A mental to figure descent angle

[CBStu]

Say I am 50nm out at 30,000 and I want to be at 2500 (maybe math would be easier using 3000) at 10nm out. Is there an easy do it in my head way to calculate what descent angle would get me there? 

[razo+r]

tan(angle)= height / ground distance (make sure you use the same unit for both distances). If that is easy to do it in your head is up to you.

 

 

 

 

[jackdaw]

@CBStu Use your velocity vector, if you put this at minus 10 degrees you wil lbe decending at a rate of 1000ft per nautical mile.

So if you are 30,000ft to be at 3,000ft at 10 degrees nose down will take 27 miles

[Tusky]

hace 2 horas, CBStu dijo:

Say I am 50nm out at 30,000 and I want to be at 2500 (maybe math would be easier using 3000) at 10nm out. Is there an easy do it in my head way to calculate what descent angle would get me there? 

The rule of thumb I use is:

Distance to = 50nm-10nm = 40nm
Altitude to lose in hundreds of feet = 30000ft-2500ft = 27500ft = 275 hundreds of feet

Descent angle = Altitude to lose in hundreds of feet : distance in nm = 275:40 = abt 7 degrees

 

Edited October 30, 2022 by Tusky

[BuzzU]

Cripes! I hated math class. Auto Shop was way more fun.

I just point the nose down and adjust from there.

[Hulkbust44]

For that specific situation the jet calculates it for you already! You actually have a TOD distance cue to a set waypoint(or TACAN) on the HSI. This is the number in the WYPT data block right below the fuel upon arrival figure. (in NM) With a ~10 degree descent at 250kts it will put you over the point at 2k feet. So if you want to end up 10nm away at 2k just add 10 to the TOD. So if it reads 16, then in 6 miles you will start your descent keeping the figure at 10. The -10 degree pitch angle at 250kts in anecdotal from a couple 2nd hand SMEs and testing within DCS, no hard logic on how it's calculated yet.

In this image the TOD is 5
Edit: TOD = Top Of Descent

Edited October 30, 2022 by Hulkbust44

[TimRobertsen]

16 hours ago, Hulkbust44 said:

For that specific situation the jet calculates it for you already! You actually have a TOD distance cue to a set waypoint(or TACAN) on the HSI. This is the number in the WYPT data block right below the fuel upon arrival figure. (in NM) With a ~10 degree descent at 250kts it will put you over the point at 2k feet. So if you want to end up 10nm away at 2k just add 10 to the TOD. So if it reads 16, then in 6 miles you will start your descent keeping the figure at 10. The -10 degree pitch angle at 250kts in anecdotal from a couple 2nd hand SMEs and testing within DCS, no hard logic on how it's calculated yet.

In this image the TOD is 5
Edit: TOD = Top Of Descent

 

 

Unless ED has changed something: this doesn't work too well with Tacan. The TOD will put you 4k-6k feet above the tacan, the height varies from map to map, I don't know why.

I asked ED about this, but didn't get a clear answar as to why there was this variation.

For Waypoints it works just fine

Keeping any particular speed isn't necessary, this can be done at any speed. But, for fuel-economy, it's best to put the throttle at flight-idle. -10 degrees is sufficient enough to keep the Hornet at a good speed, regardless of how heavy it is loaded.

[=475FG= Dawger]

Descent rate is much easier than angle.

Altitude to lose divided by minutes to go.

In your case, 27500 feet divided by 6 results in 4500 feet per minute. (Assuming 7 miles per minute or 420 knots ground speed)

Edited October 31, 2022 by =475FG= Dawger

[CBStu]

Tusky so far I like your process best. Hulkbust I may like yours but so far I haven't gotten it to work for me. 475FG your 6 comes from 40nm / miles per minute at whatever speed I want hold right? Out of time now so I will work on this more tomorrow.

[pete_auau]

On 10/31/2022 at 5:08 AM, BuzzU said:

Cripes! I hated math class. Auto Shop was way more fun.

I just point the nose down and adjust from there.

yep with you   not  like  your  flying  a jet liner  with passengers  in the  back

[CBStu]

BuzzU, that is exactly what I have been doing. I just thought it would be nice to upgrade my technique a bit.  I have done maybe 10 approaches now and, for me anyway, I like Tusky's technique. Anything involving either airspeed or time just adds one more thing I have to monitor and control.  Thanks to all for sharing their knowledge.

[BuzzU]

I just keep things simple. At the end of the day I get it all done.

I leave the formulas to the smart guys.

I'm a retired truck driver (18 wheeler). All we needed was a map and a thermos of strong coffee.

Learning the Hornet is a stretch for my brain.

I could really hunt for elk and bear though.

[=475FG= Dawger]

On 10/31/2022 at 1:36 PM, CBStu said:

Tusky so far I like your process best. Hulkbust I may like yours but so far I haven't gotten it to work for me. 475FG your 6 comes from 40nm / miles per minute at whatever speed I want hold right? Out of time now so I will work on this more tomorrow.

Its very simple.

Altitude to lose(thousands of feet)/ Minutes to get there = Feet per minute

You will only ever really need a few speeds for conversion

360 Knots = 6 miles per minute

420 = 7

480 = 8

That is about all you would ever really need to use.

You could use 7 miles per minute all the time with great success since there is no real need for much precision anyway.

If you are navigating to your crossing fix, the airplane will tell you how many minutes to go. Just use that instead of doing extra math. Maybe fudge it a little higher if you are staying fast and your crossing restriction is critical.

However, up high you can usually see the airport so just put the velocity vector in the HUD on a point a few miles short of the runway.

Do not unnecessarily complicate procedures.

 

Edited November 2, 2022 by =475FG= Dawger