Is it possible to trim this aircraft to fly hands off

[Bremspropeller]

1 hour ago, Hiob said:

To put it in a different perspective: Given a stable speed/altitude/attitude you can't go faster just by trimming. If you want to go faster and keep your FL and attitude you need to apply more thrust (and need to trim down to counter the according climb tendency)....

 

You can go faster by trimming. The airplane just won't have enough power to maintain altitude.

I have seen military-trained people get this wrong, too.

 

It helps picturing a total engine failure. If your trim-theory stands the test, it's correct. If it doesn', it's not correct in the first place.

 

You always trim for airspeed and power for rate of climb/ descent.

[Hiob]

6 minutes ago, Bremspropeller said:

 

It helps picturing a total engine failure.
 

I'm probably really slow right now - but this doesn't help me.

I mean, sure if you trim 90° nose down, you can accelerate with 9.81 m/s² (roughly) - even without an engine.

But I can't see how to achieve an acceleration in level flight without the input of power.

 

[The LT]

I'm probably really slow right now - but this doesn't help me.
I mean, sure if you trim 90° nose down, you can accelerate with 9.81 m/s² (roughly) - even without an engine.
But I can't see how to achieve an acceleration in level flight without the input of power.
 

Just try doing what the guys suggest. Trim nose down in S/L, don't change the power setting and see what happens and what speed/altitude tbe aircraft will settle at.

[Hiob]

3 minutes ago, The LT said:

21 minutes ago, Hiob said:

I'm probably really slow right now - but this doesn't help me.
I mean, sure if you trim 90° nose down, you can accelerate with 9.81 m/s² (roughly) - even without an engine.
But I can't see how to achieve an acceleration in level flight without the input of power.
 

Just try doing what the guys suggest. Trim nose down in S/L, don't change the power setting and see what happens and what speed/altitude tbe aircraft will settle at.

I will do that!

 

And please, all, don't get me wrong. I'm aware that "pitch to speed, power to altitude" is the common "principle" that is tought all around and that the people here, that support it, are not wrong. AND I assume that this approach in thinking may very well improve my warbird flying!...

But, in my personal opinion, from a physical/aerodynamic point of view, it is not entirely true - because it violates some very basic principles of energy conservation.

And from what I found online, it is anything but a settled matter between aviators as well.

https://www.boldmethod.com/learn-to-fly/navigation/how-to-control-pitch-and-power-on-a-glideslope-to-landing/

https://www.avweb.com/flight-safety/technique/pitch-or-power/

 

 from the latter:

"In powered aircraft neither one works alone. To achieve optimum performance in any setting requires balancing the two to best match the needs of the moment."

[The LT]

I will do that!
 
And please, all, don't get me wrong. I'm aware that "pitch to speed, power to altitude" is the common "principle" that is tought all around and that the people here, that support it, are not wrong. AND I assume that this approach in thinking may very well improve my warbird flying!...
But, in my personal opinion, from a physical/aerodynamic point of view, it is not entirely true - because it violates some very basic principles of energy conservation.
And from what I found online, it is anything but a settled matter between aviators as well.
https://www.boldmethod.com/learn-to-fly/navigation/how-to-control-pitch-and-power-on-a-glideslope-to-landing/
https://www.avweb.com/flight-safety/technique/pitch-or-power/
 
 from the latter:
"In powered aircraft neither one works alone. To achieve optimum performance in any setting requires balancing the two to best match the needs of the moment."

I assumed this thread was about trim in cruise phase, so the former link about the landing phase is not applicable. The latter link doesn't focus on trimming though.

[Hiob]

13 minutes ago, The LT said:

31 minutes ago, Hiob said:

 

Just try doing what the guys suggest. Trim nose down in S/L, don't change the power setting and see what happens and what speed/altitude tbe aircraft will settle at.

 

Just for the fun of it, I will make prediction and will share the result later, when I could try it.

My prediction: It will probably gain speed, but will most likely (I'm almost sure) settle on a lower altitude. (Which is, to be very precise, not what I wanted to achive) 

 

Let's see, what I will learn.

[The LT]

 
Just for the fun of it, I will make prediction and will share the result later, when I could try it.
My prediction: It will probably gain speed, but will most likely (I'm almost sure) settle on a lower altitude. (Which is, to be very precise, not what I wanted to achive) 
 
Let's see, what I will learn.

You got it!

[Hiob]

4 minutes ago, The LT said:

You got it!

Thank you for blessing me with your approval!

[The LT]

Thank you for blessing me with your approval!

You're welcome, although you should thank the gentlemen above.

[Hiob]

Question:

 

Is the following statement true?

"You can change Speed for Altitude and Altitude for Speed."

Edited September 29, 2021 by Hiob

[Lace]

6 hours ago, Hiob said:

@Lace

Still...

