Jump to content

Yo-Yo: What causes Pitch Up at lowering IAS


DD_Fenrir

Recommended Posts

Hi Yo-yo.

 

Hope you can clarify this question; what aerodynamically is happening in the Spitfire to cause the aircraft to become tail heavy as IAS drops?

 

This behaviour is counter to how most aircraft behave, i.e. in they get nose heavy as airspeed drops.

 

Please note, that I am in no way challenging the FM, I am more than happy that this is what should be happening, just curious as to what the CP is doing in relation to the CG and what makes the Spitfire fairly unique in this regard.

 

Thanks!

Link to comment
Share on other sites

  • ED Team
Hi Yo-yo.

 

Hope you can clarify this question; what aerodynamically is happening in the Spitfire to cause the aircraft to become tail heavy as IAS drops?

 

This behaviour is counter to how most aircraft behave, i.e. in they get nose heavy as airspeed drops.

 

Please note, that I am in no way challenging the FM, I am more than happy that this is what should be happening, just curious as to what the CP is doing in relation to the CG and what makes the Spitfire fairly unique in this regard.

 

Thanks!

 

I do not understand completely what you mean. What conditions? Power-on, gliding?

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

Link to comment
Share on other sites

  • ED Team

Yes, its absolutely distinctive for props, especially with low stability margin. prop destabilising effect.The more AoA is the more is the propeller lift, thus nose-up moment, so the plane getting additional instability.

 

109K behaves the same way.

 

The clear sign of it is reverse trim position of the stick vs IAS. Try to glide at different speed and watch the trim position, then try to climb and watch the same.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

Link to comment
Share on other sites

Ahh, that makes sense, particularly for aircraft with neutral stability, thanks Yo-Yo.

 

I had assumed it was something to do with differing rates of lift loss between the wings and the horizontal tailplane, had not even thought about prop effects.

 

On a separate note, I have noticed almost every Spitfire in air-to-air shots when trimmed for cruise has the elevator always slightly depressed. Indeed this great video of a Mk.V flying over Malta shows over the tail shots and the elevator barely even reaches datum with the chord line of the horizontal stabiliser through a aerobatic routine:

 

 

I would have assumed that some sort of engineering could have been accomplished so that the elevator trim 0 position for cruise would have matched the horizontal stab datum. Is this not important for trim drag?

Link to comment
Share on other sites

  • ED Team
Ahh, that makes sense, particularly for aircraft with neutral stability, thanks Yo-Yo.

 

I had assumed it was something to do with differing rates of lift loss between the wings and the horizontal tailplane, had not even thought about prop effects.

 

On a separate note, I have noticed almost every Spitfire in air-to-air shots when trimmed for cruise has the elevator always slightly depressed. Indeed this great video of a Mk.V flying over Malta shows over the tail shots and the elevator barely even reaches datum with the chord line of the horizontal stabiliser through a aerobatic routine:

 

 

I would have assumed that some sort of engineering could have been accomplished so that the elevator trim 0 position for cruise would have matched the horizontal stab datum. Is this not important for trim drag?

 

Do you take in account wing downwash stream?

 

And, by the way, different stability margin (or different neutral point) is possible for high and low CL regions.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

Link to comment
Share on other sites

I got question about elevator control linked with stick in cocpit and joystick position.

 

 

 

Without FF joystick i noticed that if joystick is in center (neutral), stick in cocpit is in center ( control zone window) but elevator surface (steer surface) is little in down position ( behind center axis) which casue to fly Spitfire more level. It looks that stick in cocpit in neutral casue elevator surface little down postion. No need full trim nose down to level flight. Much easier to fly without constant push stick to level flight.

 

 

attachment.php?attachmentid=203387&d=1548807936

 

 

If i turn ON Force Feedback on stick i noticed that joystick is in neutral ( center), stick in cocpit is little aft postion ( below center in control zone window with axis) and elevator surface is in neutral (center) position. Plane now need full trim nose down to fly more level flight but still required constant push stick - not possible to trim for level flight.

 

 

 

attachment.php?attachmentid=203386&d=1548807936

 

 

Whats is reason of these? In real Spitfire stick in neutral casue elevator in little down position?


Edited by Kwiatek
Link to comment
Share on other sites

  • ED Team

What type of FF stick do you have?

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

Link to comment
Share on other sites

Well, here its the same. Flying with MSFFB2 and 20cm Extension.

Even with full trimm i have to push the stick forward for levelflight.

With more Speed it gets better, but neutral Position is a no go with the spitfire.

 

 

Try to disable FF effect and compare things.

Link to comment
Share on other sites

  • 1 year later...
Do you take in account wing downwash stream?

 

And, by the way, different stability margin (or different neutral point) is possible for high and low CL regions.

 

What is the correct interpretation of NOSE TRIM on the Spitfire instrument panel gauge ?

