The Great Desert Turboprop Race

[ralanboyle]

The challenge is simple:

Take off from KSP and land at the Desert Airfield. 

Rules: 

Your aircraft must have a pilot onboard, seated inside a MK1, MK2, or MK3 Cockpit (inline or standard variant.)

Your craft will be powered only by  R121 or R7000 Turboshaft engines, or both. 

Propellers will be attached to attachment nodes only, without any offset. (Yes, that means 8 props max per engine.)

Your craft will not discard any parts. (A part or two broken due to a bad landing is acceptable.) 

Aesthetic part offset is acceptable within reason. Parts must touch. 

No part will be fully occluded, except landing gear (because landing gear is normally fully occluded IRL.)

No Fairings. 

Time is recorded by the game clock. It starts when you move and it stops when you stop (<2m/s)

The pace time is 60 minutes. Only runs which qualify faster than the pace will be entered on the leaderboards. 

 

Good luck! 

 

Leaderboards are divided into weight classes. 

Bantamweight = <5,000kg

@Pds314 44:20

Featherweight = 5,000-9,999kg

@Pds314 45:08

@18Watt 47:46

Welterweight = 10,000-14,999kg

@18Watt 38:56

Middleweight = 15,000-19,999kg

Heavyweight = >19,999kg

@18Watt 48:10

 

 

Edited May 21, 2021 by ralanboyle

[Pds314]

Interesting. So the distance to the Dessert airfield is about 750 km away, so the reference time is a average speed of about 0.5 mach.

[18Watt]

Here's my entry in the 'heavy' category.  (>19,999kg..)  Weight 26,635kg, time 48:59.  Uses four small turbo-prop engines, each having 8 blades.

Here's some screenshots:

Spoiler

Airplane in hangar, 26.635t.  I thought I'd need ore tanks to get the weight over 20t, but the fuel burn was quite high at high-speed, I needed a lot of fuel.

Sitting on the runway.  To save time I did a half climbing split-S after takeoff to get pointed west quickly.  

I hadn't sorted out all the settings before making the run, so much of the flight was playing with altitudes and engine/prop settings to get the most speed.

Clearing the Mountains of Madness.  The groundspeed of ~255m/s is a good speed, but later I'll get the fuel burn a tad lower.

Mach 0.794, not bad for a turbo-prop.  I know others will easily top that speed, but I was happy with my run.

Starting to worry about fuel.  I'm halfway there, but have burned half my starting fuel.  A blade angle of 71-72 degrees allowed me to maintain 250m/s+, and get the fuel burn a little lower.  Altitudes between 4-5km seemed to work well.

Real happy with 0.80M!  That's the cruise speed for the jet I fly for my job in the real world.

Can't believe I didn't ding a prop on landing.  Trip time 48:59.

Although most turboprops in the real world do not go that fast (Mach 0.80), that is actually not a ridiculously unreasonable speed for a very high-performance turbo-prop.

[Pds314]

Alright. I have an entry for the featherweight category. The Thunderstreak managed to land with the only damage being a prop strike on landing. It masses 8856 kg, of which 3400 kg is fuel, although it actually only used about 2500 kg of fuel.

The time was 45:08. It could probably have been a bit better but I didn't really know quite the right altitude it could cruise at or prop settings. 0.88 mach at 4.3 km on four prop blades is pretty quick.

The design is obviously a bit weird, so let me explain. There are telescoping rods connecting a pair of 25%-motorized engines, situated just behind and slightly below the cockpit, to the props. The props themselves use the attach nodes on pair of unmotorized tiny servos strutted to the nose.

The engines are significantly clipped into a full fuel tank. Mostly for aesthetics. I justify this by saying there is a lot of hollow space in the bottom of the cockpit and the nose/tail cone in front of and behind that fuel tank where we can imagine the displaced fuel "actually" is.  Rest assured that the stock aerodynamics are not affected by this sort of clipping.

Edited May 19, 2021 by Pds314

[Pds314]

Alright. Introducing the Kobold. It's my attempt at a Bantamweight entry and sets the all-category speed record at 44:20, beating my Thunderstreak by 48 seconds despite having a lower top speed. With a weight of 4945 kg this one barely manages to fit into the category.

