How easy is this to fly? What's the simplest launch profile?

[AeroGav]

A few months ago,  I created this medium tech ssto, the Voodoo Ray,  based off Panther and NERV tech only.     I got worried that it's too challenging too fly for your average pilot,  because my instructions talk about flying it with pitch trim to maintain target AoA within a few degrees.   It probably won't make orbit if you deviate too far from the optimum.

So, I set about making the Auto Ray.

It's wings are angled so it makes enough lift to fly when the SAS is set to prograde hold.   However,  it has a trim flap, deployable via action group (RCS button),  which toggles the plane between high lift mode (nose about 2.3 degrees above prograde even when set to prograde hold) and low drag mode (nose follows prograde almost exactly).

Other than making occasional aileron adjustments to keep wings level, it is possible to fly this to orbit without touching the flight controls at all, only staging engines and toggling the trim flap at certain flight regimes.

Here's the thing - should i give instructions telling people exactly when to toggle the flap,  or just tell them to play it by ear and trust their judgement? 
 

Here's the "play it by ear" version of the launch advice -

Spoiler

 

Fly the aircraft to orbit with SAS set to Prograde hold.   

Use RCS action group to toggle between nose up trim and neutral trim.     The aircraft starts off with nose up trim set.     When the climb angle threatens to become excessive,  with airspeed decreasing, switch to neutral trim.

If you feel the nose is dropping too far, or if airspeed is encroaching upon the transonic region (240m/s),  switch back to nose up trim.   Initial climb angles of 10-15 degrees are "about right", but this will decrease as the air gets thinner.

At some point,  the plane will start levelling off and airspeed will start heading over 240 m/s even though you're in nose up trim.  This means it's time to cross the sound barrier.

Switch to neutral trim and use the abort action group to toggle the nukes on briefly.  At 440m/s,  press Abort again to cancel the nukes.   Use nose up trim to bring the plane out of the dive but switch back to neutral to stop the climb angle getting excessive.  Ideally, we want to maintain 440-480 m/s in the initial supersonic climb.

After this, use the trim to try and level off at 12-14km for the speedrun.  When airspeed exceeds 750 m/s, start using nose up trim to get into a climb and stop it rising any further.  At 16km or whenever the speed looks like decreasing, press Space Bar to start the  nukes.

At 36km the Navball will switch to Orbit mode.   Click it to put it back in Surface, otherwise it can lead to the plane trying to fly nose-down.

 

And here's the craft file -

https://kerbalx.com/AeroGav/Auto-Ray

Video of me launching it -

 

[Chris_2]

One problem that I see here is that it takes way too long to get to orbit. Your video is over 15 minutes! Try to have your spaceplanes a good thrust to drag, so it has a constant acceleration and brakes Mach easily at a 15° AOA and gets to 1200m/s+ on airbreathing. Besides being efficient, going fast also means that it takes much less (play) time to orbit.

It might be easy to fly, but if it takes 15 minutes to get to orbit, I'm gonna take a normal rocket instead. So: "I've not flown it, but I can think of a much simpler launch profile"

Edited March 10, 2017 by Chris_2

[AeroGav]

5 hours ago, Chris_2 said:

  gets to 1200m/s+ on airbreathing

Not going to happen.    The customer had all Tier  9 rocket engines but the highest available jet engine to him was the Panther.  Thrust falls off a cliff above 750 m/s.

Quote

Try to have your spaceplanes a good thrust to drag, so it has a constant acceleration 

You can see the Delta V and TWR readings in the mechjeb display top right corner if you're interested.

5 hours ago, Chris_2 said:

Besides being efficient, going fast also means that it takes much less (play) time to orbit.

If it takes 15 minutes to get to orbit, I'm gonna take a normal rocket instead.

I enjoy flying.  I don't mind spending 15 minutes flying to orbit so long as i'm not fighting it the whole way up.   It had enough delta V at the end to go to Minmus.  I didn't because i find the actual mission tedious - a lot of waiting, and not all that much to see.  I guess it's just a preference thing.    I also think it performs pretty well given the parts available.

Back to the easy/hard thing.

Is a high thrust design easier , in terms of requiring less accurate flying ?  So, if your instructions say, take off and climb at 15 degrees pitch to orbit, and the person climbs at 20 or 10 instead, will it still go supersonic?  I'm guessing high thrust helps here.   But will it run out of fuel before they circularise, if they do this,  or  start the rocket engines 30 seconds too early, or 30 seconds too late?  A  2 panther 1 swivel design's gonna be on a tighter fuel margin.

I hoped to make it easy to "fly accurately" by having it fly to orbit on prograde hold, and having the user adjust pitch only by turning RCS on or off.   If someone doesn't read the instructions at all, it's unlikely to work.  Maybe your ssto would do better in that situation.

[fourfa]

12 hours ago, Chris_2 said:

One problem that I see here is that it takes way too long to get to orbit. Your video is over 15 minutes! Try to have your spaceplanes a good thrust to drag, so it has a constant acceleration and brakes Mach easily at a 15° AOA and gets to 1200m/s+ on airbreathing. Besides being efficient, going fast also means that it takes much less (play) time to orbit.

It might be easy to fly, but if it takes 15 minutes to get to orbit, I'm gonna take a normal rocket instead. So: "I've not flown it, but I can think of a much simpler launch profile"

This is a matter of taste.  My own SSTOs tend to be massively overpowered and low drag, so they do indeed accelerate hard at 10-15 deg climb, though if I can't hit 1550m/s on jets I mark it "FAIL" and keep working.  This does indeed keep the playtime more focused on the payload than the delivery device, which is how I tend to play.

