oh look, another plane builder needing help!

[psyper]

I have terrible trouble building planes. Everything I build ends up in a fireball at the end, side or base of the runway. So much so that I dispensed with runway launches altogether and adopted a rocket-with-jets approach. I've had some success with a vtol ssto and I'm now working on an ordinary vtol plane. I assumed not having to worry about extra mass of a nuke and oxidizer would make things more easy but alas no.

So here is my first attempt.

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She flys okay - can hit a ceiling of about 25-30k with mechjeb flameout prevention and can do speeds of about 2km/s at a push - she is ideal of doing several SmallPrint's waypoint markers. However, and its a big however - If Hardun Kerman so much as sneezes in the cockpit it spirals out of control - I can only nudge slightly out of the prograde marker a touch to change its direction - if I so much as get a couple of degrees out it spins off to the retrograde marker and sticks to it like a magnet or it just rolls and rolls between the prograde and retrograde marks spinning like cheese down a hillside!! At one time or another I've had to deploy the chutes and wait until it lands then repack the chutes and take off again. Not ideal for these stealth trips in to enemy airspace!

Help me pretty please!

The craft is listed as 'Eagle 1 sans tac' in this folder:

https://drive.google.com/folderview?id=0B8S2KVucoU9cWG1vSDNVNHZ5VTQ&usp=sharing

[eataTREE]

My first thought is that your center of lift is too far forward compared to your center of mass, which would result in the instability you describe. Try moving the CoL back or the CoM forward.

[Alshain]

Your center of lift is angled. The position relative the CoM is fine but it's pushing the craft in one direction. The arrow should be straight up but instead it's pointing below the bottom of the cockpit. That isn't good whether you plan on flying vertically or horizontally. It's going to want to turn the nose down.

Edited September 8, 2014 by Alshain

[psyper]

My first thought is that your center of lift is too far forward compared to your center of mass, which would result in the instability you describe. Try moving the CoL back or the CoM forward.

Thankyou - I'll give it a go.

Your center of lift is angled. The position relative the CoM is fine but it's pushing the craft in one direction. The arrow should be straight up but instead it's pointing below the bottom of the cockpit. That isn't good whether you plan on flying vertically or horizontally. It's going to want to turn the nose down.

I noticed that too but when I rotate the craft 90 degrees in the sph the tilt disappeared (in another screenshot on the album) - I'm not sure if thats an artefact or not. The plane is built symmetrically - once the top two wings have been created I copied the top right one and put it at the lower left so it reflected and inverted then strutted the two together. Everything on the fuselage has been kept on two-way symmetry so I have no idea where that quirk has come from.

[Wanderfound]

The tilt didn't just disappear, the CoL moved. When you rotate it, the indicators (and the air, if you do it in flight) stop seeing the wings as wings and start treating them as vertical stabilisers.

[Alshain]

The tilt didn't just disappear, the CoL moved. When you rotate it, the indicators (and the air, if you do it in flight) stop seeing the wings as wings and start treating them as vertical stabilisers.

Precisely. Thank you for explaining that, I was having trouble wording it.

Psyper, I think building a vertical take off plane is a lot harder than one that simply uses the runway. Think about it, how many planes are built to take off vertically in the real world? You have to account for a shift in position so it can fly both vertically and horizontally and that can be very tricky.

You might want to try correcting the problem with your take off and landing. My suggestion is practice practice practice, you will be surprised how easily it comes after enough of your fireballs. Spaceplanes are not for those who just want to throw something together and blast off, my opinion is they take far more piloting skill than rockets as well as much more careful planning. Build a small plane, take off, turn around and come back. Keep trying it. If landing is your biggest issue, F5 just out over the ocean while on approach and do it over and over again. I reccomend NEAR, because your planes will "make more sense" when you do. Here is a guide for plane building, and when I say small plane, I'm not kidding either. If it uses more than 1 jet engine, it's too big for practicing.

