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SSTO doesn't take off


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Hey guys :) ,

I know there are already a lots of tweets but i watched already a lots of tutorials etc... 

Well i tried to built a big cargo-SSTO. On ground it is good to turn left right but i have the problem that it cant take off :/

I have built also another one but it has exactly the same problem. I can built planes i constructed the SR1-Blackbird and it worked well but SSTOS ... are not working ^^.

One Problem i could imagine, is that the center of lift is not at line with the center of mass but I am still a noob in planes. I started 4 days ago to build planes xD.

kind regards :D

 

PS: i hope the pictures are there :D

https://imgur.com/PG1H2RQ

https://imgur.com/GmihCbH

 

 

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1 hour ago, Muddyblack said:

One Problem i could imagine, is that the center of lift is not at line with the center of mass but I am still a noob in planes. I started 4 days ago to build planes xD.

They are indeed pretty far away from each other but it may work out fine anyway. The reason you are not able to take off is a different though: The gear in the rear need to be between the center of lift and the center of mass. The elevons on the wings will not pull up your nose but they will push down your rear and as soon as your center of lift is behind the rear gears, this will actually lift your nose up. So move the gears a little bit forward and you should be fine.

Well, you can also add some more elevons/winglets to your nose though but I would suggest to move the gears instead ;)

Edited by 4x4cheesecake
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1 hour ago, 4x4cheesecake said:

The gear in the rear need to be between the center of lift and the center of mass

Beg to differ most respectfully.  I don't think the optimal position of the main gear is strongly related to the center of lift at all.  Their relative positions do not matter.  However.  Both are problems inhibiting rotation.

1. The CoL needs to be much closer behind the CoM.  2. And the main gear need also to be up closer, for a shorter take-off.

If you fixed only 1 and had a long enough runway the aircraft would lift off at high enough speed, but until it does, you cannot rotate, which is an action that increases your AoA and therefore your lift.

Looking at the images, both CoL and position of main gear need to be much closer to the CoM.  I would start with moving the wings forward and/or increasing the wing area for the same purpose.

tl;dr fix both

Edited by Hotel26
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I agree with the above- your centre of mass is a bit too far forwards and your elevators can’t produce enough leverage to force the nose up. For a plane that size you should use the larger elevons (elevons 2, 3 and 4 if I remember them right) rather than elevon 1 which has a smaller surface area and so provides less control. You could also try using the Big-S wings and elevons as they provide more lift and control respectively.

You could use some larger nose-mounted canards (or more of them) to lift the nose, and/or shift the rear wheels further forwards which will increase the leverage that the rear elevators can produce. If you do move the wheels you may need to stick a small wheel on the tail to prevent tail strikes from over enthusiastic pitching up. another wheel-related trick is making the rear wheels slightly higher than the front ones on the aircraft, which will give the whole plane a slight nose up attitude on the runway and increase lift.

You could also add some more wings near the front to move the centre of lift further forward, and if you angle those wings so the front edge is higher they’ll generate even more lift and a bit of nose up which will also help the plane get off the ground and possibly a bit more stable in flight.

I think your centre of mass needs to be adjusted, try swapping the positions of some fuel tanks and ore tanks to balance it up a bit. Are you planning to fly it into orbit, or back down, with the ore tanks full? If so that plane will become even more nose heavy as the fuel gets burnt and will be really hard to land in one piece- landing will be easy, it’s the ‘in one piece’ bit that will be the trick! Swap some ore and fuel tanks around and try looking at the CoM with different levels of fuel and ore in the tanks as it can make a huge difference; ideally there would be a setup where the centre of mass doesn’t move much/at all no matter how much fuel or ore is in the tanks.

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Well yes i tried to get the rear wheels between the CoM and CoL but it didnt help and my plane became a bit unstable while spawning and swapped while taking off but i didnt got it up. I now cheated my plane into 500 meters up here it is stable the big problem is to take off ^^.

Well CoL must be close to the CoM good the other question is with the line should it be at the same line because at the moment it is bit higher and also like you said far behind CoM

Well at the moment it has no cargo so the CoM will move if i get some Cargo in :). (dont  want to use it  just for a one time mission)

So if i got it right: 1. i should bring my front gear nearer to the CoM 

                                2. get CoL more forward near to CoM      (bring wings forward)

                                3. use bigger Elevons -> i used the elevons 5 think are big enough? 

                                4. 

1 hour ago, jimmymcgoochie said:

If you do move the wheels you may need to stick a small wheel on the tail to prevent tail strikes from over enthusiastic pitching up. another wheel-related trick is making the rear wheels slightly higher than the front ones on the aircraft, which will give the whole plane a slight nose up attitude on the runway and increase lift.

I'm german ^^ and im not able to understand this sentence here i cant imagine why could i make a wheel on my tail (looks and listen bizarre xD )

Gonna try it now :D

Edited by Muddyblack
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Update: (still problems ;( )

 

Well it is now really better it is possible to take off. Thank you guys :D  i learn more and more ^^.

here the new craft: 

kvXXLIO.pngZfWKFx7.pngYdnGHk8.pngrCsCTmP.pngCPoHn0E.png

 

Well I know many pictures xD but they explain more than thousand words xD!

This works now good BUT i have a second problem ;)  like Vanamonde said and you can see on the last picture xD the take off is not the best haha I get up to  the air at the end of the runway to 200 meters and then i fall again like a rock on mun. I have 18 R.A.P.I.E.R engines thought this would be enough :O i have still no cargo in my craft so it has not the highest weight now its 370.000 tonnes. The acceleration is very slow. I need timewarp of 4  that it is not so lame xD.

 

How can i get more thrust? 

Like always thank you for your help guys :-) 

A newbie learns oh man rockets are easy... ^^

PS: above the seond pic shows also my optoions for the elevons 

 

Have a nice evening 

 

Edited by Muddyblack
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I can't help thinking you'd be better off with a big rocket or possibly several small ones. If all you want to do is pick up some ore from a mining site on the Mun and carry it back to Kerbin's orbit or even to the surface, rockets will be a lot easier than planes.

Spaceplanes are only really useful if you're going somewhere that has an atmosphere, otherwise the wings are just dead weight you have to carry around everywhere. Planes are also harder to land when there's no air as they're designed to land horizontally, not vertically.

I find it worrying that your plane only reached 90m/s on the runway, that probably won't be nearly fast enough to keep flying for a plane that large. Holding S to pull up will slow you down as the elevons and canards produce a lot of drag when they're deployed like that, you should try to accelerate more before pulling up.

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8 hours ago, Muddyblack said:

I have 18 R.A.P.I.E.R engines thought this would be enough

Those engines have a major disadvantage at low altitudes and slow speeds. They come into their own around Mach 1.2 or so, around 450 m/s near sea level, but getting to that speed with a heavy craft is tough. Have you tried Whiplash engines to see if you can get the takeoff speed? If that works you could use a mix of those and Rapiers to get past that 450 m/s barrier, and still have some LFO engines when you run out of air.

 

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