Tail fins configuration for my SSTO - Running out of ideas

[INTERKOSMOS]

I'm currently in process of designing and fly-testing new medium-size interplanetary SSTO, capable of carrying about 4-5 tons of cargo. The results are very promising. However, I have problem with it's tail. Tail fins that i'm using right now are just temporary solution. They do not provide enough lift, and elevons do collide with each other and engine nozzle, as shown in the pictures. And that looks bad. I have tried to find some real life inspirations, but no luck so far. Perhaps some more experienced SSTO designer/engineer can help me with this one? New tail fins configuration must:

- Look aesthetically pleasing and fit the craft's overall good look and proportions. This is most important! If it looks fine, it works fine, that's my motto. (i don't mind clipping parts for maintaining aesthetics, i'm doing this quite often).

- Provide more lift force, but as little drag as possible!

- Not collide with anything while moving

- Not getting in the way of engines exhaust!

 

 

 

 

SSTO without tail fins:

 

 

Craft file:

 

see Or-11 V4X on KerbalX.com

 

 

Edited February 17, 2017 by INTERKOSMOS

[ForScience6686]

Use a top mounted horizontal stabilizer.  Add the small rectangular piece behind your vertical stabilizer.  Probably will still need to make it larger since you claim to have too little pitch authority.  Or, you could move your col closer to com, that should improve pitch.

[INTERKOSMOS]

13 minutes ago, ForScience6686 said:

Use a top mounted horizontal stabilizer.  Add the small rectangular piece behind your vertical stabilizer.  Probably will still need to make it larger since you claim to have too little pitch authority.  Or, you could move your col closer to com, that should improve pitch.

Oh, that's not the point. In fact, I'm trying to move COL backwards (right now COL is only centimeters behind COM) by increasing overall lift area at the back of my craft. It has no problems with pitching up, in fact it can easly make unplanned kulbit manouver, if I'm not careful.

[The_Rocketeer]

Can you give us a shot of CoM/CoL on the version without any tailplane?

You could try something like this, my Peregrine design (albeit quite old now) - not only are the V-stabilators on top angled up about 30 degrees from horizontal, the outer-wings are also angled down so the ailerons and elevators also combine to produce yaw when required. You will likely still need to juggle your weight distribution further forward tho.

Edit: ps cool design

Edited February 17, 2017 by The_Rocketeer

[mystik]

Why not add two small tail fins to the tips of your wings? Triple tail as per the picture below only that you mount those to the edge of the wings to. That also helps with your center of mass since it does not push weight to the end of the plane but that depends on your build. Then add control surfaces to your wings and done. You don't need too many controls because that way you won't dismember the plane when pulling hard. I made one SSTO one that was crazy maneuverable, going for 15G at turns and therefore breaking to pieces in the process.

 

Edited February 17, 2017 by mystik

[INTERKOSMOS]

1 hour ago, The_Rocketeer said:

Can you give us a shot of CoM/CoL on the version without any tailplane?

Sure, here you go:

 

I tried V-shaped fins before on some other designs, but controlls was never as good as with conventional ones, or delta wings with double vertical fins. That's why I was allways a bit suspicious about V-shapes. Maybe my older designs was faulty, or maybe that's fault of aerodynamics model in KSP? I don't know. But I will do some testing. Right now I suspect, that amount of lift I'll get from V-fins won't be high enough. I would be forced to use really big, bulky fins, or redesign my craft completely, which is not an option at this moment. Butl I will try.

 

1 hour ago, mystik said:

Why not add two small tail fins to the tips of your wings? Triple tail as per the picture below only that you mount those to the edge of the wings to. That also helps with your center of mass since it does not push weight to the end of the plane but that depends on your build. Then add control surfaces to your wings and done. You don't need too many controls because that way you won't dismember the plane when pulling hard. I made one SSTO one that was crazy maneuverable, going for 15G at turns and therefore breaking to pieces in the process.

 

I saw that picture before, when I was looking and googling for some kind of inspiration. Thank you for your idea. I never tried triple tail or anything like this. I have doubts that stock selection of parts is good enough to build such tail, and make it look like an actual spaceplane tail, not like something that was salvaged from a decommissioned airliner.

[foamyesque]

I'd probably go with canards, to be honest, and slide the main wings backwards and add ailerons to it. Probably tack on a couple of degrees of incidence while I was at it, which should solve your lift issue. I prefer standard canards performance-wise, but advanced canards look better on the Mk 2 fuselages.

[bewing]

Generally, having a moveable rudder provides almost no benefit to a SSTO. And having horizontal stabilizers in the back actually degrades the performance of the craft. Adding wing generally helps performance somewhat -- especially if you put a little bit of incidence on them. So I agree with foamyesque -- maybe replace those rear wing sections with type B structural wings to move your CoL back a little and give you more wing area. Go with canards instead of the horizontal stabilizers -- choose whichever ones look good to you. Then maybe 2 or 3 small-to-medium wing sections mounted vertically as tails, with no control surfaces on them.

