Kerbin Circumnavigation 1.0.4/1.0.5 - Aviator Challenge Continuation

[zolotiyeruki]

I'll wish you luck with that. I tried to use wing pitch to correct the AOA on a few designs but never had much success. It felt to me like they were inducing more drag than I felt with a high AOA on a craft with wings parallel to the fuselage.

I'd consider it convergent evolution. Like how Buran ended up looking so much like STS. Believe me when I say I tried a LOT of sizes and shapes to pull that flight off and would not be one bit surprised if anyone else trying the same ended up with a very similar craft. I'm sure you've realized that going that distance requires more than just a well designed craft. It will test your skills as a flight captain as well. And it will be ever so rewarding when you finally touch down.

Yeah, well, I'm a bit of a geek, so I did a lot of testing before the 4-circle run, to find the optimal altitude for the craft as it burned off fuel and lost mass. Now, I'm doing it all over again. I think since my design has a lot fewer wings and uses the flat strake instead of the Big-S strake, I have a lot less parasitic drag from the wings. That makes the parasitic drag from the fuselage a bigger factor.

I'm still running all the tests to find the optimum altitudes throughout the flight. The craft starts at 12.8 tons and runs dry at 4.8 tons, so I get up to altitude (start at 23.5km), burn down to 12t total, then enable infinite fuel and let Pilot Assistant hold the altitude until the speed/thrust stabilize. Then I write down an "efficiency quotient" = (speed/thrust). Then I go up 250 meters and do it again, and then another 250m, etc, until the efficiency starts dropping. After that, it's a matter of burning of 1000kg of fuel, dropping down to 23.5km, and then measuring the efficiency every 250m. It takes a lot of time to run all the tests (burning 1t of fuel at 0.5-0.8kg/sec takes a long time), but it has a huge impact on fuel efficiency. Just a 250m change in altitude can change the gas mileage by >5%. When you're shooting for 5x around the planet, that's a quarter of a circumnavigation right there.

[ExaltedDuck]

That's way more effort than I put into it. I took off, set a lock on heading just after retracting the gear, manually flew up to speed/altitude, locked ascent rate to near zero, then used changes in speed to dictate when/how to climb/dive. I knew roughly what my mean fuel consumption rate would have to be and I just let the calculus run mostly subconsciously.

I never aimed for a record pace or purely optimized flight plan. Just tried to do what I could to reach my mean consumption rate by the halfway mark, then kept doing it for the homestretch. There might be room for an extra lap with your more scientific approach. I'll be interested to see your results.

Also, my second-to-last prototype didn't have any wing strakes. But it ran out of gas just before the fifth desert flyover. I went with the strakes partially for aesthetics and partially to keep the extra fuel close to COM. An additional fuselage tank would have been considerably more difficult to deal with, and I only needed about 80-100 more fuel anyway. I did fill them up completely, though. Filled everything up completely, in fact. That last several hundred km didn't need that much fuel on its own, but carrying that much fuel with the extra drag meant through the previous 10000 meant that I still used most of it. I'll have to look back at my album; I don't remember explicitly noting how much remained. I was just relieved to have made it safely down without needing a reload (really didn't want the odometer reset by F9) and like I said in the original post, in a little bit of shocked state after the roll-over scare.

Edited October 8, 2015 by ExaltedDuck

[zolotiyeruki]

I seem to remember doing a comparison test with the wet strakes vs the basic ones, and noticed increased drag, but my recollection might be wrong. Your craft had 2400 fuel vs my 1600, so I have to be a lot more optimized in order to make it the same distance. I'm lucky so far with CoM--it's almost exactly in the middle of the four tanks, so there's no need to balance at any point during the flight.

Descending from 26km and 1600m/s took about 30 degrees of longitude, when I tested it. That's a fair distance!

I wonder how much fuel you could have left at home and still made the distance...

