Airplanes and Jet Power - Enforcing Synchronous Burnouts

[WanderingKid]

So I'd understood that Jet Engines had finally stopped the random crossfeed of air and would now synchronously burnout. I find I was incorrect, as a small test rig certainly burns out one side before the other.

Now, I know most of the tricks for dealing with this problem, but I'm wondering if I missed a tweakable or a setting or something that forces them to stay synched for air draw?

 

[Val]

I think, you still have to take care with the sequence of attaching intakes and engines, to get the full synchronous flameout.

At least, I still do. When a multi engine craft is done. I rip off all engines and intakes and mount them. One intake and engine pair at a time in symmetry, for each nacelle.

[AeroGav]

Short version

 

I think when engines splutter and surge asymmetrically like this, it is just a sign you need more intakes.  I can't think of many circumstances where deliberately under equipping your craft so as to cause this would be an advantage - intakes don't weigh that much or cause that much drag that it'd be worth putting up with the loss in performance, even if the control problems caused by the  asymmetric flameouts could be avoided.

Of course, even if you provide sufficient intakes, engine thrust still declines with increasing altitude, there is a lookup table in the part config file that defines this and number of intakes has no effect.  

An engine either has

• sufficient intakes to run properly - in which case it delivers thrust that declines in accordance with its config file,

or 

• it does not have enough intake, in which case it splutters and surges one engine at a time causing your craft to wobble.

 

The config file also defines the cutoff altitude,  when you pass this height, all jet engines of that type will quit , regardless of intake config. Because the engines stop at exactly the same time it does not cause handling problems.

 

Long version

This is all a legacy to the days of beta, when intake air really was treated as a resource like oxidizer.  

You could do tricks closing the intakes and stopping the engines, to save a little bit of intake air to run the jets for a few seconds in space.  Pointless and unrealistic. 

Then you got people hogging ridiculous numbers of intakes to use their jet engines all the way up to 69,999M.

I don't think the engines had a lookup table that made thrust automatically weaken as the air got thinner, however, because the intakes were gathering less and less air, you had to throttle back the engines manually so as not to suffer asymmetric flameouts from lack of air.  This made life unduly hard for people not trying to exploit and just fly aircraft normally.

So, now we have two separate game mechanics.  Intake air is just a simple yes/no check for "run properly" / "engine not run properly".

And then we have the atmospheric pressure curve in the engine config file, which influences the rate at which power is lost with increasing height, which craft design has no effect on. 

 

 

  

[Mystique]

Or you can use MJ's (or any other mod's, there definitely should be some for this case) handy "prevent jet flameout" utility, which will automatically throttle down up to point of 0 throttle and don't bother with engine/intake placement order.

[Jarin]

This is really strange... what sort of arrangements are people running that are getting asynchronous flameouts? I haven't seen one, regardless of design or build order, since... well, a long time now. Two intakes to four engines is a very common arrangement for me, and whether it's circular intakes with panthers, or shock cones with whiplashes, I've seen nothing but simultaneous flameouts.

 

[WanderingKid]

6 hours ago, Val said:

I think, you still have to take care with the sequence of attaching intakes and engines, to get the full synchronous flameout.

Well, that's frustrating.  I've never minded doing that for my one or two engine craft, but once you start building Orange Tank delivery birds that can get rather annoying.

5 hours ago, AeroGav said:

I think when engines splutter and surge asymmetrically like this, it is just a sign you need more intakes.  I can't think of many circumstances where deliberately under equipping your craft so as to cause this would be an advantage - intakes don't weigh that much or cause that much drag that it'd be worth putting up with the loss in performance, even if the control problems caused by the  asymmetric flameouts could be avoided.  

That is not the case in this scenario.  Two Circulars to two Wheesleys is more than enough intake under low altitude circumstances.  I'm purposely pushing it to limits on the runway to see what happens.

2 hours ago, Mystique said:

Or you can use MJ's (or any other mod's, there definitely should be some for this case) handy "prevent jet flameout" utility, which will automatically throttle down up to point of 0 throttle and don't bother with engine/intake placement order.

