Aircraft woes. Control issues.

[LN400]

I have this aircraft Boing (not a pun on Boeing but a description of my landing techique yessiree) and it has a nice turn rate which is probably the only good thing I can say about it right now. Using KER I have adjusted the wings so that torque is between 0 and 0.01 (full fuel/empty). My issues are

-With SAS off, adjusting pitch is on and off to the extreme. Either nothing happens or it pitches up/down waaay too much.

- Roll is equally troublesome with either nothing happening or it banks rapidly and continues to roll long after I have let go of the keys, making straight and level flight a dream and landings a wild fantasy.

 

What I would love to have, is a plane that keeps reasonably straight and level, one that reacts less violently, less sluggishly, more consistent with key presses, than what I have now.

Pics

http://tinypic.com/r/2lndbgh/9

http://tinypic.com/r/vhu62b/9

http://tinypic.com/r/30ib9xc/9

Craft file (Modular Rocket System (MRS) dependent) can be uploaded if one can recommend a decent, free file hosting site that doesn't leave me with headaches and stomach ulcers.

EDIT:

Craft file https://nofile.io/f/AtSad7nsPGW/Boing+I+G.craft (again, MRS dependent).

Edited September 16, 2017 by LN400

[Spricigo]

Apart from the responsiveness of keyword control and the all-or-nothing activation of control surfaces, the low wing make your design naturally less stable.

[AeroGav]

3 hours ago, LN400 said:

I have this aircraft Boing (not a pun on Boeing but a description of my landing techique yessiree) and it has a nice turn rate which is probably the only good thing I can say about it right now. Using KER I have adjusted the wings so that torque is between 0 and 0.01 (full fuel/empty). My issues are

-With SAS off, adjusting pitch is on and off to the extreme. Either nothing happens or it pitches up/down waaay too much.

- Roll is equally troublesome with either nothing happening or it banks rapidly and continues to roll long after I have let go of the keys, making straight and level flight a dream and landings a wild fantasy.

 

What I would love to have, is a plane that keeps reasonably straight and level, one that reacts less violently, less sluggishly, more consistent with key presses, than what I have now.

Pics

http://tinypic.com/r/2lndbgh/9

http://tinypic.com/r/vhu62b/9

http://tinypic.com/r/30ib9xc/9

Craft file (Modular Rocket System (MRS) dependent) can be uploaded if one can recommend a decent, free file hosting site that doesn't leave me with headaches and stomach ulcers.

EDIT:

Craft file https://nofile.io/f/AtSad7nsPGW/Boing+I+G.craft (again, MRS dependent).

I don't have time to install that mod right now.

What is this plane's mission? Fighter ? Stunt / Aerobatics ?    Science scout ?   Trainer ?

Bear in mind you can right click on your control surfaces and "limit authority".     This is a very good idea with ailerons,  because limit authority lowers max deflection angle.    Most of the lift occurs at lower deflection angle and most of the drag at larger deflection angle.   So large ailerons at small deflection angle produce less adverse yaw than little ones maxed out.    Another tip, you should limit which type of motion the surfaces should control.    Ailerons should only do roll, elevators/canards only do pitch, rudders yaw etc.

Also I tend not to fit big RUDDERS,  but I do like generous vertical stabilizers, note the difference.  Vertical Stabilizer being the passive surface.

[LN400]

Thanks for the replies, guys.

- Low wings: I tried high wings but then the plane would hardly respond at all. Another idea of the low wings is to fit retractable gear once I have the tech. Low wings allows the gear further out.

- Mission is science gathering and scouting. Currently it flies well at around 90m/s for more than 6 hours at around 2000m for a range of around 160 km out. Faster and the lift becomes too great for SAS and level flight.

- Thanks heaps for the tip on limit authority. I'll have to play around with it more. Btw, the 2 pair of ailerons are really 1 pair of ailerons/spoilers and one pair of reversed spoilers with no other job.

Edited September 16, 2017 by LN400

[Spricigo]

 

3 hours ago, LN400 said:

- Low wings: I tried high wings but then the plane would hardly respond at all.

Yep. That's a tradeoff,  somewhere between both extremes you may find a good balance,  not too stable nor too maneuverable.

Given the Idea of attach landing gears to the low wing, you  may consider to make it a biplane with a smaller low wing. 

Some possible wing configuration would be troublesome in real life due to turbulence but KSP don't simulate it.

That old guide is still very usefull (KSP drag model suffered a redesign since then):

 

[LN400]

Further testing reveals a consistent roll, tiiiiny but there, to the left. A single tap on the trim is too much and it starts rolling to the right. Zeroing out the trim and the left roll is back. Both engines matched up, aero overlay shows nothing peculiar. Makes me wonder if there is a connection with the ever present left veering on the runway during takeoff.