This one had a lot tighter on margins in every way. The fuel is basically exactly as much as neccessary with little or no margin for error without slowing down The only reason I had about 1.6% of the fuel  left was because I dipped into the lower atmosphere a bit earlier than intended and lost some speed. Combine this with the fact that this plane has very harsh torque due to having a single 30% power engine and that means constantly adjusting trim and using caps lock to keep it flat and level is a must. SAS cannot keep it level and I did not add a SAS-compatible trim control.

It is a m/s or two slower than my other plane, but due to the higher optimal flight altitude, it actually manages to be consistently about 0.885 mach and occasionally broke 0.89. Note that none of the pics here show it at top speed.











 

Edited May 19, 2021 by Pds314

[ralanboyle]

Congrats, @18Watt and @Pds314 , you've been added to the boards. 

@Pds314, I have not added your featherweight entry because it appears to violate this rule, "Propellers will be attached to attachment nodes only, without any offset." I read your explanation but it still appears to break the rule. The part clipping is also very aggressive. If you can show that the props are attached to the attachment nodes and not offset, then I'll count it. I don't see how that will be possible since your motor is far from the props. 

[18Watt]

I have an entry for the Featherweight category.  Weight 9,784kg, time 47:46.  Although I normally prefer horizontal takeoffs and landings (like a plane should..), you did not specify that was a requirement.  The propellers I wanted to use made horizontal takeoffs difficult.  So I launched vertically.

Screenshots:

Spoiler

Vehicle in hangar.  Two small turboprop engines, 4 blades each (to save weight for fuel..).  The engines are full-power, although I think 70% power would have sufficed.  

On runway ready to launch.  I wanted to put a spinner (small nose cone) on the rear propeller too, but that caused my launch system to fail- the plane will sit upright on the engine, but not on a pointy nose cone. 

Picking up speed and altitude to clear the mountains.

For this one an engine speed of ~215rpm and blade angle of ~71 degrees seemed to work well.  

I was getting groundspeed of ~265m/s for much of the flight.  That was about as fast as I could go in level flight, regardless of fuel flow.

Just couldn't make landing gear get the prop far enough away from the ground to work.  Broke two prop blades on landing.

 

[Pds314]

6 hours ago, ralanboyle said:

Congrats, @18Watt and @Pds314 , you've been added to the boards. 

@Pds314, I have not added your featherweight entry because it appears to violate this rule, "Propellers will be attached to attachment nodes only, without any offset." I read your explanation but it still appears to break the rule. The part clipping is also very aggressive. If you can show that the props are attached to the attachment nodes and not offset, then I'll count it. I don't see how that will be possible since your motor is far from the props. 

They are attached to attachment nodes of a demotorized servo at the end of a telescoping rod driveshaft. I can show you the mechanism in a sec.

Edited May 19, 2021 by Pds314

[Pds314]

Reference view of the craft with engine-driveshaft-prop assembly highlighted.

 

Pulling the assembly out using offset tool.



Dissassembling the coaxial.



Displaying node positions using alt-f12 cheats.

 

[ralanboyle]

@Pds314 That is an interesting solution that does not appear to violate the spirit of the challenge. Good work. 

1 hour ago, 18Watt said:

I have an entry for the Featherweight category.

Good work. I left the option for VTOL open on purpose. 

[Pds314]

34 minutes ago, ralanboyle said:

@Pds314 That is an interesting solution that does not appear to violate the spirit of the challenge. Good work. 

Thanks. I just didn't want to have a really generic looking craft for a coaxial design and I wanted the wings to be "in the middle."
Also worth mentioning. This driveshaft assembly and the struts aren't light.
That's 262 kg of extra stuff to move the prop a few meters forward from the engines.
Equivalent in weight to adding a Mk0 fuel tank 95% full of unusable fuel, an extra two large fan blades and then some, or alternatively, increasing the motor size on each engine from 25% to 46.5%.
Not a make or break difference by any stretch but definitely not equivalent to just offsetting the prop blades several meters.

