Using "throttle for GS and stick for AOA" when landing

[LJQCN101]

While preparing for the upcoming module, I found this in the NATOPS manual describing landing and takeoff characteristics of F18 FCS:

 

In the takeoff and land modes, AOA and pitch rate feedbacks are used to augment inherent airframe pitch damping and stability. The computer nulls the difference between the trim AOA and actual AOA.

 

The FCS incorporates full-time AOA feedback in the flaps HALF or FULL mode. For this reason, longitudinal trim is required when changing AOA and/or airspeed. When the aircraft is trimmed to an AOA, it tends to maintain that AOA and some longitudinal stick force or trim is required to fly at another AOA.

 

So the FCS actually encourages what we known as "throttle for GS and stick for AOA". An increase in throttle would result in a decrease in AOA, which would make the aircraft pull up by itself, so that AOA is maintained.

 

This would make carrier landing a lot easier than Su-33 IMO.

[Emmy]

Pitch For Airspeed

Power For Altitude (Glide Slope)

http://www.boldmethod.com/learn-to-fly/navigation/pitch-and-power-on-a-glideslope/

[probad]

uhhhh i think @op has the right understanding of the physics, hes just describing it from an unorthodox perspective

 

"throttle for GS and stick for AOA" is definitely an invitation for some big misunderstandings

 

anyways really not sure what this thread is meant to contribute, landing the hornet is a thread already done to death several times over.

Edited January 22, 2018 by probad

[LJQCN101]

uhhhh i think @op has the right understanding of the physics, hes just describing it from an unorthodox perspective

 

"throttle for GS and stick for AOA" is definitely an invitation for some big misunderstandings

 

anyways really not sure what this thread is meant to contribute, landing the hornet is a thread already done to death several times over.

 

Just some findings from FCS perspective which I think it's worth to expand when Wags mentioned about PA mode in the mini-updates, in case people find out that FCS is fighting their input;)

[pr1malr8ge]

I've argued this point and well so has the rest of the piloting world and on this forum.

 

So I've generally always used Pitch for air speed and throttle for "Glide Scope" in my real life flying experience. I have not been fortunate enough to fly PIC of turbine aircraft in the real world. You will notice that a lot of pilots who argue pitch for altitude and throttle for speed fly rather large turbine aircraft. I have deduced that those arguing for P/Alt T/S is the worry about delayed spool-up. Which does make sense. In Piston engines trottle response is pretty close to instantaneous vs Turbines that can and do have rather long response times at/near idle.

 

But yet I always seem to come across things like this and pilots of large turbine aircraft that say P-airspeed T-Glide scope. My cousin who flew f15cs and now flys a360s stated he uses Pitch for airspeed and throttle for glide scope..

 

While I cannot specifically state this as "Fact" as I've never flown large aircraft I personally think that those stating Pitch for altitude and Throttle for airspeed due to turbine spool up might not have the best stick and rudder abilities or simply just going by their mandated training from their employer. I feel that if you're needing instantaneous throttle response to stay on glide scope in VMC then they are behind on the aircraft.

How ever. I also can understand why airlines and aircraft with high T/O&L speeds would want the Throttle for speed and Pitch for altitude as its primary basis due to the potential for windshere where throttle response is an absolute must to avoid a sink rate that will result in structural damage or catotropic/death..

 

just my humble opinion.

Edited January 22, 2018 by pr1malr8ge

[Thump]

I've argued this point and well so has the rest of the piloting world and on this forum.

 

So I've generally always used Pitch for air speed and throttle for "Glide Scope" in my real life flying experience. I have not been fortunate enough to fly PIC of turbine aircraft in the real world. You will notice that a lot of pilots who argue pitch for altitude and throttle for speed fly rather large turbine aircraft. I have deduced that those arguing for P/Alt T/S is the worry about delayed spool-up. Which does make sense. In Piston engines trottle response is pretty close to instantaneous vs Turbines that can and do have rather long response times at/near idle.

