tetryds

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Considered doing it as a three-wide fuselage job? Less gooseneck, more of a blended-body delta design. Move four of the cabins from the neck to where the engines are now, put engines on the back and intakes on the front.

I did consider that, but a 3-mk3-wide shape sounds horrendously draggy. Will definitely investigate at some point, I did something similar ages ago that worked ( although I just ended up making bigger fuselages instead ).

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What seems to work rather well for this is just making it longer; wave drag decreased unsurprisingly, and there doesn't seem to be any change in required AoA at 20km at all, which *is* somewhat surprising. I haven't tried landing it empty yet though, might be a tad nose heavy by that point...

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If you ever rerun your Minmus tourist challenge ( which is where the original came from ) then at least I have a starting point. Must be almost double the ticket cost by now though!

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Airbrakes: in a test craft I set a couple of surfaces up to deflect 80deg upwards at roughly CoM, which worked spectacularily well on re-entry. What didn't work was using them at 200m/s on landing approach, it was only then they had a structural failure ( rather than at re-entry Q of 35k+... ). I've no idea what's going on there, what issue am I running into?

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OK, I might be wrong, I have always think that safe AoA before stall is before FAR graph lines is start to split.

On his graph they started to split at 17 degree and "safe" AoA should be below that, around 15 degree.

I'm not saying that you are wrong, but how you come up to conclusion that stall AoA is exactly 27 degree ?

Because the sudden Cl drop is what indicates when that stall is happening, and it's about 27 degrees for his craft

You may have confused the stall behavior with the L/D graph.

The thin line is the hysteresis behavior, after stalling you need to decrease your AoA to an angle lower than the one where it happens for it to stop happening.

So, the static AoA sweep shows what happens as you increase the AoA all the way to the max angle then back, that is why if you don't stall within the range you sweep at there is no thin line.

From the yellow line you can grasp how stall is happening, if at the point where the Cl drops your yellow line goes up the stall happens first somewhere in front of the COM, if it drops even more, it may be behind the COM.

You can also use that to balance your stalling in a way you can make controlled stalls that don't make your craft bounce around when it happens.

If you want to make it so you can have the highest AoA without stalling when piloting with a keyboard, just set the deflection in a way that with pitch settings on 1 your Cm crosses zero a bit before the sudden Cl drop.

Bear in mind that engine gimbal also adds to the pitch forces, so if your Cm at max pitch is exactly at the peak Cl the engines can make you cross that line and make you stall.

There is also moment of inertia, so if you make a sudden turn and pitch too fast you can stall because of that.

And also that you can end up having so much lift that pitching as much would instantly destroy your aircraft.

And also that... oh well, there are so many things.

Anyway, I think you got it.

Edited by tetryds

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Thanks, that provides even more info for fine tuning craft. I was always thinking, because of, like FourGreenFields mentioned, somwhere on forums someone mentioned that where graphs seperate there is a stall involved somewhere. Noone clarified that more, so we all was assuming that is it.

However, based on expirience with my own craft designs, I was able only to put Cm yelow neutral point(where cross x axis) just slightly into area where graph lines splits and still have more/less contolable craft. Cl drop point was 5-10 AoA higher than AoA where graph start to split. Could be that due to moment of inertia, engine gimbals or something else involved that AoA is somehow higher than expected to be and plane reached stall area regardless.

Anyway, when I started to design control authority in a way that Cm neutral point does not fall in area where graph splits, craft becomes more stable and controlable with only slight loss in maneuverability. Probably that is due to reason that even when moment of inertia or engine gimbals kicked in it was not enough to reach stall AoA degree.

Regardless, my advice to bartekkru99 is still valid, to check AoA sweep with "1" pitching and set control authority in a way that craft does not fall in dangerous AoA area.

Now we got even more info what dangerous AoA point is.

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If you're having fun building heavies, give this a go: http://forum.kerbalspaceprogram.com/threads/122243-Heavy-Lift-Economy-Challenge

Well, I might give it a go, currently I'm still searching for various mod combo that will more/less work well with each other without conflicts.

Most of them still need to be updated and still have not rechecked that temperature FAR bug that was poped up within first days after 1.0.4 release.