Edited May 19, 2021 by Pds314

[ralanboyle]

1 minute ago, Pds314 said:

definitely not equivalent to just offsetting the prop blades several meters

Yes, this is the sort of thing I wanted to avoid. 

[18Watt]

Since I've entered a MKI and a MKII vessel, I thought I'd finish up with a MKIII entry.  This one holds 20 Kerbals, and yes I actually loaded 20 Kerbals into it.  They weighed 94kg each.  I think a basic Kerbal weighs ~45kg, but I forgot to un-equip their gear.  This entry weighed 87,002kg, and did the run in 48:10.

Screenshots:

Spoiler

Here's the weight with 4 Kerbals in the MKIII cockpit.  I figure there's one pilot, a navigator, a flight attendant, and of course a bartender.  Note I was able to put prop-spinners (small nose-cones) on the back engines too this time!  Not sure if they help or not, but they look cooler.

Here's the actual takeoff weight, with 20 Kerbals- 4 in the cockpit plus 16 in the passenger cabin.

Climbing over the mountains.  Although it would have slowed me down a little, I actually could have loaded enough fuel to land at Dessert and return to KSC without refueling.

This is about the best speed I could do, ~265m/s.  My hat is off to @Pds314, I'm not able to maintain the speeds he is able to get.

Just liked this shot..

Seatbelt sign is ON.  Should be ok though.  Plane handles fine in Pitch and Yaw, but I needed a LOT more ailerons, it is very sluggish in roll control.

Well, I got close to the runway anyways.  I think my wheels were briefly in contact with the pavement at one point, but it didn't last long..

 

[ralanboyle]

1 hour ago, 18Watt said:

This entry weighed 87,002kg, and did the run in 48:10

wow

[Pds314]

2 hours ago, 18Watt said:

Since I've entered a MKI and a MKII vessel, I thought I'd finish up with a MKIII entry.  This one holds 20 Kerbals, and yes I actually loaded 20 Kerbals into it.  They weighed 94kg each.  I think a basic Kerbal weighs ~45kg, but I forgot to un-equip their gear.  This entry weighed 87,002kg, and did the run in 48:10.

Screenshots:

  Hide contents

Here's the weight with 4 Kerbals in the MKIII cockpit.  I figure there's one pilot, a navigator, a flight attendant, and of course a bartender.  Note I was able to put prop-spinners (small nose-cones) on the back engines too this time!  Not sure if they help or not, but they look cooler.

Here's the actual takeoff weight, with 20 Kerbals- 4 in the cockpit plus 16 in the passenger cabin.

Climbing over the mountains.  Although it would have slowed me down a little, I actually could have loaded enough fuel to land at Dessert and return to KSC without refueling.

This is about the best speed I could do, ~265m/s.  My hat is off to @Pds314, I'm not able to maintain the speeds he is able to get.

Just liked this shot..

Seatbelt sign is ON.  Should be ok though.  Plane handles fine in Pitch and Yaw, but I needed a LOT more ailerons, it is very sluggish in roll control.

Well, I got close to the runway anyways.  I think my wheels were briefly in contact with the pavement at one point, but it didn't last long..

 

One reason why it's hard for you to reach 285+ m/s is you're using prop blades while I'm using fan blades that are meant to break mach somewhat. I know with electric propulsion you can actually get 300 m/s with those blades (I got 301 using a pretty crazy vehicle awhile back) but it actually requires you to decrease the RPM significantly and exorbitant power expenditure and torque. The fan blades are much better at high mach. And IMO just much more forgiving in general. I'm not having to go past 50 degrees of prop pitch to get these results.

Edited May 20, 2021 by Pds314

[18Watt]

16 hours ago, Pds314 said:

One reason why it's hard for you to reach 285+ m/s is you're using prop blades while I'm using fan blades that are meant to break mach somewhat.

Oh my goodness!!!  Thank you!!!

