KerikBalm

Compound/hybrid rotorcraft

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Posted (edited)

So I'm still playing around with 1.7.3 and the props, but I want to send prop powered craft to Duna, Eve and my mod world Rald (all rescaled 3x)

With Eve, I'm not even going to try to make a vehicle capable of orbit. 3x Eve, forget about it.

I'll stick with this and be done:

Spoiler

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I was originally planning on a separate dropship for Rald and Duna (ideally, 1 craft to serve both worlds), then a rotorcraft for moving around the surface, but the dV requirements of 3x result in rather heavy designs, and both worlds have thin air. The result is that horizontal landings with wings are nearly out of the question. They need to be VTOLs. Duna VTOLs use a lot of dV for the VTOL phase, and this makes a payload carrying 3x VTOL SSTO rather hard, even before trying to have the same design work on Duna or Rald (and Rald will require airbreathers, but less total vacuum dV).I thought, why not put rockets/jets (I'm thinking rapiers) on the back of my tiltable rotors, and combine the craft.

So my main question:

Has anyone made a SSTO tilt rotor that carries a decent payload (1 full jumbo 64 tank)?

I ask because 3x Rald has a similar dV requirement to 1x Kerbin, but its thinner air makes it harder to VTOL despite the 0.5 Gs.

I ran into the problem of tilt rotors using the prop blades having insufficient lifting power when the added weight of fuel for reaching orbit is added (without getting rid of the payload).

Using helo blades gave a lot more lifting power (and reduced part count), but they can't change their pitch enough to go edge on to theairflow, as required for high speed flight to orbit.

I'm thus now considering a compound helicopter with a large rotor blade that stays horizontal for vertical flight, props (tilt props?) for horizontal electric propulsion, and rapiers for jet and rocket thrust to reach orbit on Rald or Duna...

Yet this seems too complicated. I've seen @Brikoleur make a duna copter, but I fear a rapier assisted helicopter will be impractically slow without use of the rapiers (hence the desire for props for horizontal propulsion).

Does anyone have any designs for a good rotor based VTOL with good lifting power (so it can lift fuel and engines to get it to orbit, in addition to payload), and a good top speed, that can be put in a configuration where the rotors don't cause problems when travelling >1000 m/s in the atmosphere?

Edited by KerikBalm

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Posted (edited)

Rapiers are heavy and overkill. You only need them to get off Kerbin, or use some other way to boost into orbit. 

I would make a compound copter for that purpose, but not with jets: I'd use a pair of props for forward thrust as well, now that small-diameter props are feasible. That would certainly work on both Eve and Duna and you can run them off solar power or fuel cells.

Inspiration: 

_eurocopter_x3_in_flight.jpg

Edits:

(1) For the boost to orbit, just feather the prob blades and set the main rotor collective to zero.

(2) For Duna, use Nervs instead of props for forward speed. If you really need heavy lift capability then you might want to use a higher TWR rocket motor for that purpose instead. But Rapiers are no good because of their lousy closed-cycle Isp.

Edited by Brikoleur

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2 hours ago, Brikoleur said:

(2) For Duna, use Nervs instead of props for forward speed. If you really need heavy lift capability then you might want to use a higher TWR rocket motor for that purpose instead. But Rapiers are no good because of their lousy closed-cycle Isp.

Yea, but since Rald and Duna are neighbors, I'm wondering if I can make a practical design that will serve both locations. So I need closed cycle thrust, and I need some airbreathers... I thought maybe Rapiers might be the best option.

If I don't use rapiers, then the Rald ascent needs more closed cycle dV (Rald's orbital velocity in low orbital at 3x is about 2,450 m/s, hence the Rapiers)

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I'm not familiar with Rald. If airbreathers make sense there then yes Rapiers would be a good choice. Your required lift capacity is pretty big though. 

I'm afraid I can't really help much with a 3x system as I've never played in one. Seat of the pants it feels like an SSTO helicopter might not make much sense; you are hauling up a fair bit of dry mass with the rotors. Perhaps an STOL spaceplane with tilt jets would work better?

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5 hours ago, Brikoleur said:

Rapiers are heavy and overkill. You only need them to get off Kerbin, or use some other way to boost into orbit. 

I would make a compound copter for that purpose, but not with jets: I'd use a pair of props for forward thrust as well, now that small-diameter props are feasible. That would certainly work on both Eve and Duna and you can run them off solar power or fuel cells.

Inspiration: 

_eurocopter_x3_in_flight.jpg

Edits:

(1) For the boost to orbit, just feather the prob blades and set the main rotor collective to zero.

(2) For Duna, use Nervs instead of props for forward speed. If you really need heavy lift capability then you might want to use a higher TWR rocket motor for that purpose instead. But Rapiers are no good because of their lousy closed-cycle Isp.

Cool craft design, no doubt... I might suggest a pusher prop on the tail though to decrease the craft width so it might be a bit more convenient for storage and space delivery.  I do also like those coaxial rotor designs.

the-us-military-could-soon-be-flying-one

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2 hours ago, XLjedi said:

Cool craft design, no doubt... I might suggest a pusher prop on the tail though to decrease the craft width so it might be a bit more convenient for storage and space delivery.  I do also like those coaxial rotor designs.

