Need help with my Massive Kethane Tranporter PLANE .

[AddMeGamers]

Hey guys

need help with a plane , i have tried to change nearly everything with the plane , got the center of mass right behind the center of lift . Tried to increase the gape between them , even switched them around to get the mass infront the center of lift . But i always bump into the same problem . On take off the nose flips up and does a back flip . Upone which i decided to put a massive amount of control surfices in the front to stop that from happening .

Now that does stop it but once i get up around 33,000meters high and start to descend to the ground to my kethane mining site , it again spins out of control . Either the nose drops , or the nose flips . Really depending on the center of mass in relation to my center of lift . I have tried every combination and still not luck . I always loose control and have the crash . The first version which is without any mods atleast sort of managed to get to the target but still with a massive headake .

the newer version i got the fuel balance mod installed to maybe balance out all the fuel but still the same problem , once the fuel gets low its becomes uncontrolable . Could someone download em , take em up for a nice high flight and try to land em once they are close to nearlly empty fuel and let me know what the hell i supose to do with them .

Thanks

ooo lets not forget , Happy Gaming!!!

even better if you could do the tweaks and send me the build including an explanation so i know what iam doing wrong would be very highly appreciate it .

http://addmegamers.com/amgfileserver/download/kethane-super-tanker/

Edited July 31, 2013 by AddMeGamers

[dlmarti]

I suck at aero, but I do know that the center of mass should be in front of the center of lift.

[AddMeGamers]

i tried that ....same thing tends to flip out :S ...i tried all thoes combinations but once the fuel gets to low the plan becomes uncontrollable .

[Actzoltan]

ill give it a look if your still awake ill be streaming it

[boolybooly]

The guy you really need to ask is pa1983. He is the big plane maestro, some of his stuff in in the K Prize thread.

I gave a few spaceplane hints here but I usually do smaller craft these days.

Your problem sounds like the center of gravity is shifting due to fuel use, if you load up the furthest forward tank on the craft and empty the rearward tanks it will shift the center of mass forwards. Alternatively lock the forward tank when you launch, left click, click the little triangles.

The CoM will always shift towards the engines because they are the heaviest components. You can either add stuff up front or move the cockpit forwards or add engines in a forward position to the sides in the middle of the wing.

You need to have lift behind mass and leverage from control surfaces just enough to overcome the laden weight on lift off so when flying with empty weight the lift is still just behind the mass.

[pa1983]

I cant seem to download your craft. But I do have had similar problems. People seems to agree that Center if Lift is suppose to be ahead of Center of Gravity. Problem is that has never worked for me.

One of my best crafts for transporting, The jumbo has the Center of Lift 1-2m in front of Center of Gravity still its perfectly stable with 20-40 degrees of nose up during reentry. Can do relatively sharp turns so a 180 is no problem if you have to do a go around for the runway.

Also people seems to agree that Center of Lift IS Center of Drag. Well I cant say I have noticed that. From all my testing having intakes behind Center of Gravity makes for the most stable craft assuming its balanced in all other respects. I have a good example where this matters. My latest craft that flew sucessfully just a few days ago had like 120 intakes on top of the craft behind Center of Gravity in a top mounted intake like the iconic L-1011

My craft and its resemblance.

The effects of the intakes above was a 40-50 degree nose up angle of attack during reentry to Kerbin and even Duna showed instability signs so it was obvious Center of Drag wanted to stay behind Center of Gravity in line with the Vector of the crafts traveling direction. No amount of input even with RCS could stop it. 3 jet engines mounted above Center of Gravity managed to level it of. Now drag is a big problem at reentering the atmosphere. The easy fix for me was to add them to an action key reducing drag from 2 to 0.3 by shutting them when they are not needed and after that it can be controlled fine during reentry sens they are only useful during later part of the ascent.

Now I mentioned I have had similar problems with crafts flipping or most often spinning out of control by having the nose move left or right. A good idea is to first take off the roll left or right and check if the crafts maintains its vector. if the nose moves sidways you have a serious instability problem. I had such a craft that I gave up on. That craft looked very much like the Valkyrie.

I had a cargo bay between the engines and a high nose just like that one. I do not know for sure yet why it was unstable but it always wanted to spin out even with Center of Lift at Center of Gravity. Thing was even if I moved Center of Lift back more by extending the wings a bit further back like that Valkyrie has it got more unstable.