To try that out, I took the MKI plane I used earlier in this thread, and swapped the propeller blades for the large fan blades.  I made no other changes at all.  I was easily able to get 315m/s.  Like you, I found ~50 degrees blade angle to work well.  However, I played around a tad more---

And was able to go supersonic (Mach 1.005) at 4km altitude in level flight, with a blade pitch of ~60-62 degrees.  That was in the 330m/s+ range.  I got a huge burst of thrust about the time my engine RPM dropped to ~320.  That is a bit touchy though, I have a tendency to want to tweak things to go just a little faster.  As soon as I allowed the RPMs to get out of the 'happy zone' my speed dropped rapidly back below 300m/s.

Thank you again @Pds314!  Also, I'm familiar with the thread you mentioned, I thought it was crazy how fast you guys were.  Not sure if that was an electric-only challenge or not, but again I just hit 330m/s+ with the MKI plane pictured earlier in this thread.  That's stock KSP, with no part clipping or offsetting tricks at all.  I used 6 large fan blades on both engines (front and back).

[ralanboyle]

@18Watt, sounds like it’s time for you to redo some runs with faster times...

[18Watt]

6 minutes ago, ralanboyle said:

@18Watt, sounds like it’s time for you to redo some runs with faster times...

I was just trying a run in my MKI plane, just to see...  It didn't have enough fuel to maintain that speed.  But I think I can correct that problem. 

[18Watt]

Yep, I have another entry, this time for the 'Welterweight' category.  Weight: 13,099kg, time: 38:56.  Many thanks to @Pds314 for the suggestion on prop blade selection.  I had run into a brick wall trying to go faster than 260m/s, your suggestion really opened my eyes!

This vessel is similar to my previous MKI entry.  I swapped the propeller blades for fan blades, and added another fuel tank.  Also added landing gear.  So this entry is heavier than my previous one, qualifying for the 'Welterweight' category.

Screenshots:

Spoiler

Just after clearing the mountains west of KSC.  I did NOT maintain this speed for the whole run, the fuel burn is a little higher than I would like.  But I wanted to see how fast it would go.  Sure enough it's still supersonic, even with the addition of landing gear.

Here's another shot supersonic, with a crazy high fuel burn.

Cockpit view.  I spent about 2/3 of the flight between 315-320 m/s.  It's still really fast, but my fuel burn is a LOT less.

At 315-320m/s, my fuel burn was ~0.41-0.44.  At 330m/s+ the burn jumped to 0.57.  So there was a big penalty over Mach 1.00.  But a Mach 0.99 the burn was much lower.

Mach 1.020 was about my best speed in level flight.  Here, I've realized that I am indeed going to have enough fuel to reach Dessert airfield, so I'm going fast.

Yep, definitely enough fuel to make it.  No backing off the power now.

I broke a few blades on the landing, but it wasn't as bad as it looks.  I just didn't give myself enough clearance with the landing gear.  It looked good on paper, but I forgot the gear compresses a little during a landing, and managed to ding the front AND rear prop blades.  Kept it on the runway this time though..

@ralanboyle, I realized that I forgot to take a photo in the SPH showing my mass.  I assure you it was 13,099kg, but I'll try to post a photo later, gotta run right now.

Edit, here's the image I forgot to post..

Spoiler

SPH

 

Edited May 21, 2021 by 18Watt
Added image link.

[ralanboyle]

@18Watt I believe you.

[Pds314]

8 hours ago, 18Watt said:

Yep, I have another entry, this time for the 'Welterweight' category.  Weight: 13,099kg, time: 38:56.  Many thanks to @Pds314 for the suggestion on prop blade selection.  I had run into a brick wall trying to go faster than 260m/s, your suggestion really opened my eyes!

This vessel is similar to my previous MKI entry.  I swapped the propeller blades for fan blades, and added another fuel tank.  Also added landing gear.  So this entry is heavier than my previous one, qualifying for the 'Welterweight' category.

Screenshots:

  Hide contents

Just after clearing the mountains west of KSC.  I did NOT maintain this speed for the whole run, the fuel burn is a little higher than I would like.  But I wanted to see how fast it would go.  Sure enough it's still supersonic, even with the addition of landing gear.

Here's another shot supersonic, with a crazy high fuel burn.

Cockpit view.  I spent about 2/3 of the flight between 315-320 m/s.  It's still really fast, but my fuel burn is a LOT less.