[foamyesque]

Ehhh, I find the movable rudder very useful during the glide phase, but tastes vary.

[fourfa]

I can do without a moving rudder on a very small plane (where reaction wheel alone is plenty), or if I have really solid aileron roll control (plenty of moving area, far from the centerline, with appropriate limits).  What I see in the OP is a medium size plane with very little aero roll control and not much reaction wheel, which would be very hairy to do last minute landing adjustments.  Moving rudder or no. (IDK - maybe there's tons of reaction wheels in the cargo bay)

Nice looking ship though.  Question - what's the point of the structural intakes on the outboard nacelles? The pair of precoolers are more than plenty

Edited February 18, 2017 by fourfa

[Wanderfound]

8 hours ago, INTERKOSMOS said:

Sure, here you go:

I'd be inclined to build that as a pure delta, rather than a tailed delta. Add elevons to the back of the wings, shift them back a smidgeon, add a vertical stabiliser, forget about a horizontal stabiliser. Throw in some canards if you're short on pitch authority, leave them off if not. And, as noted above: lose some intakes. A single precooler or shock cone could easily feed those jets.

But if you really want to keep it as a tailed delta, a t-tail mounted above the central jet would work.

[INTERKOSMOS]

8 hours ago, Wanderfound said:

I'd be inclined to build that as a pure delta, rather than a tailed delta. Add elevons to the back of the wings, shift them back a smidgeon, add a vertical stabiliser, forget about a horizontal stabiliser. Throw in some canards if you're short on pitch authority, leave them off if not. And, as noted above: lose some intakes. A single precooler or shock cone could easily feed those jets.

But if you really want to keep it as a tailed delta, a t-tail mounted above the central jet would work.

Ok, I see I have to clarify something.

 

I have 3 years of experience in KSP and I'm kind of Obi Wan of SSTO designs. I have started with building spaceplanes and refueling stations before I even touched typical rocketry. HOWEVER, even Obi Wan needs to consult with Yoda in some cases, because there is always someone better, more clever, with head full of fresh, never-ending ideas.

 

I know exactly what would make this spaceplane work like a charm. If I would only throw this configuration right into trash bin... But I don't want to. And this is why I have sooo much difficulties with this one. I want to combine it's PRESENT aesthetics with performance. I don't want to make another delta, I've built tons of them before, and even now I have light, delta-winged interplanetary cargo in active duty. I want to keep that wing configuration at all costs, because I like it soo much!  That's why I asked for ideas for tail fins configuration ONLY. I don't want to redesign the whole thing.

 

Perhaps a magic solution i'm looking for simply doesn't exists. But my experience in KSP tells me, that there is ALWAYS some way to solve almost any problem.

 

Ok, back to the point. Air intakes. Yes, It's an overkill. But I had to place 3 precoolers in this way to balance this thing out and to maintain fuel balance, which is almost perfect at the moment. COM shift in flight is negligible. As for ramp intakes - these are here for teh lulz. They are very light, and since intakes do not generate almost any drag in current version of the game, they do not make any noticable impact on performance. Yesterday i have replaced Whiplash with Panther engine. Taking ~5 t of cargo into orbit takes more fuel now, but after refueling, I have 600 kg less of dry mass to carry around in space, plus the tail is lighter at the very end, which is good, because I don't need AS much lift at the back right now. Still, I have a lot of thing to do here, and I'm still open for suggestions.

[INTERKOSMOS]

13 hours ago, fourfa said:

I can do without a moving rudder on a very small plane (where reaction wheel alone is plenty), or if I have really solid aileron roll control (plenty of moving area, far from the centerline, with appropriate limits).  What I see in the OP is a medium size plane with very little aero roll control and not much reaction wheel, which would be very hairy to do last minute landing adjustments.  Moving rudder or no. (IDK - maybe there's tons of reaction wheels in the cargo bay)

Nice looking ship though.  Question - what's the point of the structural intakes on the outboard nacelles? The pair of precoolers are more than plenty

I just removed these intakes, they were nothing more than a decoration, but on the second thought - I don't need so much clutter on it. 3 precoolers are more than enough (third is at the very end, 90% of it is clipped into mk2-1.25m adapter.). As for reaction wheels, there is only 0.1 t of them inside, clipped into fuselage, very near COM. I need it to maintain good flight characteristics with heavy cargo on board. This SSTO maybe doesn't look like it, but it's VERY manoeuvrable and pleasent to fly.

[Mr. Speed]

I Downloaded your craft and took her for a test flight. It's nicely balanced! So I fiddled around a bit and this is what I came up with:

It gives yaw stability but no yaw control. Not a real problem since it has enough reaction wheels I found.

craft file: https://www.dropbox.com/s/ad8p832qpg6zet7/Orzel-XI V4X Tail 1.craft?dl=0

 

[INTERKOSMOS]

Wow, now that's something I would not invent myself... Nice! Thank you, Mr. Speed, I'll test your configuration, that's for sure. And it looks quite interesting. At this last screenshot, It's silhouette looks very much like MiG-29's, i like it.