[ExaltedDuck]

I usually descend rather late... Habit from the velocity runs. IIRC I was around 27 or 27.5 km up and started a prograde dive between the west coast and KSC mountains, and a steeper dive over the mountains. I would have to have made 120-140 degrees unpowered without the extra fuel in the strakes, though. My gut feeling is that I would have had enough to go another 1/3 of revolution, so maybe 100 units or so.

Looking back, I may have been able to improve efficiency by moving the COL forward a little. I put it far enough back to make any possible fuel transfer fool-proof since I intended to fly in 4x time and tend be rather accident prone.

[SpaceplaneAddict]

Which direction is the best for a velocity run? Prograde? Retrograde? East? West?

[Xannari Ferrows]

With a velocity run it doesn't matter too much, but I would recommend a retrograde run since the distance to cover is slightly shorter.

[ExaltedDuck]

In my experience, times are the same regardless of 270 or 90 headings. Surface speeds are higher on a 90 heading, and the flight is more fuel efficient. I've taken this to mean that the entire atmosphere must be fixed to the surface and rotates as a block with the planet.

Basically it's like a headwind in the 270 direction and tailwind in 90, with scale of each being equal to the rate of planetary rotation and exactly balancing the difference in surface track length... At least that's my intuitive perception. It would be interesting to see if the math confirms it.

Edited October 9, 2015 by ExaltedDuck

[ExaltedDuck]

That said, I use the 90 heading since I can get away with a smaller fuel load.

[zolotiyeruki]

Whew, I finally have all the data I need in order to make my run. That took....a long time. Enable infinite fuel, set the weight by emptying the fuel tanks in the SPH, fly it up to 23.5km without losing stability, let it sit at that altitude for 10 minutes to stabilize speed and thrust, go up 250m, repeat the 10 minute wait, do that until efficiency drops. Then revert to the SPH, lower the weight some more, and repeat, in 1 ton increments from MTOW down to empty fuel tanks. I've got my flight profile now, just a bit of math left and I'll have to find 3.5 hours where I'll be around the house and can periodically come back and check my progress. With almost empty fuel tanks, my cruise altitude will be 27,500m (!) and my thrust will be a whopping 8.1kN. Seriously, 8.1kN will be enough to maintain that altitude at >1600m/s. No wonder re-entry from orbital velocities is so hard--there's hardly any air until you're under 30km!

- - - Updated - - -

Is that because you start at the west end of the runway?

[zolotiyeruki]

I've begun my multicircumnavigation run! I've made a few minor optimizations to my craft: eliminated the battery (I only need a little bit of torque when levelling off), emptied the monoprop tanks in the fuselage. I did some tests to see if a ram air intake would provide better efficiency, or a nose cone + precooler. Neither were better than a shock cone intake.

I also am trying something new: since my wings are already angled up, and my drag is minimized when I'm traveling exactly prograde, instead of following my carefully-plotted altitude spreadsheet, I'm using Pilot Assistant to maintain a 0 degree AoA, and as the craft lightens up, it'll naturally float to a higher altitude.

So far, the results are promising: I'm flying both faster and with lower fuel consumption than I did in my tests at the same weight. Which is good, since my ascent consumed more fuel than I had anticipated.

EDIT: 3 laps down! Efficiency is now quite close to expected values. Bill is wondering why on earth he decided to have that extra cup of coffee before taking off 2 hours ago.

EDIT2: 4 laps down. Bill was napping when he passed over the KSC. That was ok, though, since the entire KSC staff had gone home for the night anyway.

EDIT3: half way through lap 5. Bill wakes up to realize he completed more than half a circle while sleeping. His gas mileage is showing about 24km/unit (liter?) of fuel. Let's see a Prius beat that at mach 5.5!

EDIT 4:

Bill: Mission Control, I'm ready to begin my initial descent.

Mission Control: ...

Bill: Mission Control, repeat, I am ready to begin my descent.

MC: ...

Bill: Aw crud. There's nobody at the tower, is there? No lights, no beacons. (looks at fuel gauges) Well, I suppose I could go around one more time...