[Fengist]

She flys okay - can hit a ceiling of about 25-30k with mechjeb flameout prevention and can do speeds of about 2km/s at a push - she is ideal of doing several SmallPrint's waypoint markers. However, and its a big however - If Hardun Kerman so much as sneezes in the cockpit it spirals out of control - I can only nudge slightly out of the prograde marker a touch to change its direction - if I so much as get a couple of degrees out it spins off to the retrograde marker and sticks to it like a magnet or it just rolls and rolls between the prograde and retrograde marks spinning like cheese down a hillside!! At one time or another I've had to deploy the chutes and wait until it lands then repack the chutes and take off again. Not ideal for these stealth trips in to enemy airspace!

Help me pretty please!

So far, everyone here is steering you in the right direction. Your spiralling out of control is directly related to 3 facts.

1: Your center of lift is too far forward.

2. Fuel balancing. Because you have FIFTEEN fuel tanks on there and they are using fuel from front to back, by the time you hit 30km, all the fuel in your wing tanks is in the ass of the plane. This DRASTICALLY affects your center of mass, moving it rearward and thus, causing your lift to be forward of the mass and thus, causing your wild spins.

3. Flaming out. I tested a 'modified' version of your craft file and it starts to flame out at around .14 air flow. The ONLY way I could get it stable was to transfer all of the fuel from the aft wing tanks to the front. If you want to keep gaining speed and altitude, learn where you flame out then learn to throttle back. On some of my suborbital hops I've easily managed 100km by throttling back to where the engines are barely putting out thrust.

Here's a modified craft file.

You'll note I removed your vertical fins and re positioned your outer wings to be a true X shape. I also moved some air intakes in order to move the wings back. I removed some control surfaces and moved them to the outer wing to give more control.

As others have said... start simple. Design your plane horizontally and before launch rotate vertically and totally ignore the placement of mass, lift, etc. when you do. Only the horizontal positions matter. One engine, make the wings an X shape. The first thing you do with any new 'tailsitter' design is to find out where it's zero point is. Where on the throttle do you neither gain nor lose altitude when vertical. The other thing you need to learn to land one is spool up and down times. Stock engines are HORRIBLE about spool times. From the time you change the throttle position till the time the plane reacts is on the order of SECONDS. Learn how to anticipate what throttle you'll need. Those are the keys to learning how to land one. Tailsitters are finicky beasts. I know, I've created a lot.

Oh, and your skidding off the runway is most likely related to your lift and/or angle of attack. What's the angle of attack of your plane sitting stopped on the runway? Nose up or nose down? Is your lift forward or behind of the center of mass?

You'll note my throttle position. Even at 30km I'm gaining speed and not spinning. I have already moved fuel from the full tanks in the rear to the empty ones up front.

Not the easiest thing in the world to land. I almost missed. With that much weight away from the center of mass (wing tanks) think about adding some struts to prevent wobble.

Some of my other 'tailsitters' so that you know that I know what I'm talking about. You won't notice but ALL of these are designed to have the fuel in the middle so that as it gets used, the balance of the plane remains basically unchanged.

One of my favorite tailsitters. I used a modified version to make multiple trips to build a small space station in the Affordable SSTO challenge.

Perhaps the easiest flying tailsitter in my collection.

And a Kethane/Electric version on Duna.

Edited September 9, 2014 by Fengist

[O-Doc]

That's some nice metal Fengist.

Since your specific problems are more or less covered in the previous post I'll give you some advice about getting to where you want to be. That is, building HOTOL SSTOs. Load up the Ares 4a and practice getting it to orbit. Your minimum goal should be to have at least a third of its fuel left in orbit. Once you can demonstrate the ability to achieve orbit with a proven design, go back to the SPH and improve the design so she doesn't have a tailstrike hazard, doesn't flip when doing hard turns and finally, put a nuke on it and try to get to the Mun orbit and back. It's an excellent learners' SSTO with a deliberately flawed design to teach you the basics without having to build from scratch.

[psyper]

WOW thats awesome thanks everyone!!

