Terrific Beta Mustang but it is unstable: FM needs tweaking

[Smokin Hole]

Regarding the powerful torque effects seen when changing power settings at low speeds, I came across this article early in DCS Mustang development, which discusses this issue and the devastating effects in can have when mismanaged:

http://www.avweb.com/news/pelican/pelicans_perch_87_killer_go-arounds_195755-1.html

 

Forget the Mustang. That article was awsome! More idiotic behavior occurs during go-arounds than any other phase of flight.

 

Thanks for sharing!

[wolfstriked]

I have been saying for years that the ultimate controls for flight sims is not long throws but in fact very short throws with very high tension.This tension though must be a smooth progression so that you can feel minute changes in force and also the small amount of movement must be linked to gears to run a pot thru its total range.Sadly this is just not being worked on.I am not lying here when I say that I was the first person to say that a proper brake pedal is one with very small amount of very progressively hard throw and geared to use a pots full range....was ridiculed by many at Racesimcentral yrs back but now the brakes of modern racing sims controls do just that.I even sent emails to Thomas from Fanatec wheels to make a hardcore sub $200 dollar set of rudders but not even a reply back sadly.:doh:

[Nate--IRL--]

Forget the Mustang. That article was awsome! More idiotic behavior occurs during go-arounds than any other phase of flight.

 

Thanks for sharing!

 

Concur - a great read.

 

Nate

[104th_Crunch]

I use a CH Flightstick and ProThrottle. I use the trim hat (or view hat) on the Flightstick for trim, up/down for elevator trim, left/right for rudder trim. It's possible that each press imoves the trim too much, as I am always trimming through the desired value rather than nailing it. I do not have any spare axes so if trim cannot be operated effectively via a hat, my career as a virtual Mustang pilot might be a short one.

 

Hi Bahger, maybe I am reading this post wrong, but it sounds like you are using the wheels on the CH stick that you are not suppose to. If not then I'll mention this for others.

 

On the CH sticks there is only 1 wheel axis to use for which you can assign a function to trim etc. It is on the left side of the base of the joystick.

 

Then there are 2 more wheels that should not be used normally. They are on the front of the base and the right of the base. These are there as part of the design of the joystick when they are first manufactured. These 2 wheels should be adjusted so the that they sit in the center indent for each, then never touched.

 

It is peculiar that they are there as many people I am sure assume they are trim wheels, but they are not.

Edited May 8, 2012 by Crunch

[Bahger]

Hey guys, thanks for the useful replies and the excellent articles. That post-incident report serves as a warning: this is a lot of airplane and it can easily turn around and bite.

 

Crunch, I'm only using the mappable wheel, i.e. the one on the left side of the joystick; I know the others are purely mechanical in function. I had the left wheel mapped for RPM but soon discovered, thanks to another post in this forum, that it's a lot better to use it for elevator trim. Since then, I have found the Mustang to be much more stable, with less porpoising and much finer control of nose oscillations. I've now run out of usable axes so I'm thankful that rudder trim works ok when mapped to a hat and there's not tooo much need for aileron trim. It's a pain to have to go hands-off to use elevator trim on the a/c, at least, hand off the throttle and then move it across to the stick. It's worth it for the finer control it gives but I really hope the devs make elevator trim work via the stick trim hat. I don't think this compromises realism too egregiously.

[104th_Crunch]

Good to hear Bahger. A CH or Saitek quadrant is a good investment.

[PeterP]

:D Yes it is

 

 

 

But I have to speak out a warning for the Saitek quadrant:

It has really low-quality potentiometers. I had to maintain every 5(remaining orginal)axis last week to reduce the jitter to a acceptable value.

I had the left unit since 3month in use and the right is 2 years old and it started around a half year after purchase ,and on the second much quicker. As it happened with the first unit I thought it was just a faulty production, and as it didn't become much worse I accepted this.

But as it also started at the second one (and this time I knew much more about potentiometers and such) I knew it is a design-flaw...

cichlidfans unit arrived with unacceptable jitter on all axis after un-boxing...

I got it temporally fixed - but have no much hope that it will last for long.

I will replace the potis asap.

 

Please read this thread for more reference ,its topic is the trim-wheel that doesn't shows such symptoms but it contains also info about the Saitek-TQ:

http://forums.eagle.ru/showthread.php?t=87983

espacialy post #2 and #11

 

I would go for a CH Throttle quadrant next time.

Edited May 8, 2012 by PeterP

[aaron886]

The hell is that evil thing?!

[159th_Viper]

The hell is that evil thing?!

 

The FrankenPeter.

[effte]

The FrankenPeter.

 

Oooooh... that conjured up images I didn't need!

[cichlidfan]

The FrankenPeter.

 

Seriously, another name is needed! Almost anything!:megalol:

[aaron886]

Oooooh... that conjured up images I didn't need!

 

Hahahaha rep inbound. Priceless.

[PeterP]

:huh:Guys, are you making fun out of me?

Head over here to celebrate the evil baptism! >>> http://forums.eagle.ru/showthread.php?p=1453536#post1453536

[cichlidfan]

:huh:Guys, are you making fun out of me?

