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MaverickSawyer

Difficulty going supersonic with stock atmosphere...

Question

Okay, I seem to hit a wall with the Panther engines at about Mach 1.04 or so. I can't coax any more speed from my planes using them. I've limited the number of radial attach items to the essentials, so no lights, antennas, science, etc. But despite a fairly hefty TWR of 1.38 at Mach 1 and 3km, I still can't get past that blasted transsonic region. I'm about ready to resort to JATO bottles, to be honest.

 

Anyone have any tips?

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It's that damned landing gear. THAT's my drag hit.

 

I liked that gear. :(

 

EDIT: After replacing that gear from Airplanes Plus with the stock 4-wheel bogie, slightly tweakscaled, I hit Mach 1.01... In Dry Thrust mode. :D

 

Consider this one solved, gang.

Edited by MaverickSawyer
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Try angling the main wing up 1-2 degrees.

No, seriously. My design pictured above had trouble making past transsonic with perfectly level wings at 5° dihedral, but then I was pointed at this.

As soon as I tilted the wing up 1°, it blew straight past the sound barrier at 1 km altitude and accelerated straight up to Mach 2.07 at 8 km altitude without afterburners (!) for as long as I kept the thing perfectly level. More than 3-4 degrees of pitch in either direction while in flight and it starts to decelerate. 2° wing tilt had the same result, any more and the top speed didn't reach Mach 2. I then replaced the radial intake with a Structural Fuselage and a large circular intake for each engine and top speed increased to Mach 2.12. Fire up the afterburners and it topped out somewhere around Mach 2.8.

Edited by Fraktal

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13 minutes ago, MaverickSawyer said:

Okay, I seem to hit a wall with the Panther engines at about Mach 1.04 or so. I can't coax any more speed from my planes using them. I've limited the number of radial attach items to the essentials, so no lights, antennas, science, etc. But despite a fairly hefty TWR of 1.38 at Mach 1 and 3km, I still can't get past that blasted transsonic region. I'm about ready to resort to JATO bottles, to be honest.

 

Anyone have any tips?

As always, pics or it didn't happen.

In all seriousness, we need to see what you're working with in order to make an educated guess.

My uneducated guess would be that you're working with too much wing surface.

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Okay, fair request...

 

sfILap4.png

This is the X-4, where I first noticed the problem. Mass of 22.4 tonnes on the runway.  Fuel tanks are from Streamline mod, while the cockpit, mains, and rudders are from Airplanes Plus. Caps out at Mach 1.04, no matter how hard I push it at any altitude.

 

SVOaHjn.png

This is the X-5. Mass: 29.7 tonnes on the runway. Bigger aircraft, bigger wing and more powerful engines to match. I made it more to check if it was just wonkiness with the Panther or my design philosophy... Not the Panther, as it turns out. Again, caps out at M 1.04, despite a higher TWR for not much more mass. The only mod parts are the turbines (Bahamuto Dynamics) and the shield around the LV-N (Mk 2 Expansion).

I've taken two different approaches to the wing design, but have encountered the same result: I'm hitting a massive drag spike at about Mach 1.04... Thoughts?

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The second plane is in MK2 hell, and I'm surprised it even gets to mach 1. MK2 parts are much draggier than MK1.

The first plane's problem is also obviously drag -- just based on your stated performance. However, with so many non-stock parts, it's hard to say which part is the crazy draggy part on that plane. If I were to make it out of stock MK1 parts it would easily hit mach 2.5.

You aren't using FAR with this are you?

 

 

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No, I tried FAR a long time ago and swore I'd never do it again. I'm sticking to the soup of an atmosphere, thank you very much. :D  I'm about to test a fully stock plane with a ridiculously tiny set of wings and see if that can make it past the Mach 1.04 barrier.

 

Also, why are Mk.2 parts so much draggier? That seems... kinda unbalanced.

 

EDIT: Made it past, but only by pushing my TWR past 2.5. :/

 

That's interesting. Perhaps I'm not using engines powerful enough?

Edited by MaverickSawyer

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7 minutes ago, MaverickSawyer said:

Also, why are Mk.2 parts so much draggier? That seems... kinda unbalanced.

It is unbalanced for now, until we can fix it. The "drag cubes" of parts are calculated automatically based on their shapes, but the algorithm has an irrational hatred of MK2 shaped parts, and an irrational love for spheres.