 

But yet I always seem to come across things like this and pilots of large turbine aircraft that say P-airspeed T-Glide scope. My cousin who flew f15cs and now flys a360s stated he uses Pitch for airspeed and throttle for glide scope..

 

While I cannot specifically state this as "Fact" as I've never flown large aircraft I personally think that those stating Pitch for altitude and Throttle for airspeed due to turbine spool up might not have the best stick and rudder abilities or simply just going by their mandated training from their employer. I feel that if you're needing instantaneous throttle response to stay on glide scope in VMC then they are behind on the aircraft.

How ever. I also can understand why airlines and aircraft with high T/O&L speeds would want the Throttle for speed and Pitch for altitude as its primary basis due to the potential for windshere where throttle response is an absolute must to avoid a sink rate that will result in structural damage or catotropic/death..

 

just my humble opinion.

 

 

It's a question of where on the power curve your aircraft lands. It is not a matter of preference but of physics and how the aircraft performs when configured.

[Sierra99]

An increase in throttle would result in a decrease in AOA, which would make the aircraft pull up by itself, so that AOA is maintained.

 

An increase in throttle will reduce DESCENT RATE...if done properly once you have your AOAset you can control descent rate using throttles.

[GGTharos]

Throttle for descent rate, stick for speed. The aircraft will maintain the AoA of you do things right and within limits.

 

You can do this with any of the PFM aircraft, it's known as the region of reverse command and typically presents itself in low speed, moderate AoA situations.

[Guest]

All aircrafts are flown that way. From day 1 in flight school you'll be tought to change altitude with power and change airspeed with pitch.

 

It is inherent to safety procedures.

[bbrz]

Regardless of which method you are using, one doesn't work without the other. You simply can't fly the GS by only adjusting pitch or power if it's about gross changes.

 

Every power/speed change requires a corresponding pitch change.

 

The important thing is that if you e.g. grossly drop below the glideslope, you have to increase power first to get back to the GS instead of pulling back on the stick/yoke.

 

Spool up time in the approach power range isn't a factor in most jets.

Edited January 23, 2018 by bbrz

[David OC]

A great thread about landing the F18 and more with a real F18 pilot.

 

Setting realistic expectations for the Hornet

 

Thanks for all the great info neofightr, very interesting.

 

Very much looking forward to carrier ops in the F-14 (not a hornet fan, sry). I have also read that the 'standard' stick for AOA and power for rate doesn't work for the Tomcat and you have to use a combination of the two for any results, which makes for an interesting juggling act in FSX at least http://www.thedrive.com/the-war-zone/9599/a-tomcat-pilots-early-struggles-to-tame-the-mighty-f-14 OT I know - sry.

 

Regarding the island 'burble' on the carrier, I wouldn't hold your breath for any turb modelling as currently you can literally fly up the exhaust pipes of a F-15 etc with no turb effects whatsoever! But hey fingers crossed right.

 

The tomcat was considered harder to land on the carrier because it was an older design and the only other jet that was harder than that was the A-6/E/A6 an even older design.

 

For the tomcat it's engines had a longer spool up time making it much harder to control the glideslope with the throttle but let me make it clear, using the stick to nudge a descent or climb is not using the stick to control glideslope. There is no such thing as juggling the stick and thottle to remain on glideslope, doing so would lead to hook slaps and bolters almost every time. There was no exception for the tomcat, especially the tomcat with it's long tail and low clearance.

 

In the hornet I typically nudged the stick forward to start my descent once I started my turn from the abeam point (at the 180). But that was it after that it was all throttle and the stick was never considered for glideslope.

 

To do otherwise was to start a bad habit that would get you washed out of the program eventually. It was as notorious as spotting the deck. Seasoned LSOs could tell when pilots were spotting the deck (using the hud to aim the plane to the point of landing) and once they saw enough of it from a given pilot, that pilot was on a COD back to the FRS for remedial training and one more chance at keeping his job.