Head over here to celebrate the evil baptism! >>> http://forums.eagle.ru/showthread.php?p=1453536#post1453536

 

Don't worry Peter, genius takes many forms.:thumbup:;)

[lobo]

Regarding the powerful torque effects seen when changing power settings at low speeds, I came across this article early in DCS Mustang development, which discusses this issue and the devastating effects in can have when mismanaged:

http://www.avweb.com/news/pelican/pelicans_perch_87_killer_go-arounds_195755-1.html

 

Thanks for that article! Very nice. :thumbup:

 

In the sim if you come in for landing slow (90), with full flaps, and then initiate a go-around at low alt or on the runway by jammin the power to the firewall... bad things happen fast. You will be glad you are doing this in a sim and not in RL. "it's best to be gentle with the power." Golden words.

 

The author also mentions in the article 2700 rpm vs 3000, I tried both and did not notice a benefit to 2700 rpm in the beta. It still went very bad if you just jam on full power at either 2700 or 3000 rpm while slow and with full flaps. ...I wonder which manual said to use 3000? The manuals I have all say 2700 rpm for landing (as does the placard on the instrument panel).

 

Also mentioned in the article is the bounce. Using the authors technique for bounce recovery: "a small shot of power to "cushion" the next touchdown" works great with the DCS Mustang.

[effte]

The RAF Mustang III manual says prop full forward... with some tables saying 2700 to confuse matters.

 

As for lower RPM -> lower power -> lower torque, it's not quite that simple. Power is a function of torque and RPM, so for a given amount of torque you are getting more power at a higher RPM - and vice versa, more torque for a given amount of power at a low RPM. In other words, don't count on lower RPM giving you less torque to contend with, even if it does give less power.

[sobek]

To make matters more confusing, you need a certain minimum RPM to get a certain given power out of the engine, or you will overboost it, which results in detonation, which in turn is very bad for your piston rod and crankshaft bearings.

 

That being said, IMHO you don't need a lot of power for a go around. Anticipate the go around early and bring on the power easy until she starts to climb, use as much as you need but as little as possible. With full flaps, it is indeed very easy to torque spiral her into the ground. Just try taking off in that config. :)

Edited May 9, 2012 by sobek

[effte]

"Anticipate the go-around early"... wish you always had the option! :D

 

Still trying to figure out if you can overboost the P-51, or if the MAP regulator has the authority to prevent it. There are no warnings or explicit limitations in the manuals that I can find, which suggests it isn't a concern. There are the limitations specifying 46"/2700, which I interpret as never going above 46" with RPM at 2700, but that's hardly explicit.

 

The automatic boost should limit the manifold pressure, so a serious overboost shouldn't happen as long as the regulator is working. However, 61" at 2700 will fill the cylinders more than 61" at 3000. On the third hand, the engine is rated for 67" without blowing up, so you should still be fine, at least for a bit. Now, what will happen if you foolishly go to 67" without bringing the prop forward... ?

 

Plenty of speculation above. :)

[sobek]

The automatic boost should limit the manifold pressure, so a serious overboost shouldn't happen as long as the regulator is working.

 

By overboost i mean "more than is specified as maximum boost at that RPM". As far as i understood, the MP governor does not measure RPM, so detonation will certainly be an issue. :)

[effte]

That's what I wonder. Without automatic boost, the boost would go through the roof. But with automatic boost, the regulator will close the butterfly valve keeping MP at 61".

 

OTOH, we've gotten a RR limited authority boost regulator in our Mustang - does it have enough authority to prevent an overboost if you drop the RPM from 61"/3000?

 

Please try it and let me know! I'm stuck in a hotel room as usual...

[sobek]

OTOH, we've gotten a RR limited authority boost regulator in our Mustang - does it have enough authority to prevent an overboost if you drop the RPM from 61"/3000?

 

Yes it does, the MP will under no circumstances go over 61", however, i'm pretty certain that your engine will have severe detonation at the lower RPM numbers where the blower can still supply 61".

[effte]

I wouldn't consider that a given. After all, the increase in charge in the cylinder will be marginal, only due to the increased time to get air through the intake valves at a lower RPM, and WEP shows there to be plenty of detonation margin at 61". The ignition timing changes with RPM, so that shouldn't be an issue either.

 

As I said, still pondering this so let's work together and speculate endlessly. Why do you think there would be detonation?

[sobek]

As I said, still pondering this so let's work together and speculate endlessly. Why do you think there would be detonation?

 

Because Yo-Yo said it will be modelled. Your turn. :D

 

Edit: Well there is still the possibility that it will only happen under WEP, but i don't think so.

Edited May 9, 2012 by sobek

[effte]

He did? Well, that's pretty authorative. I've seen that overboosting is WIP, but that's not exactly the same. Got a link to that post of his?

 

And why would there be, considering the engineering of the aircraft and leaving forum posts aside? :)

[sobek]

Because peak cylinder pressure is raised with lower RPM, increasing the risk of parts of the mixture detonating instead of deflagrating. I certainly know that it was a problem with aircraft of similar design, so why would it not be on the mustang?