Jump to content

Excessive nose up attitude?


agathorn

Recommended Posts

You can maybe rotate and have to apply a bit of forward stick pressure initially, but latest after the first trim application you are back in trim.

With my significantly less nose up trim I need almost full aft stick as well to start the rotation.

Can't remember if there's a note in the F-5 manual, but the F-15 manual specifically states to use full aft stick for a high performance take off. Normal takeoffs require half aft stick.

 

That's one of the reasons why I apply more nose down trim, because I don't like the combination of very little required aft stick for rotation and the need to immediately retrim a lot. That doesn't make much sense to me, it feels weird/loose and especially not stable.

 

Having to apply a bit aft stick feels much nicer IRL and more stable than having to apply forward or no stick pressure.

 

AFAIK the Blue Angles even fly their F/A-18 with additional required aft stick pressure.


Edited by bbrz

i7-7700K 4.2GHz, 16GB, GTX 1070 

Link to comment
Share on other sites

Since the F-5 and most other high performance jets are using a low moment wing section (NACA65A004.8 in case of the F-5) I don't know where the large moment changes would come from which would require large pitch/trim changes.

 

I’m not sure that I see the relevance here, since from the perspective of our pilot there is no way to judge what is a “large” trim change regarding moment forces. By that, I mean that the trim system has zero interface with the horizontal stab, it is just tweaking the stick’s feel springs, and since no one here so far has real F5 time we are left guessing at the stick forces. We don’t even really know what the trim gauge is measuring since it has no units. Our only reference to how large an adjustment is in the amount of time the trim button is held down, which has nothing to do with forces on the airplane. What we do know is that the trim behavior seems correct at both ends of the speed spectrum; we have just enough authority to trim for very low air speeds and for the max certificated speeds (the total travel needed is present). So if it actually should require less trim say from 150 to 300 knots, you will be using even from 300 up to redline.

 

That said, I totally agree that nothing is wrong with tweaking it for feel in a sim.

 

Also per the -1, full aft stick 10 knots prior to calculated takeoff speed is the order of the day for the F5.

 

Also agree with the comment that it is a joy of a module to fly.

Multiplayer as Variable

 

Asus Z97-A - I7 4790K - 32 GB HyperX - EVGA GTX 1080 Ti - Corsair 750i PSU

 

TM Warthog HOTAS - TM Cougar MFDs - CH Pedals - TrackIR 5 - Samsung RU8000 55”

Link to comment
Share on other sites

By the way as an experiment I tried dialing in a few points less TO trim than the manual says and nearly belly flopped when I sucked in the gear :D

Intel i7-4770k @ 4.4ghz, 32gb ram, GTX 1080ti, Oculus Rift S

 

Advanced apologies if my post contains typos or missing letters. Many of my posts are typed on a laptop with an old keyboard that has a personality all its own.

Link to comment
Share on other sites

The problem is that the game doesn't necessarily model the moments caused by flaps correctly. When you see trim settings for take-offs, they are usually trying to compensate for pitch moments caused by takeoff flap settings. Once the flaps are retracted, the trim would need to be adjusted for the current speed / climb condition. The F-86 as released didn't need or like the takeoff trim settings. It was finally patched to reflect some sort of moment that benefitted from the takeoff trim setting. The problem is that I haven't flown any of these airplanes for real, so I can't accurately evaluate the pitch moments caused by flaps, but I can tell when the flight model isn't matching the pilot manual :P

 

But in a majority of cases, and increase in lift coefficient comes with an increase in nose-down force, which is why it is normal to have to push the tail down to keep the aircraft flying level. Lowering flaps does two things: increases the effective camber and increases the effective AoA, both of which increase the lift co-efficient for a given AoA and therefore also increase the nose-down pitch moment. This is why many aircraft that have flap down settings for take-off have nose-up takeoff trim settings. DCS World has been less than effective at accurately modeling the effects of flaps on the flight model, but their patches move in the right direction, and I lack the expertise and experience to say "when" the correction is accurate enough.

 

So my standard is very simple: if using the text book trim setting makes takeoffs easier / more controllable and retracting the flaps requires reducing/eliminating takeoff trim, then ED is in the "ball park".

 

The F-5 has a relatively small wing. It needs an extended nosegear and flaps to reduce the takeoff roll. It should need the takeoff trim setting to eliminate the need to pull back excessively to lift off the runway. Once its speed increases and the flaps are retracted, it should need a lot less nose-up trim... which seems to be the case. Hard to say whether it is modeled per the real aircraft, but it more or less seems to work the way it should.


Edited by streakeagle

[sIGPIC][/sIGPIC]

Link to comment
Share on other sites

@StrikeEagle I am in agreement with your statements regarding the aerodynamics of the high lift devices in general, but I don’t think it applies in the case of the F5 - page 1-71 of TO 1F-5E-1 describes the mechanical interconnect between the LE and TE flaps and the horizontal stab to “minimize trim changes automatically when flaps are operated.”

Multiplayer as Variable

 

Asus Z97-A - I7 4790K - 32 GB HyperX - EVGA GTX 1080 Ti - Corsair 750i PSU

 

TM Warthog HOTAS - TM Cougar MFDs - CH Pedals - TrackIR 5 - Samsung RU8000 55”

Link to comment
Share on other sites

But in a majority of cases, and increase in lift coefficient comes with an increase in nose-down force, which is why it is normal to have to push the tail down to keep the aircraft flying level. Lowering flaps does two things: increases the effective camber and increases the effective AoA, both of which increase the lift co-efficient for a given AoA and therefore also increase the nose-down pitch moment.

That's a bit of an over simplification.

 

The pitch moment depends a lot on speed, C.G., wing/tail interaction, altitude etc.

 

E.g. on a certain jet transport you need a 21lbs push when going from 0 to full flaps in one case, and under different conditions you need a 9lbs pull for the same configuration change.

 

As tom_19d pointed out, the flap/stab interconnect plays a role on the F-5 as well.

 

Again, looking at the real world video the trim changes seem to be minimal.

I don't agree that the available amount of trim automatically implies that the trim range is correct.

i7-7700K 4.2GHz, 16GB, GTX 1070 

Link to comment
Share on other sites

  • Recently Browsing   0 members

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