Need help on my SSTO

[ahmetyag3]

I made an SSTO that simply can't climb, accelerate, and can't lift off until the end of the runway. It has 6 Rapier engines and 2 nuclear engines. It can't go over 5-6 km and can't accelerate enough to reach the thinner atmosphere level. Additionally, it's not too stable. How can I fix that?

Stages: https://imgur.com/a/m4bvy8A

Engineer's Report: https://imgur.com/a/kOADqOV

From Front: https://imgur.com/a/ryxL0X7

From Back: https://imgur.com/a/nBEfWCA

From Top: https://imgur.com/a/88hFa9h

From Right: https://imgur.com/a/hXt1Rx0

(Sorry for links it didnt inserted from photos from links)

Is this amount of wing enough
https://imgur.com/a/q4hZQZK

Edited January 24 by ahmetyag3
cant reply to comments

[Vanamonde]

My main advice is to start smaller and work up.   One thing that will help specifically with that craft, though, is to move the rear wheels closer to the center of mass. Right now the length of the plane is acting as a lever to hold the plane down, whereas moving the wheels will make a better pivot point. 

[king of nowhere]

i'm not an expert of planes, but seems to me like the wings are way too small for the mass of that thing.

and 2 nervs won't be enough to circularize.

[ahmetyag3]

Is this amount of wings enough?

(I'm gonna add more nuclear engines later)

https://imgur.com/a/q4hZQZK

Edited January 24 by ahmetyag3
grammar mistake

[miklkit]

I wish you had just posted one large screenie of it in the SPH.  You could show more information that way. 

I dug up one of my early designs of about the same weight.  It is a 6X4 with 6 Rapiers and 4 NERVs.  It is also poorly built and performs badly, but still made it to Minmus. 

Yours has plenty of wing area.  Moving the landing gear will help a little bit but slapping canards on the front will help more.  Where the COM and COL are is a compromise between taking off and coming down empty.  Mine all run off the end of the runway and need to build up speed before they can climb.

  You say it will not accelerate and can not gain altitude.  That says that it is very draggy.  After takeoff hit F1 to see where the drag is coming from.  This one had misaligned engines and that drag kept it from making orbit.  Look at the length of those red lines!

[DennisB]

Those nearly vertical surfaces in the middle (at the air intakes) don't make sense for me. They make almost nothing, just drag. What are they supposed to do?

[ahmetyag3]

1 hour ago, miklkit said:

I wish you had just posted one large screenie of it in the SPH.  You could show more information that way. 

I dug up one of my early designs of about the same weight.  It is a 6X4 with 6 Rapiers and 4 NERVs.  It is also poorly built and performs badly, but still made it to Minmus. 

Yours has plenty of wing area.  Moving the landing gear will help a little bit but slapping canards on the front will help more.  Where the COM and COL are is a compromise between taking off and coming down empty.  Mine all run off the end of the runway and need to build up speed before they can climb.

  You say it will not accelerate and can not gain altitude.  That says that it is very draggy.  After takeoff hit F1 to see where the drag is coming from.  This one had misaligned engines and that drag kept it from making orbit.  Look at the length of those red lines!

 

I gues this red lines should not be this amount when i climbing at about 5 degree https://imgur.com/a/J735nkX

This is a bigger photo from SPH (i added some more wing to get more lift) https://imgur.com/a/UW3eL0C

[ahmetyag3]

12 minutes ago, DennisB said:

Those nearly vertical surfaces in the middle (at the air intakes) don't make sense for me. They make almost nothing, just drag. What are they supposed to do?

There is no vertical intake on top of this SSTO 

[miklkit]

Hmm.  At that speed at around 9 degrees AOA those lines don't look too long, but there sure are a lot of them.  It is cluttered.  The MK2 is very draggy to begin with because the body creates lift and then there are lots of little parts all over it causing drag.  It all adds up.  You could lose 2 intakes without losing any power too.  I learned a lot from VAOS on youtube about reducing drag. 

Also, the COM and COL are too close together and will cause instability.  Not so much going up but when coming down. 

[ahmetyag3]

6 hours ago, miklkit said:

Hmm.  At that speed at around 9 degrees AOA those lines don't look too long, but there sure are a lot of them.  It is cluttered.  The MK2 is very draggy to begin with because the body creates lift and then there are lots of little parts all over it causing drag.  It all adds up.  You could lose 2 intakes without losing any power too.  I learned a lot from VAOS on youtube about reducing drag. 

Also, the COM and COL are too close together and will cause instability.  Not so much going up but when coming down. 

I made this SSTO go to the mun with lots of fuel. Fuel is almost not enough (about 9k liquid fuel) wia adding some more wings but its still so draggy most of the time it can go over 10k with new wings i added (fuel is not a big problem cause i have drills but it needs to optimized)

[miklkit]

You have drills in your cargo bay?  I tried to build a copy and ended up a bit lighter.  It still got into orbit fine.  This has me wondering what your flight path profile looks like.  I take off and keep it low until it gets over 430 m/s and then let it climb.  I level off again over 8000 m and let it build more speed then let it climb.  The idea is to be going 1400-1500 ms and over 20,000 m when switching mode on the Rapiers.

[ahmetyag3]

45 minutes ago, miklkit said:

You have drills in your cargo bay?  I tried to build a copy and ended up a bit lighter.  It still got into orbit fine.  This has me wondering what your flight path profile looks like.  I take off and keep it low until it gets over 430 m/s and then let it climb.  I level off again over 8000 m and let it build more speed then let it climb.  The idea is to be going 1400-1500 ms and over 20,000 m when switching mode on the Rapiers.

ig my problem was im trying climb after about 200m/s im gonna try that on moring (2:44 am rn)

[ahmetyag3]

10 hours ago, miklkit said:

You have drills in your cargo bay?  I tried to build a copy and ended up a bit lighter.  It still got into orbit fine.  This has me wondering what your flight path profile looks like.  I take off and keep it low until it gets over 430 m/s and then let it climb.  I level off again over 8000 m and let it build more speed then let it climb.  The idea is to be going 1400-1500 ms and over 20,000 m when switching mode on the Rapiers.

I'm tried and it worked thx for help have a nice day

[DeadJohn]

7 hours ago, ahmetyag3 said:

I'm tried and it worked thx for help have a nice day

Glad you solved it.

Maybe you already know this, but another tip I didn't see mentioned is to rotate wings so they have some angle of attack/incidence. Your photos look like maybe the main wing is angled and the front strake is not angled but it's hard to tell. Rotated wings allow you to keep the nose lower while climbing. The fuselage especially mk2 parts will create much less drag, more than enough to offset any extra drag from the wings.

I like around 3 degrees of wing incidence because it creates lift while not making the plane look too weird. I've seen other people claim 5 degrees is better for supersonic speeds but I don't care for the way that looks on large wings. My usual method is to start with 0 degrees because that's easy, do a test flight, and if I need more performance then I experiment with wing incidence and position.

In order to allow easier tweaking of wing incidence when using multiple wing parts, attach the first wing part to the plane, then attach additional wing parts to the first part and offset them where you want. If you later reposition the 1st part all of the other wing parts will move with it. Consider autostruts to reduce wing flex.