I get everything you said, except:

If you fly say 250 knots IAS at 5.000 feet, and you want to accelerate to 280 knots IAS and maintain 5.000 feet, how do you accomplish that?

 

I would suggest, open the throttle, counter the pitch up tendency with forward stick pressure and then trim out the forces.

If that is the wrong way, I'm really interested in the correct procedure! (no sarcasm! honest interest!)

 

Edit: I mean, I get it, you can easily switch my example above into:

Trim down and counter the altitude loss with throttle.

But that somehow is my point - don't you need always both? Really confused right now....

 

I seem to have caused further confusion here. Of course in a practical sense you are correct in that each aircraft manoeuvre requires the manipulation of multiple controls, and in order to accelerate in S&L flight you need both trim and power.
 

Again, this is really easy to demonstrate. Trim for S&L flight and increase the throttle, don’t touch any other controls. Allow the aircraft to stabilise (give it a minute or two) and check the conditions. Are you now going faster, or are you flying higher?

 

Your trim setting has essentially fixed the aircraft speed, and no matter what you do to the throttle afterwards, the aircraft (assuming positive stability characteristics) will eventually settle back to that airspeed.  The only way you are going to get it to sit at a faster cruise speed is by turning that trim wheel nose down. 
 

edit - imagine this scenario, you are stabilised on finals, and low on the glide slope. Do you a) pitch up, or b) add power.
 

 One answer is correct, and the other is likely to end in a visit to the hospital (if you are lucky).

Edited September 29, 2021 by Lace

[Lace]

4 hours ago, Hiob said:

Question:

 

Is the following statement true?

"You can change Speed for Altitude and Altitude for Speed."

 

 
Yes. Without changing power settings, you can trade speed and altitude. Say you are trimmed S&L at 120kts, 3000ft.  You pull on the stick to trade some speed for altitude (a zoom climb). You are now flying higher but since you have not changed the power setting (which controls altitude) you will require more back pressure on the stick to maintain that new altitude.  Two things can happen now - you trim nose up to hold the new altitude and reduced airspeed (you have swapped some speed for some altitude) or you relax the stick pressure and the aircraft reestablishes 120kts by entering a shallow descent until it stabilises at 3000ft again. 
 

Try it the other way. At 120kts and 3000ft you push the nose over. Speed increases as altitude decreases, but as you get faster the stick pressure required to hold nose-down increases. You are fighting the aircraft as it wants to find 120kts (I.e. by pitching back up). Again you now need to re-trim for the faster speed, and the aircraft will level off at a lower altitude and higher speed, or you release the stick pressure and the aircraft makes it’s way back to 120kts/3000ft. 
 

From this it should be obvious that a well trimmed aircraft is essential to an accurate strafing run, otherwise as speed increases in the dive, the pilot will need to fight very heavy pitching forces and end up oscillating up and down as the aircraft is constantly trying to pitch up, while the pilot is trying to hold a steady dive angle. 

[Hiob]

@Lace

I thank you for your elaboration. I get the idea.

…and I‘m sorry for my stubbornness, but I‘m still not yet convinced that one goes without the other. (energy!)

My tradeoff question from above was aimed at the following. If you want to gain either without(!) sacrificing the other you need to put in energy (aka thrust).

There is no way around it without violating very fundamental physical laws. So you either tradeoff potential energy with kinetic energy or add energy out of your tanks. 

For every stable flight attitude you need a given equilibrium of trim and thrust. I‘d like to make the point, that you always affect both. When pitching/trimming up, you will climb but will necessarily also loose speed, and the other way round.

My best guess, why it is framed and taught in this way (pitch for speed, power for altitude) is, that it gives pilots an intuitive way of applying correct countermeasures in dangerous situations (aka takeoff and landing), when you can‘t exchange one for another because you don‘t have it sufficiently (thrust in takeoff and altitude in landing).

 

But we‘re running in circles. I know that you are right, and that this is the common teaching. I just happen to think that it‘s not the whole story (from a physical pov at least).

 

To wrap it up:

Unfortunately I wasn’t able to recreate it in DCS. I tried it with the mustang, but it won’t settle. When trimmed down from equilibrium it will just continue to dive (and accelerate of course) until either overspeed or impact. Trimming up results in climbing and loosing speed until stall.

I don’t know, if a warbird is simply not an aerodynamic stable platform, or dcs has its limits here (either due to flight model or managing inputs). I assume the latter.

 

Again, I am thankful for your input. It will certainly give me something to digest and think about!

 

GN8

Edited September 29, 2021 by Hiob

[twgin]

“Trim is speed”… what I used to tell my students when I was instructing.  Perhaps not totally germane to the current topic, but you can trim a plane to fly straight and level at a very slow speed (ask any student about slow flight).  You can also trim the plane to fly straight and level at a much higher speed (call it cruise).  And you can trim the plane to fly at any desired speed between these two regimes.  What trim is affecting is drag; trimming nose down reduces AOA (angle of attack) and hence reduces drag, conversely trimming nose up increases AOA and hence increases drag.  So as a pilot who wants to maximize efficiency, for a given power setting and desired altitude, you want to trim the plane for maximum speed (minimum drag).  Trim is speed.

