Rules of thumb

FORANE

FORANE

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FORANE
Any good rules of thumb for best economy when deciding whether to climb in a headwind? Or how high to climb for shorter flights?
Generally efficiency improves with altitude, but when flying into a headwind is there a rule of thumb for determining most economical altitude?
How about a rule of thumb for how high to climb for shorter flights?
 
Choosing an altitude for wind is best left to the internet / cellphone / ipad planning tools (or, I guess, pen+paper if you want) as you really need the winds aloft to make the best choice.

How high to climb for shorter flights really depends on your aircraft's performance. Personally, in my EZ, for a 50 mile burger run I only go up to 4500 or so. Long distance, I like to be between 7500 and 12500 depending on winds aloft.
 
When climbing into a head wind ,whatever altitude give the least wind ,that's the altitude to fly at.
 
Generally flying my plane I'll go with the altitude that gives the smoothest ride. Even just flying in the local area, I'll climb til I get smooth air. Usually that'll be between 4-7 thousand. I believe around 7,000 the book says I'll get the best TAS.

Some of it depends on passenger considerations. You might stay low and save a few kts but the trade off might be a bumpy ride. I see it a lot in the TN,NC, GA mountains. I could stay low and have a 30 kt headwind getting rocked by turbulence, or go high with a 50 kt headwind and have smooth air. Sometimes going high might even change that direct headwind into more of a crosswind.

In EMS, this is a consideration I have to take into account on a daily basis. How far to the hospital? How urgent is the patient? Can the crew even provide proper patient care (IV/blood) in this turb? In that case TAS and fuel burn are the least of my worries.
 
This time of year, I fly as high as I need to for comfortable temperatures!:D I'm heading to Destin tomorrow (225 miles) I filed for 6000 3 knot tailwind, I think 4000 was 5 knots, I'll give up 2 knots for lower temps!:D I may end up at 8000 to get above the haze layer. ;)
I don't have a strict rule of thumb in the 182, but trips over 50-60 miles I'll usually climb to 4-5K. Longer trips are based on weather, temps, tops, and winds. Generally the wind isn't all that different between 4-8K, the other factors are usually more influential in my decision. :D
 
Depends on strength of the wind and comfort. In the winter I don't rise much above a thousand feet unless I have a tail wind. In the summer I rise to the lowest altitude where I'm not battered by thermals or cooked like a hairy white omelet.

No rules though. I get enough of those from the FAA.
 
N747JB said:
This time of year, I fly as high as I need to for comfortable temperatures!:D I'm heading to Destin tomorrow (225 miles) I filed for 6000 3 knot tailwind, I think 4000 was 5 knots, I'll give up 2 knots for lower temps!:D I may end up at 8000 to get above the haze layer. ;)
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When I fly CHA to Destin this time of the year, I go high no matter what, 8 or 10 down, 9 or 11 back.

Sometimes that still doesn't keep me out of the top of the cauliflower, but it is still generally smoother and a lot LOT cooler.

What I hate is when Eglin puts you down at 2000 when you're still 30 out. The only time I've had PAX toss cookies is down low hot and bumpy into Destin.
 
I filed for 6000 going down and it was right at the tops of the clouds, so I went to 8000 and it was smooth as silk and cool! :yes: Of course 5 minutes after I got to 8K the clouds disappeared below me. ;)

Bill Jennings said:
When I fly CHA to Destin this time of the year, I go high no matter what, 8 or 10 down, 9 or 11 back.

Sometimes that still doesn't keep me out of the top of the cauliflower, but it is still generally smoother and a lot LOT cooler.

What I hate is when Eglin puts you down at 2000 when you're still 30 out. The only time I've had PAX toss cookies is down low hot and bumpy into Destin.
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I think there are too many variables to come up with a useful rule of thumb for all circumstances. As others have pointed out, differences in wind velocity at different altitudes can make the decision for you. Other considerations include: how fast are you willing to descend? If you stick to a 500 fpm descent (my choice because any faster risks ear block), then in a 120 kt airplane you will require 4 nm for every 1000 ft of descent, which puts constraints on how high it makes sense to go. Another consideration for my airplane is ROP vs LOP. I burn 11-12 gph in cruise WOTROP, but only a little over 8 gph WOTLOP at 7000 MSL and above. I would probably get a smaller but still significant fuel flow improvement at lower altitudes, but because of fuel flow balance issues, I don't feel safe running WOTLOP at low altitudes. So I lean strongly toward higher altitudes and LOP whenever it makes sense to do so -- and my rule of thumb is, everything else being equal, that means flights of 100 nm or more.
 