Fengist: thanks for all that input - it was far more than I thought I would get and would certainly take that on board. I've downloaded the modified craft and will give it a play. I'm rather fond of tailsitters so it'll be cool if I could keep the design. I did a ssto tailsitter for my space tourism hotel and jet propelled lift (http://forum.kerbalspaceprogram.com/threads/85713-Space-Tourism-comes-to-the-Kerbal-Space-Center-%28VTOL-SSTO-Space-Hotel%29) - looking back at that one now I realise that I accidentally put all my tanks along the centre of mass keeping it stable pretty much all the way in to space!

Oh and the skilled landed-on-the-VAB-shot :

I use the goodspeed automatic fuel pump so can direct fuel to any tank in turn so I could use that to send fuel to the front first as I start to use it. I also use mechjeb's flame-out preventer which helps get my plane high and fast.

I do love the look of my crafts wings so I might bring back the shape with your suggestions in order to bring the weight forward and the lift further back thanks for all the help.

O-Doc: thanks, I'm partial for vtol craft as I got really angry with my planes plowing grooves in to the runway but will give the Ares 4a a fly just to see how they are made and might build on the design - I really need a ssto to take 4 crew to space so working out a way to get a hitch-hiker can on to it might be a bit of a challenge!

Edited September 9, 2014 by psyper

[peadar1987]

It could be the drag from those intakes as well. They have biiiig drag, and do not like to be behind the centre of mass.

[Fengist]

WOW thats awesome thanks everyone!!

Fengist: thanks for all that input - it was far more than I thought I would get and would certainly take that on board. I've downloaded the modified craft and will give it a play. I'm rather fond of tailsitters so it'll be cool if I could keep the design. I did a ssto tailsitter for my space tourism hotel and jet propelled lift (http://forum.kerbalspaceprogram.com/threads/85713-Space-Tourism-comes-to-the-Kerbal-Space-Center-%28VTOL-SSTO-Space-Hotel%29) - looking back at that one now I realise that I accidentally put all my tanks along the centre of mass keeping it stable pretty much all the way in to space!

Oh and the ubiquity landed-on-the-VAB-shot :

http://i.imgur.com/v8Gan38.png

I use the goodspeed automatic fuel pump so can direct fuel to any tank in turn so I could use that to send fuel to the front first as I start to use it. I also use mechjeb's flame-out preventer which helps get my plane high and fast.

I do love the look of my crafts wings so I might bring back the shape with your suggestions in order to bring the weight forward and the lift further back thanks for all the help.

Not a problem, you just happened to hit on a subject I'm very familiar with and, normally I don't look in this forum, it was pure luck that I spotted it.

If you're going to move the outer wings back to horizontal here's my suggestion, also add in a set of identical vertical wings to match. One thing you'll find about tail sitters, they're a LOT easier to land and fly if they're symmetrical. When you're hovering and trying to position yourself, having the motion in all directions being equal will make that positioning a lot easier.

Not familiar with the fuel pump mod. I know there at least was a fuel balancing mod. I never used them. My method has always been to make sure my center of mass would stay pretty much balanced with just the stock fuel usage method. Took me a few more flights to figure out how it uses fuel, but it's one less mod I have eating ram.

As for Jeb, keep using it till you learn how it works then ditch it. I used Jeb for several months while I was learning and then it dawned on me that Jeb was having all the fun. It's a great mod for learning how to do things but I can now dock faster than Jeb and use less fuel, I can land on other planets closer to where I want and with fewer crashes than Jeb and, because I know how the plane flies rather than Jeb, I can perform maneuvers Jeb can't even envision.

Fly safe.

Edited September 9, 2014 by Fengist

[psyper]

Fengist, I noticed your modified Eagle is showing the lift dip down below the cockpit too - is this a problem?

[Fengist]

Fengist, I noticed your modified Eagle is showing the lift dip down below the cockpit too - is this a problem?

http://i.imgur.com/YZmjZE6.png

No, not a problem. As I said in my first post, completely ignore what it looks like vertical. Only the horizontal positioning matters. Build horizontal, close your eyes, rotate vertical and launch.

