Flaps deployment

[Pilum]

How refreshing with some solid research work to balance some of the previous speculation voiced in this thread.

 

Good work, Friedrich :thumbup:

Edited January 22, 2015 by Pilum

[Crumpp]

What does testing the relief valve with a mule have to do with the capacity of the pump?

[Crumpp]

The hydraulic system has multiple check valves to keep fluid moving in one direction and a pressure relief valve to keep the system from over-pressurizing.

 

1300 psi is what the system is pressurized too. At servicing, a hydraulic mule is required that can deliver 3gph at 2000 psi for 5 minutes to conduct the pressure test for leaks. The pressure relief valve is of course set to unload during this test.

 

So, if you over speed the flaps in the P-51, you would lose your entire hydraulic system. The pressure relief valve would detect the drop in pressure on the system circuit and open the pump circuit to pull fluid from the reservoir attempting to keep pressure until it emptied the reservoir.

 

The flaps would stay locked until the pressure relief valve trips depressurizing the system.

 

 

 

Here...read it in context.

[Echo38]

This is all quite confusing to me, but the one thing that everyone seems to agree on is that deploying the P-51D's flaps at high speed (and/or leaving them deployed and overspeeding) would damage something, but it doesn't in the sim. Is this assessment accurate? Whether or not the flaps should retract or freeze in place upon overspeeding is a different, though related, question:

Retract under force, but unable to deploy again due to damage?

Retract under force, but able to deploy again despite damage?

Freeze in place, unable to deploy or retract due to damage?

Freeze in place, but able to retract if the lever is returned, despite damage?

 

USARStarkey: why is Mr. Fahey so hostile toward DCS? While I enthusiastically welcome any criticism of a real warbird pilot, in the spirit of making the sim closer to the reality, I must say that the attitude displayed in the lines you (appear to have) quoted indicates vehement contempt, and I'm perplexed as to what makes him have such a low opinion of the sim as a whole. We all know that DCS isn't perfect, and is missing certain important elements such as engine idle behavior. However, the attitude that I got from your quotes isn't that merely that Mr. Fahey recognizes errors in the sim, but rather that he doesn't see an value in it at all as anything other than a mere game. And that's puzzling, because the sim is highly accurate in many areas and pushes boundaries that no other P.C. flight sim has approached (and has gained the respect of many real warbird pilots). What's the story? Why does he appear to be so emotionally opposed to anyone regarding DCS as an excellent P-51D P.C. simulator with some flaws?

Edited January 24, 2015 by Echo38

[Friedrich-4B]

The hydraulic system has multiple check valves to keep fluid moving in one direction and a pressure relief valve to keep the system from over-pressurizing.

 

1300 psi is what the system is pressurized too. At servicing, a hydraulic mule is required that can deliver 3gph at 2000 psi for 5 minutes to conduct the pressure test for leaks. The pressure relief valve is of course set to unload during this test.

 

So, if you over speed the flaps in the P-51, you would lose your entire hydraulic system. The pressure relief valve would detect the drop in pressure on the system circuit and open the pump circuit to pull fluid from the reservoir attempting to keep pressure until it emptied the reservoir.

 

The flaps would stay locked until the pressure relief valve trips depressurizing the system.

 

Here...read it in context.

 

In context: the flaps, landing gear and fairing door system is pressurized to 1050 lbs in² ± 50. To test the system a test stand delivering 4 gpm @ 1300 lbs in² is recommended:

 

The hydraulic landing gear operating struts could be tested @ 2000 lbs in² for five minutes; port C of the unloading/relief valve could also be tested @ 2000 lbs in²(see page 268 para 4: http://forums.eagle.ru/showpost.php?p=2298330&postcount=73)

 

I'm not wasting any more time on this: the P-51D hydraulic schematics, systems operation and analysis & repair procedures are all properly documented and available for all to read.

Edited January 25, 2015 by Friedrich-4/B
add fairing door system...

[IvanK]

And what does Mr Stephen Grey say about this ? ... I mean he is a current P51 pilot and deeply associated with this Sim !

 

In all the other similar vintage US fighters that have blow-back systems it is specifically mentioned in their respective manuals. I don't see any reference in the various P51 manuals to any protective blow back or limiting system. Flap speed limits are clearly mentioned which implies Dont throw them out (or exceed these speeds if deployed) above these speeds because some damage may occur.