The thing with that craft is that Center of Gravity is very far back with its rear mounted engine and so the need to have the payload fare back to meant I had a very long fuselage and lifting surface ahead of Center of Gravity but a very short one behind it. Other crafts I have made have had Center of Gravity a lot closer to the center of the craft simply by having wings further forward like more traditional craft but also having a stabilizer far back. So my theory is that even if you have Center of Lift and Center of Gravity optimally to one and another that wont mater if the craft is proportionately longer in the forward end, say the nose is 3 times longer from Center of Gravity then the rear of the craft.

I remember they discussed this in a documentary about the SU-27 but I cant remember what the phenomena was called but it allowed for more rapid response at the cost of stability. A sophisticated fly by wire system was required and decent control surfaces to aid the craft. I think thats basically what some crafts in KSP suffers from due to strange proportions.

One thing you can test in SPH is clicking on the pod or one part of the ship while you hold shift then let go of shift and you can rotate the craft like its on part. Rotate it on its side and you will see that Center of Lift is different depending on its rool or angle of attack. So Center of lift is not the same at all times even if Center of Gravity stays the same. So rolling or turning can change Center of Lift so much that I theorize that it can cause sever instability. Best thing is to make a craft that has a very consistent Center of Lift by having Center of Lift at Center of Gravity no mater if the craft is rolling, pitching or yawing.

Thats my current theory based on all the crafts I have made so my tip for a successful craft is a traditional craft with a medium to long fuselage and a center wing and a rear stabilizer. Then add intakes behind CG preferable in line with Center of Trust but if there not make sure you can close them for reentry with an action key.

I also find it easier to make the fuselage and wings first then place the engines then the fuel and then the intakes behind the fuel tanks but preferably ahead of the engines so some where in between.

Also placing fuel tanks in parallel only is the easiest way of maintaining Center of Gravity. If you build the fuselage and wings first and place all heavy parts like engines etc so Center of Gravity ends up close to Center of Lift, I prefer a tad bit ahead of Center of Gravity sens that tends to make the craft stable in level flight and avoid the nose dropping that can be a pain at high speeds and altitudes where control surfaces have little effect. Then you know where Center of Gravity is and then you can place your fuel tanks in parallel at Center of Gravity with out it moving. That way you know that Center of Gravity is the same even if the tanks are empty.

You can use non parallel fuel tank placements, second easiest is one tank forward and on tank in the rear fuselage equal distant from Center of Gravity. They should be equal size and be linked so they drain equally. Can be done with a small tank in the center used as a hub for routing fuel to the engines. More complex systems can be made once you skill increases.

Long aircraft fuselages tend to have the problem of rotating on the runway. That can be avoided by building a belly under the craft for the landing gears increasing rotation with 5 degrees.

Also spreading fuel tanks on the wings helps making the craft stronger and reduce the need for struts.

Placing a jumbo tank 1/3 from from the fuselage on the wings and only use the fuselage for payload significantly reduces stress on both wings and fuselage. Also combining this with a belly for the landing gears that extends to the fuel tanks on the wings allows gears to be placed under the fuel tanks and the fuselage to take up the weight evenly from the fuel tanks and payload. That way you craft wont flex on the runway or in the sky.

If you are interested I have a building video on youtube and I also have my latest craft that houses close to 40 tons of fuel in etch engine nacelle and another 25+ tons of payload and engines in the fuselage and it uses all the techniques and theory's I have mentioned. You can have a look at that and decide if its an approach you like to pursue.

I have a link in my signature to my channel. Crafts can also be downloaded there in the description on most videos. I also have a page on the forum but I hardly update it due to lack of interest from other users.

Edited August 9, 2013 by pa1983

[AddMeGamers]

very nice info ...thanks!!!! will dig it and try out some things as well as look at some of the vids !!

[Stir_Fry_Beans]

Your airplane might have to much lift? I would definitely listen to pa1983. I have that problem when I reach speeds of 600 m/s +. This happens because the lift overcomes the torque and controlling surfaces of your aircraft. Maybe you could try filling up your kethane tank a little bit on launch so that it weighs down the aircraft a bit? Thats my thought on it. Its going to be hard to match the lift before fueled up and after fueled up! Hope this helps a little bit!