Real life issues were kicked in between, so I still didn't recreated anything solid worth to show for 1.0.4.

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I'm working on my first SSTO in nuFAR.

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It flies beautifully below ~mach 2 and has a very hard time decelerating to land, but has a bit of a problem at high speeds.

When it gets to be around 15km up at 800m/s, it decides it no longer wants to go to space and sideslips to death. I assume this is because I have too much drag on the nose, but I have no idea how to lower this without dramatically increasing my wave drag.

Actually, a big problem in every plane I make is that I can't bring my CoL to the back of the plane. I always need some absurd amount of wing area in the back, or some tricky CoM shifting to get things to fly straight.

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When it gets to be around 15km up at 800m/s, it decides it no longer wants to go to space and sideslips to death. I assume this is because I have too much drag on the nose, but I have no idea how to lower this without dramatically increasing my wave drag.

You need a larger vertical tail

Actually, a big problem in every plane I make is that I can't bring my CoL to the back of the plane. I always need some absurd amount of wing area in the back, or some tricky CoM shifting to get things to fly straight.

Putting AoA deflection on your pitching surfaces helps a lot: maybe -100 on canards and +100 on elevators.

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Also possibly you're pulling too-high AoA, which can make the nose want to fall off sideways; solution is a bit more wing ( high gimballed engines will mask the problem too ). Agreed you need more vertical surface though.

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Like other already advised, more vertical surfaces on tail. Slight dehadrial elevtors or even wings could help too with both, sideslip and roll problems. Even 1-3 degrees to can help a lot with it.

Too much dehadrial angle could be overkill on some designs, you may need to find your own middle ground.

Also you may expirience serious backfliping problems with AoA of 10 or more degrees.

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I tried to convert it to stock aero. Terrible. For me, since I started designing this crate in FAR, it really shows it's superiority.

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Well my speedbrakes still survive re-entry to explode off the craft ( taking the wings with them ) at low speed, no idea what is going on with them.

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Fences in the middle of the wing, nothing unusual/I haven't done before.

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I've been away from where I could answer these last few days...my apologies.

Okay -

What is the safest way to calculate? Right after a scene reload or without exiting SPH? I think the CoL indicator is all wonky too.

I'd say right after a fresh reload of the craft as a rule. You're also right - the CoL indicator does not work with FAR installed, which is a real shame; to be honest it's the only thing I don't like about FAR, though if you know how to interpret the data FAR gives you then you don't really need it. That said, it'd be a nice thing to have; I have a design right now that I suspect is going unstable when the craft is out of fuel (and I need to test it to see if that is indeed the case).

With regard to the other questions:

*What's the takeoff mass of the plane?

50 t.

*How much of that mass is dedicated to rocket fuel?

Well, LF + O's total mass is 28 929 kg. (These can be seen in the shots)

*What is the vacuum thrust of your rockets?

Vacuum thrust of the rocket engine(Kiwi from NecroBones' SpaceY Heavy Lifter pack) - 425

*What is the vacuum Isp of your rockets?

295. The only other engines I have unlocked are the stock Swivel and Reliant ones. They don't have enough oomph for that craft.

Alright, thanks.

Okay...so when I go to design a FAR spaceplane, I usually try to shoot for ~1800 in rocket delta-V. That's usually just enough to get me into orbit with some wiggle room in case I botch my ascent profile - which probably happens more often than it should. Based on these numbers, your plane has got 1,581.59 m/s of delta-V, about 220 short. So yes, that'll get you sub-orbital; you need just a little more to make the final transition to orbit. Your options - either add another four tonnes worth of LF+O (the equivalent of an FL-T800) or use a different rocket with a vacuum Isp of no less than 335. Myself, I'd shoot for the higher Isp rocket; it's generally easier to swap out an engine for one that's more efficient. And by easier I mean that it usually causes less of a change to your overall drag profile. Of course, your options would be quite limited if you're picking between stock rockets...Terriers, Poodles, Nervs, Rhinos and Aerospikes are the only stock rockets with a vacuum Isp that high, and the ones that are the same size as the one you've got aren't renowned for their overall levels of thrust (the Aerospike, maybe - but it still only gives 175 kN of thrust and it doesn't gimbal, two big downgripes). I don't know if B9 would have another option available or not.