[Crumpp]

The hydraulic landing struts

 

:doh:

 

Why are you talking about the landing struts??

 

Do you think the pressure of the struts is relevant for some reason to the flaps? I hope not but I do not understand why you are even discussing them.

 

Look on the schematic and find the landing struts....

 

 

 

Why are the landing struts not on the hydraulic system schematic....because they are not connected to the hydraulic system!

 

:thumbup:

 

I fail to see the reason you took to the time to write about and underline something so completely irrelevant to the topic of the flaps system.

 

You are just posting pictures and making comments without understanding what you are even talking about.

 

 

'm not wasting any more time on this: the P-51D hydraulic schematics, systems operation and analysis & repair procedures are all properly documented and available for all to read.

 

Good thinking.

[Pilum]

With the caveat that hydraulics is a bit out of my area, I looked at the pdf Friedrich posted in #73 and based on this I think Crumpps theory that the system will drain and need a reset if overloaded is overly complicated and wrong and I have a different theory which is simpler and if I'm right would also mean that the P-51 engineers did a better job of designing the hydraulics system:

 

Looking at figure 309, this I think is how the system looks like when at rest. So it could depict flaps up or at any of the setting the pilot can select. Note that in this state all of valves are closed. Now if the pilot moves the flap lever in cockpit to a different setting, this opens up 2 of the 4 valves in figure 329, either moving flaps up or down until the valves are closed by the follow up arm as depicted in figure 330.

 

Then the question of usage within and without operting limits: Taking the 10 deg setting as an example going from the flap up position, if within limits when moving the flap lever, this would open the 2 valves (Figure 329, upper figure) and keep these open until the flap reaches 10 deg at which time the follow up arm (see figure 330) will close the valves and the system will be back at rest as described above.

 

Now if we from this state for example dive past the 400 mph limit, the pressure on the rod holding the flap in place at 10 deg will increase. However, all the valves are now closed so there is nowhere for the hydraulic fluid to go (see figure 329) so the presssure will just build up until something gives. This could either be the hydraulic circuit or more likely something in the mechanical linkage. So to me it looks like is you manage to get the flaps out, they will stay in that position (which the manual also states, see post #60 by Solty) until the pilot moves the lever or something gives.

 

The finally, what happens if you try to deploy flaps a higher speeds than the operating limits? Well when the pilot moves the lever to the 10 deg position from the up position, he opens the valves as before and the flaps start to move. However, in this case if the speed is high enough, the hydraulic pressure will not be enough to move the flap to the 10 deg position and the follow up arm in figure 330 will consequently not close the valves so the system will be stuck in this configuration. Now nothing dramatic will happen here as far as I can see, the flap will simply not move past the point where the flap angle balances the system pressure, which will be somewhere between 0 and 10 deg and the system will simply maintain the design pressure trying to move the flap, i.e. nothing leaks out, unless as Friedrich already pointed out, the system is damaged and there is a leak somewhere.

 

Just my $ 0.02 and given I'm not a Leonardo da Vinci endowed with superior understanding of piloting, aerodynamics, engine & fuel performance, flight mechanics, weight & balance, roll and turn performance, aviation physiology and g-tolerance (did I miss something?:)) I may well be wrong.

[Crumpp]

And what does Mr Stephen Grey say about this ? ... I mean he is a current P51 pilot and deeply associated with this Sim !

 

I asked Nick Grey about it. And the way the flaps are realised in DCS corresponds to his answer. That corresponds my technical consideration, too.

 

No engineer is going to design a hydraulic system that will structurally damage the aircraft. At least that is the goal to have the hydraulic system fail before the aircraft structure.

 

When it fails, the flaps will come back up as depicted in the game. The question becomes a technical one based on the inner workings of the pressure relief valve.

 

Crumpp says:

 

Obviously they cannot overcome physics....

You only have 1300 psi to work with. I got the operation of the check relief valve from the maintenance manual description. The only thing that bothers me is the small valve on the pressure relief valve that is part of flap system circuit. It does not say in the description if it fails to the closed position. I would call the P-51 mechanics and ask them that question as it is not clear in the description. It looks like that valve just returns fluid from the system back to the reservoir when the system is pressurized to prevent over-pressurization and that is what it says in the description. If that is the case, you would lose your hydraulic system as I described.

