Vertical Speed Indicator

[juanca]

At last!!!  someone that understood my query!!!!

Thanks OTTOL.

I first reduce power, lets the nose drop a few degrees and then trim pitch.....I try to maintain a constant speed in my desend, lets say...260Knts,  and a constant rate of descent 1500 to 2000 fpm, but the needle in the VS keeps going up or down, and then i have to adjust the trim again and again.

I know this may take practice but, the thing that bugs Me is that I have to keep adjusting the rate of descent with the trim or the throttle all the way down, wich can be very exhausting, and you also have to keep in  mind other factors....

Thank you all for for taking the time for your replies

[Nexus]

[quote]How are you adjusting your pitch trim Juanca?

Contrary to popular public simviation opinion, constant RATE descents are not only possible, they are taught at the most

[juanca]

I do my descents jus t like that...... I first
determine the descent point and then calculate the initial descent rate, and every few thousand feet  look at the ground speed and revise the descent rate!!!!.  
(just like that)

Lets say I'm at fl320  and want to descend at fl180

Determain my descent point and program my rate of descend at 2000fpm....

Adjust power first, pitch second and trim last (ok).....
The needle reads  2000fpm... .

But here is my problem.......The airplane  can only  maintain that vs for as much as 5 seconds..... then the needle tends to go up (or down)  and I'm forced to keep retriming......... or else I will end to high or to low from the deck  (I keep a constant ground speed)

The only explanation I encounter is wind sheer, but I find this improbable because wind is 0.

I'm sorry for my persistance but this topic I consider very important to having  a smooth and happy descent home.

Juanca

[oldhorse]

 HI again
First Let me thank you all for an education In jet aerodynamics.
I Sid I didn`t know about those new finagled Axial Flow Blow Torch,
Spent most of life, working on or round real airplanes.  ;D

I think I pick up ace of spades here (constant ground speed)
The airplane is not flying on the ground, It going through
a moving mass of air constantly changing directions And speed
there is no way to maintain constant ground speed, without A
computer. Use indicated air speed and adj to meet eta

             Rich

[Nexus]

Your goal is not to maintain a constant ground speed, but to use it as a reference for your vertical speed. Like I wrote earlier as you descend the GS will obviously decrease hence the need for the constant revisions of the vertical speed.

Many jet pilots use groundspeed x 5 for descent rate, it's an easy formula to remember, that along with the required altitude loss x 3, creates reliable descent rates and descent points.

[OTTOL]

 HI again
First Let me thank you all for an education In jet aerodynamics.
I Sid I didn`t know about those new finagled Axial Flow Blow Torch,
Spent most of life, working on or round real airplanes.  ;D

            Rich

I used to be a mechanic on CV-440's, DC-4/6 and even worked on one of your beloved A26's one time.
Ergo, I have plenty of "round engine" experience. One thing that I have learned around here is "don't assume anything!"
I fly jets now but don't consider an old  classic like the A26 to be below me. So I think you can drop the blow torch routine. You are absolutely correct.........PITCH TRIM, at it's core duty, controls airspeed BUT to maintain a constant RATE of descent in a modern jet, continuous pitch trim and power adjustments must be made.  
You can control vertical speed solely with power BUT the aircraft will react too slowly and will cycle through the parabola  "porpoising" that I mentioned earlier.
Here's how I do a standard manual descent in the real airplane:
Calculate the Top of Descent (TOD).
There are two basic ways to do it.
a) Use the 3:1 rule.
b)Determine groundspeed, calculate the distance travelled per minute, and finally determine the distance using your desired descent rate.
 IE:360kts groundspeed=6miles/minute(2000fpm@36,000ft)=36,000/2,000=18minutesX6miles =108miles
So.......I would start my descent at 108miles.
Now.....this is the way that I do it in real life.
With the 3:1 rule, I simply take my altitude and multiply by three to come up with a TOD distance. 36,000ft=36x3=108!
Maybe  you can see why THIS method appeals to me! I can hear the naysayers allready! "What if you have a big tailwind or head wind?" I  look at my groundspeed using the GPS or DME and take a WAG(that's wild assed guess for the uninitiated). Or I can use the groundspeed vs. rate method to establish my initial descent and then continue the rest of the descent with the 3:1 method. I simply check my altitude and distance and then adjust my descent rate accordingly. IE: my descent started at 36,000ft and 108 miles. If I get to 25,000 feet and my DME/GPS reads 60 miles instead of the intended 75 miles, I have a strong tailwind and must increase my rate of descent.
NEXUS I realize that you communicate with these guys flying big airplanes but perhaps they're not taking ALL scenarios into account. Yes, generally on a descent, RATE is not all that crucial. There are many scenarios encountered during normal daily routine flying that DO require a constant or SPECIFIED(by ATC) descent rate.
If I fly into New York Metro area, LAX, MIA or Chicago Metro, I  know not to anticipate but EXPECT phrases like " I need at least a 4,000fpm descent rate" from ATC. Also there is a big difference between Autopilot and HandPilot  ;)  . When I flew as a First Officer, deviations from anything other than RATE +/- 100 feet, while hand flying,  resulted in a serious lecture from the Captain. Now, in turn, I expect the same from MY first officers.
It is NOT impossible or even impractical, it just requires practice.
If you are not already using a trimming device on your joytsick JUANCA, I would recommend it. Make small corrections and anticipate the reversal of the VSI needle before it occurs. Even an IVSI is not truly instant.

[oldhorse]

 Mr Ottol
Read Your post 4 times. I believe we are Talking about The same thing,
Just wish I Had The Experience And Background To to have explained
it that Well.
  The blow torch routine was met in fun, leave it there.
I am well aware that the Jet engine has it place in this world AND
for many good reasons, Oil leak for one.
 I want thank you all for allow me to be part of decision I have
learned some things like swept wing is more pitch sensitive
          Rich

      J-3 Cub Still the best,  you get there when you get  there
 if the wind blowing the right way, No Hi Tech just fun  

[OTTOL]

      ..........no harm.  ;)

                     

  J-3 Cub Still the best        

Pitts Special/top of the list

            S2 .........I need the extra seat, so that I can take my friends up and make em' sick!

[Nexus]

I asked them, and they said they rarely do it, I don't know if they are just too lazy to tell me thruth  ;D
Or maybe it's because european airspace differs quite much from american?
It beats me, but it does not  beat those informative posts of yours, thanks  8)

[juanca]

Thanks a lot Ottol and everybody

[OTTOL]

I have found that when I fly to Europe, they tend to just put people into holding when "the works" get stopped up. In the US they tend to just make everybody "fit" into the same airspace. This entails more specified requirements of aircraft and crew. A "flying anvil" descent is just ONE such example.