fourfa

that... only took 9 years 6 months

I wonder if they remember these forums exist

I'll just keep updating here. I'm having a lot of fun with these and hope to share the learnings... So far I'm finding pretty consistently that max speed happens between 1200m and ~2000m. I'm guessing it's the best balance between decreased fuselage drag and still-near-peak blade thrust. Another effect has to do with number of blades per motor. Here I was playing with number of RS-25 (the largest ducted-fan part) blades per EM-64S motor: 10, 12, 14, 16, 20. At 10 and 12 I was nearly always pegged out at the 460 max rpm limit and getting lower speeds - so clearly the motor has surplus torque to spin more blades there. 20 would drop way down to 220rpm at max speed and lower speed - clearly too many blades. 14 was slightly better than 16 by 1-2m/s overall. So I settled on 14 RS-25 per EM-64S and got an easy +35m/s here: Going to repeat this with RS-12 on the EM-64s but I'm pretty sure 64 each is pretty close (56 and 72 are both slower than 64). This is a lot of part count, but it's a lot lower profile for small planes. RS-25s on EM-64s look good on larger planes. The ducted fan blades do seem to spank the regular props across the board FWIW. This Mk3 jumbo is super usable - one thing I hadn't appreciated is how short takeoffs and landings can be. The props control the speed very precisely, and you can approach your LZ at almost mach 1, slam on 10G of brakes by dialing blade pitch down to +7, and drop right down to 50m/s. Then practically VTOL back again. It's great fun on rough terrain. Next, to try a streamlined speedster with the RS-25x14 motor...

Right, the problem is lack of control authority. The reaction wheel power in the probe core is quite low, less than a tenth of the Mk1 command pod. Since we almost always end up with the non-gimballing Reliant as a stage 1 lifter, and since the available steerable fins are rather too large and heavy, reaction wheels end up as the most efficient option a lot of the time. Slap a 0.625m reaction wheel on the probe core (same 5 torques as the command pod) and you should be good to go. If you don’t have that yet, you’re going to need gimballing engines for the first stage. A pair of Thuds will do. Not as efficient, but the power is just right. Might help to turn down the gimbal amount to 2/3 or 1/2. Then the Terrier’s gimbal an take care of you in the upper atmosphere. Once in space, even the weak probe core reaction wheels are enough (but you need some patience as they’re still slow).

It's a mod

Because why not

Same feedback as your other thread - the raw text of the craft file is not easy to diagnose. Take a screenshot of the whole vehicle in VAB or pad (in daylight!), upload to imgur or image host of your choice, paste [image].jpg here

Neat! Though worth noting - your screenshots are pure black, no craft visible at all

Turning on Rigid Attach for every part on the spindle (all blades, even the nose cones) seems to enable 2x physics timewarp without glitching! That alone makes these more usable in career... Unfortunately it also seems to knock a dozen m/s off top speed Addendum: the trailing-edge motors are the biggest single source of drag in my craft. Enclosing them with a tightly-fitting fairing, closing on the motor spindle, does shield them from drag while leaving the moving part of the spindle and the blades outside the fairing. Very tweaky but this is how I would set it up to use in career personally. This got me to 364m/s. I propose we allow motor fairings but be specific about what's OK and what's not https://kerbalx.com/fourfa/Speed-Demon-3-364ms-stock-props This version is really fun and easy to fly, I'm really happy with where this thread has gotten

Dman how does it fly in physics timewarp? Someone asked for a kerbalx link for my previous craft: https://kerbalx.com/fourfa/Speed-Demon-2

Alright! FYI in the future you should make sure to zero out that vertical speed - even just that little negative 5.7 m/s dive would have given me a few extra m/s. But I have no doubt that craft would have mine beat in level flight regardless. Did you find maximum power just scraping the water? Some of mine did, though the last two I showed seemed to gain speed up to about 1500m and I always found my best pass with them in a very slow climb, so it would rise slowly through its ideal altitude band And we’ll need a ruling on using KAL1000s to boost power over stock for this challenge

355.6m/s, Mach 1.033 larger spindle motor was a bust. Working on drag and mass reduction got a few more m/s here

The Spark has plenty of thrust to land and take off on Mun actually, and it can be slightly more efficient overall due to its lower mass. But it's not enough to work as a Kerbin launch upper stage, so usually it ends up overall more efficient to hang on to a single Terrier for launch and all stages of flight at Mun despite how overpowered it is

I suspect mounting the blades on the larger-spindle large motor variant may achieve more lift and higher speed. Just needs a different tail section for clearance if we're avoiding visible clipping

Blade pitch assigned to H/N (translate forward/back), motor torque on Main Throttle. There's so much power, it's like 8G of acceleration when taking off! It's really a thrill to fly

All surface attached; I've never seen any problems doing that. A little offset nudging to pack them all in but all still on the spindle. Looks kinda evil like real turbine blades - but feel free to make a challenge rule if it's questionable

OK this got fun. I noticed that even with 3 rows of 8 props per motor on the craft above they're all still at max RPM. Also that the leading-edge motors have a lot more drag than the trailing edge motors. I built a new airframe for minimum drag and maximum props per motor, and looking more like an experimental speed platform. I didn't get the motor to slow down until 8 rows of 8 props each. https://kerbalx.com/fourfa/Speed-Demon 351.1m/s ... and Mach 1.016!!!

