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

How do you trim for on speed AOA in the SU-33?

How do you trim for on speed AOA in the SU-33?

Fly a steady glideslope with the throttle first, and adjust pitch trim until on-speed. E.g. If you find your AOA a bit high, trim forward.

Trim point will be different depending on C.G. location. You can play with different fuel state and store config.

Fly a steady glideslope with the throttle first, and adjust pitch trim until on-speed. E.g. If you find your AOA a bit high, trim forward.

 

Trim point will be different depending on C.G. location. You can play with different fuel state and store config.

It's much easier to trim on speed level before descending

Even the A-10C will try and seek it's AOA when coming down the ILS GS.

Again, that's not the way you usually fly an aircraft (apparently with the exception of the F/A-18 and most likely a few other FBW aircraft.)

You don't let an aircraft 'seek' anything or let the nose pitch up and down on its own.

As mentioned before flying FBW aircraft is more like steering a computer game as you are totally disconnected from the actual plane and there's zero feel about what the aircraft is doing.

E.g. an A320 is more stable on the ILS than non FBW aircraft but it's in fact more difficult to fly since you have to adapt to the lack of feel, it's different and it's more like painting by numbers than real flying...apparently similar to the F/A-18.

How do you trim for on speed AOA in the SU-33?

Quick video showing you on speed AOA level flight and only using the throttle to control "balance" or "seesaw" LOL the on speed AOA.

There is no forward or back stick movement here at all, I'm just playing with the throttle to go in and out of on speed AOA, she's is touchy bird compared with the A10, I'm guessing more than the F/A-18 FBW system also?

If you can get this quite stable in the pattern (Try straight in first) cornering and holding on speed AOA takes some practice, then all you should basically have to do is come off and on the throttle down the Glide Path or in the Su-33 case, put the little round thingy in the big round thingy.:)

Put the little circle (ILS Guidance Mark) inside the big circle (Flight Director) don't look at the deck and try to land on a spot, fly the (ILS Guidance).

DCS: F/A-18C Hornet - Episode 6: VFR Airfield Landing

Watch Wags make the turn to final while On speed AOA to see what you need to practice.

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Again, that's not the way you usually fly an aircraft (apparently with the exception of the F/A-18 and most likely a few other FBW aircraft.)

 

You don't let an aircraft 'seek' anything or let the nose pitch up and down on its own.

 

As mentioned before flying FBW aircraft is more like steering a computer game as you are totally disconnected from the actual plane and there's zero feel about what the aircraft is doing.

E.g. an A320 is more stable on the ILS than non FBW aircraft but it's in fact more difficult to fly since you have to adapt to the lack of feel, it's different and it's more like painting by numbers than real flying...apparently similar to the F/A-18.

I do get where your coming from bbrz, try the A10, she really sits in that AOA groove well, yes the F/A-18 has FBW, it will still float around some, it's in the air. :D

I think it would not be the best idea to fight against the oscillations to much and let the FBW or aircraft to sort it out and stabilize where possible, other wise you might be worse off perhaps? The aircraft is trying to find it's on speed AOA groove (seek it;)), you cannot put it there and hold it with pitch, well you will be fighting it if you do, the aircraft is the only thing that can really feel how it wants to sit with the power and trim set for on speed AOA.:)

Example of using no pitch, no wind or turbulence set here, the A-10C has a good range of on speed AOA, rock solid Green Doughnut when moving the throttle around following GS.

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Again, that's not the way you usually fly an aircraft (apparently with the exception of the F/A-18 and most likely a few other FBW aircraft.)

The word your looking for is navy aircraft. Look up some cockpit videos, or research it if you don't believe me, anyone with experience will corroborate what I'm saying if you don't believe me.

In the Su-33, I use Auto-throttle, and I keep the aircraft within the ball on the HUD. It works just fine. But the way I do does sound wrong. I am keeping my aircraft within the ball using the pitch, instead of throttle, since the throttle is being controlled by the aircraft systems.

I find quite impossible to keep my A-10C aligned with the yellow bars on the ADI using just throttle though, I need to pitch up and pitch down a bit, but just a bit, using the trim. But the altitude is mainly controlled by the throttle.