 

(On a flip side, found out one can stow away sience stuff inside the empty fuselage section under "structure". No need for the cargo bay then and 50 kg shaved off. Plane rebalanced and shows up fine in the hangar. If only it would show up that nice in the air too...)

[AeroGav]

1 hour ago, LN400 said:

On a flip side, found out one can stow away sience stuff inside the empty fuselage section under "structure". No need for the cargo bay then and 50 kg shaved off. Plane rebalanced and shows up fine in the hangar. If only it would show up that nice in the air too...)

This hides them visually but they still get drag and heating.   So an asymmetric layout here could cause a yaw or roll in one direction. 

I  think there's a glitch in the physics engine that causes this slow roll.  It's especially bad if you  attach engine nacelles to fuselage then wings to engine nacelles.  If you want to make sure all parts are attached to fuselage straight, use angle snap mode and give things a tweak one notch tin one direction then back to centre again, but make sure you press F with angle snap selected to make sure you're in "Absolute" not "local mode".

Also,  yaw stability leads to roll stability, have you tried increasing fin area? (but make sure it, and the tail cone are straight!)

For science missions, if worst comes to worst,  you can design your plane to fly on prograde hold mode.

Either angle the tailplane in SPH,  or click " deploy" in cruise flight, then set prograde hold.  You can adjust the nose attitude by tweaking authority limiter slider.   The prograde hold reduces lateral deviation.      Its difficult to completely stop airplanes wandering off course, which is why i rarely accept long distance survey contracts.   Long tedious hand flying for not much reward.

[LN400]

I've just about had it with planes in this game. Several totally different designs, playing with CoM, CoL and CoT, control throw, angles, torque, and all planes fly like grand pianos in a hurricane.

 

Anyone have a craft file for stock 1.3 they are happy with, and want to share so I can have a look at how it's supposed to be done?

[bewing]

OK, try this:

https://drive.google.com/open?id=0BzAticeo-5-BYUhwaGw2TXRZclE

 

[LN400]

Mucho gracias. I'm off now but will test and report back as soon as I get back to KSP.

[AeroGav]

13 hours ago, LN400 said:

I've just about had it with planes in this game. Several totally different designs, playing with CoM, CoL and CoT, control throw, angles, torque, and all planes fly like grand pianos in a hurricane.

 

Anyone have a craft file for stock 1.3 they are happy with, and want to share so I can have a look at how it's supposed to be done?

https://kerbalx.com/AeroGav/simple-bird

Flies fairly straight on Prograde lock.

All the lift surfaces are angled up at 5 degrees in the SPH.   This means it still makes lift when SAS is on prograde lock, and the body is pointing directly into the wind.

 

The downside is that if you go too fast at low altitude, it creates too much lift and starts pitching up into a loop.      So on a long science flight, you have to use some other method till above 7km, or go gentle on the throttle.

 

I tend to only accept these atmo science contracts when i'm desperate.     As soon as I can build a space plane ( I can do that with Junos and terriers)   I do so,  and forget about grubbing Kerbin.

[LN400]

Thanks tons for your help guys. FINALLY came up with something that flies rather well even without SAS.

https://kerbalx.com/LN400/Boing-2-D

[A_name]

I’m a bit late to the party but I wanted to share these recommendations:

 

-Base your design from the beginning around having a COM that doesn’t move as you burn fuel. Use the right click menu to empty all your fuel and make sure the COM marker doesn’t move. You can also use the RCS build aid mod that gives you a dry COM indicator: https://forum.kerbalspaceprogram.com/index.php?/topic/33124-12-rcs-build-aid-v091/

 

-Once you have the plane’s base design built, use the rotate tool to give your main wing a tad bit of incidence, just one or two clicks of the rotate tool with angle snap turned off should do it. This will help to avoid losing vertical speed when flying level.

 

-Once you’re done rotating the wing, use the move tool to adjust your main wing so that your COL is almost directly over the COM, just one or two clicks of the move tool with angle snap off behind it.

 

-If you did the previous steps correctly, your plane will fly level without any input on the controls.

 

-Do yourself a favor and install Atmospheric Autopilot, which apart from the autopilot functions also includes a simple fly-by-wire module that provides stability assist only but is dramatically superior to the stock SAS: https://forum.kerbalspaceprogram.com/index.php?/topic/124417-122-130-atmosphereautopilot-1510-looking-for-maintainer/

[Palaceviking]

My two cents.....a little dihedral stability goes a long way and will help an unstable aircraft 'settle' into a stable position when you leave the controls alone

[Spricigo]

7 hours ago, Palaceviking said:

My two cents.....a little dihedral stability goes a long way and will help an unstable aircraft 'settle' into a stable position when you leave the controls alone

Case on point, OP's craft have some. Not enough to compensate for the low wing (and other possible factors).

