what is wrong with these wings?

[Lechu]

After unlocking Whiplash and Airspike engines I have thought that my "almost able to reach orbit" spaceplanes will get enough oomph.

The problem being, when I am reaching the speed about 1500m/s, the wings are just ripped off. No matter how many struts I put there.

How to strengthen these wings further?

[AHHans]

Are they ripped off, or do they explode due to overheating?

The FAT-455 are airplane wings and have a maximum heat tolerance of 1200K - in contrast to 2400K of the Big-S "space shuttle" wings and the modular wing parts. And at 1500m/s heating becomes a significant factor.

Some other comments: I don't know if adding more struts between the same parts actually add strength, so it might be better to add struts from the wings to more different parts than. (But I don't know!) What I do know is that a) that many struts add quite a bit of drag. You also don't usually need so many air intakes. (Well, I don't know hoe many engines you have.) One shock-cone intake should be able to supply three whiplash engines (or maybe even more).

[fourfa]

Those particular main wings have a fatal flaw - their max temperature rating.  They're intended to be airplane wings, not spaceplane.  I suspect they're blowing up from over-temping, not being ripped off by aero forces - so struts won't help.  

edit: ninja'ed.  And looking at the previous answer - it seems in 1.9 (and 1.8?) struts no longer have aerodynamic drag.  Nothing reported when aero info is activated per part.  Did squad decline to fix the old excessive strut drag problem, by simply deleting drag?

Edited March 6, 2020 by fourfa

[Lechu]

Thanks for the answers. You may be right, it may be an explosion. But I do not see the overheating gauge, the way it is shown when the engines overheat. How do I check the wings' temperature?

I have just tried to put pre-coolers and large radiators on the wings, no luck,  but I guess it is not working that way.

[bewing]

54 minutes ago, Lechu said:

How do I check the wings' temperature?

Either you can hit F3 just after the wings explode, and the report will tell you what happened to them, or you can turn on the extended temperature debug readouts in the debug menu. Then open the context menus for the wings while you are in flight and watch the numbers change in realtime.

[UncleManuel]

With these "normal" airplane wings you'd have to get VERY high to minimize heating. But by that time your plane is already going ballistic. And above 30000 meters on Kerbin wings are pretty useless, you have already move faster than 1200 m/s to stay afloat - and that's already more like a rocket trajectory... 

Long story short: if S.A.S. isn't doing too much crazy up there your wings basically burn up. You can test that theory by using the Big-S delta wings & rudders. And have an eye on the CoL and CoG indicators during the build phase...

[Lechu]

Thanks for the F3 tip, I was unaware of it.

Why the thermometer, attached to the wing, is not showing wing's actual temperature?

Using Big-S delta I was able to exceed 1500 m/s, but only slightly. No explosion, just plane would not go faster. It is pointless then, I was hoping to accelerate to something like 4000 m/s, on air breathers only, before heading out of the atmosphere.

Giving out on this goal for now however, and adding more oxidiser instead, I was able to put my first pure (without detachable engines and tanks) SSTO plane into orbit with some decent dv  remaining. Success.

[AHHans]

48 minutes ago, Lechu said:

Using Big-S delta I was able to exceed 1500 m/s, but only slightly. No explosion, just plane would not go faster. It is pointless then, I was hoping to accelerate to something like 4000 m/s, on air breathers only, before heading out of the atmosphere.

Sorry, not going to happen.

Have a look at the velocity curves on the jet-engine wiki page (you'll probably need to expand the relevant section to see them). The air-breathing mode of the RAPIERs is the engine that can work up to the highest speeds (Mach numbers), but even that drops sharply above Mach 4 and looses all thrust when it gets to Mach 6.2.

[DeadJohn]

On 3/8/2020 at 12:10 PM, Lechu said:

I was hoping to accelerate to something like 4000 m/s, on air breathers only, before heading out of the atmosphere

Your screenshot shows you have mods installed, so I'll take this opportunity to recommend some good spaceplane mods below. Sustained 4000 m/s in air is a near-impossible challenge due to overheating, but you might be able to do it with high TWR and a suborbital trajectory, rather than the typical SSTO "level off and accelerate" approach.

• Mk2 Expansion: Adds a very fast scramjet engine with the challenge of only working after other engines build up speed first. Also many other engines and heat-resistant parts.
• Mk3 Expansion: Similar to the above. No scramjets but has other parts suitable for larger spaceplanes.
• OPT (Orbital Portal Technology): A huge parts pack with some super-powerful parts, such as "warpjets" powered by atmosphere and electricity, no fuel required.

 

[UncleManuel]

On 3/8/2020 at 5:10 PM, Lechu said:

Using Big-S delta I was able to exceed 1500 m/s, but only slightly. No explosion, just plane would not go faster. It is pointless then, I was hoping to accelerate to something like 4000 m/s, on air breathers only, before heading out of the atmosphere.

Nope, even the Whiplash looses steam above 1000 m/s and/or 21000 meters above ground. You can click the stage tab on the bottom left of the HUD to see what actual thrust the engines are producing in flight. 

To go faster you'll have to use hybrids or rockets. Jet engines have their limits... 

Edited March 9, 2020 by UncleManuel
yes

[JadeOfMaar]

On 3/8/2020 at 12:10 PM, Lechu said:

Why the thermometer, attached to the wing, is not showing wing's actual temperature?

The thermometer's purpose is to show the ambient temperature around the craft. It doesn't show the temperature of itself or any nearby parts. Outside of being an experiment, it's useful for if you find yourself in the atmosphere of a lava planet and the exact temperature of the atmosphere suddenly becomes very interesting. As someone else tells you, turn on the Thermal debug in PAW option via the console.

As @DeadJohn mentions above, OPT Spaceplane and Mk2 Expansion provide options for scramjets or augmented air-breather engines that don't hold themselves to the conventions and limits of typical jet engines.

This mod here also provides a (radial Mk3) scramjet among other things, particularly if you're looking for a Mk3 scramjet.

I must mention by the way that since you're playing stock scale, you're going to have a hard time either: enjoying trying to reach 4km/s; staying in Kerbin's atmosphere at 4km/s; surviving at all at 4km/s. You may quickly grow to want more room to stretch your new-found legs if you try the mods. And you may find yourself looking for Sigma Dimensions and going to 2.5x or 3.2x.

Scramjets are half the reason I don't like stock scale anymore.