Mk.3 fuselage keeps stalling no matter what I do.

[The Blazer]

Hi, I’ve been playing KSP for a while, and I’ve made some very functional mk.1 and mk.2 jets and spaceplanes (both SSTO and shuttles) however whenever I use the Mk.3 fuselage, I literally ALWAYS go into a stall on every single turn or simply by pitching up or down a minimal angle it just stalls, or does a full 360 degrees turn then stall. 

I do have some knowledge on aviation and I know about CoM, CoL and CoThrust. I also kinda know how to use the angle of attack of the wings to make the aircraft fly better at either low speeds or high speeds, however I just can’t find the problem and literally all my mk.3 aircrafts go into stall whenever I move the controls just a bit. I’ve tried different altitudes and speeds, and nothing, still stalling.

is anyone else experiencing this? Maybe do you guys have some tips for flying these heavy aircrafts?

[JIMMY_the_DOG]

mk3 planes are very big and  even with 3 of the biggest turbofans the velocity isnt great enough to turn/ do an evasive maneuver, so either add more wing or add more thrust. I suggest putting several of the "Panther" afterburning turbofans and put it on "Wet" mode, which uses more fuel yet adds more thrust.

 

Hope this helps.

[Caerfinon]

1 hour ago, The Blazer said:

Maybe do you guys have some tips for flying these heavy aircrafts?

I usually find a stock MK3 plane on KerbalX and try that out to see how it goes and from one of those designs I figure out better ways to build my own. 

This one: KC 10A Seabird is a particularly fun MK3 to fly. It lands on runways and water.

As a general rule they are slower and require-more patience but if you go too slow you stall. Flaps and spoilers can help a lot to lower your stall speed and stop you on a short runway.

 

[18Watt]

It’s sometimes hard in KSP to tell which surface is stalling.  If you think you have enough wing, then it is possible the tail surface(s) are stalling.

Especially with larger (mk3) planes, it is critical to have the COM and COL placed correctly- and this is sometimes difficult to determine accurately in the SPH.  If your COL is too far behind the COM, then your tail control surfaces (pitch control) will not be able to keep the nose up.  This is amplified in turns.  Try moving your COM further aft, or your COL further forward.  With large (mk3) planes, I find they often are basically on top of each other when viewed in the SPH.

Another related problem is it is common to see planes with not enough pitch control surfaces, or they are not placed far enough away from the COM.   If your COM is fairly far aft (back) on the plane, then the distance from the COM to the pitch control surfaces may not be great enough- and the lever arm is insufficient.  In other words, the pitch moment generated by the pitch control surfaces is too small.

If you need more pitch control, try also putting some canards on the front (nose) of the plane.   If your plane’s COM is towards the aft (back), then using canards on the nose will give you a lot of pitch control- because the arm between then and your COM is going to be large.

Finally, a screenshot of the plane giving you trouble would be helpful.  Otherwise we are just guessing.

[18Watt]

Here's a few examples of large planes.

B36:

Spoiler

I made this to somewhat replicate a B36 bomber, using 6 turboprop engines, and 4 jet engines.  The engines are not important.

What is important is the distance from the COM/COL to the pitch-control surfaces on the tail.  It is a long distance, the tail surfaces have a very long lever arm when trying to adjust the pitch attitude.  

Again, note that the pitch-control surfaces (elevators) are large, and placed very far aft of the COM/COL.

SSTO Spaceplane:

Spoiler

This is an SSTO plane I made, hauls 16 Kerbals to orbit- twice without refueling if needed!  It weighs nearly 100T at takeoff.  Note the wings are not very big.  I highly suspect your problem is NOT the wings stalling, but rather not enough pitch authority to keep the nose up.

Unfortunately, I don't have a screenshot showing the COM/COL on this one- so you'll have to take my word on it.  The COM and COL are on top of each other.  Moving the COM forward (or COL aft) makes it too difficult to keep the nose up.  I assure you, this plane does not stall, and is very maneuverable.  It maintains flight at AOAs (angle of attacks) above 30 degrees, no problem.

