported load, would start to be uncontrollable at 11000'. The pilot will have some splainin' to do.