Dublinpilot’s is much better – easiest remembered as “clock code”.
You can directly read that stuff from the DG, if installed. Just use it al a unit circle. The cosine of your wind angle gives the crosswind component factor, the sine the headwind component factor.
Airborne Again wrote:
The one-in-60 rule is the most useful one for me as it is applicable in many situations
Second that!
Rule of thumb?
Archie wrote:
Rule of thumb?
depends a bit on arm length…
mh wrote:
depends a bit on arm length…
Which scales back with thumb length 
Ps: we are talking average and normal proportions here
My rule of thumb for performance on non-complex propellers:
- Clean configuration level flight: slow speed to max cruise goes from 2/3*max RPM to max RPM, this give you RPM for any speed in between
- Clean configuration decent: RPM drop is the ROD when you keep speed the same
(2/3 has to do with quadratic relationship between RPM and speed from stall to max cruise)
My rule of thumb for VFR navigation,
- Think in terms of time with 6/12 min being your standard clock tick (distance = speed/10 or distance = 2*speed/10)
- Fly fixed magnetic HDG on your compass each 6/12 min and calculate next HDG correction as 20/10 degrees for each 1 nm off-track
This requires visual or gps fixes for ground track each 6/12 min, after two good fixes it magically converges, so no need to get precise figures for wind, wca, variations or use 1/60 rule while in the air…
Probably, a bad habit for navigation that I need to get rid of during my IMC navigation training: I do good VOR/DME tracking on non-aligned DI…
From here
And whilst there is certainly some unusable formula out there
It is very simple. 1% slope is worth 10% more (or less) runway.
For uphill, it works only for small angles so e.g. a 10% UP gradient won’t work because even powerful GA planes will not climb above 10% so will not taxi up a 10% hill
Peter wrote:
It is very simple. 1% slope is worth 10% more (or less) runway.
Yes but that is the no wind case. How do you weigh that against a mild tailwind? Or a not so mild one? I guess that is the unusable formula @boscomantico was referring to?
For example the DA40NG manual gives a 10% increase of landing distance for every 3 kts tailwind, but it’s not symmetrical – for headwind it’s a 10% decrease for every 20 kts. Those numbers would indeed support favouring a slight tailwind over a downhill landing in the general case or am I missing something?
I will start a new thread when I get a moment.
A 1% runway upslope is worth 6.5% extra runway length needed.
A 1% runway downslope is worth 5.7% less runway needed.
So if you work on 1% slope being worth 7% runway length in both cases, you are doing OK. The two values are anyway equal (calculus of small changes) for small values of slope, and wind.
I need to dig out the tailwind versus downslope equivalence but recall it is something like 7kt and 1%.
It is hard to get this out of POHs because manufacturers are required to use 50% of the wind, etc.
As rule of thumb, tailwind speed ratio to stall speed should not exceed up slope gradient… it’s one vague approximation without getting into limited excess power on takeoff or using breaks on landing
With 60-70kts stall in IFR touring machine, I would say 6-7ktsfor each 1% slope
At -10kts tailwind (2%) one likely hit the limit of tailwind operations and with +5% slope it’s “one way runway”: you always land uphill and takeoff downhill, irrespective of wind
Peter wrote:
A 1% runway upslope is worth 6.5% extra runway length needed.A 1% runway downslope is worth 5.7% less runway needed.
Thanks. That’s quite useful. Are the figures experience-based or derived somehow?