[psyper]

It could be the drag from those intakes as well. They have biiiig drag, and do not like to be behind the centre of mass.

Yeah I noticed the drag on my ssto - I have them close on the same hotkey I have the switch to fuel/liquid ox switch. Bringing the intakes further forward - thanks

Not a problem, you just happened to hit on a subject I'm very familiar with and, normally I don't look in this forum, it was pure luck that I spotted it.

If you're going to move the outer wings back to horizontal here's my suggestion, also add in a set of identical vertical wings to match. One thing you'll find about tail sitters, they're a LOT easier to land and fly if they're symmetrical. When you're hovering and trying to position yourself, having the motion in all directions being equal will make that positioning a lot easier.

Not familiar with the fuel pump mod. I know there at least was a fuel balancing mod. I never used them. My method has always been to make sure my center of mass would stay pretty much balanced with just the stock fuel usage method. Took me a few more flights to figure out how it uses fuel, but it's one less mod I have eating ram.

As for Jeb, keep using it till you learn how it works then ditch it. I used Jeb for several months while I was learning and then it dawned on me that Jeb was having all the fun. It's a great mod for learning how to do things but I can now dock faster than Jeb and use less fuel, I can land on other planets closer to where I want and with fewer crashes than Jeb and, because I know how the plane flies rather than Jeb, I can perform maneuvers Jeb can't even envision.

Fly safe.

Ah yes I'm figuring it out now - looking back I noticed that the plane would spin a certain way when vertical landing and again looking at my ssto it has symmetrical wings too (why I didn't just take that same design and removed all the LqO2 is beyond me!!

With fuel pump you can set each tank with a number between 0 and 8 and it drains the highest first - its a god send when doing fuel runs from kethane - pumps fuel from the kethane miner to the surface-2-station lifter - then pumps fuel from the storage tanks on that to the station - then pumps fuel from the station to the minmus-kerbin transfer tug then pumps fuel from that to the lko fuel station then from that to any docked ships - saved a whole load of hassle and its fun watching your centre of mass shift as soon as you dock!

I mainly use Jeb for all the features people use engineer for - distance from ap, pe, horizontal acceleration, vertical speed, suicide burn, closest distance from target etc It means I don't have to keep switching to map mode to watch my ap when going for a gravity burn or rendezvous or keeping an eye on my actual height above the ground rather than sea-level and winging it. Basically the tools nasa and the first Apollo astronauts had all those years ago. I did use the translatron for docking with my minmus base as you cant use feather controls for your thrust levels so its hard to just hover above the surface while you use reaction thrusters - if you could then I wouldn't need that. I also have limit thrust to terminal velocity for heavy launches - again nasa uses the same thing during the shuttle launches. And lastly as mentioned the anti-flame-out system which I think should be inbuilt in to the engines - not that hard to incorporate irl and I'm sure we would have that in place if we ever have decent ssto's!! I do all my docking manually as well as intercepting ground bases when landing - all thanks to Scott Manley of course - and, of course, fly safe to you too!!

[Fengist]

Yeah I noticed the drag on my ssto - I have them close on the same hotkey I have the switch to fuel/liquid ox switch. Bringing the intakes further forward - thanks

Ah yes I'm figuring it out now - looking back I noticed that the plane would spin a certain way when vertical landing and again looking at my ssto it has symmetrical wings too (why I didn't just take that same design and removed all the LqO2 is beyond me!!

With fuel pump you can set each tank with a number between 0 and 8 and it drains the highest first - its a god send when doing fuel runs from kethane - pumps fuel from the kethane miner to the surface-2-station lifter - then pumps fuel from the storage tanks on that to the station - then pumps fuel from the station to the minmus-kerbin transfer tug then pumps fuel from that to the lko fuel station then from that to any docked ships - saved a whole load of hassle and its fun watching your centre of mass shift as soon as you dock!

