Descend rate vs weight
 

Hey guys,

Question:Same aircraft, why is the descend rate at const.speed at light weight f the aircraft higher than that of a heavier aircraft??

I have no clue,


Thanks


OD

heeeee...
What about the weight vs lift relationship? Higher weight requires more lift :8

Now slightly deeper...
What is, in the given case, the difference between the lighter and the heavier craft? Yes dude, weight.
To maintain a given airspeed (IAS), you will therefore need more lift for the heavier craft (climbing, level, descending).
More lift? Yes, increase your AOA. And produce more drag. Result is a lower ROC during the ascent, lower airspeed (or MN or FC) in the cruise, and a higher ROD pointing the nose to the Planet.

(much brain storming in this heat ;) )

2 a/c identical type similar atmospheric conditions but with diff weights...
lets assume both plan a descend at idle thrust and say 250 kts.....
they both are like gliders at this point(discount the residual thrust at idle pwr).the heavier one say achieves a rod of 2500fpm. now the lighter has to increase its rod to maintain 250kts. instead if it tries to maintain 2500fpm its speed would wash off to something lower.:8
WHY: because a component of the wt vector cotributes towards the speed............:rolleyes: hope that helps

gearpins has it the right way around.

at a fixed speed and fixed power setting, a lighter aircraft will have a greater rate of descent than a heavier aircraft, due, as he notes, to the weight component along the flightpath contributing to "thrust".

Olendirk,

I agree with gearpin and Scientist versions but in other words my answer is:

Because an aircraft is restricted to maximum speed during descent, the heavier aircraft has to maintain a lower rate of descent than a lighter one, otherwise it would overspeed. Remember, heavier aircraft have a greater momentum and this weight driven momentum will produce a greater speed in in a vertical dive. Therefore, a heavier aircraft has to start its descent earlier than a lighter aircraft because it has to maintain a shallower descent.
In other words, a lighter aircraft can descent later and quicker than a heavier aircraft because it can maintain a greater vertical descent profile without overspeeding.

Hope that answers yours question.

TFCM :ok:

Another way to look at the same problem
Best glide speed, (max distance for min hieght, not to be confused with min ROD, which will normally be min clean) is a function of wieght, that is why gliders carry water ballast. They can go faster for the same hieght lost against distance.
Now, given the aircraft descend at the same speed ( assuming it is above best L/D) then the heavy aircraft is in fact closer to its (higher) best glide speed, so is more efficient.
If you change the descent speed, to say best L/D the lighter A/C will always win.
In the triple 7, ( esp the 300 or er) a heavy A/C can be a bi***h to get down if you get slowed down, 250 is close to best L/D and you need boards to keep any sort of profile.

Lots of recent discussion on this one. Use the search function...

.... gone take a shower, was in need, thanks guys :\