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Fastest Juno-powered aircraft


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On 7/5/2018 at 2:46 AM, RealKerbal3x said:

Got a few more entrants. Thanks guys! :) I’ll sort you all out later :P

How many "updates" for an entrant do you think it's nice? I'm trying to minimize mine to prevent being a sas-mohole :P but I got some improvements on my score. ;) 

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1 minute ago, Lisias said:

How many "updates" for an entrant do you think it's nice? I'm trying to minimize mine to prevent being a sas-mohole :P but I got some improvements on my score. ;) 

Unlimited really. As long as you don’t break the rules of the forum or challenge, it’s fine.

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Tried going a different direction. Dropped the MK2 parts and went to a simpler more aerodynamic shape.

mBDmGa4.png

765 m/s level flight. Acceleration is insane up to 650 m/s.

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672 in level flight with a Mk3 Cockpit:

MxKUlLo.png

718 in a shallow dive:

6eiUgpC.png

For some reason my altimeter mod goes wonky over water, but you can just make out the Kerbal Engineer readout.   This shot is at 524m (I did not manage to pull out of this one, but have on others).

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1 hour ago, Klapaucius said:

For some reason my altimeter mod goes wonky over water

It's measuring the altitude from the bottom of the sea, probably. 

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10 hours ago, Klapaucius said:

672 in level flight with a Mk3 Cockpit:

MxKUlLo.png

718 in a shallow dive:

6eiUgpC.png

For some reason my altimeter mod goes wonky over water, but you can just make out the Kerbal Engineer readout.   This shot is at 524m (I did not manage to pull out of this one, but have on others).

WOW MK3?????????

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On 7/1/2018 at 7:15 PM, RealKerbal3x said:

Actually you're only the second Mk2 plane; @Klapaucius entered first using Mk2 parts

Technically third, since @Klapaucius entered two different eligible Mk2 planes, in separate posts.

 

19 hours ago, Klapaucius said:

672 in level flight with a Mk3 Cockpit:

That draggy open node in the back is killing all that excess thrust - it's like flying with a giant deployed airbrake.

Remember my Dodo from a few pages back? It doesn't take all that many Junos to push a streamlined Mk3 craft close to Mach 2 and beyond. The added weight of the extra parts is well worth it:

Spoiler

F72jOY2.png

659.6 m/s on 4 Junos

mnXARSW.png

697.8 m/s on 5 Junos.

V60Hxa5.png

With just 7 Junos, it's tickling Mach 2.1, 735.8 m/s.

 

On 7/2/2018 at 6:27 PM, GDJ said:

She's as fast as she's gonna get since MK2 parts are basically as aerodynamic as a brick.

Mk2 planes can be quite fast with a minimum of Junos too:

Spoiler

zVQCVeD.png

Breaking Mach 2 with an Mk2 plane on just 3 Junos.

PYNqCj3.png

Add just two more, and we can push past Mach 2.1 (748.5 m/s).

 

Make it so the fuselage angle of attack nears zero (and thus body drag), and you'll slice through the air on a minimum of thrust, even when using the notoriously draggy mk3/mk2 parts.

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11 minutes ago, Gman_builder said:

I made this on accident today and thought id submit it. Note,  check the altimeter. This was done at over 9000 meters. The intake i used generated the high performance at high altitude.

I like the texture mod you're using! That probably contributes to the pretty!

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Just now, Andetch said:

Also, that high you must be nearing the flameout speed! Good job!

The engine was still making 6.7kn of thrust which was amazing. It was cruising along nicely at ~300m/s until i hit about 7,500 meters and thats when the turbo kicked in and sent it to Mach 2. I genuinely had no idea that it would do that. I imagine it was the Radial ramp intake that made the difference.