 

If it does fail in the closed position then it will lock the pressure in the flap system and your flaps are stuck.

 

Overspeeding would then damage the flaps, hinges, wing warping, and ultimately failure of the wing just like a mechanical system.

[Pilum]

:doh:

 

Why are you talking about the landing struts??

 

Do you think the pressure of the struts is relevant for some reason to the flaps? I hope not but I do not understand why you are even discussing them.

 

Look on the schematic and find the landing struts....

 

 

 

Why are the landing struts not on the hydraulic system schematic....because they are not connected to the hydraulic system!

 

:thumbup:

 

I fail to see the reason you took to the time to write about and underline something so completely irrelevant to the topic of the flaps system.

 

See figures 319 and 320 in the pdf Friedrich posted and you will see the connection between the landing struts and your figure 309 Crumpp. :doh:

Edited January 25, 2015 by sobek

[MiloMorai]

LOL Pilum beat me to it. It is very obvious that the landing gear actuation strut system is connected to the flap actuation system

Edited January 25, 2015 by sobek

[Pilum]

LOL Pilum beat me to it. It is very obvious that the landing gear actuation strut system is connected to the flap actuation system.

 

Or maybe there is a rubber band you can pull or hand wheel to operate the landing gear somewhere? I mean, this would for sure be useful if you run out of hydraulic fluid?

Edited January 25, 2015 by sobek

[Crumpp]

ee figures 319 and 320 in the pdf Friedrich posted and you will see the connection between the landing struts and your figure 309 Crumpp.

 

That is the operating strut that pull the gear and doors up.

 

 

 

It is not the landing struts.

 

 

:smilewink:

 

That is why you would lose the ability to raise the gear if the flaps system failed because that system is connected.

 

However there are additional lines on the reservoir that allow the emergency hand pump to draw additional fluid from the reservoir to operate the gear.

[Shahdoh]

Pretty sure I have heard somewhere that a mustang has damaged its flaps and connected systems from putting its flaps down to far at to high of a speed. Question is, was it some other failure that allowed it to do so, but seems like the systems may of allowed the pilot to do so, thus causing the damage. I think deformation of the flaps and other damage was caused. Will have to see if I can find the info again.

[MiloMorai]

Why is it every one else understood it was the operating strut and you didn't Crumpp?

[Pilum]

Pretty sure I have heard somewhere that a mustang has damaged its flaps and connected systems from putting its flaps down to far at to high of a speed. Question is, was it some other failure that allowed it to do so, but seems like the systems may of allowed the pilot to do so, thus causing the damage. I think deformation of the flaps and other damage was caused. Will have to see if I can find the info again.

 

OK, that is interesting info. Please post it if you find it again!

[Pilum]

That is the operating strut that pull the gear and doors up.

 

 

 

It is not the landing struts.

 

 

:smilewink:

 

That is why you would lose the ability to raise the gear if the flaps system failed because that system is connected.

 

However there are additional lines on the reservoir that allow the emergency hand pump to draw additional fluid from the reservoir to operate the gear.

 

But the operating strut in figure 318 is also connected to the hydraulics system which you claimed it was not Crumpp :music_whistling:

 

Really, I think you will have a hard time extricating yourself from this one......

 

It's Saturday and dinnertime here now so time for me to go but I'll be back tomorrow if you post some more goodies be sure!

[Crumpp]

Pilum says:

 

the operating strut in figure 318 is also connected to the hydraulics system which you claimed it was not Crumpp

 

That is a complete fiction. No where do I say this at all.

 

Friedrich-4/B says:

 

The hydraulic landing struts could be tested @ 2000 lbs in²

 

 

It is just not productive to not understand the parts and systems you are trying to claim work a certain way.

 

Once more, it has nothing to do with the flaps failing or the topic of this thread except to prove what the Maintenance Instructions already tell us....

 

If you lose the main hydraulic system, the gear will not operate. That was pointed out in my first post on this subject.

 

Crumpp says:

 

In theory the check valves will lock the pressure in until the system over-pressurized and trips the relief valve. You get to hand pump the gear down and the flaps should retract when pressure relief valve trips as it depressurizes the entire system.