E.g. an A320 is more stable on the ILS than non FBW aircraft but it's in fact more difficult to fly since you have to adapt to the lack of feel, it's different and it's more like painting by numbers than real flying...apparently similar to the F/A-18.

I found that in A320, there's no control logic change when landing gear down or flaps down, unlike F-16 or F/A-18. You'll be flying the aircraft in Flight Mode on approach, which means it still trims for 1G hands-off, until you transition to Flare Mode at 50' RA.

F/A-18 however trims for a specific AOA when flaps half or full. This would result in a huge difference in handling.

I found that in A320, there's no control logic change when landing gear down or flaps down, unlike F-16 or F/A-18. You'll be flying the aircraft in Flight Mode on approach, which means it still trims for 1G hands-off, until you transition to Flare Mode at 50' RA.

 

F/A-18 however trims for a specific AOA when flaps half or full. This would result in a huge difference in handling.

This works for non-fbw aircraft too. The first time you're introduced to this in training you have manual trim and hydraulic controls with no fbw and it works the same. In GA aircraft when you think you're trimming for an airspeed it's really an AOA, just start a turn and you'll see your airspeed increase in order to maintain the AOA you're trimmed at

This works for non-fbw aircraft too. The first time you're introduced to this in training you have manual trim and hydraulic controls with no fbw and it works the same. In GA aircraft when you think you're trimming for an airspeed it's really an AOA, just start a turn and you'll see your airspeed increase in order to maintain the AOA you're trimmed at

Yeah, I believe most FBW fighters would adjust their control laws to mimic the stability characteristics of a conventional aircraft when landing.

To name a few, F-16, F-18, M2000, JF-17, all of them (IIRC) utilise AOA feedback in Landing Mode to try to handle like a conventional aircraft.

Su-27 and Su-33 uses dynamic pressure to schedule their pitch trimming law, but the results are similar.

I can do the entire approach in the Su-33 with just trim and roll input. Pretty easy. The A-10C is a bit more complicated, but it's also easy and it makes 100% sense. Just follow the instruments. In the Su-33 you're following a ball, no throttle at all.

I.e; keeping the aircraft datum in the middle of the Nav mark.

I think it would not be the best idea to fight against the oscillations to much and let the FBW or aircraft to sort it out and stabilize where possible, other wise you might be worse off perhaps? The aircraft is trying to find it's on speed AOA groove (seek it;)), you cannot put it there and hold it with pitch, well you will be fighting it if you do, the aircraft is the only thing that can really feel how it wants to sit with the power and trim set for on speed AOA.:)

Example of using no pitch, no wind or turbulence set here, the A-10C has a good range of on speed AOA, rock solid Green Doughnut when moving the throttle around following GS.

I wouldn't call controlling pitch, 'fighting' at all. If this method only works in calm weather with zero wind and zero turbulence it doesn't make much sense to use it at all IMO.....

The word your looking for is navy aircraft. Look up some cockpit videos, or research it if you don't believe me, anyone with experience will corroborate what I'm saying if you don't believe me.

This one doesn't look like your description....https://www.youtube.com/watch?v=hAqpKg9YXAA

I found that in A320, there's no control logic change when landing gear down or flaps down, unlike F-16 or F/A-18. You'll be flying the aircraft in Flight Mode on approach, which means it still trims for 1G hands-off, until you transition to Flare Mode at 50' RA.

I never said that there's a change with gear or flap extension. Btw, there's no such thing as a 'flight mode' in any (FBW) Airbus and it does not simply trim for 1G hands off flight ( C* law / flight path stability).

I can do the entire approach in the Su-33 with just trim and roll input. Pretty easy.

If you are using trim then you are actively controlling the pitch attitude.

I wouldn't call controlling pitch, 'fighting' at all. If this method only works in calm weather with zero wind and zero turbulence it doesn't make much sense to use it at all IMO.....

 

 

This one doesn't look like your description....

 

 

I never said that there's a change with gear or flap extension. Btw, there's no such thing as a 'flight mode' in any (FBW) Airbus and it does not simply trim for 1G hands off flight ( C* law / flight path stability).