 

It was even easier to see when pilots were using the stick to control glideslope, not only could an experience LSO see the nose movement but they would see the AOA repeater in the nosewheel confirming the behavior. This too was another way pilots eventually washed out.

 

If you are using the stick and throttle to maintain glideslope you are doing it wrong, period regardless of platform. The stick is used for alignment to centerline and maintaining a constant AOA. That is what the pilots are doing in the videos when moving the stick, they are trying to keep that green donut lit and rock steady on the AOA indicator while using the throttle to maintain glideslope by keeping the meatball lined up with the datum lights. That's how it works, period.

[bbrz]

Throttle for descent rate, stick for speed. The aircraft will maintain the AoA of you do things right and within limits.

 

You can do this with any of the PFM aircraft, it's known as the region of reverse command and typically presents itself in low speed, moderate AoA situations.

 

The region of reversed command happens only on the back side of the drag/power curve where in increase of speed requires a decrease of power and vice versa.

 

Normally you are on the 'correct' side of this curve during the approach.

[LJQCN101]

Throttle for descent rate, stick for speed. The aircraft will maintain the AoA of you do things right and within limits.

 

You can do this with any of the PFM aircraft, it's known as the region of reverse command and typically presents itself in low speed, moderate AoA situations.

 

Yeah, you can do this with any speed stable aircraft, either aerodynamically or mimicked by FCS.

 

In a F18, you'll experience an even stronger speed stability since it directly uses AOA feedback to automatically trim for on-speed AOA.

 

 

You simply can't fly the GS by only adjusting pitch or power if it's about gross changes.

 

Every power/speed change requires a corresponding pitch change.

 

Well, I tried many times with Su33, that you can manually trim for a point where AOA donut is green with zero pitch rate. From then on, an increase in speed of only 10 km/h will result in pitch up by the aircraft itself, without touching the stick. A decrease in speed will make the aircraft pitch down as well. It's just a matter of how speed stable the aircraft is.

Edited January 23, 2018 by LJQCN101

[bbrz]

In a F18, you'll experience an even stronger speed stability since it directly uses AOA feedback to automatically trim for on-speed AOA.

Speed stability doesn't occur on the back side of the drag/power curve (region of reversed command).

[LJQCN101]

Speed stability doesn't occur on the back side of the drag/power curve (region of reversed command).

 

You mean the speed stability will go negative when the aircraft would pitch up with a decreasing speed and a neutral stick? May happen above stall AOA though.

Edited January 23, 2018 by LJQCN101

[bbrz]

You mean the speed stability will go negative when the aircraft would pitch up with a decreasing speed and a neutral stick? May happen above stall AOA though.

No, speed stability has nothing to do with AoA. It only means that a plane tends to keep its present speed.

 

E.g. if you reduce power just a bit that speed does reduce a bit as well and that it doesn't decrease even more, the slower you get. (e.g. when flying on the backside of the drag/power curve)

Edited January 23, 2018 by bbrz

[Precog]

Regardless of which method you are using, one doesn't work without the other. You simply can't fly the GS by only adjusting pitch or power if it's about gross changes.

 

Every power/speed change requires a corresponding pitch change.

 

The important thing is that if you e.g. grossly drop below the glideslope, you have to increase power first to get back to the GS instead of pulling back on the stick/yoke.

 

Spool up time in the approach power range isn't a factor in most jets.

 

Totally agree and what my instructor told me.

[LJQCN101]

No, speed stability has nothing to do with AoA. It only means that a plane tends to keep its present speed.

 

E.g. if you reduce power just a bit that speed does reduce a bit as well and that it doesn't decrease even more, the slower you get. (e.g. when flying on the backside of the drag/power curve)

 

If talking about F-18 with FLAPS half/full, even flying at the backside of the power curve, releasing the stick would immediately cause nose drop and a strong tendency to return to 8.1 deg AOA (with neutral pitch trim). If you want to keep flying on the backside of the curve, an increasing amount of back pressure on stick is needed. Basically it's still like speed stable, but it wants to return to a constant AOA.