I'm not a fan of MechJeb, personally.  I prefer my mods a lot smaller.  MJ's too overpowered.  To quote a line from Dresden: "He handed you his big jumbo airplane because you needed a reading light, because that's the only unit of power he had to work with."  If I can find a dedicated mod (or near dedicated) I'd be more apt to use that.

35 minutes ago, Jarin said:

This is really strange... what sort of arrangements are people running that are getting asynchronous flameouts? I haven't seen one, regardless of design or build order, since... well, a long time now. Two intakes to four engines is a very common arrangement for me, and whether it's circular intakes with panthers, or shock cones with whiplashes, I've seen nothing but simultaneous flameouts.

Well, this is a two and two with Wheesleys with mirrored attachments, the left hand engine flames out before the right one loses intakes:

 

This is the exact same craft after doing the 'engine-intake-engine-intake' attachments like we used to do (stays synchronous):

 

Edited November 4, 2016 by WanderingKid

[Jarin]

30 minutes ago, WanderingKid said:

Well, this is a two and two with Wheesleys with mirrored attachments:

That's interesting. I see the same thing if I exactly duplicate what you have there. But taking the same craft in flight to the Wheesleys' flight ceiling and they both stay solidly at 100% until they die. They stop producing thrust long before there could be a flame out. 

Spoiler

The imbalance only appears if the craft is held perfectly stationary so no airflow increases for the intakes.

 

Edited November 4, 2016 by Jarin
put image in spoiler for space

[WanderingKid]

Fair enough, I've been mucking about with Turbojet assisted rocket launches so I ended up with this curious rig.  However, I also just found out that apparently KER is lying for TWR.  TWR 1.41... will not take off straight up.

 

Edited November 4, 2016 by WanderingKid

[Jarin]

4 minutes ago, WanderingKid said:

TWR 1.41... will not take off straight up.

Yeah, same issue. Not enough air to feed the engines when stationary so you're not even getting a third of their full thrust. A kicker engine or just taking off horizontally, first (anything to get the intake air flowing), and you'd get up to that TWR.

[AeroGav]

13 minutes ago, Jarin said:

 

The imbalance only appears if the craft is held perfectly stationary so no airflow increases for the intakes.

 

Indeed.  The amount of air an intake pulls in grows with airspeed, decreases the further away from prograde that it's pointing.

Subsonic intakes pull in a decent amount at low speed, but the amount they gain intake value more slowly with increasing speed, than supersonic optimised intakes like the shock cone, which start out weaker.    

The wheesley probably uses more air at 0 m/s than any other 1.25m jet engine.     The panther has slightly less static thrust rating, but gains quite a bit of power as you get supersonic, where the wheesley stays flat then tails off.   The panther obviously has afterburner mode too, which increases thrust nearly double without taking in hardly any more air - at the price of bad fuel consumption.   

Must admit i've not really used the wheesley much, but didn't see this problem in a normal aircraft, because it takes time to spool up to max rpm by that point you're already moving down the runway with some velocity.

Still,  mixing a high speed engine with a low speed intake can cause issues if you're close to the minimum number of intakes anyway. I've not seen a problem with one panther per circular intake on my career spaceplanes, but when powering Rapiers off the radial mount adjustable ramp intakes, the craft worked fine up until mach 3,  by which point the intake air flow has peaked and isn't going to go up any more with increasing speed, but the rapiers hit max power at mach 3.7.

It is , like i say, very easy to add more intakes however.  There's no practical difference in drag compared to a nose cone and don't weight penalty isn;t much compared with all the engines you're lugging.  So you can/should put one on the front of every 1.25m stack if you;re having air problems (one on  the front of the main fuselage, one at the front of every nacelle).  Inline intakes like the engine pre-cooler create hardly any more drag than a mk1 liquid fuel fuselage of the same size, though they don't hold anything like as much fuel.  Since the engine and intake aren't radially attachable, you need an inline intake or mk1 fuel tank anyway to create the body of the nacelle. 

[WanderingKid]

Val was correct in regards to the initial problem, thanks Val.  Still up for continuing the conversation but marking this as answered.

[AeroGav]

7 minutes ago, Jarin said:

Yeah, same issue. Not enough air to feed the engines when stationary so you're not even getting a third of their full thrust. A kicker engine or just taking off horizontally, first (anything to get the intake air flowing), and you'd get up to that TWR.

