Decent rate question

[LV-ARG]

Anybody tried this on a flight sim? 10k, 140kias, chop the power and start the timer. Note the time to descend spiraling at 50º and compare it to the non turning descent time.

My results: From 10,000 down to 1,000 it took 5:02 - wings level descent - and 4:06 - 50º bank descending spiral-.

Airplane was loaded at 1.5 - 1.7G's during the spiral

 

[shdw]

Anybody tried this on a flight sim? 10k, 140kias, chop the power and start the timer. Note the time to descend spiraling at 50º and compare it to the non turning descent time.

My results: From 10,000 down to 1,000 it took 5:02 - wings level descent - and 4:06 - 50º bank descending spiral-.

Airplane was loaded at 1.5 - 1.7G's during the spiral

:clap: The math is right, unfortunately it isn't easily understood. Anyone else could repeat this experiment, in any 'typical' aircraft with similar results.

 

[ryan1234]

One of the things I've noticed from doing the "experiment" in a pragmatic sense from 10k is that in real life - there's gyroscopic precession.. that you want to leave in for the drag during the descent - this makes the rate of descent faster according to the VSI - the speed is at the bottomish of the yellow arc.

Another pragmatic question that seems to play out is the higher the G load (in a turn) the less the convective lift effects of the weather... is this safe to assume?

Chopping the power in a recip at 10k down to pattern altitude is generally not an accepted practice if you value the life of your engine.... turbines are different. Usually you want to leave in at least 15'' for a O-470 ... with a slow transition to around ~300 on the CHT on the way down.

 

[z987k]

Chopping the power in a recip at 10k down to pattern altitude is generally not an accepted practice if you value the life of your engine.... turbines are different. Usually you want to leave in at least 15'' for a O-470 ... with a slow transition to around ~300 on the CHT on the way down.

There is actually no evidence to support this claim.

BTW, don't run oversquare either, it kills baby kittens.

 

[shdw]

this makes the rate of descent faster according to the VSI

While I'm unsure of the truth behind your post, I don't see the relevance. Notice:

My results: From 10,000 down to 1,000 it took 5:02 - wings level descent - and 4:06 - 50º bank descending spiral

The poster gave results in time, not instrument readouts. It would be more difficult to find errors in this method of data collection. Multiple experiments to get more data would give a more accurate answer for the difference between 50 bank and wings level in this aircraft. However, similar experiments can be done in any aircraft.

Also, we can easily find the descent rate for comparison:

Climb/Descent rate = feet changed / time (in minutes)

In a 50 degree descent rate is: -9,000 feet / 4.1 minutes = -2,195 FPM

At wings level descent rate is: -9,000 feet / 5 minutes = -1,800 FPM

 

[z987k]

Those are very slow numbers compared to what I see real world. I don't know how much I'd trust the physics of MSFS.
I think we can all agree a turning descent is going to give you a greater rate of descent all else equal then a level one.

 

[ryan1234]

While I'm unsure of the truth behind your post, I don't see the relevance. Notice:



The poster gave results in time, not instrument readouts. It would be more difficult to find errors in this method of data collection. Multiple experiments to get more data would give a more accurate answer for the difference between 50 bank and wings level in this aircraft. However, similar experiments can be done in any aircraft.

Also, we can easily find the descent rate for comparison:

Climb/Descent rate = feet changed / time (in minutes)

In a 50 degree descent rate is: -9,000 feet / 4.1 minutes = -2,195 FPM

At wings level descent rate is: -9,000 feet / 5 minutes = -1,800 FPM

The poster gave the results based in MS sim - I'm not sure how much you could value the information.

My point before wasn't contesting anything.... only mentioning that from doing a job that involved descending from 10,000+ feet everyday, multiple times a day... there are several real-time, non-MS fight sim variables present every time....

Either way I don't know of anyone that flies jumpers that puts the flaps down and pushes over the Vfe (maybe I'm wrong - maybe they'll speak up) in the descent.

Anyways, actually flying the profiles versus sitting in a room crunching numbers can yield different results for any number of reasons... the question of being 'unsure' of the truth behind anything actually done in a real airplane is largely unfounded.

@z987k

There are a lot of DZs that replace cylinders due to shock cooling all of the time. I'm not say that pulling the power to idle once or twice in a descent - but it can, over time, contribute to cylinder cracks depending on the rate of cooling. I've physically seen cylinders that this is happened to.

 

[tgrayson]

The poster gave the results based in MS sim - I'm not sure how much you could value the information.

The value of the results can't be expected to be too close to reality, but the notion that the flight model expects that there SHOULD be a difference is worth noting. I calculate that the increase in descent rate for a c172 in a 45 degree turn is in the neighborhood of 100 fpm and that's using numerous approximations. Unless the air is very calm, it might be hard to notice a consistent difference.

 

[z987k]

The poster gave the results based in MS sim - I'm not sure how much you could value the information.

My point before wasn't contesting anything.... only mentioning that from doing a job that involved descending from 10,000+ feet everyday, multiple times a day... there are several real-time, non-MS fight sim variables present every time....

Either way I don't know of anyone that flies jumpers that puts the flaps down and pushes over the Vfe (maybe I'm wrong - maybe they'll speak up) in the descent.

Anyways, actually flying the profiles versus sitting in a room crunching numbers can yield different results for any number of reasons... the question of being 'unsure' of the truth behind anything actually done in a real airplane is largely unfounded.

@z987k

There are a lot of DZs that replace cylinders due to shock cooling all of the time. I'm not say that pulling the power to idle once or twice in a descent - but it can, over time, contribute to cylinder cracks depending on the rate of cooling. I've physically seen cylinders that this is happened to.

There's also pilots that will fly full power up to altitude and run peak egt the whole time. CHT's at 500* or so, then below 100 in 10 seconds I can see being a problem... but 400 down to 150 over the course of 2 minutes should not be. With the cowl flaps closed and the ever so slightest amount of power in, that's what my CHT's do. 400 to 150 over 2ish mins. A lot of people call that shock cooling. It is not. We got 2100TBO last time on the O-470, much much better than most people that baby their engines.