The obvious next step (double the power) gets 334.6m/s. Interestingly the max seems to be Mach 0.955 independent of altitude - as altitude increases, density decreases, speed decreases a little, but Mach number stays exactly 0.955 Scraping sea level (<100m) same craft gets 336.2m/s

Well that trajectory is (again) pretty different from the advice that's been given here. 45 degrees at 20km is going to be inefficient. Rather than repeat myself ad infinitum I'll move on to other tricks One: there's no need to circularize at Mun - if you just want to grab science and trigger achievements, your Ap can be pretty high (just inside Mun SOI, trial and error to figure this out) and Pe just below the "space low over Mun" threshold altitude (under spoiler tag) Two: When ejecting from Mun orbit the standard single-burn advice is to cancel out the Mun's orbital speed around Kerbin; ie burn on the side of Mun that's leading in its orbit, so your Ap increases on the trailing side. In other words when you transfer from Mun SOI back to Kerbin SOI, you have relatively little sideways motion, and fall almost straight down with a very low Kerbin Pe. With abundant fuel, patched conics and maneuver nodes (not allowed here) you can easily plan a single burn of ~280m/s that lands you at a safe atmospheric re-entry. Without that it's a lot of guesswork, and when you get it wrong (you will; we all will) the correction burn performed around Mun's orbital height is relatively expensive, and you'll likely run out of fuel before getting the Pe down to Kerbin atmosphere. The other option is to burn for prograde ejection on the trailing side of Mun, raising the Ap on the leading side. Then when you exit to Kerbin SOI, your Ap may be extremely high (perhaps as high as Minmus), and Pe still nowhere near atmosphere. Counterintuitively, this is a good thing! It takes longer but when you orbit all the way around to that high Ap, you will find that adjustments to Pe are MUCH cheaper than they are from Mun height. Often this will be enough to get you home. Be aware, though, that reentry will be at higher speed and much care is needed on proper Pe choice - nothing wrong with setting it high and taking a few laps to slow down. But don't despair, you're right that this is pretty hard. Orbiting Minmus is far easier. Properly orbiting Mun and returning probably isn't possible without the Terrier (I assume you have this already) and it helps a lot to have Advanced Rocketry and Fuel Systems unlocked to free up part count. Landing on Mun and returning with a probe is certainly possible (though it implies a good relay network), many examples in this thread and earlier ones. Landing and returning alive with a single-launch crewed pod is not. I'd love to be proved wrong though! In my late-NCD run I've only just gotten crew on Mun with a lander-can-based ship; the pilot then waits for rescue in medium Mun orbit. That requires Fuel Systems (to reduce part count), Advanced Construction (for fairings as the lander can has absurd drag on launch without them), Advanced Flight Control (lander can and RCS for rescue craft), Miniaturization (docking ports), Electrics (probe core to enable sending an empty rescue pod). That's more than halfway through the final tech tier, so yeah, it's hard. While I'm here I'm fairly proud of the long-range Kerbin science plane I came up with on this run. Can bring every experiment to every biome on Kerbin with just Aviation and Basic Science nodes: https://kerbalx.com/fourfa/The-Long-Ranger

Will need a challenge rule on whether RasterPropManager and associated IVA mods are allowed, as it’s basically trivial if so

The best predictor of how a part will fare through reentry is its 'max temp rating,' visible when you right click items in the VAB/SPH selection menus. You will find your answers there. (P.S. it's an attachable part, it's not at all involved in the seat inventory system)

It’s really hard to get the Science Junior to re-enter (just look at its temperature max in the VAB). It’s a lot easier to use the Experiment Storage Unit to pull the data, toss the Science Junior, and re-enter with the box.

For instance this is all motor, 4 fuel cell arrays running full blast. The medium size ducted fan blades seem to be goldilocks between RPM and thrust per blade. So... 323m/s

Alright just for a point of reference: https://kerbalx.com/fourfa/Ducty 314m/s. This was an experiment on a stowable ducted fan / turbine as launch stage for a nuke-only SSTO; still working on shielding the fan blades from drag when the service bay closes. Perhaps a bit clippy for the IRL-alike spirit of the rules so far; but this accidentally became my fastest prop Generally I have the sense that the motors and prop parts were not extensively tested for balance before release (and the early update patches). The motors are WAYYYY to powerful for realistic-looking planes, they just make more and more power as you slap on more and more blades. For 2-3-4 blades you only need like 2% on the motor size slider, and you'll struggle to make 100m/s. Speed record planes are likely to have lots of fuel cell power, lots of blades, but only a couple full-power motors

All the speed record planes I’ve seen (claiming this or that on youtube) use props that are offset way out into open air, not visibly connected to the craft. Typically needing some tall launch tower for ground clearance, or VTOL routines diverging pretty far from reality. I’ve got a 300+m/s ducted fan craft I can throw up later, since we seem to just need a stake in the ground to get this rolling