This great guide  provide a lot of insight. IMHO a bit more 'advanced' then the one I linked previously. 

[LN400]

Thanks again, guys. Greatly appreciated.

 

Been testing Boing 2 D and so far it has been really nice. Docile but not sluggish, takes off and lands almost hands off, tiny inputs to keep it on course and altitude but nothing more than one would expect from an actual plane, I guess. I think this is my keeper for those long trips.

[Scarecrow]

I built this one some time ago in the style of the old Vampire aircraft.  It still works in 1.3 and has pretty docile flying characteristics.

It uses action group keys, but only two.  1 toggles the afterburner on the engine and 2 toggles the flaps.  The flaps really help slowing the craft down when coming in for landing.

 

https://www.dropbox.com/s/a3ir9sr9v5548iq/Voodoo.craft?dl=0

 

 

Or something a bit bigger, which is capable of flying 1/2 way round Kerbin and back, which I use for recovering returning Kerbonauts who miss landing back at KSC.

Video in another KSP thread here : https://forum.kerbalspaceprogram.com/index.php?/topic/140861-supersonic-plane-challenge-results-are-out/&page=2

Craft file : https://www.dropbox.com/s/zawb97dektsfrhj/Twingo LDRV.craft?dl=0

 

With perseverance and a bit of tinkering, it's amazing what you can get to fly in KSP, so don't give up and don't be afraid to experiment.

 

Edited September 20, 2017 by Scarecrow

[AeroGav]

On 18/09/2017 at 7:31 PM, A_name said:

Once you have the plane’s base design built, use the rotate tool to give your main wing a tad bit of incidence, just one or two clicks of the rotate tool with angle snap turned off should do it. This will help to avoid losing vertical speed when flying level.

 

Very important caveat - when adding incidence, wings at the front should have equal or greater incidence angle than those at the rear of the aircraft.    This insures that the front end of the aircraft stalls first and the plane pitches down when stall approaches , rather than the back end losing lift and the plane pitching up into a flat spin.  

On a conventional tailplane layout, you can just add incidence to the main wing,  since that gives it more than the tail has.

On a canard, you must also add incidence to the canards and leading edge extensions/strakes (if fitted) or the airplane might bite you.

 

[Spricigo]

19 minutes ago, AeroGav said:

Very important caveat

Same incidence on all wings always worked with no issues for me. So I'd guess is not difficult to get away with that 'design flaw' with other factors providing a good  balance. 

[AeroGav]

2 minutes ago, Spricigo said:

Same incidence on all wings always worked with no issues for me. So I'd guess is not difficult to get away with that 'design flaw' with other factors providing a good  balance. 

 

36 minutes ago, AeroGav said:

wings at the front should have equal or greater incidence angle

equal is fine.   Less is not fine.    

[Spricigo]

30 minutes ago, AeroGav said:

equal is fine.   Less is not fine. 

Point taken.

...however equal don't ensure [front wing stall first, craft pitches down] behavior. Or I'm missing something?

 

 

[Boris-Barboris]

20 minutes ago, Spricigo said:

Or I'm missing something?

Stock aero has no stall per se.

edit: it's not rapid, surfaces just smoothly loose lift with increased AoA. Not fast enough to make your canard weak and kick the plane back to prograde.

Edited September 20, 2017 by Boris-Barboris

[AeroGav]

37 minutes ago, Spricigo said:

.however equal don't ensure [front wing stall first, craft pitches down] behavior. Or I'm missing something?

 

Well, if your airplane is basically stable, and has CoL behind CoM,  the only way to get high AoA in the first place is to get the canards to lift the nose, by increasing their angle of attack.

So if you got 5 degrees of incidence on the wing and the canard, but your're deflecting the canard at 15 degrees further by yanking the stick back, it's gonna stall first for sure, and drop the nose.     Actually as @Boris-Barboris says, it's not violent,   all that happens is the canard runs into "diminishing returns" first, and gains less lift than the main wing  as AoA increases, making it increasingly difficult to raise the nose any further.

So my advice is just playing it super safe.   My space planes aren't meant to do air shows.    So long as i can pull 10 degrees AoA,    that's enough.   Most of the flight is done at 0 AoA,  and if I pull more than 10 on takeoff or landing,  we're probably going to tailstrike and bust the engines off,  red faces all round.

[Spricigo]

12 minutes ago, AeroGav said:

canards

Most of the time I dont have those.  But got it, deflection of control surfaces taken  in consideration.

29 minutes ago, AeroGav said:

So my advice is just playing it super safe.  

Well there we maybe should agree to disagree. A bit of risk can be fun, as long as one is prepared to deal with the consequences.