[bbrz]

If talking about F-18 with FLAPS half/full, even flying at the backside of the power curve, releasing the stick would immediately cause nose drop and a strong tendency to return to 8.1 deg AOA (with neutral pitch trim). If you want to keep flying on the backside of the curve, an increasing amount of back pressure on stick is needed. Basically it's still like speed stable, but it wants to return to a constant AOA.

What you are describing has nothing to do with speed stability and releasing back pressure on the stick causes the nose to drop on basically every plane.

Edited January 23, 2018 by bbrz

[LJQCN101]

What you are describing has nothing to do with speed stability and releasing back pressure on the stick causes the nose to drop on basically every plane.

 

No quite the case in F18 if FLAPS is at AUTO, when the system trims for 1G hands-off flight and you actually have to push the stick forward to fly out of the backside of the curve and gain speed. That's neutral speed stability.

 

In contrary, with FLAPS at half/full, the system trims for 8.1 deg AOA hands-off so the speed stability of the aircraft changed to positive. Then speed change would result in pitch up/down, nothing to do with the power curve.

[bbrz]

No quite the case in F18 if FLAPS is at AUTO, when the system trims for 1G hands-off flight and you actually have to push the stick forward to fly out of the backside of the curve and gain speed. That's neutral speed stability.

Looks like we are talking about different things. You are not talking about speed stability.

 

Again, positive speed stability is the tendency of a plane to accelerate with power application and deceleration with a power reduction.

 

With negative speed stability it's the other way round (e.g. region of reversed command)

 

To accelerate out of the backside of the drag/power curve you should increase power, not decrease the pitch attitude.

[LJQCN101]

Looks like we are talking about different things. You are not talking about speed stability.

 

Again, positive speed stability is the tendency of a plane to accelerate with power application and deceleration with a power reduction.

 

With negative speed stability it's the other way round (e.g. region of reversed command)

 

Looks like it does have different ways to measure speed stability.

 

In longitudinal stability & control, speed stability is measured with aircraft (including throttle) trimmed to maintain a certain airspeed. With airspeed increase/decrease after a disturbance, a speed stable aircraft tends to pitch up/down and return to it's original trimmed airspeed. Notice there's no throttle change here.

 

Also here's another explanation:

SPEED STABILITY

In practice, flight test for certification of static longitudinal stability by the U.S. Federal Aviation Administration measures speed stability, a parameter equivalent to Cm-alpha. Simply stated, speed stability is a measure of the control force required to hold the airplane at an airspeed other than the trimmed airspeed. The throttles are fixed at the trimmed thrust setting to eliminate pitching moment changes due to thrust. Speed stability is measured by trimming the airplane in level flight, with throttles fixed at the trimmed condition, then slowly varying airspeed with control column input.

http://www.boeing.com/commercial/aeromagazine/aero_02/textonly/fo01txt.html

 

In flight control systems, we have neutral speed stability control law which is characterised by 1G hands-off auto trim, with the aircraft not pitching up and down when changing airspeed. You can find some mentions about speed stability in DCS Su-27 manual, longitudinal control systems part, where it have a airspeed trimming law to mimic a speed stable aircraft.

Edited January 23, 2018 by LJQCN101

[bbrz]

As expected we are talking about different things. I'm not talking about longitudinal stability, only speed stability, specifically since this thread was about the backside of the drag/power curve.

 

https://www.pprune.org/professional-pilot-training-includes-ground-studies/491636-speed-stability-differences-between-jet-aircraft-propeller-driven-aircraft.html

Edited January 23, 2018 by bbrz

[LJQCN101]

As expected we are talking about different things. I'm not talking about longitudinal stability, only speed stability.

 

https://www.pprune.org/professional-pilot-training-includes-ground-studies/491636-speed-stability-differences-between-jet-aircraft-propeller-driven-aircraft.html

 

We just have the same word, it is also speed stability, in stability & control region.

[bbrz]

A bit confusing, isn't it. ;)