Is it getting confused by the Vacuum rating of the Terrier not being realised down on the deck?

BTW are you decoupling those jets or taking them to orbit?  They are 1.5 tons each and don't produce much power at high speeds.

If you are making an early career spaceplane, it might do better with a more horizontal flight profile above 10km. Since you want to be going at near the highest speed you can get out of them before the air gets too thin for them to work anyway.

From the config file 

J-33 "Wheesley" Turbofan Engine
 

velCurve
        {
            key = 0.53 0.834 
            key = 1.3 0.96 
            key = 1.674 0.843 
            key = 2.5 0 
        }

At 0.53 mach it gives 83.4% of it's static thrust rating.

At 1.3 mach it does 96% of the static rating.

By 1.674 mach we're back to 84%

Then a rapid decline, falling to 0% thrust by mach 2.5

J-20 "Juno" Basic Jet Engine

velCurve
        {
            key = 0.44   0.897
            key = 1   1 
            key = 1.3   1.03
            key = 2   0.68 
            key = 2.4   0 
        }

At 1.3 mach it does 103% of the static rating.

At mach 2 it's down to 68%, then falls to 0 by mach 2.4

The atmospheric pressure curves are harder to interpret, because rather than having altitude along the X axis, they use an atmospheric pressure number which you'd have to cross-reference with the atmospheric pressure gradient on kerbin - more math than i can handle.

Still, comparing numbers

J-33 "Wheesley" Turbofan Engine
 

        atmCurve
        {
           key = 0.337    0.4            

           key = 0.072    0.092
             
         }

J-20 "Juno" Basic Jet Engine

        atmCurve
        {
            key = 0.42   0.578       
            key = 0.16   0.28  
            key = 0.072  0.13
        }

So, at 0.337 atmospheres the Wheesley does 40% of it's sea level thrust, falling to 9.2% at 0.072 atm 

The Juno does 57.8% thrust at 0.42 atm and still has 13% at 0.072 atm.

From what i can tell with excel, the juno might have a slight edge in fast/high performance

[WanderingKid]

11 minutes ago, AeroGav said:

From what i can tell with excel, the juno might have a slight edge in fast/high performance

It's more than likely it does, I haven't broken it down to that depth.  However, a big component in career early space planes is also part count.  So while you're probably right as to the atmospheric value of the Wheesley, it takes 6 Junos to match a single Wheesley in raw thrust.  Let's say the ratio is a proud 5:1 since the values at the upper area is where we really care.

For a single wheesley, it takes 3 parts: Intake, Engine, Something to Hang them on.  For 5 Junos that's 15 parts, almost half the part count without upgrades.  I'm still exploring the new Aero (I'm still working with the first level wheels in my career game) and just what you can eek out of it, so that info will help, if not directly.  Thanks!

As to not ignoring the Terrier, I can change the TWR of the ship when I engage it, so it's not looking at that.  I think KER just isn't looking into the performance thrust of the engine instead of its max, might just be looking at the wrong variable which under most circumstances (like when you actually HAVE air) isn't an issue.

[Jarin]

2 hours ago, AeroGav said:

From what i can tell with excel, the juno might have a slight edge in fast/high performance

Now that would be strange. I'm almost positive in actual use that Junos are basically useless past 8km, while Wheesleys keep running much higher. That could be an issue of intakes, though. With a 1/1 ratio of mk0 intakes, the Junos actually flame out below 10km. I wonder if they'd live up to their "better than Wheesley" potential if given more air...

_{... oh god, not the return of airhogging, I thought we'd left that behind. <.<}

2 hours ago, WanderingKid said:

I think KER just isn't looking into the performance thrust of the engine instead of its max, might just be looking at the wrong variable which under most circumstances (like when you actually HAVE air) isn't an issue.

I assume KER is using the engine's "optimal" numbers, which take a bit of speed to work up to. 

Edited November 4, 2016 by Jarin

[AeroGav]

5 minutes ago, Jarin said:

Now that would be strange. I'm almost positive in actual use that Junos are basically useless past 8km, while Wheesleys keep running much higher. That could be an issue of intakes, though. With a 1/1 ratio of mk0 intakes, the Junos actually flame out below 10km. I wonder if they'd live up to their "better than Wheesley" potential if given more air...