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Here comes my Mark 3 entry. 785.83 m/s

Curiously, the max speed is always reached at 10 m altitude. Even on a step descent, I never reach the speed I get on level flight at 10 m/s. I imagine that I cold get some cm/s more by flying at 5 m, but that would be suicidal. Now and then the craft drops some meters and then climb it again, and 10 m is the altitude in which I didn't crashed. Yet. :-)

FLIGHT_785_LEVEL.png

This baby flies nice at 16.600 meters. I can reach 17.500 or a bit less without flame-out, but curiously I can't maintain the altitude. She is stable in the 16.600 meters (bit more, bit less).

FLIGHT_FORCES_1.png

I think I'm reaching the limits of this airframe. It is too light, the Terminal Velocity is too low and so Gravity doesn't helps me on descents. I'm also unsure about the ideal number of Junos. On my previous designs, there was a point where increasing Junos decreased the max-speed - the extra kick didn't was enough to compensate the weigh and drag added.

The number of engines for this entry could be probably optimized, but my time window for this entry just closed, so I'm publishing what I got. :)

Craft on Kerbal-X.

 

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35 minutes ago, Lisias said:

Here comes my Mark 3 entry. 785.83 m/s

Curiously, the max speed is always reached at 10 m altitude. Even on a step descent, I never reach the speed I get on level flight at 10 m/s.

I am no expert but I think that may be because the engine thrust output decreases with height. So 10M above sea level is where the engine is producing the most usable thrust - as you say 5M would be too risky!

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10 hours ago, Andetch said:

I am no expert but I think that may be because the engine thrust output decreases with height. So 10M above sea level is where the engine is producing the most usable thrust - as you say 5M would be too risky!

Exactly. But Junos also loose thrust with speed - the fast you go, less thrust they give you. KER is absolutely a must have on this.

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10 hours ago, Lisias said:

Curiously, the max speed is always reached at 10 m altitude. Even on a step descent, I never reach the speed I get on level flight at 10 m/s. I imagine that I cold get some cm/s more by flying at 5 m, but that would be suicidal. Now and then the craft drops some meters and then climb it again, and 10 m is the altitude in which I didn't crashed. Yet. :-)

Juno engine power curve, it's not surprising. It's worth the risk dipping as low to the surface as you can if you are just a few decimals away from reaching the next full m/s. The 5 m difference could help, but you would definitely need to switch to fine controls (why are you not using that?), and disengage SAS entirely and fly on trim (I can't tell from your screenshots if you do or not). It also helps to lower your elevator authority to 10% or less, to make your pitch control more gradual and accurate.

 

10 hours ago, Lisias said:

This baby flies nice at 16.600 meters. I can reach 17.500 or a bit less without flame-out, but curiously I can't maintain the altitude. She is stable in the 16.600 meters (bit more, bit less).

Not that curious either: there's an equilibrium point where the aerodynamic forces, gravity, and remaining engine thrust balance out, allowing the plane to keep cruising without loss of airspeed. You can briefly dip above that, but this is basically done by exchanging airspeed for altitude, which makes airspeed and lift drop below the balance point, until you inevitably lose the gained altitude again.

 

10 hours ago, Lisias said:

I think I'm reaching the limits of this airframe. It is too light, the Terminal Velocity is too low and so Gravity doesn't helps me on descents. I'm also unsure about the ideal number of Junos. On my previous designs, there was a point where increasing Junos decreased the max-speed - the extra kick didn't was enough to compensate the weigh and drag added.

I think you are partly drawing the wrong conclusions. The role of gravity in maximizing your craft top speed is almost negligible compared to the aerodynamic forces (drag!).

I do agree you could do with a lot less Junos though, and still get more speed out of that frame. I did a quick rebuild in 1.3.1 to test:

Spoiler

wHternJ.png

I had to rebuild it, 1.3.1 doesn't like 1.4.x files. I kept the fuselage the same, but I did replace the wing/control surfaces, and downsized it from 37 to 8 junos.

Ug1bqsa.png

Elevon-4's were used for the elevators and tail/rudder. The pair of elevon-3 serve as main wings, deployed to provide a manually adjustable angle of incidence, starting at 35% for easy hands-free take-off.