 

Example : when flying at a cruise setting of 6 boost and 2650 rpm at around 260 mph the DCS Spitfire can be trimmed for level flight with about 3/4 notch of NOSE UP trim per the gauge. When looking at the tailplane one sees the elevator horn balance slightly raised above the tailplane horizontal centerline. This seems to be correct as when looking at photos of real Spitfires in level flight their elevators are often trimmed slightly down with the horn balance slightly raised.

 

With an elevator trailing edge trimmed slightly downwards one would imagine that the aircraft is being trimmed to raise the tailplanes, ie it is being trimmed aircraft nose down.

 

So how does one explain that the aircraft is physically trimmed slightly nose down while the gauge indicates slightly nose up ?.

 

At greater trim settings the gauge correctly translates what is effectively happening to the aircraft a-o-a, so why does it seem to show an inverse reading at cruise settings ?

 

To conclude, I guess that DCS more or less correctly models the elevator trim action, as when winding the trim up or down it does have the correct effect on aircraft pitch. Is the issue more to do with the in-flight centering of the cockpit gauge ? Or have I missed something ?

Does the seemingly bizarre effect in DCS exist in the real aircraft ?

Set up : Intel Core i7-6700 CPU @ 3.40 GHz, RAM 16,00 Go, 64 bits, GeForce GTX 970, Philips 32PFH4101, 1920x1080, 60Hz, Spitfire Histories replica Spitfire MkIX flying controls (for prop), TM Hotas X (for jets), CH Pro pedals, TrackIR5, TS & SRS. Member of EAF.

Link to comment
Share on other sites

Check the manual of the module (the part with elevator trim description). Apparently the gauge is geared in such a strange way, that neutral trim correponds to arrow pointing two notches above level. So that 3/4 you see in flight is in fact 1 1/4 nose down trim.

i7 9700K @ stock speed, single GTX1070, 32 gigs of RAM, TH Warthog, MFG Crosswind, Win10.

Link to comment
Share on other sites

  • 2 weeks later...
Check the manual of the module (the part with elevator trim description). Apparently the gauge is geared in such a strange way, that neutral trim correponds to arrow pointing two notches above level. So that 3/4 you see in flight is in fact 1 1/4 nose down trim.

 

The manual is wrong.

Link to comment
Share on other sites

From my observation Spit fly level at 1 notch up in trim gage. When i fly level, When i climb i don't trim plane im just holding the stick.

I think ppl are trying to trim spit to climb off hands, it is very difficult to do, small variation of speed in climb will change needed trim.


Edited by grafspee

System specs: I7 14700KF, Gigabyte Z690 Aorus Elite, 64GB DDR4 3600MHz, Gigabyte RTX 4090,Win 11, 48" OLED LG TV + 42" LG LED monitor

Link to comment
Share on other sites

The manual is wrong.

 

It very well might be to some extent (I find it counterintuitive myself), but unless you have something quantitive to back up your statement, just saying "it's wrong" doesn't cut it.

 

I can only see the gauge behaviour in DCS corresponds to what we can see on various onboard recordings in cruise power conditions (ie. arrow pointing between 0 and 1 notch above level), which, coupled with a trademark nose down position of elevator, as seen on most shots and vids, suggests the manual is right.

 

We would need someone from ED, or Nick, to clarify this thing once and for all.

i7 9700K @ stock speed, single GTX1070, 32 gigs of RAM, TH Warthog, MFG Crosswind, Win10.

Link to comment
Share on other sites

neutral elevator trim or 1 div nose down? Iam taking off with trim 1 div up. putting elevator trim to 1 notch down would be crazy in DCS, unless i miss understand this

FDqDvrm.png

Oh btw for ppl who dont use 12lbs for take off

0m2iEq5.png


Edited by grafspee

System specs: I7 14700KF, Gigabyte Z690 Aorus Elite, 64GB DDR4 3600MHz, Gigabyte RTX 4090,Win 11, 48" OLED LG TV + 42" LG LED monitor

Link to comment
Share on other sites

neutral elevator trim or 1 div nose down? Iam taking off with trim 1 div up. putting elevator trim to 1 notch down would be crazy in DCS, unless i miss understand this

FDqDvrm.png

Oh btw for ppl who dont use 12lbs for take off

0m2iEq5.png

 

I've always taken off with trim 1 notch down, 1 notch up makes your plane try to take off wayyy too early for its own sake.

Same for power, I find +8 to end up perfect for the take off run.

All in all, I follow exactly what your images say, and it works perfectly

Whisper of old OFP & C6 forums, now Kalbuth.

Specs : i7 6700K / MSI 1070 / 32G RAM / SSD / Rift S / Virpil MongooseT50 / Virpil T50 CM2 Throttle / MFG Crosswind.

All but Viggen, Yak52 & F16

Link to comment
Share on other sites

I will try with 1 notch nose down but i think my spit will do prop strike then.