Many other players are drawn to efficiency challenges, making maximum use of that advantage of SSTOs.  This inevitably means being rather underpowered (by my standards) and having a detailed and lengthy routine to nurse the ship carefully to orbit.  Once there, these ships often have the ability to continue on to many interplanetary destinations when my overpowered ones are gasping on fumes just to deorbit and land.  The engineering challenge of maximizing efficiency may be the reward all by itself.  Gav is a frequent contributor here, with a unique and characteristic style to his planes, and they're usually in this category.

Confusing one style of play for another doesn't really lead to helpful feedback, which was what the OP asked for.  Or perhaps you misread the thread title as something more general, rather than specific to this exact craft.

@AeroGav I didn't have time to fly it yet, but with these kinda ships I say don't bother dumbing it down for people who don't really spaceplane.  Let Voodoo Rays be Voodoo Rays, and let them lead the user to mastery of the technique rather than just plain old orbit.

Edited March 11, 2017 by fourfa

[Gordon Fecyk]

I ended up flying this using a similar profile to your D45-N:

1. Extend canards before launch, and take off with SAS hold until... what was it... 8000 m? I forget. Then retract canards.
2. With the AeroGUI up I waited until angle of attack was approaching zero, then hit SAS prograde. The craft started descending around 10 km, then started ascending on its own.
3. Staged LV-Ns when the Panther's thrust was around 80 kN; I think this was about 13 km up and exceeding Mach 2.
4. Re-extended canards as I was approaching about 22 km apoapsis. Lift picked right back up and I think I just scraped AP before increasing time to AP again.
5. When I hit near 99 km AP (Wasn't paying attention!) I retracted the canards and coasted to AP. Before I closed orbit I was at 95 km AP and 1.5 km PE. Closing orbit took less than 100 m/s.
6. Ended up reaching 95 km orbit with 800 units liquid fuel left, giving me 2200 m/s and change.

Even stuffed the service bay with a Z-200 battery and some reusable science kit.

I want to see if I can adapt it for Ferram Aerospace. While there'd be less drag, I think you have the drag problem covered with your strategic use of nose cones. Usually I have to add or enlarge tail planes to maintain control on liftoff, and add drogue chutes to land safely.

In Stock aero though? I guess it's just a matter of figuring out the best time to extend and retract the canards, and not touching the stick. With this much dV to spare, as long as you're around 10 degrees pitch before igniting the LV-Ns you can get to orbit and back. Then it's an exercise in efficiency.

[AeroGav]

Woah 2200dV in  a 95km orbiit?   Beats my 1900 at 75km.

I did [put a few of my stock designs into FAR and found they had excess transonic drag, due to area ruling probs.  However these could be corrected with small changes, a few minor offsets, after which high speed performance is better than stock.   However, 100ms plus stall speeds aren't fun.

[Gordon Fecyk]

14 hours ago, AeroGav said:

[in FAR] 100ms plus stall speeds aren't fun.

That's what drogue 'chutes are for. Every one of my successful space plane landings required a drogue or two.

Even the Shuttle had to use one drogue to slow down on landing, and that had to descend after travelling 8 km/s in low Earth orbit. Curiously, the thing touched down at 100 m/s. assuming my math is right in converting from 226 mph.

[AeroGav]

1 hour ago, Gordon Fecyk said:

That's what drogue 'chutes are for. Every one of my successful space plane landings required a drogue or two.

Even the Shuttle had to use one drogue to slow down on landing, and that had to descend after travelling 8 km/s in low Earth orbit. Curiously, the thing touched down at 100 m/s. assuming my math is right in converting from 226 mph.

I suppose this means you don't have to worry about touching down near the start of the runway and only have to worry about lining up laterally.   My 100 m/s landings though usually ended in disaster before stopping ever came into it.    Compared with an approach speed under 40 m/s,  you absolutely need to touch down on the runway and be well lined up - going off the side a bit and running over a taxiway will kill you.   Landing in the gently undulating grasslands will instantly cause a gear collapse and will kill you.  So you have to line up perfect, but that's much harder at three times the speed.    Touch down hard or with wings not perfectly level and you flip over.   Any part of the body touches the ground at those speeds it is instantly destroyed.  With stock aero you can crash land gear up.

Also, at 100 m/s,  if you make an error and descend on a 5 degree glideslope instead of 3,  your rate of descent is still moderate and the gear will absorb the impact.  At 100 m/s,  start writing a letter to Jeb's next of kin. 

[Gordon Fecyk]

34 minutes ago, AeroGav said:

I suppose this means you don't have to worry about touching down near the start of the runway and only have to worry about lining up laterally.

Pretty much. Check out this recent Rick Kerman Report; skip ahead to the 8:40 mark for the approach. Not my best approach; a metre to the left and I'd have been hosed. Cut to Peter Mansbridge at The National: "A tragedy today at the Kerbal Space Centre..."

Edited March 16, 2017 by Gordon Fecyk
Grammar

[DualDesertEagle]

I once made a plane that I wanted to use for science contracts taking place on kerbin. I wanted to make it qucik but not too powerful, so I used 2 Mk2 jet engines I had installed with an Mk2 expansion pack. Their description made them look pretty weak, which was what I was looking for. So I finished the plane, took it to the runway for a test flight and was absolutely shocked by the performance of those engines, but see for urself:

Conclusion: These Mk2 jet engines are probably the most efficient way to make an SSTO that can even make it to a solar orbit just using them. Their fuel consumption compared to their sheer power is just tiny. Any rocket engines strapped to an SSTO that uses these Mk2 jet engines are only gonna be needed to circularize and de-orbit / on interplanetary missions just to maneuver outside of kerbins SoI until u return to kerbin.