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Thread: How High Is High Enough?

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    Member BARTFRNCS's Avatar
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    Default How High Is High Enough?

    Talking about mountain flying today with several pilots and got to talking about the bare minimum horsepower necessary to cross the Rockies On a GOOD DAY. The magical 180 kept coming up. What say you?

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    How did all the early cubs, pacers, cessna 150s, and cessna 170s make it to the west cost? Big power is nice but if you don't have it start climbing early and do it in the morning.
    DENNY

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    Member Float Pilot's Avatar
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    The CAP likes to use 60 horses per passenger. So a CAP C-172 has 180 horses and usually goes aloft with a 3 person crew.

    I used to have a 160 horse Cessna 150.... I crossed the Rocky's a couple tines in that... But I have also done it in an under-powered J3... It just took a lot longer.
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    This is a site about Alaska, not the Rockies.

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    Member Float Pilot's Avatar
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    BARTFRNCS:

    Type in Wrangels or Mount McKinley to replace Rockies to represent a high altitude mountain range or pass.....so as not to excite the Walters of the world.
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    Then change the density altitude to make it appropriate for ALASKA.

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    Question, I think that the closer you get to the equator the more thick / dense is the atmosphere becomes (therefore Cumulo Nimbus that build to 60k ft.), with less overall atmospheric density in AK, polar region when it heats up is density altitude worse here than closer to the equator?


    Taking off from Bold Strip at Chugiack St Park late this afternoon I was supprised at the take off roll, although there are a lot of rocks to get started over.....

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    BARTFRNCS:

    This summer it was 70-80 degrees for several days up high over the mountains across the bay from Homer. Only 7,500 feet but oddly warm...
    Actually warmer up high rather than down low....
    My 90 horse Cub was struggling for climb power with a flat seaplane prop.. After 5,000 feet I barely had any climb at all. And to make matters worse there was zero wind and a lot of moisture content was displacing the oxygen molecules in the air... So my engine thought it was even higher and I was also making ice....
    Landing on a higher elevation lake worked,,,,,once..... but taking off with two people and gear would not... So we camped out until 4 am...

    Considering how lightweight that 90 horse is,,,, even a 150 horse Super Cub would have had a time getting out.... A C-185 came in with two guys and gear... and they managed to use lots of lake to get out... But that big engine and a constant speed prop let them go home for dinner..

    Years ago I had a 125 and a 135 horse Cubs... They seemed to do anything a 150 horse would do down low... But once you went up over 4,000 ft the 150 and 160 horse Cubs left me behind. Flying from Homer to Kodiak for example over open water....

    You don't always need mountains around to feel the need to go high. Big waves scare me....
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  9. #9

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    Look at what altitude the plane is rated for not what power it has. A big wing light plane will climb better than a heavy short wing plane. I recently spent 22 hours running with a J3 100 hp. He was light and had squared out wings. He could out climb my heavy 160 hp stock wing cub. I could out run and carry a lot more but could not out climb because of load. If you work on doing a lot with a little you will someday be able to do anything with nothing.
    DENNY

  10. #10

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    I've crossed the Rockies twice, both times in Tri-Pacers. First time with a tired 135 hp engine and airplane at gross weight. Second time with a 150 hp in better shape, and a little useful load to spare. Probably depends on exactly what the parameters are and what sort of flying you are willing to do. If you need to get there on a schedule and want to be able to climb and go direct, that is a different set of requirements than if you are willing to wait for a decent day and fly the passes.
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    Quote Originally Posted by ocnfish View Post
    Question, I think that the closer you get to the equator the more thick / dense is the atmosphere becomes (therefore Cumulo Nimbus that build to 60k ft.), with less overall atmospheric density in AK, polar region when it heats up is density altitude worse here than closer to the equator?


    Taking off from Bold Strip at Chugiack St Park late this afternoon I was supprised at the take off roll, although there are a lot of rocks to get started over.....
    It used to be that cooler air was the more dense. I guess that's changed since the government took over the weather . . . . .

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    Hmm...an interesting question actually. The troposphere is a lot thinner in polar regions than at the equator, 20,000 feet versus 60,000 feet. This is well-known and characterized in the climbing world, where a climb of Denali, at merely 20,000 feet, is regarded as equal to or harder than climing some of the Himalayan peaks above 26,000 feet, due to less air at the top of Denali than at the top of those more exotic, more equatorial, peaks.