 

 

If you are using trim then you are actively controlling the pitch attitude.

Funny you use that example, because if you notice, every time he pushes/pulls the stick the indexer immediately follows with a fast/slow indication.

Your opinion has no say in how naval aircraft get aboard the ship, and again, because it doesn't make sense to you doesn't mean it's correct. Again, there's a reason it's done this way whether you see it now or not. You don't fly it, you don't have any experience with it, so what's the point of arguing with people that actually do this on a daily basis?

Again, that's not the way you usually fly an aircraft (apparently with the exception of the F/A-18 and most likely a few other FBW aircraft.)

 

You don't let an aircraft 'seek' anything or let the nose pitch up and down on its own.

 

As mentioned before flying FBW aircraft is more like steering a computer game as you are totally disconnected from the actual plane and there's zero feel about what the aircraft is doing.

E.g. an A320 is more stable on the ILS than non FBW aircraft but it's in fact more difficult to fly since you have to adapt to the lack of feel, it's different and it's more like painting by numbers than real flying...apparently similar to the F/A-18.

Pitch for AOA and throttle for glide slope is also know as the backside technique. It predates fly by wire control systems. The backside technique is first recommend by the Naval Safety Center in June of 1959. NASA had looked into earlier of that year.

The Flight path angle is = D/L - T/W + dV/dt/g

Thereby flight path angle is a function of lift to drag ratio at approach speed, thrust to weight ratio and the rate change of airspeed.

It was found in a lot of aircraft configurations that the lift to drag ratio decreases at high lift coefficients. Total drag increases with decreasing airspeed, this is as the region of reverse command or the backside of the drag curve.

The speed for minimum drag will also be the speed for neutral speed stability. At speeds higher than that for minimum drag, the airplane will return to the trim speed following a disturbance. At lower speeds following a disturbance the aircraft will diverge in speed.

So what happens when you pitch up to correct for a low glide slope. First you change the L/D and add more drag thus slowing the aircraft down. You’re now on the backside of the drag curve. As the craft slows, your sink rate increases. You’ve also slowed the craft to where it’s no longer stable. Now you’re sinking and slowing.

If we’re pitching to fix glide slope, at this point we would pitch up further to correct for our increased sink rate… you’re in a death spiral. Each increase in pitch compounds your problem, as L/D gets worse and you slow down more and drop at a faster rate. You pull back trying to fix your problem and stall. If you’re flying a turbofan with a engine lag, like an early jet or an F-14, or a aircraft with a low thrust to weight ratio, you may be out of options. The engines won’t spool in time to save you.

Even if you manage to stay on the throttles to fix your speed problem and avoid a stall, you’ve put the aircraft into a state where making a precision landing will be extremely difficult. Remember what said about speed stability, Well because we pitched up and slowed down our speed stability is gone and the now the aircraft is a a phugoid. The task of controlling the approach with any precision is now orders of magnitude more difficult as the craft pitches about while changing speed.

The key aspect to understanding why this technique is used is often overlooked and relates to stability. The start of this technique is predicated up on the fact that we are trimmed for level flight before turning on final.

If the aircraft is in a steady state, we say that all the forces acting upon it are in equilibrium. Thus

Our speed = 17.2* Sqrt Gross Weight / Wing Surface / Lift Coefficient.

Or 17.2 * Sqrt of Wing Loading / Lift Coefficent

So if we pull back on the stick, we increase the lift coefficient on the tail, and increase the total lift coefficient. Thus reducing our speed. Hence we pitch for speed.

In a steady state our rate of climb or descent in feet per minute, is = 33,000(Power available - Power Required for level flight / Gross Weight)

So our sink and climb rate is a function of excess power. Since we can modulate the amount of excess power with the throttle and maintain speed stability, we use the throttle to control glide slope.

Really the best guides to understanding why this technique is used are the primary sources.

Aviation for Naval Aviators offers a in-depth expiation in chapter 6.