Btw you should try take off with 18lbs lots of fun :)

System specs: I7 14700KF, Gigabyte Z690 Aorus Elite, 64GB DDR4 3600MHz, Gigabyte RTX 4090,Win 11, 48" OLED LG TV + 42" LG LED monitor

Link to comment
Share on other sites

neutral elevator trim or 1 div nose down? Iam taking off with trim 1 div up. putting elevator trim to 1 notch down would be crazy in DCS, unless i miss understand this

FDqDvrm.png

 

That's the whole problem - we don't know for sure what datum pilot's notes refer to and where the proverbial "neutral" actually was. In DCS cranking the arrow one division below level makes the plane extremely nose heavy.

 

The way the 3D model parts are animated doesn't help either - level arrow corresponds to tab being flat with elevator if I recall correctly, but that still moves the elevator to nose-heavy attitude, not to mention the fact that in DCS animations are in general not exactly tied to FM and ballistic calculations anyway.

 

Back to subjective preferences - I often takeoff with arrow where it is at spawn - two notches up, which might be "neutral" if (and that's a big "if") DCS manual and implementation are correct. Thus, when I roll on the runway with stick centered or slightly pushed to raise the tail, the plane lifts off on its own when it best feels like doing it and I don't need to pull the stick at all. That's nice, but it climbs steep and raising the landing gear makes the plane even more tail heavy then, so I understand why many players prefer to use arrow-1-notch-above-level setting, which makes the plane handling more neutral and takes them straight to level cruise.

i7 9700K @ stock speed, single GTX1070, 32 gigs of RAM, TH Warthog, MFG Crosswind, Win10.

Link to comment
Share on other sites

  • ED Team

The most safe method is to have force center of the stick in the position that establish tail lift-off by itself.

So, this process does not depend on pilot's input.

For example, the manual for Dora directs not to force tail raising, just stick neutral and wait.

Of course, trained pilot can acts different but it is depends on it skill and luck.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

Link to comment
Share on other sites

Art, I've noticed a discretion between those in my squad with MSFFB2 sticks and those with spring tensioned Warthogs - all the MSFFB2 users like myself routinely say my recommendation of 1 division nose down is spot-on; however all the Warthog or spring-tensioned stick owners say, like you, that that provides too much nose heaviness and instead unanimously choose 1 division nose up. Why this is or what this means I am still grappling with but it is definitely a thing...

 

The primary thing that makes me say that the 2-3 divisions nose up from horizontal is not neutral trim position is that it represents the approximate position I require for landing; a combination of low speed, low power and drag from flaps and gear all making the nose very heavy. Logically, why would you as an aircraft designer provide a trim neutral point at such an extreme end of the flight spectrum? When are you ever - in normal operating conditions - going to need more nose up trim than that?

 

This combined with a non-disingenuous interpretation of the elevator trim gauge, makes me believe that the manual is erroneous.

Link to comment
Share on other sites

  • ED Team
Art, I've noticed a discretion between those in my squad with MSFFB2 sticks and those with spring tensioned Warthogs - all the MSFFB2 users like myself routinely say my recommendation of 1 division nose down is spot-on; however all the Warthog or spring-tensioned stick owners say, like you, that that provides too much nose heaviness and instead unanimously choose 1 division nose up. Why this is or what this means I am still grappling with but it is definitely a thing...

 

The primary thing that makes me say that the 2-3 divisions nose up from horizontal is not neutral trim position is that it represents the approximate position I require for landing; a combination of low speed, low power and drag from flaps and gear all making the nose very heavy. Logically, why would you as an aircraft designer provide a trim neutral point at such an extreme end of the flight spectrum? When are you ever - in normal operating conditions - going to need more nose up trim than that?

 

This combined with a non-disingenuous interpretation of the elevator trim gauge, makes me believe that the manual is erroneous.

 

I will try to explain. Recommended setting is for safe taill raising. If I determine correctly, -1 gives diamond position for FFB joystick as it shown below.

The plane lifts for about AoA of 7 degrees at 100 kph. At 145 kph you need to apply very small stick pull.

You can not wait that the plane will keep the same balance with IAS increasing because it is a complicated sum of wings lift, main gear reaction (depends on wings lift), P - factor (decreases with AoA), etc.

 

It's not a problem neither for real plane nor for a joystick with not so aggressive center point as Warthog has.

So, the neutral force point avoids pilot from the relatively fast tail raising and then only slow stick reaction is needed to keep 7-8 deg tail-heavy position.

Screen_200318_172042.thumb.png.52bc53f77dfca4e8e6d08af9f804db05.png

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

Link to comment
Share on other sites

The plane lifts for about AoA of 7 degrees at 100 kph. At 145 kph you need to apply very small stick pull.

 

Did you mean plane lifts tail at 100 kph = 60 mph, i don't think so that spitfire will lift at 60 mph from ground.Or i did not understand that right.

System specs: I7 14700KF, Gigabyte Z690 Aorus Elite, 64GB DDR4 3600MHz, Gigabyte RTX 4090,Win 11, 48" OLED LG TV + 42" LG LED monitor

Link to comment
Share on other sites

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...