IoV4LW0.png

Once in stable supersonic flight SAS is turned off, deployment is adjusted for top speed (6% here), and pitch trim is applied to stay level with the ocean surface. 788.2 m/s on 8 Junos, without fine tuning.

31FnMyk.png

It performs pretty well at altitude too, close to Mach 2 at 15 km. It would require only a fraction of the available tank volume in fuel to circumnavigate Kerbin.

 

You could do even better by entirely removing the two Mk1 LF tanks - they are just adding superfluous mass and drag to the craft, as even just the 200 LF in the intake is enough to reach any place on Kerbin within an hour.

Spoiler

M8lya90.png

nxmStpn.png

Full imgur album for a few more screenshots: https://imgur.com/a/NFuHvSK

The above craft are simple WYSIWYG stock rebuilds based on your screenshots, with offset adjustments on snap to move CoM/CoL where I wanted. No real fine tuning was done, leaving potential for better numbers by either fine tuning, adding extra Junos, or replacing parts for better alternatives (pre-cooler comes to mind). Any other 'tricks' used to achieve the results (elevon deployment, flight method, etc) are visible in the screenshots. Use to your advantage.

 

2 minutes ago, Lisias said:

KER is absolutely a must have on this.

I would feel inclined to disagree. :wink:

Edited by swjr-swis
look ma, no readouts!
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12 hours ago, swjr-swis said:

I do agree you could do with a lot less Junos though, and still get more speed out of that frame. I did a quick rebuild in 1.3.1 to test:

Yep. You was right. This airframe has still some juice to give. 797.17 m/s. ;)  

FLIGHT_797_LEVEL.png

Apparently, I managed to build an airframe that follows religiously the Sacred Way of Kerbol: MOAR THRUSTERS. :D 

The hard part is taking off… Geez...

—— EDIT — — (revised)

I made a little study about the elevons as lift surfaces. My conclusion is that they are not necessarily a better option. They provide less drag, but algo provide less lift. So just take the part that provide the lift you need (and not more), and you are ok.

STUDY_DRAG_CONTROL_SURFACES.png

Since I'm going to heavier designs, I need more lift. And since with more lift, you got more drag, forget about drag on lifting/control surfaces: use parts that provide the lift you need (and no more).

A better approach is to choose the lighter lift/control surfaces that provides the lift you need.

Originally, I was trying to use the Delta Deluxe Winglet. It provides even more lift than the AV-R8 I'm using now, but its control authority is weaker and my craft became uncontrollable on high speeds. The AV-R8, besides giving me a bit less lift and being a bit more heavy, has huge control authority so it is the best option for my current design (I'm not claiming my design is the best).

But the four AV-R8, by themselves, didn't made my craft to fly - I think that KSP's flight modeling (or perhaps SAS and auto-pilots) need a fixed lifting part somewhere to act as pivots. I choose the Basic Fin because it's the lightest lifting part providing the least lifting (even less than elevons), and so, with the less drag.

I already had all (and probably more) the lifting on the 4 AVR08 I need - all I need is something to make the craft fly with her nose pointing to the skies, not the ground. :) 

Edited by Lisias
study on drag/lift - addendum
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  • 2 weeks later...

Sorry guys. I haven’t really posted here in a while, nor have I updated the leaderboard. It’s kind of boring to trawl through the thread to look for new entries before doing the maths to figure out who’s in what place and who has what speed.

I feel playing KSP is a lot more fun than managing this challenge, but I promise I’ll get back to this soon :)

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  • 2 weeks later...

Maybe there should be a lower maximum limit on the number of engines or require the craft to be.. you know.. a plane... that can take off and land...

Edited by Pds314
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51 minutes ago, Pds314 said:

Maybe there should be a lower maximum limit on the number of engines or require the craft to be.. you know.. a plane... that can take off and land...

I dunno.....the challenge is not directly to build a plane.... There have been several people who have created a kind of Juno-powered 'missile' and I'm fine with that.

And sorry for the extended hiatus guys. I am now back! Hit me with your supersonic Juno missiles!

Edited by RealKerbal3x
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