Rule of Thumb

[Bryan Wood]

I'm currently reading Sparky Imeson's "Mountain Flying Bible" and just can't get enough of his little tricks or rules of thumb to quickly figure out information that is very useful. I've been playing around with this one quite a bit and even used it to make up spreadsheets in Excel for flight planning. His rule of thumb that I'm refering to is to quickly calculate how long a flight will take without all of the steps used the way we are taught in groundschool. While this is crude and just a ballpark I have found it to work out within a minute or so on all the examples that I've tried as compared to figuring the old tried and true method. No, it doesn't account for wind, but since all the possabilities are charted in Excel different charts can quickly make comparisons. Here is an example, which you can see works out within a minute using both methods.

Assume a 300nm flight with a cruise speed of 165 knots with a cruise altitude of 7500'. Using a traditional method to get an approximation of time enroute and knowing the typical climb performance of my RV it would take 9 minutes to reach 7500' at a indicated airspeed of 105 knots and would cover 16nm's. With 284 remaining at 165 knots it would take 1 hour and 44 minutes to cover the distance for a total of 1 hour and 53 minutes.

Using Sparky's method it would go like this. Take the total distance of 300nm and the cruise speed of 165 knots for a enroute time of 1 hour and 49 minutes. Now take the cruise altitude and divide it by 2000 (2000 for a constant speed RV, use 1500 for a fixed prop RV, and 1000 for a typical spam can) and add the answer to the 1:49. 7500/2000=3.75 This results in 1 hour and 52.75 minutes compared to the above example of 1 hr. and 53 minutes. Pretty neat isn't it?

Here are a couple of more of his little tricks, only without the explanation. They are really self evident, but also neat. If any of you know any useful little tricks like this please share them. My mind is starving for more of these neat little bits of experience.

More examples:

Do not climb more than 10 minutes for each hour of en route flight time.

In the Northern Hemisphere if you stand with your back to the wind the low pressure will be to your left, and the better weather will be to your right.

Drop the last digit of your groundspeed and you will fly that many miles in 6 minutes.

Regards,

[alpinelakespilot2000]

Your very right, Bryan. I liked so many of his rules of thumb that I just photocopied the pages in which he lists them together. That set of 2-3 pages then goes in my kneeboard pocket all the time, just so that I remember to review them periodically. Probably more common sense in that book than any flying book I've read.

[Rick6a]

Originally Posted by Bryan Wood

I'm currently reading Sparky Imeson's "Mountain Flying Bible" and just can't get enough of his little tricks or rules of thumb.............. .........If any of you know any useful little tricks like this please share them.......Regards,

Brian,

You shilled me. Just ordered a copy from Amazon. I like anything that cuts to the chase without overloading my one good brain cell with arcane minutia.

In the unlikely case this tip has not been covered in Sparky's book, a quick way to mentally convert knots to MPH is the 10% and a half trick. Example:

Airspeed indicates 160 knots. 10% of 160 is 16. Half of 16 is 8. 16+8=24. 160 knots plus 24 = 184MPH.

The exact conversion for those demanding individuals who for whatever reasons insist upon Swiss accuracy, the precise conversion is 160 knots = 184.124 711 684 mile/hour (mph).

P.S. Thanks to your helpful post, my wallet is a bit lighter today and as a bonus....I'll never think of the wind at my back in quite the same way.

Rick Galati RV-6A "Darla"

[uhhuh35]

Hello everyone, longtime lurker, first time poster.
The book sounds really interesting, could someone elaborate on this for me?:
"Do not climb more than 10 minutes for each hour of en route flight time."
I'm still a student pilot and should be finishing my PPL this year or next.
I remember my grandfather telling me the same story about having the wind to your back with low pressure to your left. He flew B-24's and B-50's and was slated to fly P-80's but, if you believe his story, was too big to fit in the cockpit!
Thanks in advance.
Robert Jones,
Waldorf, MD
-9A Tail Finished

[RJDickensheets]

That one got me thinking also. Rules of thumb are nifty but when planning your flight and flying your plan there are just too many variables to stick to a certain rule.

Altitude selection is an art form with fuel, wind, terrain, oxygen, turbulence, clouds, temp, airspace, performance and probably other factors involved. And an altitude that is good one minute, may be awful the next.

Flying is an endless series of small adjustments.

rd

[osxuser]

How very true. I fly on a competitive college flying team, and one of my main events is the Navigation event. This is where we make a dead reckoning flight plan, then fly it based on visual checkpoints on the ground. All naviagtion equipment is covered, and you are disqualified if any covers are removed.

When I would do a flight plan, I would simply plan for 15kts less than my normal cruise speed. This allowed me to not bother taking wind into account, and simply throttle up and throttle back as necessary to maintain planned speed. Scoring is based of how many seconds off your time you are at your intended checkpoint, and by how close your fuel estimate is. The winners of the event are usually within 10seconds on all of their legs, and within 30sec of their total time, with their fuel right on the money. It's all about the small adjustments