_{... oh god, not the return of airhogging, I thought we'd left that behind. <.<}

I assume KER is using the engine's "optimal" numbers, which take a bit of speed to work up to. 

This was under 1.05 

Unfortunately the Bandicam watermark obscures the altitude, but the video starts at mach 1.5/14km and the engines flame out at mach 1.9 and a few km higher up.   14 Junos... O-:

I had a mind to revisit this, and try with more rocket fuel and less jets.   14 junos allows you to get supersonic on pure jet power, to supercruise, but that's so much engine weight you can't accelerate to orbit if you take them with you after flame out.  And dumping so many is costly.

A brief test, i was able to get supersonic at 7.5km on a 4 juno,  4 xft400 tank 1 terrier design, and drag did seem to reduce after passing the transonic region.   Whether we can ssto or not is another matter.

I need to find a way to leave the landing gear behind on takeoff, but not destroy them in the name of re-use. Radial decoupler to a sled of some sort.  Ditch in the water on return.  Take them to altitude and the basic non retractable gear burn off anyway.

[WanderingKid]

35 minutes ago, Jarin said:

Now that would be strange. I'm almost positive in actual use that Junos are basically useless past 8km, while Wheesleys keep running much higher. That could be an issue of intakes, though. With a 1/1 ratio of mk0 intakes, the Junos actually flame out below 10km. I wonder if they'd live up to their "better than Wheesley" potential if given more air...

_{... oh god, not the return of airhogging, I thought we'd left that behind. <.<}

Use Circular Intakes for Junos and you can find out quickly enough.  I'm currently abusing a different design of the earliest career build I can Science Bomb (with return) Mun with, so strange and curious designs will have to wait before I get a chance to abuse it.  The Circular is .6 m2 intake with 2.0 intake air while the Small Intake is .1 m2 with 0.5 intake air.  It'll certainly decide if the Juno or the air is capped at 8km.

[AeroGav]

On 04/11/2016 at 11:15 PM, WanderingKid said:

Use Circular Intakes for Junos and you can find out quickly enough.  I'm currently abusing a different design of the earliest career build I can Science Bomb (with return) Mun with, so strange and curious designs will have to wait before I get a chance to abuse it.  The Circular is .6 m2 intake with 2.0 intake air while the Small Intake is .1 m2 with 0.5 intake air.  It'll certainly decide if the Juno or the air is capped at 8km.

https://kerbalx.com/AeroGav/Juno-basic-ssto

Did you have any success making a pre-panther SSTO wander?

Up till now, the best i've been able to do is anachronistic engine shedder designs like Icarus.   Today though,  I finally managed 100% re-use.  It even fits in the 30 part limit ! Not sure if my design skills have improved, or aircraft in general got buffed in 1.2

[WanderingKid]

2 hours ago, AeroGav said:

https://kerbalx.com/AeroGav/Juno-basic-ssto

Did you have any success making a pre-panther SSTO wander?

In a word: No.

I figured out the biggest problem for the Wheesley: It never gets more thrust due to speed.  The Juno maxes ~Mach 1.3.  The Wheesley just... doesn't do anything.  Mach 0 at sea level is its max thrust!

Due to this, the big deal for carrying a Wheesley (that it can run higher, ~19k off an Engine Nacelle) is negated by the fact that it gets like 2.3Kn of thrust up there.  It's pointless if you're carrying enough fuel to reach orbit, and adding more engines simply doesn't help.  I'm sure it's fine for gliders, though. 

I'm experimenting with the idea that the early SSTO engines are basically going to only take off the first 1k of the 3500 I need to orbit.  So, I want to have 2,500 Dv when I engage my engines, and I want a strong TWR when I do.

However, I've been a bit distracted.  My main career currently has 7 different science bombs heading to/from the Mun and my tour bus is on a solar exit path, along with some other minor things.  I got myself a Panther style Spaceplane with 2 passenger cargo (so, 1t capacity) to work so far, but that was partially out of frustration of "Okay, fine, let me figure out how this is SUPPOSED to work before I go back to mucking with things in low tech."

