V speeds / service ceiling for a Quicksilver

In the January issue of EAA's Sport Aviation, Robert Rossier says in an article on V speeds that Vx increases about 1% per thousand feet, and that Vy decreases by approximately the same amount.

He adds that at some altitude the two speeds merge and that is the absolute ceiling of the aircraft.

The POH for my Quicksilver Sport 2S says that Vx and Vy are 43 and 45, respectively. Assuming standard conditions and Mr. Rossier's numbers, those speeds would merge at 2300'.

However, the POH says that the service ceiling is 12,500' !

That's only a difference of 10,000'! Can anyone help me to understand where my confusion lies?

Mr Rossier is applying a guesstimated rule of thumb. As you can see, those sorts of generalizations often fail upon contact with the real world. And of course we are assuming that the folks who wrote your operating book did their work correctly.

Now if you need another excuse to go flying, you yourself can flight test to get the numbers at different altitudes. You can draw the graph, apply a little math, and determine the real numbers for your aircraft. Ed Kolano has some great articles on how to do this that have appeared in Sport Aviation and Experimenter. Not hard to do.

Now the service ceiling of an aircraft is supposed to be the altitude where your rate of climb has degraded to 50 fpm. So another excuse to go flying is to climb as high as your aircraft will go.

Frankly, I will be surprised if your aircraft will get to 12,500. But of course the way to find out is to try to go there. Wear warm clothes.

Best of luck,

Wes
N78PS

Wes, thanks. I did wonder how close the approximations could apply to all aircraft. I also find it hard to believe the Quicksilver would get to 12,500'.

I will look for the Kolano articles.

Quote:

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Originally Posted by WLIU

Frankly, I will be surprised if your aircraft will get to 12,500. But of course the way to find out is to try to go there. Wear warm clothes.

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It might.

My Sprint II did in 2005.

I took a picture at altitude.

I could have probably coaxed it to just under 13K but it was climbing about 25 feet a minute at full power according to the EIS and I'd had enough.

I would think your Sport 2S would do it if the Sprint II with floats did it.

Yes, dress warm. I got some strange looks taking off in a winter coat, hats and gloves in August. It was cold at altitude.

GREAT photo Buzz!

Very cool! Literally!

Empirical data beats speculation any day.

Another excuse to go fly on a warm summer day.

Best of luck,

Wes

Quote:

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Originally Posted by martymayes

GREAT photo Buzz!

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Getting my wife to climb out on the compressions struts to take the picture was the hardest part of the flight.

She really hates when I make her do that.

Buzz

The airpark owner told me he had a man that kept his quicksilver here for a few years. This man would take off and circle to 10,000' then shut the engine off and glide down sometimes riding the thermals on the way down. He would then land restart the engine and do it again.

Being right next to class C airspace I am amazed no one ever said a word to him about this practice.

Tony

Quote:

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Originally Posted by Buzz

Getting my wife to climb out on the compressions struts to take the picture was the hardest part of the flight.

She really hates when I make her do that.

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You did inform her there's a whole line of wemen willing to take her place?


(on second thought, maybe you should keep that to yourself.....)

Quote:

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Originally Posted by Buzz

It might.

My Sprint II did in 2005.

I took a picture at altitude.

I could have probably coaxed it to just under 13K but it was climbing about 25 feet a minute at full power according to the EIS and I'd had enough.

I would think your Sport 2S would do it if the Sprint II with floats did it.

Yes, dress warm. I got some strange looks taking off in a winter coat, hats and gloves in August. It was cold at altitude.

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My Sprint/standard 447 got to about 15,300' (by GPS) over Mt. Shasta. Used a smaller main jet, and I did go up the windward side. See http://youtu.be/KiqFy2BFOxc
That's a snowmobile suit and felt-lined boots you see.
Bill