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Ducted area ruling for engines is pretty awesome. I thought my massive RAPIER/nuke engine clusters would never work in FAR, but now they have no trouble

screenshot15_zpsqswk9cmo.png

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Well I am back in the SSTO cargo business. My new light cargo/utility SSTO space plane.

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SP-265 is based on some new design philosophies and lessons learned in designing better fighter aircraft, now we are making sleeker, meaner, and faster SSTOs.

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Aw crap...what's this "ducted" area ruling business?

In other news, the design I mentioned in my last post turned out to have dynamic lateral instability up in the Mach 2-4 regime when it was low on fuel - something I suspected. But, I did have a Reaction Stabilizer installed and it turned out to be sufficient to keep attitude control until the plane regained stability closer to the trans-sonic regime. Shuttle-style (i.e. high AoA) re-entry also helped, I think. I'll have to post some screenies for y'all next opportunity to see if there's anything else y'all think I might be able to improve.

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Aw crap...what's this "ducted" area ruling business?

I believe that's the dev build - intakes and engines provide a degree of pass-through for the airflow, lowering their drag. I think :P

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Well I am back in the SSTO cargo business. My new light cargo/utility SSTO space plane.

http://imgur.com/a/ioOZT

SP-265 is based on some new design philosophies and lessons learned in designing better fighter aircraft, now we are making sleeker, meaner, and faster SSTOs.

Those Mk2 air intakes - are those from Mk2 extended mod ?

Nice looking craft btw.

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Those Mk2 air intakes - are those from Mk2 extended mod ?

Nice looking craft btw.

Yeah they are from the MK2 extended mod, along with the linear aerospike engine and the other two outboard engines. Thanks for the compliment, I am trying a new wing design out on that craft, and I am liking it so far.

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Directed here from official FAR thread.

I have a question regarding the building of airplanes/spaceplanes. While flying, my SNC Dream Chaser replica tends to go into combined pitch and yaw, resulting in unrecoverable stall.

I've read somewhere that dihedral wings "under" the COM make a stable combination. However, it seems that is not the case here. I haven't took any pictures yet so you'll have to wait a bit.

Thanks in advance!

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Directed here from official FAR thread.

I have a question regarding the building of airplanes/spaceplanes. While flying, my SNC Dream Chaser replica tends to go into combined pitch and yaw, resulting in unrecoverable stall.

I've read somewhere that dihedral wings "under" the COM make a stable combination. However, it seems that is not the case here. I haven't took any pictures yet so you'll have to wait a bit.

Thanks in advance!

Actually, wings above CoM increase roll stability, as do dihedral wings. Mounting dihedral wings below CoM will still (usually) lead to a stable plane, while mounting dihedral wings above CoM may lead to too high roll stability and/or dihedral effect (which is basicly that your plane rolls in the direction it yaws towards).

Seems more likely to me your plane isn't stable on pitch and yaw axis. Move CoM forward/CoL back + bigger tail fin.

Other than that: When does it happen?

Low speed flight? High Mach number? When pulling? When rolling? When using rudder? Only a combination of several controls (like rudder, and opposite ailerons)?

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When you go to take your screenies, be sure to take at least one with your wave drag pattern, one with your trans-sonic numbers, and one with the stability derivatives at the altitude and speed at which you're experiencing issues. And (of course) some profiles of the craft itself.

This Dream Chaser, eh? I can see that one being a true challenge to get to fly as intended in KSP...I'll have to look at Ferram's response to your question again.

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When you go to take your screenies, be sure to take at least one with your wave drag pattern, one with your trans-sonic numbers, and one with the stability derivatives at the altitude and speed at which you're experiencing issues. And (of course) some profiles of the craft itself.

This Dream Chaser, eh? I can see that one being a true challenge to get to fly as intended in KSP...I'll have to look at Ferram's response to your question again.

I imagine it would be a challenge but with the right mods, it shouldnt be impossible. Would be a fun challenge.

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