So, right now I'm screwing around with an inline cockpit, an engine nacelle on the front of that, a wheesley off the back to get to ~8k before it gives up, and a pair of Thuds.  I'm nearly there.  I think I just need to adjust for a pair of Junos as well to support the Wheesley and I might have something that's consistent.

Edit: Which didn't work.  The Wheesley goes to 60kN ~4,700m.  The Junos (was ~310 m/s, just under mach 1) were pushing ~12.9kN each.  I didn't get a chance to write it down, but in that range.  So 4 Junos whould be ~50-53kN, 5 would roughly match.  I'm pretty sure a single intake can fill 2 or 3 Junos, so that would help on part count, even if the engine kicks it at 8k.

Drawing Board time.  Also, those Thuds are nasty to the aerodynamics, I don't care HOW rounded they look.  That isn't helping.

Edited November 15, 2016 by WanderingKid

[AeroGav]

3 hours ago, WanderingKid said:

 

Edit: Which didn't work.  The Wheesley goes to 60kN ~4,700m.  The Junos (was ~310 m/s, just under mach 1) were pushing ~12.9kN each.  I didn't get a chance to write it down, but in that range.  So 4 Junos whould be ~50-53kN, 5 would roughly match.  I'm pretty sure a single intake can fill 2 or 3 Junos, so that would help on part count, even if the engine kicks it at 8k.

Drawing Board time.  Also, those Thuds are nasty to the aerodynamics, I don't care HOW rounded they look.  That isn't helping.

I'd forget about the 30 part limit, it's not very expensive to upgrade the hangar to level 2, but getting the science for extra techs, especially if you are doing an airplane only challenge, is the hard bit.

I don't see how else you can attach a juno to a fuselage except by putting a load of mk0 fuel tanks radially around the main mk1 body.   Juno on the back of each mk0 tank obviously, but you really need a size 0 intake on the front also, to avoid the flat plate drag penalty.

Something you could try, with either a Juno or Wheelsy design, is to target a lower jet speed.

For example,  to get fully supersonic on Junos needs 6 Juno per Terrier engine.    Getting the rocket up to mach 1.7 at 15km before starting it is great, but the downside is that rocket must now carry 6 junos to orbit from there as additional payload.

I went with 4 Junos and 1 terrier in the above example.  The Junos need a brief burst from the rocket to get fully supersonic and max out slightly slower, but that's less jet engine mass to be carried to space.

What if we only went 2 or 3 junos, and only targeted a "jet only" speed of 0.82 mach ?  Basically, the Terrier is really efficient at 10km and up, a better engine than the swivel from here onwards.  Forget about going fast, just have the jet engines lift us to this altitude where the terrier does its best work?

[WanderingKid]

2 hours ago, AeroGav said:

I'd forget about the 30 part limit, it's not very expensive to upgrade the hangar to level 2, but getting the science for extra techs, especially if you are doing an airplane only challenge, is the hard bit.

What if we only went 2 or 3 junos, and only targeted a "jet only" speed of 0.82 mach ?  Basically, the Terrier is really efficient at 10km and up, a better engine than the swivel from here onwards.  Forget about going fast, just have the jet engines lift us to this altitude where the terrier does its best work?

And yet, I find science relatively easy to get once you have fairings, however it's certainly not airplane only.  I personally usually upgrade the runway first.  In hard mode that SPH upgrade costs 450,000 funds, not a small value.  You can get your Tracking Center and Mission Control and runway for the same price.  As to attaching more Junos without Mk0 tanks, I'd forgotten the octagon strut isn't available pre-upgrade.  Whoops.

Targeting a lower jet speed is something I've been playing with.  What I'm trying to do is determine the value trade.  Let's start with some assumptions: It takes 3,500 d/v to go from a standing start to orbital result with a rocket.  What does getting to 8k with no upward angle to speak of and minimal horizontal speed get us?

Using a ship I've flown quite often with almost no changes in 1.2x, my Mun/Minmus Science Bomb, my gravity turn has me at 10k with the following: 2,000 d/v left of my 3,500 for orbital. Speeds at: vertical 273.63, horizontal 329.08, total surface speed 428 m/s, prograde aimed ~40 degrees.  Finally a current Apoapsis of 14,270m.  In case we need a price comparison for value it costs me roughly 15,500 funds (depending on recovery distance) for 132 science from Mun, tech is all pre-upgrade.

