zolotiyeruki

Kerbin Circumnavigation Challenge - updated for KSP 1.10

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I've never been into aircraft before on KSP but decided to give this a try... ended up with the most stable aircraft I've ever built. Only achieved the basic endurance challenge, round the world non stop. Version 1 only just made it back - running out of fuel over the mountains west of the space centre but it glided to the runway. However, it had a small wing clipped into the nose fairing so I disqualified it. Version 2 without clipping and more fuel made it back with plenty to spare despite drifting south quite a long way when I had to go AFK forgetting to pause.

Both tries were manual flights with no automation or reloading so it got quite tense on the landings! It's my first post so I think it will have to wait to put up images - the craft is an approximate tribute to an F-14 which totally justified playing the top gun anthem for the last 3 minutes of flight and landing :)

Duration 4 hours 30 minutes, 29 sec. 7,691,874m traveled. Cruising altitude 10-12 km, 250-280m/s powered by 2 Panthers at full throttle.

 

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I tried my hand at speed. I bet I could cut down a minute or so by flying the entire flight in 1x and monitoring it more closely, but ultimately I'm more concerned about my aerodynamics- I'm cruising at around 17-19km and hitting a cap of about 1.7km/s with RAPIERs. The theoretical cap is around 1.9km/s, IIRC. I might need more air intakes... 

https://imgur.com/gallery/vsMME9v

I was thinking it might be cool to have a category where any engine is allowed, with the condition that the craft stays under 20km and maybe remains under a certain mass (say, 100t). A NERVA-powered plane might be interesting. 

Edited by KingDominoIII

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Latest tweak got me around in 39:33.  Not official yet, this was just a test flight.  I got to a sustained speed of 1732+ for the latter half of the flight. Ran out of fuel at just the right moment.

It now has 10 Rapiers, during ascent 4 are shut down, they are lit at altitude, this to try to save a bit of fuel.

The descent is scary.  I was essentially doing a 45 degree dive at 1400m/s.  The test overshot the runway, I miscalculated how much this design floats at low speed.

Just a big ball of fire:

1px9KzB.png?1

Sunrise:

qBrvBPb.png

Edit:  Managed to get to a sustained speed of 1742 without exploding, at 23000m high.  I can get sustained speed of 1745 at 22000, but it explodes about 100km short of the space center (cabin gets too hot).

Edit 2:  I figured out how to deal with the overtemp issues on the cabin.  Got a sustained speed of 1745 m/sec at 23000.   And even had some fuel left over.

I think I'll make an official submission in a day or so.

Edit 3:  Just saw something I never did before.  I got going so fast that the engines flamed out, and then immediately restarted.  This happens just past 1750.6 m/sec, so during the flameout I lose about 5-6 m/sec.

 

Edited by linuxgurugamer

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On 9/20/2020 at 11:50 PM, Lt_Duckweed said:

What AoA are you using?  Hypersonic lift/drag ratio of wings begins to fall off after 5 degrees AoA so if you are using, say, 10, that would degrade your l/d ratio, while also having you flying at a higher altitude, meaning more drag and less thrust for a lower top speed overall.

I believe it was 8 deg. The idea was to keep the fuselage level and maximize altitude. This does reduce fuel consumption while also reducing the speed, but the speed loss was less than the fuel rate reduction. I was assuming high AoA was better because the L-I-D was still small compared to the total drag. And I was assuming nearly all of the total drag minus L-I-D was due to the fuselage.

Anyway, you're both telling me to stick with 5 deg. so I'll try that. Maybe add a third set of wings like @swjr-swis suggested... might help. 

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2 hours ago, Krazy1 said:

And I was assuming nearly all of the total drag minus L-I-D was due to the fuselage

That's where ksp gets tricky.  L-I-D is the drag that comes as a result of the fact that in ksp the lift from wings is parallel to the wing surface, not the velocity vector.  This vector gets decomposed into actual lift, and lift induced drag.  The actual drag listed in the action windows for wings, or displayed via the F11 arrows, is considered to be parasitic drag. The true lift induced drag will be both of these drag values added together.  The true fuselage parasitic drag will be quite low.  On the setup I've been toying around with:

Cruise altitude: 22300m at start of cruise.

Cruise speed:1658m/s at start of cruise.

Mass: 37,934 kg

DeltaV: 47,367m/s

Total drag: 33.32 kn

Lift to drag ratio: 4.191

Fuselage parasitic drag: 2.80 kn (0.75kn from rapier engine, 2.05 from everything else)

Game "lift induced drag": 12.02 kn

Game "wing parasitic drag": 18.5 kn

True lift induced drag: 30.52kn

 

Thus the breakdown of drag on my craft is:

Fuselage parasitic drag: 8.4% (Rapier: 2.25%, rest of the body: 6.15%)

Lift induced drag: 91.6%

 

Thus it can be seen that it is VASTLY more important to optimize lift induced drag by mounting your wings at an optimal angle of incidence.

This also plays into my opinion that the rule against rapier rear cones is dumb, sure it's ~25% of total body drag that you would save, but in the grand scheme of things it's only about 2% of your total drag, and thus one of the least important things to optimize.  You save more by learning to build a well optimized craft in general.

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1 hour ago, Lt_Duckweed said:

-snip-

With my craft, I got around this problem by using winglets so I could change the angle of incidence in flight. I would highly recommend trying it if you like really fast landings, since it helps to minimize the amount of drag from wings

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