EDIT 5 (End of circle #6!):

Bill: Mission Control, can I land yet?

MC: Bill, the morning shift just got in. Can you give us 20 minutes to get set up?

Bill: Seriously? In 20 minutes I'll be halfway around the globe again!

MC: You don't have enough fuel for that, do you?

Bill: Oh, I've got plenty of fuel. It's just that Bob ate all the snacks again, and I'm starving!

Edited October 11, 2015 by zolotiyeruki

[zolotiyeruki]

And we now have 7 TIMES AROUND!

Bill arrived safe at KSC after a nearly 5-hour flight, having circled the planet 7 times. Whew, I'm going to bed.

Had a bit of a hard time staying on the runway after such a long flight, but so would you!

Javascript is disabled. View full album

Werner Kerman just realized that if they can squeeze about 1% more efficiency out of this thing, Bill can make it to 8.

[SpaceplaneAddict]

#NoLifer

#RadicalDude

[zolotiyeruki]

#NoLifer

#RadicalDude

It's remarkable how much you can accomplish in life if you eschew social situations.

[nicky4096]

whaaaaaaaaaaaaaaaa!?

nice

[Noname117]

And we now have 7 TIMES AROUND!

Bill arrived safe at KSC after a nearly 5-hour flight, having circled the planet 7 times. Whew, I'm going to bed.

Had a bit of a hard time staying on the runway after such a long flight, but so would you!

http://imgur.com/a/cVwVl

Werner Kerman just realized that if they can squeeze about 1% more efficiency out of this thing, Bill can make it to 8.

Well, that just became very impressive very quickly. I'm now beginning to wonder how many laps around Kerbin is just possible. Very nice run there!

[zolotiyeruki]

FWIW, I wasn't sitting in front of the computer the whole time. I would take a screenshot, set a 20 minute timer, go do something else, then come back to take a screenshot. Thank heavens for Pilot Assistant!

[Xannari Ferrows]

And we now have 7 TIMES AROUND!

Bill arrived safe at KSC after a nearly 5-hour flight, having circled the planet 7 times. Whew, I'm going to bed.

Had a bit of a hard time staying on the runway after such a long flight, but so would you!

http://imgur.com/a/cVwVl

Werner Kerman just realized that if they can squeeze about 1% more efficiency out of this thing, Bill can make it to 8.

Part of me wanted to see your average time, minus the first time going around the planet. That would've been interesting.

Ordinarily this wouldn't cut it for the lack of the runway in view or an F3 window, but I can judge from your distance and visual angle of the launchpad that you're close enough, and you get 1 free pass.

I feel like the planes are slowly morphing into sausages.

I'll remind everyone that it's in your best interest to keep your free pass with you. It's very easy to forget if you have it or not.

http://www.datainterlock.com/Kerbal/circumnavigator%20resized%20expedition.png

[zolotiyeruki]

Part of me wanted to see your average time, minus the first time going around the planet. That would've been interesting.

Ordinarily this wouldn't cut it for the lack of the runway in view or an F3 window, but I can judge from your distance and visual angle of the launchpad that you're close enough, and you get 1 free pass.

I feel like the planes are slowly morphing into sausages.

I'll remind everyone that it's in your best interest to keep your free pass with you. It's very easy to forget if you have it or not.

http://www.datainterlock.com/Kerbal/circumnavigator%20resized%20expedition.png

I consider myself rightly chastised. I *do* have a quicksave from just before I started my descent, so maybe I can go back and re-do the landing, and stick it on the runway this time

I took screenshots more or less over KSC on each circumnavigation (can we just call 'em circles?), and it looks like the first time around took 42 minutes from takeoff to passing over. My speed started off at 1694 and gradually decreased as I got lighter and higher, down to about 1655. Bill was passing over KSC for the 5th time at 3:17 (hh:mm), so that gives an average time of about 39 minutes for circles 2-5. Given the fact that I had no landing or takeoff time for those circles, that makes those 38-minute runs really impressive!