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/00-80T-80.pdf

The early NASA document on landing approach speeds does a nice job of explaining as well.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19980232089.pdf

And the review on powered approach speeds criteria from Nav Air provides a history of the development of the backside technique in chapter 2. Though the whole thing is worth the read.

http://www.dept.aoe.vt.edu/~durham/2002-71.pdf

^ Possibly the most informative post I've seen on the forums. Too bad they got rid of the rep system. I just know what goes on in the cockpit, but the engineer side of the house produces something of quality every once in awhile. +1

Guys, due to the absence of the Hornet in DCS i´m trying to practise Carrier Ops in FSX. As far as I understand this Throttle and Stick thing i use the stick for holding the plane "on speed" and the throttle to center the horizontal ILS-needle, right? Well, what i experience is that the plane is getting way too fast when i push the throttle to get onto the GS (at this moment i´m too slow). Any suggestions to this? I´d really want to get that thing right...

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If you are using trim then you are actively controlling the pitch attitude.

That's 100% correct. I am using the trim in order to control the pitch attitude, but that's because I am using auto-throttle. Just checked it with a buddy, and the procedure is backwards compared to the standard one, without ATC. Trim for AoA and throttle for altitude/glideslope.

Great post!

 

How's the theory with Auto-throttle however? Since you aren't managing the throttle anymore, how are you going to keep a correct glideslope without pitching up and down?

 

As I said above, I keep the Su-33 datum within the Nav mark on the HUD, using just the trim. No throttle at all. Can't use the throttle, otherwise it wouldn't be auto-throttle right? :D I would like to know if this is the correct way to do it.

Auto Throttle is a powered approach compensator. It's a sort of a fly by wire system. It will attempt to hold a specific angle of attack and has it's own set of logic. When engaged you would fly it conventionally, that is stick for glide slope. Usually what happens when you pull back on the stick is that the engines throttle up. So the aircraft flys the backside technique for you. So if you're using the auto throttle and trim it's mostly correct.

Guys, due to the absence of the Hornet in DCS i´m trying to practise Carrier Ops in FSX. As far as I understand this Throttle and Stick thing i use the stick for holding the plane "on speed" and the throttle to center the horizontal ILS-needle, right? Well, what i experience is that the plane is getting way too fast when i push the throttle to get onto the GS (at this moment i´m too slow). Any suggestions to this? I´d really want to get that thing right...

If you're flying the VRS Superbug or the default FSX accel Hornet. Neither has the fly by wire logic implemented for the powered approach mode. So they both handle unrealistically around the boat. VRS's work around is to use the auto throttles. I'm not sure if there is currently a version of Hornet that implements the Powered Approach mode correctly.

Auto Throttle is a powered approach compensator. It's a sort of a fly by wire system. It will attempt to hold a specific angle of attack and has it's own set of logic. When engaged you would fly it conventionally, that is stick for glide slope. Usually what happens when you pull back on the stick is that the engines throttle up. So the aircraft flys the backside technique for you. So if you're using the auto throttle and trim it's mostly correct.

 

 

If you're flying the VRS Superbug or the default FSX accel Hornet. Neither has the fly by wire logic implemented for the powered approach mode. So they both handle unrealistically around the boat. VRS's work around is to use the auto throttles. I'm not sure if there is currently a version of Hornet that implements the Powered Approach mode correctly.

yeah, it´s the Acceleration Hornet (default).... so i can spend my time better than practicing the throttle/stick handling in order to be prepared for "our" Hornet?

I never said that there's a change with gear or flap extension. Btw, there's no such thing as a 'flight mode' in any (FBW) Airbus and it does not simply trim for 1G hands off flight ( C* law / flight path stability).

Well i see but basically the same with a blend of Nz and pitch rate feedback. Unless they are using the C*U law, there's still no airspeed feedback to provide artificial speed stability. Hence do not apparently similar to a hornet.

ref http://www.icas.org/ICAS_ARCHIVE/ICAS2012/PAPERS/605.PDF

the C* control algorithm destroys the natural speed stability of the aircraft. There is no "trim speed" in the classical sense of trimming out the stick force to stabilize at and hold a desired speed. The change in speed due to a constant stick displacement (or stick force) is infinite, because the pilot must get out of the control loop to stop the pitch rate.