Oh space is no concern, this thing is to carry cargo around the surface (at least the rotorcraft), and to and from orbit. It's the cargo carrier. I have ways of getting oversize payloads to orbit, worry not :p

7 hours ago, Brikoleur said:

I would make a compound copter for that purpose, but not with jets: I'd use a pair of props for forward thrust as well, now that small-diameter props are feasible. Tsed-cycle Isp.

Not to be mean, but that's what I said in the first post: 

"I'm thus now considering a compound helicopter with a large rotor blade that stays horizontal for vertical flight, props (tilt props?) for horizontal electric propulsion,"

What I envisioned to start with was a tilt rotor craft for moving stuff around the surface, but not too and from orbit. As it seems I need to make my surface to orbit shuttles VTOL, I thought I could combine them. If you see my tilt rotor example above, the bottom of the tilting rotors is just a nose cone, I could easily put rocket or jet engines there to help achieve orbit.

2 hours ago, Brikoleur said:

I'm not familiar with Rald. If airbreathers make sense there then yes Rapiers would be a good choice. Your required lift capacity is pretty big though. 

Warning, tooting my own horn and pic heavy in the spoiler,  its images of rald, from various versions of varying size, atmo thickness, atmo color, and gravity:

Spoiler

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So my most recent version of Rald:

1) Goes where Duna is, Duna becomes a moon of Rald (well, its more like a binary planet system). Ike also becomes a moon of rald, but much farther out (more like minmus to kerbin)

2) Is based on a mars heightmap, but made proportionately larger, given an ocean, and green color (life) at low elevations near the ocean

3) Stats (for 1x): 

Radius: 450 km (3/4 of kerbin, just over 1.4x Duna's radius)

Sea level Gravity: 0.53 G

Rotation period: 23.4 hours (mutual tidal locking with Duna)

Sea level pressure: 0.20 atmospheres.

Atmosphere MW: 33.6 (not the 43 of a mainly CO2 atmosphere like Eve or Duna, not the 28 of a mainly N2 atmosphere like Kerbin or Laythe, but in between)

Oxygen: Yes

Quote

I'm afraid I can't really help much with a 3x system as I've never played in one. Seat of the pants it feels like an SSTO helicopter might not make much sense; you are hauling up a fair bit of dry mass with the rotors. Perhaps an STOL spaceplane with tilt jets would work better?

Well, that was my original plan, but I started considering using rotors to accomplish the STOL part instead of rocket/jet thrust, at which point I wondered if a single design could serve instead of 2.

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Bah, I'm giving up.

The demands of orbit on 3x Rald are too high to have an all-in-one design for a surface to orbit shuttle, and a surface to surface transporter, for Duna AND Rald.

I needed 16 large heli blades just to lift the craft with fuel but no payload, then all those blades caused problems with center of drag and gave it a 10 degree up AoA at high speed and stopped it from breaking mach 1.

I'm going back to a tilt jet/rocket engine design for a surface-orbit shuttle. One design for Duna, 1 for Rald.

I think the relative gravity and air thicknesses do mean that I could have 1 tilt-rotor design for surface-surface payload movement on Rald and Duna, but 2 vessels will need to be sent anyway as they'll be stuck on whatever planet they land on. Plus I might as well use an airbreathing design on Rald for simplicity since I'll be setting up ISRU anyway.

My tilt prop design worked on Rald, but only with no payload and nearly no fuel for the fuel cells (but could be solar powered in horizontal flight), but I really need large rotors for lifting any kind of decent payload.

Spoiler

This is a Nope on Rald unless that adaptor tank is empty, and there's no Jumbo 64 in that cargobay:

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horizontal flight like this is still fine though:

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I have a feeling this would do much better, particularly with 4 blades insead of 2 per rotor:

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I'm still going to compare a compound design to a tilt rotor design.

I think the compound design might be easier to get to orbit. A tilt rotor with heli blades can't feather the blades enough to have the nacelles horizontal, and keeping them vertical adds drag from the nacelles.

In with nacelles vertical, they act as unwanted wings, but they will on a compound design too. I may have to piggy back it on my SSTO (which uses nukes), instead of sticking it on my 2 recoverable 2 stage design (No nukes, but the same or better payload fraction, fewer parts, faster time to orbit) which puts payload at the front of the 2nd stage rocket, and shifts the carrier plane forward or back along the 2nd stage rocket to adjust CoM and CoL. Overall its less tolerant of a payload with a lot of lifting surfaces. Maybe I can make a modified 2nd stage rocket that has the payload at the back.

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Here's a pure-electric Duna flyer.  When empty of fuel, it can fly indefinitely on solar power, and can do a vertical lift-off.

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More photos in spoiler.

Spoiler

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Haven't yet tried landing it with a full fuel load to see if it can get back to orbit.  I know it handles high-speed aero transit well without going kablooie. :)

 

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