The semi old school turboprop challenge.

[Flying dutchman]

Long before the breaking ground expansion kerbalkind was already flying turboprop driven aircraft. These unwieldy machines with their homemade bearings managed to take flight despite all odds.

 

Now i would like a make a new challenge. Since we have bearings in the breaking ground expansion that part will be taken care of. However you are not out of the woods just yet. Why you may ask? 

 

Because you are only allowed to use the motor as a bearing. All the rotational power for the props must come from jet engines. Oh and i forgot the mention that you can use exactly NONE of the BG propellors. That means you can only use wings or control surfaces as propellors.

 

 

The challenge is quite simple:

 

Build your machine that must somewhat resemble an airplane. Take off from the ksc runway. Do a full lap all the way around the island where the island runway is and land back at the ksc runway.

 

Scoring will be:

time - up to 30 seconds in style points.

 

 

Edited March 15, 2020 by Flying dutchman

[Flying dutchman]

Here is my entry:

 

 

24.29 i'll give myself 10 style points so that would be 24.19

 

[Pds314]

Oh. You're on.

 

And I'm not even sure I'm gonna use the breaking ground bearings.

 

Can we add a rule that the jets must be used as blowers, not bladetip thrusters?

[Pds314]

Oof. I forgot how to fly my own plane. Also maybe I shouldn't have started with one that has such anemic performance.

[Pds314]

Squad, what on Kerbin did you do to physicsless parts....
 

What on Kerbin... well... i guess I need to design new engines. The ones from 1.1 don't work so well...

Edited March 15, 2020 by Pds314

[Pds314]

Do I even want to know....

Ok, well, everything about the engine is truly archaic, even for this particular engine from 1.1 era, as it's about 100 parts more complex and 20 tonnes heavier than the final iteration of the same engine, but... it does technically turn...




*Screams internally at bearing design* Alright I should have an entry by the end of 2020.... I don't even remember why I did everything here... why are the prop and turbine blades like a meter recessed behind where they are in flight????

 

Edited March 15, 2020 by Pds314

[Pds314]

Yeah.... I need to find a newer version of the engine/plane with less parts and more reliability... Watching 701 parts explode on takeoff is not the best thing ever...

Edited March 16, 2020 by Pds314

[Flying dutchman]

@Pds314 good luck.  

did you know that kerbals make bearings out of explodium?

 

Maybe you can see why i permitted the bg rotor as a bearing? It makes the challenge a bit easier

[Flying dutchman]

 

A second set of jet engines and the speed has increased from 55 to 75 m/s!

this makes for a time of 18 minutes and 38 seconds.

[Flying dutchman]

i've made some modifications and it is now able to reach 90m/s in level flight But sadly the propellor is not realistic anymore so i will give myself a penaltie of 5 style points when i make my run later this day.

[Pds314]

Well the BEARING didn't break...

The turbine melted and the prop has permanently become an eldritch abomination (which didn't used to happen), but hey, the bearing works...

Edited March 22, 2020 by Pds314

[Pds314]

They must have made the thermal issues MUCH more problematic. I can just barely sustain a ratio of 1:1 engines to atmofluids and for solar panels as bearings, 1:2 solar panels is not sustainable. Some of my old engines had like 5:1 atmofluids or 1:1 solar panels.

Still, for an engine just a bit over Mk2 with 16 engines, static thrust of 275 kN at 457 RPM is not that bad. I doubt it will get that much when moving but it will probably get at least useful amounts when moving.

Edited March 22, 2020 by Pds314

[Pds314]

Testing engine statically: absolutely no problems.

Testing engine on the aircraft: this

[Pds314]

Well, it isn't the fastest thing ever, but I do have a functioning engine now with an all-stock bearing. I think the big problem is that it just has an absurd amount of drag.

Edited March 22, 2020 by Pds314

[Flying dutchman]

4 hours ago, Pds314 said:

Well, it isn't the fastest thing ever, but I do have a functioning engine now with an all-stock bearing. I think the big problem is that it just has an absurd amount of drag.

I'm impressed!

[Pds314]

Alright. It isn't gonna set any straight line speed records or anything, and I did come a bit close for comfort on fuel reserves so I slowed down a bit at the end, but I did a lap.

Time: 16:30

Engine start: Decoupler is slightly explosive.


Revving up:


Take off:


Climbing off the runway:


We start heading for the island:


Engine performance: Probably deserves a bigger prop.


Lift and drag. Note the insane drag from the engine pods:


Approaching the island:


A nice slow banked turn. I am not gonna risk breaking an engine.


We go low around the edges of the island:


Time to head back home:


Being at low fuel, we reduce blade pitch so we can get almost the speed we were doing before on 65% throttle.


Final approach. Because this thing has a lot of drag, I keep the engines on and the prop pitch at useful numbers for now.


Prop pitch to max to reduce the risk of damage on landing and to reduce speed.


Gears are down.


Touchdown and throttle off!


Slowing down...


And finally we come to a complete stop at 16:30. With 7% fuel to spare, and some oxidizer in the right engine that probably doesn't need to be there.

Possibly worth noting: my prop efficiency is rather low. At 90 m/s and 84 kN, that's only 7.56 MW of thrust per engine.

Compare:
the blower torque: ~570 kN*m
Times the rads/s: ~45.5.
= 25.9 MW of engine power per engine.

So my prop is only translating about 29% of the turboshaft power into thrust. Probably because it's too small and has to operate at an excessive angle of attack to avoid throwing away it energy into overrevving.

Compare: BG cheatprops on motors, which can have an efficiency of >1000%.

Edited March 23, 2020 by Pds314

[Pds314]

@Azimech
@Gman_builder

Perhaps a turboshaft race is in order? Do any of your old ~200 m/s+ craft work?

Edited March 23, 2020 by Pds314