In Cessnas, Pipers, Ercoupes, we carefully considered altitude for winds, etc. Comfort was a secondary consideration, especially on short ( less than 50 mile) flights.

In the RV, comfort is paramount, simply because it is so effortless to get to a nice, smooth altitude.

Example: Yesterday, going to Brenham, TX, I parked my butt at 11,500' -- not because it was economical, but because it was smooth, above the afternoon buildups, and 60 degrees.

In the Pathfinder, we would have probably stayed low.

So, the Rule of Thumb is different depending on your aircraft. In general, however, comfort trumps economy.
 
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Dave Theisen said:
I was in Destin This weekend. Probably their busiest weekend of the year.
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It was crazy! The airport wasn't as bad as usual for a holiday, I use the old Miracle Strip Aviation and they had plenty of ramp space. Destin Jet seemed more crowded, it's owned by the same guy, so I guess it doesn't matter which one you choose! :D
 
Jay Honeck said:
So, the Rule of Thumb is different depending on your aircraft. In general, however, comfort trumps economy.
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Exactly! I'd prefer a smooth 5 knot headwind to a bumpy 5 knot tailwind! :D
 
Here's my piston descent rules of thumb:
-a 90 KIA descent at 500 FPM works out to be 3 nm/1000'
-a 120 KIA descent at 500 FPM is 4 nm/1000

Fuel Burn rules of thumb:
O-235: 6 gph
O-320: 8 gph
O/IO-360: 10gph
IO-540/550: 25 gph
 
Gas engines burn 12hp per gallon per hour. So If you are burning 10 gph, you are producing 120 hp.

Going west, you will usually encounter a headwind. You will also have more time of day as you change timezones (or even if you don't change timezones, the sun will set later further west).

Going east, you lose time due to earlier sunset, but you get tailwinds.

So it works out about the same.

Have a tailwind? Fly later in the day, it will probably be more intense later on. Climb higher and you will probably have more tailwind.

Have a headwind? Leave early and fly low.

Obviously, not all of these "rules of thumb" are always true. there are many exceptions.
 
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hook_dupin said:
Here's my piston descent rules of thumb:
-a 90 KIA descent at 500 FPM works out to be 3 nm/1000'
-a 120 KIA descent at 500 FPM is 4 nm/1000

Fuel Burn rules of thumb:
O-235: 6 gph
O-320: 8 gph
O/IO-360: 10gph
IO-540/550: 25 gph
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The fuel consumption sure seems to jump going from 4 to 6 cylinders. Seems disproportional. I am not questioning it as I have zero hours behind a 6 cylinder, just seems greater than it should be for the incremental increase in HP.

I was taught a similar rule for descent calculation during transition training in my Lancair. We used 3 miles per 1000 feet descent needed at typical 180 kt cruise and 1000 FPM descent rate.

In another thread I noticed someone mention a takeoff rule of thumb stating get to 70% speed by 50% runway. Sounds like a good example for this thread.
 
hook_dupin said:
Here's my piston descent rules of thumb:
-a 90 KIA descent at 500 FPM works out to be 3 nm/1000'
-a 120 KIA descent at 500 FPM is 4 nm/1000

Fuel Burn rules of thumb:
O-235: 6 gph
O-320: 8 gph
O/IO-360: 10gph
IO-540/550: 25 gph
Click to expand...

25 gph average with an IO540 or 550? I don't think so.
 
FORANE said:
The fuel consumption sure seems to jump going from 4 to 6 cylinders. Seems disproportional. I am not questioning it as I have zero hours behind a 6 cylinder, just seems greater than it should be for the incremental increase in HP.
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That's not the form I heard it in, but it works far better than one might think.

Airplanes, cars, lawnmowers, dirt bikes, chainsaws, tanks, you name it. If it's a four-stroke internal combustion engine and the mixture is correct, it burns a little less than 0.5 lb/hr/HP. At 6 lb per gallon, thats really close to 12 HP / GPH. That's slightly low in that form; it's more like 14 HP / GPH.

Here are a few data points:

Cessna 172N. 160 HP @ 75% power = 120 HP, or 8.5 GPH
Cessna 182Q. 230 HP @ 75% power = 173 HP, or 12.3 GPH.

Check the book numbers. That's spot on.

It just so happens one of those is a 4banger, the other 6.
 
Drop the last number in your groundspeed and that is how many miles you will travel in six minutes.

Push forward and the houses get bigger.
 
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Let my aspen do the work,gives wind speed and direction.
 
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