Also note the canards, or pitch control surfaces on the nose of the airplane.  Even with those HUGE elevators on the rear of the plane, I still did not have enough pitch authority.  Adding the canards to the front solved that problem nicely.

Here's a shot of the same plane maneuvering to get to the runway.  At this weight (very light), the plane will fly just fine at about 80m/s.  Although the AOA in this photo is small (about 7 deg), the plane can make very tight turns at up to 30 deg AOA if needed.  That bleeds off speed rapidly, but the plane won't stall.

Here's an overhead shot of the plane, to give you an idea of it's dimensions.  Those two tiny canards on the nose of the plane probably do just as much for pitch control as the giant elevators on the back- they are critical on this plane.  The wings are not large at all- again this plane weighs 100T on takeoff.

Again, here are some suggestions you might try:

•  Move your COM and COL to be closer together- they might need to be right on top of each other.
• Use larger pitch-control surfaces, and make them as far away from the COM as possible.
• Use front-mounted pitch-control surfaces if needed (canards).

Good luck, and if you still have trouble please post a screenshot of your plane.  If possible, post a shot from the SPH, showing the COM and COL.

 

[18Watt]

I took some screenshots of my MK3 SSTO in the SPH.  The photos may surprise you, and be somewhat counter to what we all know the COM/COL ratio should look like.

SPH Screenshots:

Spoiler

Does anyone see anything wrong in this picture?  Yes, My COL is actually ahead of my COM!  This is what the plane looks like at launch, weighing 100T.  And if flies fine.  Normally you would expect this to be unstable, we usually understand that the COL needs to be AFT of the COM.  However, the picture you get in the SPH is misleading.  If you are having pitch problems, try moving your COL forward, or your COM aft.  In some cases, it will appear that the COM is actually aft of the COL, like in this photo.

This next screenshot looks even worse!  This is a typical load when I've used up most of my fuel.  In this case, the weight is down to 48T, most of the fuel is gone.  The COM now appears to be even further aft of the COL.  But the plane flies fine like this.  In fact, in order to keep it controllable, I normally have to actually move most of the remaining fuel to the back of the plane, making the COM even further aft still!

My point with those screenshots is to be suspicious of what the indicators in the SPH are telling you.  Yes, they are a good starting point.  However, if you are having pitch issues, and the nose keeps dropping when the wings are flying just fine, it is time to take matters into your own hands, and correct the balance problems on your own.

Despite the fact that the SPH screenshots suggest the plane would be unstable, it is not.  In fact it flies fantastic that way.  The info from the SPH is obviously not telling us the whole story- we have to figure that out on our own.

[FleshJeb]

1. Pictures ALWAYS help.

2. CorrectCOL is a fantastic, reasonably easy to use mod that gives you a more accurate picture of the aerodynamics as well as a stability graph for all angles of attack. (See my sig for links).

3.a. I'm not sure if the bug still exists, but cargo and service bays, and fairings should have their internal attachment nodes occupied by something of the appropriate size. For Mk3 parts, that's a 2.5m part. Otherwise the drag on the cargo bay is hellacious, even when closed.

3.b. Also an old bug: Don't use any of the above cargo parts as the root part of your vessel, because they will be super-draggy.

4.  I set all my control surfaces to 5 deg or less, fly in precision mode (Caps Lock) and have no problems. Canards ARE highly recommended.

5.a. When using wings with AOA, make at a good amount of horizontal tail area unmoving, and with 0 AOA. This will damp out a lot of pitch problems. You can put the COL (as shown by CorrectCOL) right on the COM and have a very good plane.

5.b. I recommend flying SAS Surface Prograde for the above setup. The plane will tend to fly just a hair nose down, so you can add 5 deg of anhedral to that flat tail and it will damp your roll as well. If you've successfully balanced the plane to take out the phugoid oscillations, you can circumnavigate the planet without touching the controls.