Short and sweet T-6 video with Scott

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Medtner
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Short and sweet T-6 video with Scott

Post by Medtner »

If you haven't seen this already:

https://www.youtube.com/watch?v=aWfJzxPrBhE

A question for Scott:

The hydraulic pressure reads 0 before and during the takeoff. The needle jumps as you pull the gear-lever, and after raising the gear it settles on the correct pressure, but then falls after you've lowered the MP to 30. Is this normal?
Erik Haugan Aasland,

Arendal, Norway
(Homebase: Kristiansand Lufthavn, Kjevik (ENCN)

All the Accusim-planes are in my hangar, but they aren't sitting long enough for their engines to cool much before next flight!

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Tim-HH
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Re: Short and sweet T-6 video with Scott

Post by Tim-HH »

That's a great video! It always amazes me how well A2A captures the sound of an aircraft :)
Medtner wrote:The hydraulic pressure reads 0 before and during the takeoff. The needle jumps as you pull the gear-lever, and after raising the gear it settles on the correct pressure, but then falls after you've lowered the MP to 30. Is this normal?
Yes, according to my T-6G flight manual that is exactly how the hydraulic system works:

Image

It would be interesting to know why it works differently in the A2A T-6G.

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Tim
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AKar
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Re: Short and sweet T-6 video with Scott

Post by AKar »

By system description, it seems this is normal (can't see the video right now, so I'm on your description as well :)).

The constant flow (per RPM) is entirely diverted to the reservoir, so that the normal hydraulic pressure indication when no systems are commanded is low, close to zero. When either the landing gear or the flaps are operated, the power control valve closes the return, and only the relief valve keeps the pump from slamming its head against a brick wall, effectively providing a max-pressure regulation. As the pump's displacement is apparently low in comparison to the peak demand, the pressure ought to establish to a figure below the nominal. When the hydraulic cylinders in motion reach their final positions, they accept no more flow, and the fluid has no other way to go but the relief valve, which pops the pressure up to the nominal.

The power control valve is in some way apparently a time-delay device. I don't know how it functions, but I'd assume it has a some sort of hydraulic pressure accumulation delay control, which apparently eventually brings back the return flow, and brings the pressure back to zero or thereabouts, supposedly after some time about twice the gear and/or flaps actuation time.

Edit: Only after posting I saw Tim's post that exactly quotes the text I was after, together with the schematic on the previous page. So the RL video seems correct (this is not always the case! Real airplanes can indicate pretty badly, but this doesn't seem to be the case here.)

-Esa

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Medtner
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Re: Short and sweet T-6 video with Scott

Post by Medtner »

Interesting reading!

This means that the A2A T-6 has either a different system (more like we are used to in other Accusim-planes), or that it is faulty somehow.
Erik Haugan Aasland,

Arendal, Norway
(Homebase: Kristiansand Lufthavn, Kjevik (ENCN)

All the Accusim-planes are in my hangar, but they aren't sitting long enough for their engines to cool much before next flight!

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AKar
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Re: Short and sweet T-6 video with Scott

Post by AKar »

There could be explanations to it, but on the other hand, in my experience these details are exactly where we are running at when speaking the limits of our depth of simulation in the top products available. In that sense, I wouldn't be shocked if it was just a some misapplication of a generic hydraulic system model of full-time relief when running with no demand. A true, real-life physics simulation of such a hydraulic system even in a loose approximation takes the analysis to the s-domain really, or to some mere scripts to skip that.

-Esa

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Medtner
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Re: Short and sweet T-6 video with Scott

Post by Medtner »

AKar wrote:There could be explanations to it, but on the other hand, in my experience these details are exactly where we are running at when speaking the limits of our depth of simulation in the top products available. In that sense, I wouldn't be shocked if it was just a some misapplication of a generic hydraulic system model of full-time relief when running with no demand. A true, real-life physics simulation of such a hydraulic system even in a loose approximation takes the analysis to the s-domain really, or to some mere scripts to skip that.

-Esa
If it is a simple misapplication I'm sure it can be fixed easily - Accusim seems to be thoroughy deep enough to just "turn it around" so to speak.
Erik Haugan Aasland,

Arendal, Norway
(Homebase: Kristiansand Lufthavn, Kjevik (ENCN)

All the Accusim-planes are in my hangar, but they aren't sitting long enough for their engines to cool much before next flight!

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AKar
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Re: Short and sweet T-6 video with Scott

Post by AKar »

Medtner wrote:If it is a simple misapplication I'm sure it can be fixed easily - Accusim seems to be thoroughy deep enough to just "turn it around" so to speak.
I'm sure they fix this at first convenience. :)

Just saying that these are not trivial problems, if done in a real-time physical way, because the numerical simulation of these would be somewhat difficult even outside the limitations of the flight simulation, even if the T-6's hydraulics are rather simple with no pressure accumulators and with no pump flow demand control.