 

http://forums.eagle.ru/showpost.php?p=2297528&postcount=63

[NineLine]

So let me ask a simple question, are you guys arguing because you think that maybe ED will model something wrong because one of you might not be explaining it right, or are you guys just trying to show each other who is smarter? Just trying to figure out what we are going for here...

[Friedrich-4B]

So let me ask a simple question, are you guys arguing because you think that maybe ED will model something wrong because one of you might not be explaining it right, or are you guys just trying to show each other who is smarter? Just trying to figure out what we are going for here...

 

Not trying to argue; just providing documentation and information based on that documentation. If other people want to waste their time quibbling over one missing word, that's their problem.

[NineLine]

Remember kids, it takes two to tango...

 

Post info that you might think is helpful, but its really up to ED to decide how to interpret that info or what is useful and what isnt... everything else is just silliness... you guys want to fight... there are a few WWII servers out there, just post the results and vids on the forums for us ;)

[MiloMorai]

It is more than helpful, and informative, besides to ED.

[Pilum]

I only ask you, what makes you so confident that P-51 flaps can be deployed against the forces much greater than normal? Or what factor can hold the flaps as they were already deployed against increasing forces? It could be kinematic design like in Yak-18, a latch... did you find something in P-51? Anyway, there are several manuals for P-51 with hydraulics schematics... if you prove using these sources that the pressurized chamber of the actuator cylinder is completely sealed from the entire system with a check valve and there is no releaf valve to this part of tubing - it could be a base to recheck flaps in DCS P-51.

 

To answer the questions above on what factor can hold the P-51 flaps down against increasing forces and if the pressurized chamber can be shown to be completely sealed off from the rest of the system, I think the pdf of the P-51 hydraulic system Friedrich posted in post #73 actually provides proof of this:

 

Looking at figure 309 in the pdf, this I think is how the system looks like when at rest. So it could depict flaps up or at any of the setting the pilot can select. Note that in this state all of valves are closed. So the flap hydraulic circuit is cut off from the pump, relief valve and reservoir. Now if the pilot moves the flap lever in cockpit to a different setting, this opens up 2 of the 4 valves in figure 329 connecting the circuits and admitting pressure to the flap circuit, either moving flaps up or down until the valves are closed by the follow up arm as depicted in figure 330.

 

Assuming a scenario of high altitude flight with IAS lower than 165 mph, the pilot moves that lever to the 50 deg position. This would open the 2 valves (Figure 329, upper figure) and keep these open until the flap reaches 50 deg at which time the follow up arm (see figure 330) will close the valves and the system will be back at rest as described above. Note that since all valves are closed, this seals the flap actuator circuit from the main circuit including the relief valve.

 

Now if we from this state dive and ignore the placard IAS limits and don't move the lever in the cockpit as prescribed, the pressure on the actuator rod holding the flap in place will increase. However, all the valves are now closed so there is nowhere for the hydraulic fluid to go (see figure 329) so the flap will stay at 50 deg and the pressure will just build up in the actuator circuit (now sealed from the main circuit since all valves are closed) until something gives. This could either be a component in the sealed off flap actuator hydraulic circuit or more likely something mechanical in the wing, flap, torque tube or linkage system.

 

So based on the above reasoning it looks like the currently modeled behaviour in DCS where the P-51 flaps are forced up if the flap setting IAS limits are exceeded is not correct.

[Crumpp]

Holtzauge,

 

The thermal relief valve will open at 1400 to 1600 psi and return the excess fluid to the reservoir.

 

Take a close look at the path it takes to get there. When that pressure hits the system, the pressure relief valve will open.

 

It works as described.

 

the way the flaps are realised in DCS corresponds to his answer.

 

http://forums.eagle.ru/showpost.php?p=2296827&postcount=29

 

Why? Well just look at the system and you will see it was designed:

 

tell any aero-engineer dealing with hydrolics that he has to design a hydro actuator with force capacity much more that it needs for safe operation.

 

http://forums.eagle.ru/showpost.php?p=2296825&postcount=27

[Crumpp]

If the hydraulic system is malfunctioning then there will be structural damage. There is a very good reason why it gets tested on a regular basis.