So, to orbit from 10k, we need a baseline.  Working from rockets, if we had a 40 degree prograde, would require roughly 2,000 d/v + difference of 430 - current in m/s and a TWR pushing 2.0 or better.  If we can get that working in some form, we can start trimming it to account for d/v not needed due to lift. 

Putting together some simple math against the TWR formula, a 10 ton craft with dual Terriers running at full power (60 kN) would have a TWR of 1.22.  10 tons is two T800s + the Terriers.  All that fuel does mean we'd get 3,469 standing d/v, but obviously that's not valid.  So, let's look at this slightly differently.  For 1t of engine we get 120 kN at 345 ISP.  I know, until you're over 25k you're not getting that, you're actually getting 50kN or so at 10k and it rises eventually, but I'm running rough numbers here.  The swivel, for 1.5 tons, gets us 215 kN at 320 ISP, we've snuck in 35 free kN for the weight cost.  In reality though we want the Reliant for tonnage to power here: 1.25 tons for 240 kN at 310 ISP.  For an extra .25 tons we've gotten ourselves double the TWR for 90% of the fuel efficiency.  Since TWR matters so much to climb speed, that seems a viable trade off to me, especially since climbing after reaching 8-10k seems to be a beast.

Using a Reliant instead of twin Terriers, we end up with a TWR of 2.44 at 10 tons, 2.03 at 12 tons, 1.74 at 14 tons.  At a little shy of 12 tons, four Junos gives us a runway TWR for takeoff of .68 or so.  I ended up with a test rig having 7 units of wing area at ~12.5 tons takeoff for .65 twr on the runway.  The fuel for four mk0's is giving me a 200-250 d/V for the reliant burn.

Some testing indicated that after 10k Junos brick, speed drops, lift drops, it doesn't matter.  After liftoff a 5 degree AoA is maintained (until after 8k).  A max horizontal speed of ~325 m/s is attainable without kicking in the Reliant, which happens ~3k alt with 15.2 kN/Juno.  5k: 315 m/s H at 13kN/Juno.   Mk0's at 36.88 fuel. 6.5k: 297 m/s H at 11.1kN/Juno, 33.5 in Mk0s.  Approaching 8k (target altitude on Junos) sees the AoA having to ride up to maintain lift at 18 m/s.  8k: 270 m/s H, 9.4kN/Juno (TWR 0.33) 30.81 fuel/Mk0. 

Rocket burn to pitch to 45, Junos cut out at 15k.  following typical gravity burn for rockets from this point.  I should have named it the phoenix.  Either or, 2,000 d/v from that point gets me 1780 m/s H with an apoapsis of 60k.  I'm short ~400 m/s d/V.

Second attempt sees two 800's instead of an 800 and a 400, bringing gross weight (with additional wings) to 14.616 tons... and 30 parts, and I adjust the fuel available for the Junos to 35/50.  Runway TWR is .55.  Same general plan during liftoff to 8k sees max speed reach ~320 m/s at 3k.  At 7,300 meters the horizontal begins to brick once TWR drops under 0.31.  Reliant engaged, AoA used 20 degrees.  Junos cut out at 12k.  AoA 10 degrees at 20k.  Idea works, burn too long, blow stuff up on plane.  More height, less heat.  Ow. 

AoA of 20 with lowering the throttle to stay in the 2.2 - 2.5 TWR range keeps me from overheating and gets me to 75k orbit with 50 d/v to spare, just enough to bring the periapsis down to 21k and 50 units of fuel left (total) for the Junos.   I'll need to experiment with the AoA on the orbital burn stage to see if that can be cleaned up and possibly mess around with the Terrier as an alternative, but it works... barely.  I'll post pictures and the craft file and what not tomorrow, it's really late here and I need sleep.

[AeroGav]

You do not need a rocket TWR over 1 in a spaceplane !

A good airframe should get lift:drag ratio of 4:1 or so.    This means your "gravity losses" are effectively 1/4 of what they are in a rocket.   Also, at the start of the burn, you are still getting some jet thrust.  Junos maintain reasonable power out to mach 2, you probably don't want to use too much rocket power  through this bit or you're just reducing the contribution of the jet engines.  Once they flame out, ok gun the throttle if that's your thing !