I mainly use Jeb for all the features people use engineer for - distance from ap, pe, horizontal acceleration, vertical speed, suicide burn, closest distance from target etc It means I don't have to keep switching to map mode to watch my ap when going for a gravity burn or rendezvous or keeping an eye on my actual height above the ground rather than sea-level and winging it. Basically the tools nasa and the first Apollo astronauts had all those years ago. I did use the translatron for docking with my minmus base as you cant use feather controls for your thrust levels so its hard to just hover above the surface while you use reaction thrusters - if you could then I wouldn't need that. I also have limit thrust to terminal velocity for heavy launches - again nasa uses the same thing during the shuttle launches. And lastly as mentioned the anti-flame-out system which I think should be inbuilt in to the engines - not that hard to incorporate irl and I'm sure we would have that in place if we ever have decent ssto's!! I do all my docking manually as well as intercepting ground bases when landing - all thanks to Scott Manley of course - and, of course, fly safe to you too!!

IMHO, people put way too much stock into mathematical calculations in KSP. Me? I just fly the things. If they crash, I did something wrong. Back to the SPH. If it don't fly by the seat of my pants, it ain't fun.

[Fengist]

Also, you may have noticed that my second screenshot is a non-symmetrical tailsitter. This is from a challenge I created based on the Google Wing project. While it does fly and land, I can safely say it's not my most stable design. You can have success with them, just don't expect them to be all-star performers.

Edited September 9, 2014 by Fengist

[Fengist]

Here, this may teach you a few things if you're interested in VTOL's. It's a challenge I created months ago: The Ultimate VTOL Challenge

[peadar1987]

Yeah I noticed the drag on my ssto - I have them close on the same hotkey I have the switch to fuel/liquid ox switch. Bringing the intakes further forward - thanks

Sorry, that should say in front of the centre of mass. You want them as far back as realistically possible.

[psyper]

IMHO, people put way too much stock into mathematical calculations in KSP. Me? I just fly the things. If they crash, I did something wrong. Back to the SPH. If it don't fly by the seat of my pants, it ain't fun.

Theres two types of KSP players. I'm more the lets do this the way space-x or nasa would do it - but without many of the safety features... oh and everything is a simulation until it works right f5-f9 is my friend most of the time! I do like to read up on some of the posts on mathematics with huge formulas but at the end of the day I prefer to use websites and mods to do the calculations for me - heading towards a spacestation at 100k/s there isn't time to work out when I should start burning the nukes to stop me in time!

Also, you may have noticed that my second screenshot is a non-symmetrical tailsitter. This is from a challenge I created based on the Google Wing project. While it does fly and land, I can safely say it's not my most stable design. You can have success with them, just don't expect them to be all-star performers.

I can't really tell from the screenshot - do you have any more - I was tempted to build a reverse craft which had two cockpits separated by a large wing and control surfaces - I can then use that as a rescue mission (not sure if kerbals weigh anything while in the craft?) but I couldn't even get normal craft off the ground but it might be something to play around with later on in the game.

Here, this may teach you a few things if you're interested in VTOL's. It's a challenge I created months ago: The Ultimate VTOL Challenge

There is all kinds of awesome on that thread - certainly worth a look through. I'm always eager to view how people solve these challenges - some come up with really unique ways I never knew you could do on stock. I can spend hours going through the moonbase and spacestation megathreads taking a note of different configurations that I like the look of or solutions to problems I've had in the past.