Proof for your plane built with stock parts (23.8 t):

Vl0HXOT.jpg

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Hmph. I guess I'm just not any good at more modern spaceplanes... I did really well back before the current jet engines came out. Run most of the way on jets and a fairly decent pair of wings, and switch to rockets for the last 200-300 m/s. :P

 

I guess I never unlearned that. :/

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6 minutes ago, MaverickSawyer said:

Hmph. I guess I'm just not any good at more modern spaceplanes... I did really well back before the current jet engines came out. Run most of the way on jets and a fairly decent pair of wings, and switch to rockets for the last 200-300 m/s. :P

 

I guess I never unlearned that. :/

Are you switching to wet mode for the panthers? A panther really can't get you above 900 m/s at altitude. You certainly need more like 1300m/s out of your rocket to get a panther-based SSTO to orbit. A Rapier engine will get you going a lot faster in airbreathing mode, but they are even harder to get through the sonic barrier.

 

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3 minutes ago, bewing said:

Are you switching to wet mode for the panthers? A panther really can't get you above 900 m/s at altitude. You certainly need more like 1300m/s out of your rocket to get a panther-based SSTO to orbit. A Rapier engine will get you going a lot faster in airbreathing mode, but they are even harder to get through the sonic barrier.

 

Yes, I'm running the AB in Zone 5. :wink:

Will retry with an altitude run here soon.

 

Also, that little dart of a plane I was talking about did in fact make it to Mach 2.71 at 13 km+. So perhaps I'm trying to go too fast too low?

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I'm having similar problems with a Mk2 and Panthers.

DNFC8oJ.jpg

Scenario: at level flight, plane stops accelerating past 0.96 Mach. Switching to wet mode or firing up the inline 909 allows the plane to accelerate all the way up to Mach 2 but as soon as I switch off the extra thrust, it immediately starts decelerating. Sometimes I find a sweet spot where the plane stops decelerating beyond Mach 1.5 but it's extremely rare.

I'm fairly sure it's the control surfaces: if I switch off SAS, the plane immediately starts accelerating beyond Mach 1, but also slowly noses down to about 7-8 degrees below horizontal at first, then 10-20 degrees if I keep going without pulling up. It used to nosed down much harder until I added canards, but I can't add anything more or the thing will become unstable. I also switched from two diagonal vertical stabilizers to a single completely vertical one to eliminate the torque caused by the off-center lift, but no dice. Could it be possible that the engines are air-starved? I mean, the right one flames out if I try to go 100% throttle from a standstill on the runway.

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In case any of you have ModularPods installed please check that thread. It had a bug that could significantly mess up your drag. Even when not using any ModPod parts! The bug has been identified, found and fixed.

Edited by Tex_NL

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Hmmm... can confirm @bewing's report on the Mk.2 Drag Hell. The stock Mk.2 cockpit generates an insane amount of drag at transsonic speeds.

 

Anyone know of a fix for that other than waiting for the devs to find a solution?

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Hmm to break Mach speeds with panther and Mk2 I get to somewhere around 8km then pick up speed at around .85 -.95 Mach and then do a dive, it'll pick up enough speed to break the sound barrier and from here i just level, get to Mach 1.2 and start climbing slowly.

Edited by Poofer

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On 2/11/2018 at 9:44 PM, bewing said:

It is unbalanced for now, until we can fix it. The "drag cubes" of parts are calculated automatically based on their shapes, but the algorithm has an irrational hatred of MK2 shaped parts, and an irrational love for spheres.

Proof for your plane built with stock parts (23.8 t):

Vl0HXOT.jpg

Can the impact of this be remedied or at least lessened by enabling  "Replace Drag Cubes With Spherical Model" or "Apply Drag As Acceleration Instead of Force"?

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6 hours ago, kevnuke said:

Can the impact of this be remedied or at least lessened by enabling  "Replace Drag Cubes With Spherical Model" or "Apply Drag As Acceleration Instead of Force"?

Give it a whirl and see. I haven't tried it yet.

 

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Are you using the Panthers in Wet Mode or Dry Mode? I have checked, and the Wet Mode yields far higher thrust. Also, I would do away with the Panther engine for supersonic aircraft altogether, as the Whiplash yields a thrust of 130 kilonewtons at a standstill and a maximum thrust of over 750 kilonewtons at Mach 3. However, the Panther in Wet Mode yields a thrust of about 300 kilonewtons at Mach 2.5, and a thrust of 85 kilonewtons at a standstill. Thus the Whiplash is far better than the Panther.

However, if the Panther is all that you have, It should work for Mach 2.5 or less.

J-404_Panther_Afterburning_Turbofan_veloJ-X4_Whiplash_Turbo_Ramjet_Engine_veloci

(Please note that the above images are from the wiki, and show the thrust MULTIPLIER based on Velocity, not altitude.)

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On 2/13/2018 at 3:53 PM, MaverickSawyer said:

Hmmm... can confirm @bewing's report on the Mk.2 Drag Hell. The stock Mk.2 cockpit generates an insane amount of drag at transsonic speeds.

 

Anyone know of a fix for that other than waiting for the devs to find a solution?

Welp, 1.4 has apparently fixed this issue, as I'm happily able to use Mk.2 parts and go orbital without issue. :D

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