This whole "On Speed" thing....how does it work?

[Wingnut172N]

Alright, I've never been accused of being the sharpest knife in the drawer, but this has me somewhat confused...

If I am flying downwind in a Clown Jet, configured gear down, flaps full, boards out and trimmed on-speed (which is a big assumption for my SNA self, I realize)...and I roll into my approach turn without touching the trim, shouldn't I be on speed once again when I roll out of the approach turn on the ball?

What I'm seeing is that the jet seems to need a few clicks of nose-up trim on final to keep from going fast, even though it was trimmed on-speed on the downwind. My question is why this happens? Shouldn't the jet seek the same AOA it was trimmed for regardless of whether I am climbing, descending, flying upwind, downwind etc...

Yes, Scoober, I realize I'm completely geeking out...

 

[Recovering LSO]

"Don't think Meat, just pitch...."

As soon as you roll into a 27-30 degree AOB turn you're going to see an approximate increase of 10-12 KIAS to maintain on speed due to decrease in vertical component of lift vector. When you roll out of turn you need to reduce power to work off excess airspeed and lift vector gets "more vertical" - you know this as your "wings level transition". You had to adjust trim into the turn because of change in LV/increase of IAS. It makes sense then that you would need to re-trim out of the turn because of decrease in IAS / adjustment of LV. Finally, and this may be completely out in left field but it also may be worth considering the differences between the "downwind" (tailwind) and a headwind once rolled out in the groove. May not have as much of a factor and the repositioning of the LV, but probably still has some small impact.

"Don't think Meat, just pitch"....

 

[MasterBates]

RLSO is correct.

Less thinking. More flying. Keep the happy donut happy.



Sent from a van down by the river via Tapatalk

 

[wlawr005]

I've found on-speed to be a magical place between fast and slow that appears transitory and quite elusive.

 

[Wingnut172N]

RLSO, at the risk of sounding like an academic nerd....if I don't trim into the approach turn though, shouldn't I come out on speed again when I roll out? I understand I have to accelerate in the turn, then decel during my wings level transition, but shouldn't the jet seek on speed again on final if I don't trim after it's on speed on downwind?

 

[JD81]

RLSO, at the risk of sounding like an academic nerd....if I don't trim into the approach turn though, shouldn't I come out on speed again when I roll out? I understand I have to accelerate in the turn, then decel during my wings level transition, but shouldn't the jet seek on speed again on final if I don't trim after it's on speed on downwind?

Yes, but you are only trimmed for that airspeed at which you entered the approach turn. You are trimmed for that specific AOA, if that AOA is lower, hence you are faster, your trim will not stabilize the airplane until you are back at the previous on speed AOA.

Think less, just feel it. Best advice I ever got was always finding the neutral power setting quickly. Once I was able to do that and do it quickly, the rest just fell into place and I stopped getting frustrated and started having fun because I finally figured out how to be more precise, rather than just sawing logs on the quadrant and throwing the ball all over the place.

 

[BigBadBoJenkins]

It's really frustrating on a day with a lot of bumpy air. It seems like I can't ever get it on speed because of the turbulence. I fluctuate between fast or slow, so I just try to average it out around the approach turn.

 

[kmac]

"Think less" is a cop out answer to the question. The question is, why would there be two different trim settings for the same AOA? I believe the actual answer lies somewhere in the realm of trim vs power setting. In other words, trim isn't only relative to the airspeed but is relative to the engine/thrust as well. It's obvious in the COD because we have big P-factor forces, but I bet something similar exists even for a turbofan. Rolling into the groove, less power is required for the same airspeed which would necessitate a nose up trim to counteract the reduced force from the engine. The airspeed would be the same for the on-speed as it would be on downwind, but the power setting would be less.

Maybe I'm in left-field... thoughts?

 

[MasterBates]

In the aero nerd ballpark.

Sent from a van down by the river via Tapatalk

 

[kmac]

Ok, I'll try one better. The change in thrust off-axis with the center of gravity causes a larger/smaller moment, requiring an equal/opposite counteraction by the horizontal stab. Thus, the trim required to set this new horizontal stab position must change.

Bam!

 

[Wingnut172N]

Kmac...that's more what I was looking for, and it that makes sense, now that you mention it. I would assume then that such a change would be much larger in something like a T-2 where the thrust line is farther from the axis of the CG? Could anybody confirm that?

 

[MIDNJAC]

Alls I know is that I trim 8.1 or 3252 downwind, and when I am in the approach turn, I either need to increase aft stick pressure to maintain "on-speed" or I need to trim a click or two of nose up trim. I like to just hold the extra pressure in the app turn so that when I roll out, I'm still trimmed on speed hands off.

Somewhat related to this topic of conversation, it is really easy to influence the stick and your speed as you chase glideslope. Even without noticing it. When you are perfectly trimmed out, you will not only not really need to do this, but you will also notice it when you do it.

 

[EODDave]

Auto. Works every time.

 

[MIDNJAC]

Auto. Works every time.

Lucky (sim Napoleon Dynamite)

 

[BigBadBoJenkins]

"Think less" is a cop out answer to the question. The question is, why would there be two different trim settings for the same AOA? I believe the actual answer lies somewhere in the realm of trim vs power setting. In other words, trim isn't only relative to the airspeed but is relative to the engine/thrust as well. It's obvious in the COD because we have big P-factor forces, but I bet something similar exists even for a turbofan. Rolling into the groove, less power is required for the same airspeed which would necessitate a nose up trim to counteract the reduced force from the engine. The airspeed would be the same for the on-speed as it would be on downwind, but the power setting would be less.

Maybe I'm in left-field... thoughts?

I do notice that fluctuating power can cause fluctuating AOA, as if the jet sits up a little bit when you're higher up on the power because of the thrust. That's how I imagine it anyway, not being an engineering type.