Climb gradient equation

[Phrogs4ever]

Does anyone know the quick equation for converting climb gradient percentage to rate of climb in fpm? A comprehensive search has turned up plenty of discussion, but no math. It also is not in the rule of thumb section. Thanks.

 

[KnowledgeSeeker]

I just got my flight time "pilot's rules of thumb" book in the mail today...really love the instument flight review one (it's my favorite book).

Anyway in there it states to multiply the climb gradient percentage by the groundspeed...

3.3% climb gradient X 120kt ~ 400fpm

if you want a little book with a ton of info cramed into a pocket size edition... www.flight-time.com

 

[100LL... Again!]

Here is the fastest way to convert, and it is quite accurate.

Take your GROUNDSPEED on climbout. If unsure, estimate slightly FAST.

Convert groundspeed to miles per minute.

60KT = 1 mi/min
90KT = 1.5 mi/min
120KT = 2 mi/min
150KT = 2.5 mi/min

Multiply by the gradient - presto! Required climb rate.

Suppose you are taking off in a Duchess with a climb groundspeed of 90. Departure procedure requires 400 ft per nm.

90 = 1.5 mi/min.

1.5 x 400 = 600 fpm required.

If anyone cares, I can show you how to calculate descent rate for crossing restrictions using the same method. Fast & accurate.



BTW: Using % may work, but most DPs are published with a gradient in ft/nm instead of %.

 

[msw]

I would like to know your method for calculating descent rate to meet a crossing restriction. Maybe others would also. Please tell us. Thanks.

 

[100LL... Again!]

There are a bunch of ways - here's what I use.


Normal descent:

Plan 3:1.

Altitude (in thousands) to lose times 3 = When to start down before fix

Groundspeed (in nm per min) times 300. (333 if you're a stickler) = rate of descent required.


Suppose your clearance is to cross 30 nm before ABC vor at 6000'

Current Altitude= 210

Approx groundspeed in descent= 300kt


21,000 - 6,000 = 15,000 ft to lose

Start down at 15x3 miles prior to the fix - 45 nm



Groundspeed in Kts / 60 = 5. Multiply 5 by 300 (which is nothing more than the ft/nm for a 3:1 descent).

Rate of descent= 1500 fpm.

Sure, it's a bit of math, but it is VERY accurate. You may want to pad the distance (in this case 45 nm) by 5 nm or so to give you some slop.


Now you may ask how you can account for varying groundspeeds on descent. Suppose our carefully calculated descent gs of 300 becomes 330.

This is a 10% increase. Increase descent rate by 10%.

Presto!



If you have need of a steeper descent to avoid ice or if ATC keeps you hanging up there, use a 2:1 descent, and multiply gs by 500.

Same example as above, with the steeper descent:

15K ft to lose x 2 =30. Start down 30 nm out (plus some for slop).

Rate? GS (in nm/min) x 500.

5 nm/min x 500 = 2500 fpm.


I could also show how to do it EXACTLY with a whiz wheel, but who wants to carry one of those around. Not me, I'd never do that.

 

[vixin]

Or you can type it into your FMS and do what it tells ya!! The heck with all that math stuff. HAHA!