Sorry, that should say in front of the centre of mass. You want them as far back as realistically possible.

ah makes more sense now, thanks - moving them to the rear later tonight

Well I had a play around with a new ship taking on board all the suggestions in this post - I launched it without SAS switched on and watch it climb with little deviation - when i did the first turn in to horizontal flight the prograde dropped down below my vector and it was very hard to keep flying horizontal as the weight is more forward than SAS could cope with but that can easily be solved by going vertical until I get my speed up and then slowly turning to horizontal flight a little at a time - the added speed on the wings help to keep it more stable at higher speeds and I'm able to get stable horizontal flight. Once I got it over 1km/s I tried to do a sharp turn and managed to get it, under control, around 90 degrees from my current heading before (of course) flame out occurred - before I'd go off 5 degrees from my current heading and it would spin out of control so this is a major improvement over my original design. And my SAS held it where I put it so I could point it at a target, kick in the SAS and wait for the craft to catch up to where I wanted it to go. I next cut the engines, rotated the craft to its retrograde heading and switched the engines back on - I managed to slow the crafts horizontal velocity so that it was descending vertically - full throttle stopped my decent and got me climbing again with no issues, no spinning or anything - it was bliss! Even threw the craft in to a spin on purpose kicked in the SAS and it eventually got the craft stable and I was able to point the craft at a 30 degree angle and punch it back in to a climb. It was amazing how a couple of simple changes made all the difference!! I was having way too much fun too late at night to get screenshots so will post them later today when I get home from work.

I'm tempted to put some winglets (canards?) at the front just behind the cockpit just for aesthetics do you think that would cause any issues at all?

[Fengist]

I'm tempted to put some winglets (canards?) at the front just behind the cockpit just for aesthetics do you think that would cause any issues at all?

Glad to hear you're having some success. Soon, you too shall master the lazy man's way of landing.

As long as you have it balanced it should all work. Keep in mind that the way KSP works is the further you get away from direction or reverse direction of travel the more likely you'll lose complete control of the craft. That's also affected by how much total lift you have. The craft in my last two videos has a HUGE amount of lift and is very difficult to lose control of. That's how I was able to accomplish that 'nosedive' video in a very short space. The more 'control' surfaces the quicker it reacts and the more likely you'll go in an unintended direction.

Here's how accurate and balanced it is... it's sitting on a clampotron. Oh, and you'll notice canards on the nose, again in an X pattern.

And, Per your request, another screenshot of the Google Wing mockup.

Edited September 10, 2014 by Fengist

[Laie]

Your center of lift is angled. The position relative the CoM is fine but it's pushing the craft in one direction. The arrow should be straight up but instead it's pointing below the bottom of the cockpit. That isn't good whether you plan on flying vertically or horizontally. It's going to want to turn the nose down.

The CoL arrow always points a little forward. Haven't you noticed before? This may be different with FAR (and other mods that display all kind of fun stuff in SPH), but in stock, the arrow never point straight up.

That said, I suspect moving center of mass. The vessel as pictured has the CoM sufficiently ahead of the CoL -- but look at the tanks. The tank immediately behind the intakes will be drained first, the one next to the engines will be drained last. Thus the center off mass moves towards the rear.

[Moonfrog]

Not sure if this has been mentioned, but one thing about planes I have started to do that helps a lot is. Place fuel tanks as close to the centre of the craft as possible. Have the fuel tanks make up the middle part, then have the centre of mass in the middle of the craft. This way when the fuel drains out, it has much less impact on moving the Centre of mass, than say if the fuel tank was on one end to the other. I also use structural fuselage to extend the aircraft to make this easier. Means even in stock u don't really have to worry about the fuel tanks. Also emptying the tanks with tweaking helps u see the difference.

[Alshain]

Not sure if this has been mentioned, but one thing about planes I have started to do that helps a lot is. Place fuel tanks as close to the centre of the craft as possible. Have the fuel tanks make up the middle part, then have the centre of mass in the middle of the craft. This way when the fuel drains out, it has much less impact on moving the Centre of mass, than say if the fuel tank was on one end to the other. I also use structural fuselage to extend the aircraft to make this easier. Means even in stock u don't really have to worry about the fuel tanks. Also emptying the tanks with tweaking helps u see the difference.

Just be aware that's just for stock. With FAR you want more mass at the front the faster your craft gets and more mass at the back for subsonic speeds. It's common to move fuel around as you transition between subsonic and supersonic. With NEAR it may improve stability slightly, but it has less of an impact.