 

As a result, the C* algorithm does not meet the Federal Aviation Regulations Part 25 for static longitudinal stability, which requires a pull force to achieve and maintain a steady state speed decrease relative to the trim speed and vice versa.

In the Su-33, I use Auto-throttle, and I keep the aircraft within the ball on the HUD. It works just fine. But the way I do does sound wrong. I am keeping my aircraft within the ball using the pitch, instead of throttle, since the throttle is being controlled by the aircraft systems.

 

I find quite impossible to keep my A-10C aligned with the yellow bars on the ADI using just throttle though, I need to pitch up and pitch down a bit, but just a bit, using the trim. But the altitude is mainly controlled by the throttle.

Vitormouraa, the big secret here! No secret... Trim for on speed AOA (rock solid Green Doughnut) in "LEVEL FLIGHT"

Read this below...

The key aspect to understanding why this technique is used is often overlooked and relates to stability. The start of this technique is predicated up on the fact that we are trimmed for level flight before turning on final.

Thanks Curly for the detailed response, very interesting :thumbup:

Try this in the A10 Vitormouraa, trim AOA for "level flight", then hit the glide slope, modulating the throttle, it's a good way to fly, very stable and takes a little off the workload when trying to fly imc, ILS approach.

The A10 is a good aircraft to practice this, it sits very well in the on speed AOA, use the ILS to practice following Glide Slope (GS) with throttle only and bank to say aligned (No Pitch) "practice" (I went to change the pitch a few times when practicing:(), the A10 is close to the same speed as the F/A-18 when landing also.

Guys, don't use those other sims to practice this, the FM's are very questionable and no FBW etc. A good example is the majestic Q400 for IRL sim pilot training. They had to used an independent Flight Dynamics Engine (FDE) outside of both those sims to get the FM where it needed to be. This one I believe?

Also, I would not use the Auto throttle setting to learn this, Navy pilots are graded on landings without Auto throttle to keep up proficiency, using the Auto throttle takes away practicing the skill, so when you comeback to being graded you would struggle, this is only for the guy's that want to do it how it's done, from what I've read on my travels, the Navy pilots here can fill us in with more detail.;)

I wouldn't call controlling pitch, 'fighting' at all. If this method only works in calm weather with zero wind and zero turbulence it doesn't make much sense to use it at all IMO.....

bbrz, I'm here too learning off the pro's, there are many Navy pilots here who got past all that training:cry:

I think they know this stuff right, they practice this technique skill set for the boat, many here are trying to wrap there head around this and why it's done, like ttaylor0024 has said it's tried and tested in blood.

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Maybe you misunderstood what I said but I have no problem landing the Hawg with near to or zero visibility. It's quite easy once you understand how everything works. But I've never been a fan of doing perfect patterns and all that stuff when landing so that's why I said that :D although IFR has been one of my priorities since I started learning the module. I just don't have patience to do the patterns used in real life.

Maybe you misunderstood what I said but I have no problem landing the Hawg with near to or zero visibility. It's quite easy once you understand how everything works. But I've never been a fan of doing perfect patterns and all that stuff when landing so that's why I said that :D although IFR has been one of my priorities since I started learning the module. I just don't have patience to do the patterns used in real life.

I find quite impossible to keep my A-10C aligned with the yellow bars on the ADI using just throttle though, I need to pitch up and pitch down a bit, but just a bit, using the trim. But the altitude is mainly controlled by the throttle.

The reason for the response is for you to try it without....

"I need to pitch up and pitch down a bit, but just a bit"

Are you pitching up for height, back on GS here or chasing the on speed AOA? if (on speed) AOA, this will lower your sink rate more and you will need to add much more power to hold (on speed) AOA.

Give it a go without doing that and you will see it pitch up itself (lowing the descent rate) when adding throttle and still stay on speed AOA (Green Doughnut):thumbup:

Watch the A10 video, no pitch at all (I show the control gauge), on speed AOA (Green Doughnut) all the way down.

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Yep I do need to improve that. But it definitely needs a better approach to the runway. Otherwise I will have to use the stick due to the changes I need to do, which are considerably high due to the poor approach! So a nice approach will give you less work to do once you are aligning with the runway I believe.