 

But talking about the DCS Mosquito (and most other planes in most other simulators), it is almost impossible to stabilize the airplane at some combo of power, altitude and trim.  First off the bat, you are missing the feedback of stick forces (unless FFB, of course).  I also have the feeling that the Flight Model(s) just don’t do equilibrium very well (even the sim that begins with X and it’s theoretically better FM has this same issue).

 

So what can you do… I have reduced the trim value in the .lua file from 1.0 to 0.25 and this makes the Mosquito easier to handle certainly.  Also, try to fly with the Altimeter, not the Vertical Velocity Indicator, which, if properly modeled, is a lagging indicator (compared to the altimeter which gives real time information).  Unfortunately, the Altimeter in the Mosquito is unrealistically jumpy IMHO which makes this more difficult than it should be.

[Hiob]

The general problem with trim in DCS seems to be that, if you ever have the slightest imperfection (which is inevitable) in balance, it will slowly but increasingly roll/climb/dive out of balance... and as far as I was able to test it - never settle in a stable attitude.

 

I wonder, if trim in dcs actually simulates the counter deflection of a trim tab on the control surfaces, or just apply a "stick-offset".

(...and I'm not totally sure, if that makes a difference to be honest - since we can't feel "trim out the forces" anyway)

Edited September 30, 2021 by Hiob

[huchanronaa]

it was not possible to fly the aircraft "hands off" except on the climb, and trimming is difficult.
This is the focus of the manual during World War II

[DD_Fenrir]

3 hours ago, huchanronaa said:

it was not possible to fly the aircraft "hands off" except on the climb, and trimming is difficult.
This is the focus of the manual during World War II

 

Which manual?

[Hiob]

2 minutes ago, DD_Fenrir said:

 

Which manual?

I think he's referring to the manual, that was posted on the first page of this thread. If it applies to our mosquito is uncertain, as far as I'm aware.

[Bremspropeller]

On 9/29/2021 at 4:04 PM, Hiob said:

I'm probably really slow right now - but this doesn't help me.

I mean, sure if you trim 90° nose down, you can accelerate with 9.81 m/s² (roughly) - even without an engine.

But I can't see how to achieve an acceleration in level flight without the input of power.

 

Picture this: You're flying stationary, level and there's no acceleration.

 

*BOOM*

 

You've lost all your engines.

What is going to happen now? The aircraft has insufficient power to attain level flight at trimmed speed. It will decelerate and hence nose-down, to seek trim-speed.

This will happen in a phugoid motion, until the aircraft is descending at a stationary rate to attain it's trimmed speed.

 

Want to go faster? Just trim nose-down. The aircraft will also descend steeper.

Want to go slower? Just trim nose-up. The aircraft will descend slower.

 

You can precisely control the demanded airspeed by just adjusting trim.

This is exactly how glider-pilots control airspeed.

 

Power is only needed to descend slower, keep altitude or even climb.

[Hiob]

6 hours ago, Bremspropeller said:

 

You've lost all your engines.

This is exactly how glider-pilots control airspeed.

 

Yeah, thank you. That is exactly what I have not asked for.

We're running in circles guys, so leave it be. @Lace sufficiently elaborated everything I wanted and needed to know, and I have the impression he knows what he's talking about.

He didn't convince me to 100%, but that's due to my skeptical nature -

There is no need to lecture me further, because I understand the concepts - I just happen to come to a different conclusion, of what that actually means... and since I easily find several aviators and flight trainer online, that - at least to a degree - share my viewpoint, I figure that the matter is not black and white and the answer is - as often -

it depends.

 

Have a good night, all!

[Bremspropeller]

24 minutes ago, Hiob said:

He didn't convince me to 100%, but that's due to my skeptical nature -

 

That's because you're making it harder than it needs to be.

If you don't need a throttle to make a glider go x knots, then it's not necessary in any airplane.

 

A theory is only a theory, if it can explain special cases like not having an engine in the first place.

 

25 minutes ago, Hiob said:

and since I easily find several aviators and flight trainer online, that - at least to a degree - share my viewpoint, I figure that the matter is not black and white and the answer is - as often -

it depends.

 

Not really. The way they teach it, there's a "reverse of command" on the "backside of the power curve".

You don't need that kind of a crutch when you accept that pitch is airspeed and power is altitude. Because this is true on either side of that curve.

 

[Hiob]

12 hours ago, Bremspropeller said:

 

If you don't need a throttle to make a glider go x knots, then it's not necessary in any airplane.

 

That you can exchange Altitude for Speed was never the question.

