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

[Swanee]

SNA learning to trim the goshawk = monkey on crack strapped to a seat with nothing to play with but a ball point pen. Click away monkey, click away.

 

[Recovering LSO]

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!

A T-45 is not a COD.

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?

Keep asking the question until you get an answer you want.? It should be obvious to you why you want to trim into the approach turn and then re-trim the aircraft once wing level - and the whole vertical component of your LV really provides all the answer you need. Off-axis this, on axis that.... Remember your current ride has one engine that sits on the longitudinal axis. You're not producing enough torque to affect this.

At the risk of sounding snarky - I'll again encourage you to just try to get the feel and fly that - don't over think it. I'm giving you that advice with some level of credibility when it comes to teaching guys to fly the ball.

 

[Wingnut172N]

Keep asking the question until you get an answer you want.? It should be obvious to you why you want to trim into the approach turn and then re-trim the aircraft once wing level - and the whole vertical component of your LV really provides all the answer you need. Off-axis this, on axis that.... Remember your current ride has one engine that sits on the longitudinal axis. You're not producing enough torque to affect this.

At the risk of sounding snarky - I'll again encourage you to just try to get the feel and fly that - don't over think it. I'm giving you that advice with some level of credibility when it comes to teaching guys to fly the ball.

I kept asking because you didn't answer the question I asked (or was trying to ask)...the question was why are there two different trim settings for the same AOA, one on downwind and one in the groove? The approach turn doesn't really come into play.

This is more of an Aero E Nerd question, to satisfy my own curiosity, rather than a question about how to fly the ball.

 

[Harrier Dude]

Could it be that you are very slightly lighter and in slightly denser air in the groove than at the 180?

 

[Recovering LSO]

This is more of an Aero E Nerd question, to satisfy my own curiosity, rather than a question about how to fly the ball.

Good luck in your quest...

 

[Swanee]

I kept asking because you didn't answer the question I asked (or was trying to ask)...the question was why are there two different trim settings for the same AOA, one on downwind and one in the groove? The approach turn doesn't really come into play.

This is more of an Aero E Nerd question, to satisfy my own curiosity, rather than a question about how to fly the ball.

I think I remember this from a brief in which an LSO went way to far into the weeds for us:

Have you ever noticed that gusts affect the AoA? You're getting those gusts in the face on the ball, but up the ass on downwind.

That increase of wind in your face means your wings are seeing more air, which means more speed, so less AoA; hence you give it a couple of clicks nose up to increase the AoA and get it back on speed.


Eventually you'll get to a point where trim isn't an issue as you won't have to think about it, you'll just do it.

 

[Recovering LSO]

Have you ever noticed that gusts affect the AoA? You're getting those gusts in the face on the ball, but up the ass on downwind.

That increase of wind in your face means your wings are seeing more air, which means more speed, so less AoA; hence you give it a couple of clicks nose up to increase the AoA and get it back on speed.

may be worth considering the differences between the "downwind" (tailwind) and a headwind once rolled out in the groove.

 

[Wingnut172N]

I think I remember this from a brief in which an LSO went way to far into the weeds for us:

Have you ever noticed that gusts affect the AoA? You're getting those gusts in the face on the ball, but up the ass on downwind.

That increase of wind in your face means your wings are seeing more air, which means more speed, so less AoA; hence you give it a couple of clicks nose up to increase the AoA and get it back on speed.

The jet is moving relative to the air mass though, so while wind affects your ground speed, the airplane should fly into the wind the same as it does away from the wind, no? Sort of like that airplane on a treadmill thing...

 

[Swanee]

He also added in some stuff about higher rates of decent on the ball vs at the 180. I'm not sure though, it was hard to tell as I had zoned out pretty hardcore by then.

 

[Wingnut172N]

...I guess this falls into the category of 'nobody cares'.

I'll go shut up and color

 

[whitesoxnation]

The jet is moving relative to the air mass though, so while wind affects your ground speed, the airplane should fly into the wind the same as it does away from the wind, no? Sort of like that airplane on a treadmill thing...

Are you auditioning for a sim instructor position?

 

[Swanee]

The jet is moving relative to the air mass though, so while wind affects your ground speed, the airplane should fly into the wind the same as it does away from the wind, no? Sort of like that airplane on a treadmill thing...

No, because that air mass is moving against you. You carry that momentum through that air mass, you don't slow down as soon as it meets you. So you go faster.

Think about how some high performance sailboats and windsurfers can sail on apparent wind. When a gust hits you don't slow down, you actually get a speed burst. Then once that burst is gone you're still going a bit faster because now you're drawing that air across your foil. You get more air because you're faster, but because you're faster you get a lot more air. The cycle slowly builds, and it reduces your AoA. In a windsurfer you get to a point where you will be going almost dead down wind with the sail sheeted all the way in and raked back. I've gone 30kts in 15-20 kts of wind.


It's a bit different, but it's also the same type of principal. Only you also have a motor on a jet, and multiple foiled in (mostly) different directions.

 

[Wingnut172N]

Okay, then given enough time, the On-Speed trim would slow the jet back to on speed once it stabilized into the wind, correct? So are we just helping it get there faster with a slower trim setting in the groove?

 

[Swanee]

Okay, then given enough time, the On-Speed trim would slow the jet back to on speed once it stabilized into the wind, correct? So are we just helping it get there faster with a slower trim setting in the groove?

Given enough time yeah. But 15-18 seconds isn't enough for a 15K lb airplane to lose that momentum and seek equilibrium. Have you flown a stupidly long straight in and flown the ball from as far out as possible? Not much trimming there once on speed.


Wait till you they schedule you for FCLPs in July in the middle of the afternoon. It's bumpy and gusty as all get out and no one is every constantly on speed. And everyone gets yelled at in the debrief about how they don't know what they are doing and are going to DQ at the boat if they fly like that.

 

[kmac]

Given enough time yeah. But 15-18 seconds isn't enough for a 15K lb airplane to lose that momentum and seek equilibrium. Have you flown a stupidly long straight in and flown the ball from as far out as possible? Not much trimming there once on speed.

Actually, it wouldn't stabilize there because of the different thrust.