Fastest vehicle measured by body lengths per second

[mister_goo]

Today I learned a new unit of measure: body lengths per second. This unit is often used to measure the speed of animals. According to wikipedia, the cheetah, the fastest land mammal, scores at 16 body lengths per second.

The challenge is to create the fastest rover, aircraft, boat, or submarine, or other creative vehicle type measured by body lengths per second. Rockets are excluded from this challenge since a short and wide rocket is too boring/ugly.

A slightly harder challenge is to measure speed by body sizes per second where the body size is `max(length, width, height)`.

 

[hexeract]

Here's my entry:

please ignore the mouse cursor. also "somali" captions are actually the english captions and might be necessary for context

Length: 6.9m

Max Speed (m/s) = 1490 m/s (safe speed) or 1700 m/s (unsafe speed)

Max Speed (body lengths / second) = ~216 body lengths / second 

Craft file: https://kerbalx.com/hexeract/Bug

Edited July 6, 2022 by hexeract
Recommendations for those who dare watch the video

[mister_goo]

The smallest aircraft I tested is a 2m long drone. Flying at 700 m/s at sea level scores 350 body lengths per second.

Also a 1.3m rover. Unsafe at any speed due to the lack of brake.

[hexeract]

4 hours ago, mister_goo said:

The smallest aircraft I tested is a 2m long drone. Flying at 700 m/s at sea level scores 350 body lengths per second.

Also a 1.3m rover. Unsafe at any speed due to the lack of brake.

Nice, you beat my entry. for now, that is

[sevenperforce]

I think this should approach the maximum efficiency without a bunch of clipping.

The Wonky Wing has remarkably good handling thanks to an abundance of reaction wheels.

With a TWR well over 1, takeoff is easy.

Rapidly supersonic.

The highest speed I've hit in approximately-level flight was 789.6 m/s, which at a body length of 1.3 meters gives me a score of 607.38 which seems pretty decent. I've taken it up to 10 km and then done a number of dives at various descent angles to try to get the highest impact speed...it's hard to get the perfect combination of thrust and drag based on the Juno's thrust curve and altitude and airspeed all at once. The highest I've gotten it in a dive was 792.7 m/s which is a score of 609.77 body lengths per second.

This is probably close to the limit of velocity on Juno engines with anything resembling a controllable setup. If you start a bunch of ridiculous clipping and offsetting and aero exploits you might be able to get the body length under 1.3 meters but the smallest retractable landing gear are about that long anyway so you'd either have to go with jettisonable landing gear or use the fixed ones, and drag will be an issue with the fixed ones.

The Juno should get better all-around performance than the Wheesley. Once you move up to the Panther, your engine length alone is already 1.5 meters so if you add the shortest intake (0.5 meters) you've already set your score back by 54% right out of the gate. With afterburner the Panther can get you up to around 1,034 m/s at sea level but that still would yield a lower score than the Junos.

The shortest intake + the RAPIER can get you down to 1.8 m/s so theoretically that should be able to beat the Juno approach.

 

[sevenperforce]

UPDATE: I tried using RAPIERs but apparently they have a wildly offset center of mass and as a result it is impossible to put them in anything remotely resembling a stable flight configuration for a horizontal takeoff unless it's substantially longer.

As ugly as it might be, there's actually no clipping, other than the clipping into the wing. All of the pieces are node-attached. The longest span is the air intakes and the small sized nosecones.

This "plane" with the RAPIERs can of course be launched vertically to terrific effect but then it becomes more of a rocket, even with the RAPIERs in airbreathing mode. I've experimented with a few different launch profiles and the best speed I've gotten is 1562 m/s which at 2 meters in length gives a score of 781 body-lengths per second.

Better than the Junos but not by as much as I expected. The trick with the RAPIERs is getting high enough to find reduced drag and not burn up but not so high that you run out of air before you've gotten to your top possible speed.

I used infinite fuel for this run because I wanted to get a feel for what was possible. I could of course replicate readily enough without infinite fuel by using drop tanks.

Edited July 7, 2022 by sevenperforce

[swjr-swis]

I would like to enter the BumbleBee II, a 2.2 m RAPIER-based drone clocked at 1751.3 m/s or 796 body lengths per second.

Form and length are dictated by the nacelle intake dimensions and the need for thermal protection at RAPIER top speeds.

The invisibly protruding RAPIER CoM is balanced by a disabled backward-facing  RAPIER, leaving CoM in a very manageable and almost centered position.

The otherwise relatively conventional design manages to clock 1751.3 m/s, which at 2.2 m in length makes a 796 body lengths per second.

Obviously clipping and offset have been used, but all parts are regularly attached and fully exposed to the game's thermal and drag physics, and no cheats were required, the drone uses fuel and air. It results in a quite viable-looking design, which is at least as worthy of consideration along-side more esoteric non-clipping (but mechanically/structurally/aerodynamically questionable, respectfully) entries.

 

21 hours ago, sevenperforce said:

This is probably close to the limit of velocity on Juno engines with anything resembling a controllable setup. If you start a bunch of ridiculous clipping and offsetting and aero exploits you might be able to get the body length under 1.3 meters but the smallest retractable landing gear are about that long anyway so you'd either have to go with jettisonable landing gear or use the fixed ones, and drag will be an issue with the fixed ones.

Junos max out at 820 m/s at sea level, there's been challenges before that proved that. It's not too difficult to make a very controllable/stable drone to do this (has to be if you need to skim the surface for max speed). So at 1.3 m with landing gear that maxes out at 631 bl/s.

With clipping and droppable gear length could be shortened max to 0.5 m, using only elevons 1's, the length of the Juno setting the limit. So potentially, values of up to 1640 bl/s could be reached, which is completely outside the feasible with any other engine, RAPIER included.

A non-entry example, just going for the shortest length (0.5 m) reaches 1305 body lengths per second on a single (thrusting) Juno:

 

Edited July 8, 2022 by swjr-swis
added example of minimal length Juno craft

[swjr-swis]

On 7/6/2022 at 6:19 PM, hexeract said:

Craft file: https://kerbalx.com/hexeract/Bug

Missed this one before... I think the forum hid the video link from me. Spiffy-looking craft, I like it!