    But in flight, other than the initial ground school where they mention the shape of the troposphere once, I've never heard it mentioned in a way that relates it to flight characteristics. Alaska certainly has the benefit of colder air, which makes a huge difference. But I wonder if, at the higher altitudes, it makes less difference. Curious question, I really don't know, but both Grizzly and ocnfish may be right...despite disagreeing...
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    Well the key to flying safely in the mountains or for that matter in general, is the religious use of performance charts and doing weight and balance along with a good dose of good judgment and knowing how your individual aircraft performs. You be surprise on how many pilots will never look at the performance charts once they get the written passed. I always tell my students and I do myself, what ever the performance charts tell me what I will get out of the aircraft on a given set of conditions, I will add 10% to that and think about what my out is going to be. You may have to leave fuel on the ground, or some baggage or take one less person or a combo of all three. Then there is the planned route of flight. I flown a lot in the Rockies in Single engine airplanes with and with out turbo charging. I got most things that I was required to do done with a 172 @ 150 hp if it was just me in the airplane, and 3/4 fuel and the outside temps were with in reason, that was the gut min performance I was comfortable with and yea I would use the passes. Then again I have crossed the rockies on number of times in Cessna 150's- pre flight planning, then flying the plan, subject to making changes if the planned flight is not going according to the plan, that is where adding a fudge factor will keep you out of trouble. In IFR conditions well that is a whole new ball of wax, I want turbo charging and if there is any Ice forecasted or reported, then the better part of the decision would be not to fly at all, not always the case when you are flying Freight, then again a Cessna 208 has a bit more horse power and performance over a 172 but with a full load, not much. it takes time to develop the piloting skills and making the judgment calls. And even then some times it will just bite you. The rockies and it goes for Alaska to are full of wrecked aircraft- learn form other pilots misfortune. The accident reports can be very very valuable in learning what not to do. Human nature being what it its, its easier said in a hanger bull session than to put into practice. Keep your steps small and what you can handle and you will be ok. And never stop learning!

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    Remember that there is a difference between air temperature and air pressure, though they are related. Cooler outside air means more oxygen per volume than does warm air. Your airplane's engine loves oxygen. Generally, and I don't mean at excessive, oxygen-starved altitudes, a normally aspirated aircraft engine develops more horsepower at lower temperatures.

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    Here I am again .... I think the altimiter reading, field height above msl and air temperature is the key on take off but I still question high altitude performance at the equator and the north pole, I think that you will still fly higher in say Fiji than a northern location like Barrow, what do you think?

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    I think that you will still fly higher in say Fiji than a northern location like Barrow, what do you think?
    It depends on the quality of the drinks being served in business class.
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    Quote Originally Posted by ocnfish View Post
    Here I am again .... I think the altimiter reading, field height above msl and air temperature is the key on take off but I still question high altitude performance at the equator and the north pole, I think that you will still fly higher in say Fiji than a northern location like Barrow, what do you think?
    The only thing that matters is density altitude where you are. It's going to be lower at the NP than the middle of the pacific(for obvious reasons), so you can climb to a higher pressure altitude, but your density altitude where the airplane reaches it's absolute ceiling will be the same.

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    Quote Originally Posted by Mr. Pid View Post
    This is a site about Alaska, not the Rockies.
    But maybe he thinks some of us Alaskans know how to fly the mountains . . . . .

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    Quote Originally Posted by ocnfish View Post
    Here I am again .... I think the altimiter reading, field height above msl and air temperature is the key on take off but I still question high altitude performance at the equator and the north pole, I think that you will still fly higher in say Fiji than a northern location like Barrow, what do you think?
    Nope. Warm air is expanded air, less oxygen molecules to a given volume of air. You're right, though, about density altitude. It's just that it will be more favorable in cooler temperatures. Try Lake Tahoe, for example, in both summer and winter. On a cold winter day, the old C-150 will depart the airport at South Shore and fly directly to Reno. On a warm summer day, it will have to circle the lake once to get sufficient altitude for the trip. An old Seabee can make it off the water all right in the cooler winter weather, but in the summer it may have to be lifted out and trucked away.

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