Descent Tables for Propliners

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ste55
Airman
Posts: 15
Joined: 04 Nov 2017, 11:53

Descent Tables for Propliners

Post by ste55 »

Greetings again.

I've created several Descent Tables for different descent rates. It allows you to quickly determine the distance or time when to start the descent to your destination.
The tables are calculated for a descent to 3000 feet MSL. Normaly I add around 10nm to 20nm to the numbers for descelerating and to be on altidude 10nm short of the airfield.
Please note that these tables do not take any winds into account.

The picture below for example shows the table for 500fpm (Time in minutes).
The PDF file contains descent tables from 500fpm to 1000 fpm.

Image

Download: Descent_Tables.pdf

Kind Regards

P*Funk
Airman
Posts: 34
Joined: 18 May 2017, 06:34

Re: Descent Tables for Propliners

Post by P*Funk »

Are these just pure time/speed/distance tables, meaning if I intended to descend from say 15000 to only 6000 I could just read from 12000 to get the right number?

ste55
Airman
Posts: 15
Joined: 04 Nov 2017, 11:53

Re: Descent Tables for Propliners

Post by ste55 »

Hi P*Funk, I've never thought of doing this kind of calculation, but you are right.
If you want to lose 9000 feet of altitude, you look at the 12000 feet row and get the right number. (Just add 3000 feet)

The formula is:

Time = Altitude Loss / descent rate
Distance = groundspeed / 60 * Time

During my flights I discovered that these numbers are just aproximate distances. If the groundspeed is changing due to wind change or because the plane is accelerating, those numbers are not accurate.
BUT for an average this table is quite handy. On my flights I was just too lazy to calculate everything everytime again.

One tip, I noticed a speed increase of about 10 to 20 knots during my descents. Just add this to your groundspeed and look at the corresponding column before you start your descent.

Cheers

flapman
Staff Sergeant
Posts: 457
Joined: 10 Oct 2013, 21:35

Re: Descent Tables for Propliners

Post by flapman »

May be helpful for new propliner pilots,
Aerial navigation is 4D not 2D. Consequently DME is always irrelevant to ToD planning whether or not we have it in our cockpit today. Some real world procedures may appear to disagree with that statement, but I will explain why they don't below. ToD always depends on the weather today, never where we are. If we must lose 10,000 feet to reach our MSA before the IAF, (in a piston engined propliner), since we always plan to descend at minus 500 VSI (see later), we always descend 20 minutes before the IAF. We don't need a graph, or a diagram, or a calculator!

Because we always PLAN to descend at minus 500 VSI, we descend 20 minutes before the IAF, if we are cruising 10,000 feet above the MSA for that IAF,

If our cruising velocity is 180 KTAS and there is a 0 KTS headwind we must descend at 60 DME today.

If our cruising velocity is 180 KTAS and there is a 60 KTS headwind we must descend at 40 DME today.

If our cruising velocity is 180 KTAS and there is a 60 KTS tailwind we must descend at 80 DME today.

DME has no role to play at all. It does not influence *when* we must descend. GPS also has no role to play at all. The gauge we use to plan and execute descent is called a *clock*. Aerial navigation is 4D not 2D. That is not just a meaningless phrase, it means that aerial navigation is performed using a clock and a flight plan both carefully calibrated and updated using a concept called 'minutes' with an estimate for the (every) next waypoint in minutes, not some other useless random gauge that does not display minutes.

If we need to lose 10,000 feet we descend 20 minutes before the IAF *every* day using the *clock* and our DME is different and irrelevant every day, because the wind and weather are different every day. 2D navigation techniques that we may have learned in powered terrestrial vehicles, involving consideration of place and distance and speed are utterly useless in aeroplanes. Aerial navigation must be 4D and is based instead on TIME.
From In response to "Planning descent with no DME"

BTW ste55, nice job on the checklist 8)

ste55
Airman
Posts: 15
Joined: 04 Nov 2017, 11:53

Re: Descent Tables for Propliners

Post by ste55 »

Hi flapman, thanks for your reply.
Now I had the time to fully read the propliner tutorials. Everything makes sense now.
Planning time of descent (TOD) could not be simpler. The simplest solution is the only solution that is always correct and never dangerous.
From the FSAviator Propliner Tutorial. (http://www.calclassic.com/propliner_tutorial.htm)

I used only the clock to determine the time of descent on my last two flights. It worked and yes, it IS easy and safe. It seems that there's no need for those distance tables at all :? .

Thanks for those tips.

Kind regards

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