Edited February 18, 2017 by INTERKOSMOS

[INTERKOSMOS]

Ok, I've built my own version of your twin T-fins. Here's how it looks. Val seems to be very enthusiastic, but Bill is not so sure....

 

 

Close up:

 

 

Overal look:

 

 

As you can see, I have placed Big-S elevon's 1 to increase lift, and it works like a charm. Plane is highly maneuvrerable, very stable and pleasant to fly. But i'm still not fully convinced about it's new look. But I feel we are making a big progress here.

 

Craft file, second prototype:

see Or-11 IMCS V4X on KerbalX.com

Edited February 18, 2017 by INTERKOSMOS

[AeroGav]

On 17/02/2017 at 3:22 PM, mystik said:

Why not add two small tail fins to the tips of your wings?

The problem is that being close to CoM, they won't be very effective at stabilizing yaw.  The further aft of CoM the better,  but on the other hand you don't want the tail to strike the ground when you pitch up!I often use twin tailbooms coming off the wing,  but the OP wants a good looking aircraft above all else (it certainly is) so i don't want to go suggesting things which drastically change the appearance.

Spoiler

 

23 hours ago, INTERKOSMOS said:

I just removed these intakes, they were nothing more than a decoration, but on the second thought - I don't need so much clutter on it

I actually like the look of those radial intakes.  They are useless,  but honestly the drag is negligible compared with the vast barn door drag he's going to be getting off the mk2 fuselage parts, so personally I'd just leave them on because they look nice and logically this plane should have some intakes (pre-coolers really "shouldn't" work on their own).

I do think the OP is really setting himself a mission impossible though, wanting an interplanetary mk2. If he can make it work, I'll be very , very impressed.

The drag off those mk2 fuselages is huge.   You can ameliorate that by adding incidence to the wings but if you're after aesthetics and have the OP's eye for detail, that's not an option - there is a nice flat chine running the whole length of the fuselage that's meant to blend smoothly into the wing all along it's chord.  If he adds incidence,  the leading edge will stick up above it and not connect with the fuselage at all while the trailing edge droops below.

That drag means he needs 3 jet engines, weighing 5.2 tons, to get hypersonic.     He needs a ton of oxidizer to get to orbital velocity.  The  mk1 in the spoiler above,   has a 37 ton TOW  and can get hypersonic on one rapier thanks to low drag.   It has so much lift and so little drag, it can continue to  climb and accelerate with 2 nervs only (the rapier never uses closed cycle mode).   After reaching 150km circular orbit, it still has 3700dV left, and a 0.35 TWR on the two nukes.

To cap it all, the pointy cockpit looks amazing but due to overheating will not allow the most efficient flight profiles, getting to 1600m/s on air breathers.  Interplanetary designs tend to have lower TWR, but with a pointy cockpit you need a high TWR and not stay around in the upper atmosphere.Here's a mod of a craft someone else posted on the forum,  I managed to get 3700+dV out of it in LKO, but it has angled wings to lower drag.   The mk1 fuselage tanks running either side of the body help to hide the messy wing/body join that results.   Without angled wings,  it'd probably need more engines to hit mach 1, and i'd need way more than 440 units of oxidizer to get to orbit (as it stands,  a small kick to get us from 1400 to 1700 m/s is enough for the nukes to take us the rest of the way),

Spoiler

 

For the first 9 months or so playing this game,  I created mk2's with flat wings.  The best i could manage was a design with 1 rapier and 2 whiplashes, 2 nukes.   It would jettison the whiplashes once flamed out, and it had enough delta V in orbit to reach Minmus, where it could refuel off my surface base. Fully SSTO I don't think i could even manage that.

[INTERKOSMOS]

Work is going well. Right now I'm in the process of fitting my SSTO with equipment she'll need in deep space. RCS thrusters, docking ports etc.

 

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Thank you for interesting facts, AeroGrav. I assure You, that this spaceplane can and will visit other planets. It has no problem reaching orbit, both with empty cargo bay or with few tons of equipment. When empty, I can circularise at 350 km with ~370 units of LF left. With 4,5 ton cargo, ~320 units (I expect these parameters to drop a little after fitting over 0,5 t of extra equipment). BTW 350 km is my parking orbit for interplanetary travell. This is where I've put my orbital refueling station. (any of my interplanetary carfts must be able to reach that orbit - that's one of key requirements). At this altitude, 370 units are enough to pass Mun orbit (and potentialy I could use it's gravity to leave Kerbin system). But after refueling.... wooo hooo! With 2000 units of LF on board i can visit Laythe's orbit, leave some satelites there, and still have enough fuel for something like half way back (if my estimations are correct). But when I will get my interplanetary network of ISRU and orbital refueling up and running, my spaceplanes will rule the Kerbol system! Buwahahahaha!!

 

Uhm.... sorry.

Edited February 19, 2017 by INTERKOSMOS

[foamyesque]

I strongly suspect @AeroGav meant "interplanetary from launch, no mining staging or refuelling", which is, while certainly possible, a much taller order