Also, your fuel burns off and mass starts going down.  And, as you get above mach 4, orbital freefall supports more and more of your weight, meaning you need less lift . Less lift requirement at same lift:drag ratio, means less drag.

edit - check out the data i highlighted in red.

Weight 72KN

Lift 67KN

Lift/Drag 4.3 to 1

Drag 15KN

Thrust 58.3KN

 

The key to good lift:drag ratio is no radial parts (except aerodynamic surfaces), cones on everything, and the wings are at 5 degree angle to prograde while the fuselage is angled at 0.  If i pitch the nose up another 5 degrees my lift drag ratio halves.

This plane does come close to overheating on ascent.   This means it has about the minimum about of wing you can get way with.   Larger wings mean you gain altitude faster and will be at a higher altitude by the time you hit mach 5, so less heating.   You can also avoid heat by pitching up more (terrible for lift drag ratio) or throttling back (gravity losses).

BTW the stats on that plane - 11.2 tons,  1 terrier.      I upgrade the SPH before the runway, because the level 1 runway supports up to 18 tons.

Edited November 15, 2016 by AeroGav

[WanderingKid]

9 hours ago, AeroGav said:

You do not need a rocket TWR over 1 in a spaceplane !

A good airframe should get lift:drag ratio of 4:1 or so.    This means your "gravity losses" are effectively 1/4 of what they are in a rocket.   Also, at the start of the burn, you are still getting some jet thrust.  Junos maintain reasonable power out to mach 2, you probably don't want to use too much rocket power  through this bit or you're just reducing the contribution of the jet engines.  Once they flame out, ok gun the throttle if that's your thing !

I'll have to poke at it some more when I get time.  This is becoming quite the investment.  While amusing at first, re-lifting to 6,500 meters every time I want to change something (if I want to be able to revert to not kill off Valentina as well) is becoming tedious.  The single terrier/4 Juno build I went with just missed orbit.  I will need to try a 5 degree pre-built angle to the wings and see if that gets me there. 

I can get the reliant version to orbit pretty consistently but it *must* be throttled as you go up for heat concerns and you have to get out of the drag reasonably quickly, negating wing value.  Basically it just uses the Junos to trim ~1,000 d/v from the takeoff then rockets, allowing the wings to allow for a more shallow approach from 15k-30k.

As to throttling the rocket engine while leaving the jet engines on full: I don't want it to be that fiddly.  If I have to be screwing around in tweakables during flight I'm going to use a different design.

One other thing.  I know your ship gets to orbit, but I'm saving two parts for a battery and a single solar panel.  Yours can do the same if you dump the rear elevons.  The canard handles pitch and roll quite effectively.  Also, you're running a dual tail instead of a single tail fin, another part I was able to save on.  Why DO you run dual uprights, anyway?  It looks at first glance to be counter productive for drag concerns.

[AeroGav]

12 minutes ago, WanderingKid said:

 

As to throttling the rocket engine while leaving the jet engines on full: I don't want it to be that fiddly.  If I have to be screwing around in tweakables during flight I'm going to use a different design.

 

My version basically flies hands off with prograde assist set, so it's  not a problem to do that.  If you were manually controlling pitch then no fun.

re: test flights

I keep starting new sandbox games when the old one gets too laggy.  I cant be bothered to land stuff out of career mode, so orbit is full of planes and duna looks like a boneyard.  I keep having to recruit more kerbals to replace the ones i strand.

 

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One other thing.  I know your ship gets to orbit, but I'm saving two parts for a battery and a single solar panel.  Yours can do the same if you dump the rear elevons.  The canard handles pitch and roll quite effectively.  Also, you're running a dual tail instead of a single tail fin, another part I was able to save on.  Why DO you run dual uprights, anyway?  It looks at first glance to be counter productive for drag concerns.

I guess i'm obsessed with handling , but its an obvious sacrifice to make if needs be.

As for dual tailbooms, i heard that having the vertical stabilizer close to cg minimises unwanted secondary roll moments produced by that surface, so i got in the habit of using smaller ones rather than one big tall one.  Could be a load of bunk.