EDIT: Ok, I went back and re-did the landing, and updated the imgur album to show the F3 screen. I swear, this thing doesn't want to land when it's empty. It naturally sits with the nose down a bit, but the wings are still angled upward. The approach was still hot, so when I flared in order to land on the main gear first, the stinkin' thing started climbing again. I thought I was going to have to fire up the engine and go around, but I finally got it down and stopped right at the end of the runway.

Edited October 12, 2015 by zolotiyeruki

[zolotiyeruki]

Had another run at it last night. Started the flight, went to bed and got up 5 hours later for the landing. I ended up about 170km short of 8 circles. Splashed down within sight of KSC's continent. Two more minutes of fuel, at initial cruise speed/altitude, would have got me there. About 0.7% of my total flight time. Literally 28 units of fuel. I don't think there's much I can do to improve efficiency once I get to my target altitude/speed, so somehow I've got to squeeze 30 units the fuel out of my ascent.

Unless... I've seen people use control surfaces without associated wings. I'm currently using an AV-R8 winglet as my vertical stabilizer, and it's grossly oversized for the task. Would an Elevon4 have less drag? Heck, if I could replace my AV-R8 canards with an Elevon 1 (the skinny one) or a pair of Elevon 4's, that would save me 180Kg, or about 1.5% of MTOW and nearly 4% of my dry weight.

Edited October 12, 2015 by zolotiyeruki

[nicky4096]

try flipping the intake at the front

it won't help much and it might actually be detrimental because of less intakeair but it has slightly less drag that way.

one other thing to try: replace the inline cockpit with the whats-it-called, the little grey conical one (i really should play KSP more, damn Minecraft!) and offset it in a bit. should shave off some weight and drag

Edited October 12, 2015 by nicky4096
pesky MC

[xendelaar]

Here's my entry for the velocity circumnavigators challenge:

Time to circumnavigate: 38 min 58 seconds

Top Speed: 1739 m/s

Javascript is disabled. View full album

I ran out of fuel as I entered the airspace of the KSC-continent... So I had to coast across the mountains for a half a minute... But I made it.

I don't know why it's stated I reached an altitude of 31km, because I don't recall doing so (it would cause way to much flame out time!). Anywho...If my entry is disqualified due to the highest altitude reading, I will do a reattempt later on. It was a nice challenge!

Edited October 12, 2015 by xendelaar

[zolotiyeruki]

try flipping the intake at the front

it won't help much and it might actually be detrimental because of less intakeair but it has slightly less drag that way.

one other thing to try: replace the inline cockpit with the whats-it-called, the little grey conical one (i really should play KSP more, damn Minecraft!) and offset it in a bit. should shave off some weight and drag

Wait, intakes have less drag if they're pointed toward the back? How on earth...!?

Using the Mk1 Command Pod is an interesting idea. The 160kg of weight loss is nothing to sniff at. How would that affect drag, since the forward end of the command pod is so much smaller than the back end of the intake?

Some experimentation is in order, methinks.

[Xannari Ferrows]

Here's my entry for the velocity circumnavigators challenge:

Time to circumnavigate: 38 min 58 seconds

Top Speed: 1739 m/s

http://imgur.com/a/KgIwu

I ran out of fuel as I entered the airspace of the KSC-continent... So I had to coast across the mountains for a half a minute... But I made it.

I don't know why it's stated I reached an altitude of 31km, because I don't recall doing so (it would cause way to much flame out time!). Anywho...If my entry is disqualified due to the highest altitude reading, I will do a reattempt later on. It was a nice challenge!

...

So...

Where did you land?

[ExaltedDuck]

And we now have 7 TIMES AROUND!

Bill arrived safe at KSC after a nearly 5-hour flight, having circled the planet 7 times.

Nice run. Congrats.

[Noname117]

...

So...

Where did you land?

Well, I doubt he got his fried chicken if he didn't land at KS(F)C.