The question was to accelerate in level flight without sacrificing altitude, but by applying thrust. Tell me how exactly a glider is here of any use as an example?

 

Oh and btw. I'm aware, that in a glider pitch is pretty much the only way to gain speed (except maybe tailwind).

 

12 hours ago, Bremspropeller said:

 

Not really. The way they teach it, there's a "reverse of command" on the "backside of the power curve".

You don't need that kind of a crutch when you accept that pitch is airspeed and power is altitude. Because this is true on either side of that curve.

 

 

Let's break it down. How is lift generated on a wing? You need airflow over the wing, since the wing is curved, the air needs to travel a further way and therefore accelerates. Accelerated flow creates an area of low pressure over the wing -> the wing is pulled up (or to be precise pushed up, by the relative high pressure below the wing...). The central point here is Airflow.

How do you generate the airflow? By forward motion. How do you generate the forward motion? By thrust. So the chain of cause and effect is the following:

Thrust -> Motion -> Airflow -> Lift.

You can easily observe that, because when you apply thrust, the aircraft will first accelerate and then climb. I repeat my point. One doesn't work without the other, you can't do either of them isolated.

 

Pitch for Speed, Power for Altitude is a mnemonic and not the whole story.

Edited October 1, 2021 by Hiob

[Bremspropeller]

39 minutes ago, Hiob said:

That you can exchange Altitude for Speed was never the question.

The question was to accelerate in level flight without sacrificing altitude, but by applying thrust. Tell me how exactly a glider is here of any use as an example?

 

Again, because it shows the relations between airspeed, altitude and power.

 

39 minutes ago, Hiob said:

Let's break it down. How is lift generated on a wing? You need airflow over the wing, since the wing is curved, the air needs to travel a further way and therefore accelerates. Accelerated flow creates an area of low pressure over the wing -> the wing is pulled up (or to be precise pushed up, by the relative high pressure below the wing...). The central point here is Airflow.

How do you generate the airflow? By forward motion. How do you generate the forward motion? By thrust. So the chain of cause and effect is the following:

Thrust -> Motion -> Airflow -> Lift.

 

Thrust is not required to create lift. See above.

It's only required if you want do descent slower than your given L/D properties are dictating. If you want do descent faster than your given L/D, you'll need additional drag, so you won't accelerate.

 

Maybe we should start with asking the question what trim actually is and what it does.

Trim is required to counter the resultant pitching-moment for any given q (dynamic pressure) and AoA.

Imagine an aircraft with no trim at all.

With this airplane, you're having a fixed relation between your wing and tail moments and hence you'd be in trim for a certain, given airspeed/ AoA (stationary flight). Any airspeed above or below will induce a pitching moment - slower will let your nose go down below the horizon, until the aircraft is again at trimmed speed. The oposite will happen with an airspeed above trim speed.

 

This is the same, which will happen with an aircraft at trimmed speed in cruise. Add power and the aircraft will climb (as it wants to accelerate beyond trimmed speed, so it pulls the nose up to decelerate back to trimmed speed, aphugoid will result). Pull power off and the aircraft will descend, as it's decelerationg below trimmed speed.

The aircraft will actively seek trimmed speed whenever the balance is disturbed.

 

What determines your speed is not power, but trim. Power only determines if the aircraft has enough to stay at the same altitude, or not.

 

When you "acelerate", you add power. Yes, you'll need to do that to reach a higher kinetic energy state. Again, what determines speed is your trim.

If you just add power, you'll just begin to climb. You'll need to adjust the trim to make the aircraft actually go faster. Normally, you'd do that by applying control-forcefirst and then gradually trim that control force away.

 

39 minutes ago, Hiob said:

You can easily observe that, because when you apply thrust, the aircraft will first accelerate and then climb. I repeat my point. One doesn't work without the other, you can't do either of them isolated.

 

Next time you are in cruise, just pull the power and observe what happens. Then add power and observe what happens.

Iterate.

 

When you apply thrust, the airplane will accelerate a few knots, so the resultant climb will develop. The aircraft will then seek and ascend at trimmed airspeed.

The amount of knots it needs to accelerate is a function of the aircraft's static speed-stability. The more stable, the less acceleration beyond trim-speed is necessary to initiate the phugoid. What's determining the airspeed is not the thrust, but the trim. Thrust is only determining the resultant ROC.

 

Edited October 1, 2021 by Bremspropeller

[rkk01]

Trims easily, surely???

 

You do need the trims mapped though - the Mossie is a handful if your looking around the pit and trying to fly

[truebrit]

7 hours ago, rkk01 said:

Trims easily, surely???

 

You do need the trims mapped though - the Mossie is a handful if your looking around the pit and trying to fly

Ya, my eyes are not so good so I need to zoom right in to set the bombs, by then the plane is usually in a dive or inverted.