At 315-320m/s, my fuel burn was ~0.41-0.44.  At 330m/s+ the burn jumped to 0.57.  So there was a big penalty over Mach 1.00.  But a Mach 0.99 the burn was much lower.

Mach 1.020 was about my best speed in level flight.  Here, I've realized that I am indeed going to have enough fuel to reach Dessert airfield, so I'm going fast.

Yep, definitely enough fuel to make it.  No backing off the power now.

I broke a few blades on the landing, but it wasn't as bad as it looks.  I just didn't give myself enough clearance with the landing gear.  It looked good on paper, but I forgot the gear compresses a little during a landing, and managed to ding the front AND rear prop blades.  Kept it on the runway this time though..

@ralanboyle, I realized that I forgot to take a photo in the SPH showing my mass.  I assure you it was 13,099kg, but I'll try to post a photo later, gotta run right now.

Wow. Broke my best time by 5.5 minutes and also the sound barrier and both props xD

[OHara]

I can't think of any way to do better, but I plotted the lift/drag curves from the configuration files to help understand what is going on around the sound barrier.

This challenge excludes non-Breaking-Ground control surfaces as propeller blades, because those cannot be node-attached; I included their lift/drag only for comparison.   

The Breaking Ground propellers have lift drop to zero as their speed through the air passes Mach-1, the fan blades working a bit faster.

And, for their speed through the air, KSP uses the speed of the purple markers at or beyond their tips, that we see with the F12 visualisation.

At maximum rotational speed, and a fan blade with purple markers about 5m from the axle, the tips move 250m/s.   Then if the plane is moving forward 250m/s, the purple markers are moving through the air at 350m/s already, and blades at 45° would slice through the air with zero lift.   The angles in the plots above are relative to the airflow across the purple-markers, so deployment of 50° would give 5° angle of attack.

Edited May 21, 2021 by OHara

[18Watt]

This is addictive.  Here's an entry for the 'Middleweight' category.  Weight: 16,159kg, time 38:33.  I added yet another fuel tank, now it has enough fuel to run full blast the whole way.  I also added a little more wing, seems to go faster with a lot of wing.  Finally, I also set an action group for RPM limits on the engines.  Before I was controlling RPM either with blade pitch, or just setting the limit in the SPH.  I was able to have a little better control by having an action group for RPM limit.

Screenshots:

Spoiler

SPH.  One huge problem with a long fuselage with 4 tanks is the COM (CG) shifts a lot during flight.  This worked great for most of the flight, but eventually the COM shifted forward.  Normally that's easy to fix by moving fuel.  However, there is a lot going on already at Mach 1.0+.  Controlling throttle, blade pitch, RPM, and trying to keep the thing pointed the right direction.  Also, my game wouldn't let me transfer fuel while the Blade and Engine windows were locked open.  So transferring fuel was awkward.

On runway.  It's now capable of a horizontal takeoff, but I actually like doing the vertical takeoffs.  That way I don't waste precious seconds going the wrong direction..

I didn't really try to reach supersonic in the climb, but got fairly fast quickly.

I hit Mach 1.0+ shortly after clearing the mountains.  Since I had plenty of fuel, I never reduced power, and maintained that speed for almost the entire flight.

I was never able to go faster than ~329m/s.  An earlier version with no landing gear and less fuel was able to get a little faster, but didn't have enough fuel to reach Dessert at those speeds.

Didn't break anything this time, except the time record..  38:33.  I gave myself a little more landing gear clearance, but still need to land fairly flat to protect the rear prop.

Here's another attempt which wasn't quite as good..

Spoiler

@ralanboyle, you don't need to count this one, the one I listed above will be my 'Middleweight' entry.

I tried using the big wings which hold fuel, in order to get more fuel.  It worked well, but the big fat wings are a little more draggy, I think.  I wasn't able to reach Mach 1.0 with this design, although it actually did very well.

This was about as fast as I could get it.  A little higher up I was able to get ~322m/s, but never broke Mach 1.0.  This design did handle extremely well though, easy to fly.

A few seconds slower than my actual Middleweight entry in the above spoiler window.  This one also needs to land at a fairly flat attitude to protect the rear prop.