What are the fastest speeds that can be reached by electric propeller craft?

[Guest]

Just wondering what the upper limit of speed is for an aircraft using only electric props

Edited January 24, 2020 by Guest

[XLjedi]

Without attempting some sort of airspeed record craft... 

I find the ducted fans produce best results and for a two engine commuter jet type design, I get far better performance from a pair of pusher-prop ducted fans than I do from a pair of similar sized juno engines.  Not to mention the craft can circle the globe 5x or more on a single fueling (infinite flight if 100% daylight).

For my stated dual-prop ducted fan commuter, sustained average cruising speed at 500m altitude (or below) is in the range of 290m/s in Kerbin atmosphere.  I don't bother to test or quote max speed in a dive as it serves no useful mission purpose.  Acceleration and low altitude performance is also far better than its juno-powered counterpart easily winning sprints to the Island Base and able to reach max speed within that relatively short distance.

[Guest]

agreed @XLjedi I'm finding ducted props way more impressive than Junos.

[Lt_Duckweed]

The fastest I have been able to get at sea level on Kerbin is 377m/s.

On Jool the same craft was able to get to around 800 m/s.

[XLjedi]

20 hours ago, Lt_Duckweed said:

The fastest I have been able to get at sea level on Kerbin is 377m/s.

On Jool the same craft was able to get to around 800 m/s.

Would you mind sharing: 

1. straight & level sustained flight or a max speed dive?
2. which engine/blade combination?
3. how many sets of these engine/blade combos?
4. weight of craft in tons?
5. are we talking stock aerodynamics?

I'm kinda interested in plotting results to see if I can discern anything from the data.

[Lt_Duckweed]

14 hours ago, XLjedi said:

Would you mind sharing: 

1. straight & level sustained flight or a max speed dive?
2. which engine/blade combination?
3. how many sets of these engine/blade combos?
4. weight of craft in tons?
5. are we talking stock aerodynamics?

I'm kinda interested in plotting results to see if I can discern anything from the data.

1. Level flight skimming the ocean.

2. 1 medium rotor powered by 8 rtgs, with 4 of the largest fan blades, with the blades offset towards the center of the rotor by I think 2 shift snaps.

3. 2 contra rotating.

4. About 4.5 tons.

5. Yeah stock.

 

Here's a pic of it: 

[XLjedi]

@Lt_Duckweed  Thanks, and the pic is a bonus!  

 I'm not sure what this means?   "1 medium rotor powered by 8 rtgs"

I was hoping a few more folks might post the same info so I can plot a weight to engine ratio or something...  I can't get any info on these things regarding TWR and it doesn't do me much good to try to plot a curve of my own craft because I haven't seen anything faster than mach 1.0.

My craft specs:

•  2x:  EM-32S Standard Rotor
•  Blades  8x:  R-12 Ducted Fan Blade  (8 per engine)
•  Weight:  6.75 tons

I may take it to a separate discussion thread...

Edited January 28, 2020 by XLjedi

[RizzoTheRat]

On ‎1‎/‎26‎/‎2020 at 10:11 PM, Lt_Duckweed said:

The fastest I have been able to get at sea level on Kerbin is 377m/s.

On Jool the same craft was able to get to around 800 m/s.

That's about Mach 1 at sea level isn't it?  I guess the physics doesn't model the blade aerodynamics   In real life the record is about Mach 0.8

[linuxgurugamer]

I think that Mach 1 on Kerbin is 343 m/sec

[XLjedi]

4 hours ago, RizzoTheRat said:

That's about Mach 1 at sea level isn't it?  I guess the physics doesn't model the blade aerodynamics   In real life the record is about Mach 0.8

Yes, but it also opens up the possibility for me to create an enclosed system of ducted fans and label the result "Lectric-Jet"

So let's just ignore that statement so as not to call down the Nerf-Mongers on another favorite craft design of mine.   

[Lt_Duckweed]

5 hours ago, XLjedi said:

@Lt_Duckweed  Thanks, and the pic is a bonus!  

 I'm not sure what this means?   "1 medium rotor powered by 8 rtgs"

Sorry, it's a EM-32 rotor.  And I'm providing the ec it needs using rtgs rather than batteries, fuel cells, or solar panels.

5 hours ago, RizzoTheRat said:

That's about Mach 1 at sea level isn't it?  I guess the physics doesn't model the blade aerodynamics   In real life the record is about Mach 0.8

Mach 1.062 to be exact!  Ducted fans actually can still provide thrust with blade tip speed exceeding Mach 1 thanks to the shroud.  But the effects of the shroud aren't simulated in ksp, it's just baked into the blade instead.

[RizzoTheRat]

50 minutes ago, Lt_Duckweed said:

Mach 1.062 to be exact!  Ducted fans actually can still provide thrust with blade tip speed exceeding Mach 1 thanks to the shroud.  But the effects of the shroud aren't simulated in ksp, it's just baked into the blade instead.

According to google the fastest prop is the TU-95 Bear, and thanks to it's supersonic blade tips it can be detected by underwater microphones designed to detect submarines

I guess supersonic tipped ducted fans would be a bit quieter but sure'y the shrouds would take a hell of a beating from the shocks?

[Lt_Duckweed]

Take a look at high bypass turbofans.  They are essentially ducted fans powered by a small jet engine.  It's not uncommon for them to have a blade tip speed eceeding 400m/s