Wing panel orientation, and altitude effects

[Guest Space Cowboy]

I have confirmed in the SPH that wing orientation drastically affects lift produced. Structural Wing Panel A and B, if oriented similarly, yield noticably different lift

DIFFERENT COL FOR SIMILAR PANELS:

STRUCTURAL WING TYPES A & D

STRUCTURAL WING TYPES B & E

Fine.

My real issue I am trying to troubleshoot: My COL seems to be moving in flight with a change in altitude. I am empty with infinite fuel selected during these tests. This is a big wing and many panels and in numerous orientations. My question is do the various wing panels reduce their lift capability at different rates with altitude, and also could this effect be exacerbated by numerous wing orientations? The craft seems to become nose heavy to the point of loss of control, with an increase in altitude. THANK YOU

[Starwhip]

Grab the entire ship, and rotate it. Watch your Center of Lift. This will confirm if it moves or not.

I do not know any fixes for a moving CoL rather than to not change your angle so viciously.

EDIT:

Oh, and by the way, welding wings is a horrible idea: you'll definitely get problems there because when you weld them, it doesn't calculate the lift properly.

[Guest Space Cowboy]

Grab the entire ship, and rotate it. Watch your Center of Lift. This will confirm if it moves or not.

I do not know any fixes for a moving CoL rather than to not change your angle so viciously.

EDIT:

Oh, and by the way, welding wings is a horrible idea: you'll definitely get problems there because when you weld them, it doesn't calculate the lift properly.

I am not sure which axis to rotate about, to see what you're saying, so I tried rotating about all 3 axes, separately, one at a time, but noticed no ill effects.

re: welding - on this craft only the engine nacelles (minus the 4 actual engines) are welded. None of the components welded generate lift, and the welded part itself does not generate lift.

[WhiteKnuckle]

Can we get a shot of your CoM and CoL? If the CoM is too far in front of the CoL the aircraft is overly stable and will want to lawn dart, at low altitude your control surfaces have enough bite to counteract this, but as the soup thins they can't counteract the natural tendency to nose dive

[Rhomphaia]

A wing with the side to the airflow will not produce any lift. So in the configuration you used for structural wings A and D, those wings are essentially useless in that orientation. use B and E instead if you want more lift

[cantab]

The orientation effect you note has been found before. The stock wings and aero model generate full lift if rotated either 0 or 180 degrees from their default orientation, but zero lift if rotated 90 degrees. Your experiment is confounded because you're using the Mk2 fuselages that generate lift of their own - build a small plane using regular fuel tanks to see the effect much more clearly.

There are subtle cues to the orientation - the front and back edges look different to the side ones. But the general rule is to build your wings in bands sideways outwards from the fuselage, then strut the bands together. Don't attach wing pieces to the front or back of other wing pieces or get fancy with the rotation tools, unless it's for looks and you're happy with not having the lift.

As for the centre of lift appearing to shift, in stock aerodynamics I don't think it will. However what will happen is the control surfaces will have less control authority at higher altitudes because of the thinner air. All stable planes are nose-heavy to some extent, so when you get high enough that the control surfaces can't compensate the plane will dive. The solution is to provide more or alternative control. If it's a spaceplane you'll want decent reaction wheel torque and/or RCS to maintain control in the upper atmosphere (and in space). If it's a high-altitude aeroplane consider more/bigger control surfaces, or ensuring the centre of lift is quite close behind the centre of mass to reduce the control authority needed.

[Guest Space Cowboy]

Yes cantab the problem occurs with a change in altitude.

The craft becomes nose heavy with altitude, as if the COL were moving aft...

I have even flown it (or it flew itself lol...) back down to sea level, and it recovered. I had pitch authority again.

Someone wanted to see this

[WhiteKnuckle]

Well your CoL is in front of your CoM, fix that first then report back.

[Guest Space Cowboy]

Well your CoL is in front of your CoM, fix that first then report back.

It's close enough don't you agree?

[pincushionman]

…But the general rule is to build your wings in bands sideways outwards from the fuselage, then strut the bands together. Don't attach wing pieces to the front or back of other wing pieces or get fancy with the rotation tools, unless it's for looks and you're happy with not having the lift…

Good to know, but this runs counter to other gudelines posted on this forum, which say to build out and then forward-back, so you can grab the whole wing by its "root" and position it as a unit, ending by strutting to the fuselage. If you build outward then strut front-to-back, positioning the wing strips is a chore.

Using the "correct" wings would then be tough, as when you attach them to the back of the forward wing, they point the wrong way (long edge fore-aft). Which is why we've been using the "wrong" ones - they end up looking right in the editor. But maybe there's enough play offered in the offset/rotation tools to put the "right" one on "wrong", then translste/rotate to "right."