-Esa

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Medtner
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Re: Short and sweet T-6 video with Scott

Post by Medtner »

AKar wrote:
Medtner wrote:If it is a simple misapplication I'm sure it can be fixed easily - Accusim seems to be thoroughy deep enough to just "turn it around" so to speak.
I'm sure they fix this at first convenience. :)

Just saying that these are not trivial problems, if done in a real-time physical way, because the numerical simulation of these would be somewhat difficult even outside the limitations of the flight simulation, even if the T-6's hydraulics are rather simple with no pressure accumulators and with no pump flow demand control.

-Esa
It's not trivial, but I'm sure the T-6 has a deeper system than we can see - this update video on the P-40 and its hydraulic system shows off some of what Accusim looks under the hood. I'm sure this is further updated since that time too (this video is from 2011),

https://www.youtube.com/watch?v=LTL8KtJawTQ
Erik Haugan Aasland,

Arendal, Norway
(Homebase: Kristiansand Lufthavn, Kjevik (ENCN)

All the Accusim-planes are in my hangar, but they aren't sitting long enough for their engines to cool much before next flight!

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Re: Short and sweet T-6 video with Scott

Post by crippy »

Love seeing videos from A2A. They really set my day off on a positive note!
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DHenriques_
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Re: Short and sweet T-6 video with Scott

Post by DHenriques_ »

Medtner wrote:If you haven't seen this already:

https://www.youtube.com/watch?v=aWfJzxPrBhE

A question for Scott:

The hydraulic pressure reads 0 before and during the takeoff. The needle jumps as you pull the gear-lever, and after raising the gear it settles on the correct pressure, but then falls after you've lowered the MP to 30. Is this normal?
The early T6's (I flew an SNJ5 as well as the G) had a Power Push in the cockpit that you had to use before raising or lowering gear or flaps. That performed what the power control valve does in the G. So basically all they did was incorporate pressurizing the hydraulic system into an internal valve that does the work for you taking the Power Push function out of the equation.
I've not taken the hydraulic system apart on the G but I believe we have it right for the sim. The system is depressurized until either flaps or gear is selected as pressure in the latent system is returned to the reservoir.
When you select gear or flaps the system is then pressurized and pressure supplied to the system. This accounts for the gauge reading low then high then low again.
Dudley Henriques

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Medtner
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Re: Short and sweet T-6 video with Scott

Post by Medtner »

But, Dudley,

Doesn't this mean that it is upside down in the Accusim T-6? As it is now it is pressurized all the time the engine is running, only to lowered a few hundred pounds when using the system, and then raising to full nominal pressure.
Erik Haugan Aasland,

Arendal, Norway
(Homebase: Kristiansand Lufthavn, Kjevik (ENCN)

All the Accusim-planes are in my hangar, but they aren't sitting long enough for their engines to cool much before next flight!

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AKar
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Re: Short and sweet T-6 video with Scott

Post by AKar »

I think you Erik indeed are on to something. In the way I read the schematic & description, it should go like this:

1. With no gear/flap selection, the pump is turning with the engine, but all the oil is diverted straight back to the reservoir by the power control valve. We must remember that pumps, on the first order, do not create pressure, but flow. Now there is very little restriction to the flow, so the pressure remains very low.

2. Select gear up for example. Now the flow control valve blocks the return, and the oil is diverted to the landing gear actuators instead. The flow remains the same, and the pressure is determined by the effort required to move the gear leg, so it is somewhat dynamic.

3. When the gear reaches its up position, the flow still remains constant. But it slams against a brick wall, with nowhere to go in that direction. Therefore the relief valve is pushed open, with its closing spring pressure calibrated to counter more or less exactly the nominal hydraulic system pressure. All the fluid again circulates back to the reservoir, but it needs to counter the relief valve spring pressure, so the pressure remains high, at around nominal.

4. After the time delay function, how ever on the Earth that works precisely, the power control valve opens the direct return to the reservoir while closing the line to the landing gear, dropping the pressure back to very low value.

-Esa

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DHenriques_
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Re: Short and sweet T-6 video with Scott

Post by DHenriques_ »

Medtner wrote:But, Dudley,

Doesn't this mean that it is upside down in the Accusim T-6? As it is now it is pressurized all the time the engine is running, only to lowered a few hundred pounds when using the system, and then raising to full nominal pressure.
I've never actually seen the system apart in the shop (real world) but what AKar has said sounds about right to me. Not sure how we dealt with this in the sim but pinged Scott for you on Skype in the hope he can shed more light on it.
DH

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Scott - A2A
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Re: Short and sweet T-6 video with Scott

Post by Scott - A2A »

Well this is a bit odd because the schematic we used to build the hydraulic system didn't really show this behavior, but now that I'm looking at it again, I can see how this is happening. Once we have some time to revisit the 6, I'll review the flights again and get deeper into what is happening here but at face value, it looks pretty simple and straight forward.

Scott.
A2A Simulations Inc.

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