If that doesn't make any sense, I'll see if I can drum up some screenies tonight to explain what I'm talking about.

[Guest Space Cowboy]

what will happen is the control surfaces will have less control authority at higher altitudes because of the thinner air.

You nailed it.

I added 6 canards and I was able for the first time to fly to cruise altitude with positive pitch control. I am guessing, even undeflected, the control surfaces lose lift with altitude at a different rate than the 'normal' lifting surfaces. This NEEDS to be in the WIKI

Edited February 4, 2015 by Space Cowboy

[cantab]

Good to know, but this runs counter to other gudelines posted on this forum, which say to build out and then forward-back, so you can grab the whole wing by its "root" and position it as a unit, ending by strutting to the fuselage. If you build outward then strut front-to-back, positioning the wing strips is a chore.

I've not come across those guidelines, but I'd say that in stock aero they're bad. Yes, you can use the rotation and offset gizmos to make it work that way, but it's a lot of complication and someone not knowing the importance of wing orientation or not being very careful about it will end up carrying useless white boards.

As for the big plane, the CoL does look slightly ahead of the CoM. The numerous intakes aft of the CoM will help stabilise it, and I'd expect a twitchy but controllable plane. If you want to shift the CoM forward a little, the easiest way is probably to put a locked fuel or RCS tank in the nose as ballast.

[Guest Space Cowboy]

I need to emphasize the craft has NEVER had control issues at low altitude.

Big thanks to cantab for the assistance and everyone else. Thank you.

Edited February 4, 2015 by Space Cowboy

[numerobis]

Lift is linear in pressure, for both control surfaces and lifting surfaces. I'm not sure what you're seeing, but it's not that control surfaces lose lift faster than wings.

[Guest Space Cowboy]

Increasing nose down tendency as altitude increases on an otherwise perfectly balanced craft. Perhaps the large scale of it is revealing a programming anomaly. Perhaps it has to do with skipping aerodynamic calculations with altitude increase.

[Red Iron Crown]

Good to know, but this runs counter to other gudelines posted on this forum, which say to build out and then forward-back, so you can grab the whole wing by its "root" and position it as a unit, ending by strutting to the fuselage. If you build outward then strut front-to-back, positioning the wing strips is a chore.

I used to use the method you describe as it made it easy to adjust the CoL/CoM relationship by moving entire wing assemblies, until someone pointed out to me what cantab mentions and I started building in "strips". More tedious, but my planes perform a lot better now. A possible workaround if you want to be able to easily reposition the whole wing is to make two "spines" out of beams attached flush to the fuselage, then build your wings in strips from the spines. If you need to adjust the wing, grab the spine and move it, the whole wing goes with it.

[Starhawk]

It seems to me this is what's happening.

As you climb into thinner atmosphere, you have less lift. Given that your lift is decreasing, you need more pitch to maintain altitude at a given velocity. But, since lift from control surfaces is decreasing as you climb, you may run out of pitch authority when you need it most, and find yourself unable to maintain altitude, i.e. increasing nose down tendency.

Correct me if I'm wrong, but this seems to fit with what you describe.

[ajburges]

Control authority in low atmosphere is an easy problem. You just use elveron parts or canards.

For high atmosphere accent, your engine gimbals can give you proper authority if you have proper TWR.

For reentry and air hoggers, you lack good TWR and atmospheric density. RCS or reaction wheel torque are needed to overcome asymmetric drag an maintain heading.

My planes suffer in the last mode because of lack of MK2 SAS parts and the late unlock of MK2 done core. One way to compensate is to minimize course corrections in high atmo. I burn near prograde for my accent and my reentry is fine as long as I don't try course correction before lighting engines or reducing altitude (using prograde follow SAS).

Anyone know a good ballpark rotational speed in orbit to maintain authority in high atmo?

[Guest Space Cowboy]

It's not a loss of total lift but rather a shift in what in the real world is sometimes called "aerodynamic center". It is moving aft as I climb. The COM and COL balls are ON TOP OF EACH OTHER IN THE SPH AND THAT IS WERE THE FUEL IS ALSO LOCATED (lol).

Oh and I did rebuild the wing. I did use the new small rectangle wing panel transversely, (yes - rotated 90 degrees and generating no lift) to provide a movable base for the entire wing for very fine control of placement of the COL ball. I'll post pics of the new wing construction hopefully it doesn't irritate anyone. This is crazy.

I did move the wing aft after the last photo ...

Edited February 4, 2015 by Space Cowboy