Author Topic: The Reaction Engines Skylon Master Thread (2)  (Read 575935 times)

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #40 on: 01/14/2013 08:05 PM »
REL should use a biplane design for LAPCAT, would eliminate the sonic boom.

http://news.discovery.com/tech/biplane-could-go-supersonic-120320.htm

Great idea. Add another level of complexity to an already enormously complex project.

LAPCAT is more a concept. REL maintain hypersonic flight is much harder than SSTO. With orbital launch in 15 mins you're either in orbit, returning to the runway or in pieces over the ocean.

But note some of the REL team had Concorde involvement. It was designed to have good subsonic fuel economy and I'm not sure how much a problem boom will be at the operating altitudes of a hypersonic airliner.

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Offline flymetothemoon

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #41 on: 01/14/2013 08:34 PM »
LAPCAT is more a concept. REL maintain hypersonic flight is much harder than SSTO.

For clarification, I get the impression they say this because it is a endurance / materials issue. Unlike Skylon, the engine and airframe for a hypersonic aircraft would have to sustain high-MACH, in-atmosphere, very high-temperature flight for 5 hours per flight.

Unlike Skylon's minimum life expectancy of 200 cycles, a commercial hypersonic jetliner would probably also be expected to achieve tens of thousands of cycles to be cost effective.
« Last Edit: 01/14/2013 08:35 PM by flymetothemoon »

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #42 on: 01/14/2013 09:24 PM »
For clarification, I get the impression they say this because it is a endurance / materials issue. Unlike Skylon, the engine and airframe for a hypersonic aircraft would have to sustain high-MACH, in-atmosphere, very high-temperature flight for 5 hours per flight.

Unlike Skylon's minimum life expectancy of 200 cycles, a commercial hypersonic jetliner would probably also be expected to achieve tens of thousands of cycles to be cost effective.
Correct. While the continuous acceleration profile has some problems cruise does not its very short duration (mins not hours) gives you design options that are not feasible for longer flights.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Dalhousie

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #43 on: 01/14/2013 09:34 PM »
Christmas-New Year holiday!

You also need to factor in UK tech companies for doing stuff rather than talking about it.

I think REL's approach falls somewhere between Blue Origins ("A few months ago we did some stuff. It was cool. Here's a video") and say Xcorp. a bit more informative but still quite "discrete")

Their game plan for the 250m they were looking to raise was to design a sub scale ground test SABRE for full up testing of the engine system and the Nacelle Test Vehicle, a very sub scale Skylon shaped vehicle to refine the nacelle design, along with the full drawings of the full size SABRE4.

A lot of this stuff is not very "showy" until hardware gets completed. The upside is that a full SABRE will pull the airflow through the pre-cooler much better than the jet engine they have been using.

I think RE have hit the balance between endless hype (SpaceX) and stony silence (Blue Origin) about right.
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Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #44 on: 01/14/2013 10:57 PM »
I think RE have hit the balance between endless hype (SpaceX) and stony silence (Blue Origin) about right.
TBF Spacex updates can be quite informative to a point but it's quite clear you see only what they want you to see.

The REL stockholders photograph is still one of my favourites for corporate PR.  :)
I'm still not sure there entirely convinced they really need a website at all.  :)
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline grondilu

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #45 on: 01/16/2013 08:20 AM »
User 93143 posted this in the FalconR vs Skylon thread:

Or, better yet, use REL's numbers directly.

The C1 spreadsheet

I had a look at it and I have two questions:
* why does the speed decrease a bit in the last 30 seconds of the air-breathing phase? Is it because the engine is beginning to lack oxygen?
* there is a gap of about 400 m/s between the end of air-breathing and the beginning of rocket-mode.  Why?
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Offline 93143

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #46 on: 01/16/2013 08:30 AM »
The speed decrease seems to be related to the pull-up maneuver.  You'll note that at this point the climb angle and vehicle AoA start to increase dramatically.

The velocity difference is due to table organization.  U != Uabs; the difference is the Earth's equatorial speed.

Offline grondilu

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #47 on: 01/16/2013 08:33 AM »
The speed decrease seems to be related to the pull-up maneuver.  You'll note that at this point the climb angle and vehicle AoA start to increase dramatically.

The velocity difference is due to table organization.  U != Uabs; the difference is the Earth's equatorial speed.

Ok.  Makes sense.   Really cool data anyway.  Thanks.
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Offline 93143

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #48 on: 01/16/2013 08:40 AM »
You're welcome.  Since I've been citing it a bunch, I figured it was about time I posted it...

...looks like their new website has been updated.  The spreadsheet wasn't there immediately after the facelift, but it is now.  I guess I can go change that Wayback Machine link...

A clarification:  the velocity difference isn't exactly Earth's equatorial speed.  For one thing, the launch isn't on the equator; it seems to be from Kourou.  I still can't get the speed to match up; perhaps there's something I'm not thinking of...  Well, the difference is small.  It's probably nothing...
« Last Edit: 01/16/2013 09:09 AM by 93143 »

Offline grondilu

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #49 on: 01/16/2013 09:07 AM »
I have a probably silly question and I hesitated a bit before asking it, but what the heck...

It's about the under-carriage:  how much will it weight and does Skylon really need one?

I mean, it's not too difficult to imagine a system for take-off and landing that could be done without it.  I can't help thinking that it's a bit of a shame that Skylon has to bring to orbit something so heavy which is useful only for a task as trivial as touching the ground.
« Last Edit: 01/16/2013 09:08 AM by grondilu »
Space is pretty much literally an astronomically-high hanging fruit.

Offline 93143

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #50 on: 01/16/2013 09:21 AM »
The undercarriage is expected to be about 1.5% of the total mass, IIRC - so about 4 tonnes for C1, and maybe 5 for D1.  This is similar to the mass fraction achieved by the B-58 back in the day.  They manage this in part by using water-cooled brakes to deal with fully-loaded runway aborts, and dumping the required 1200 kg or so of water after a successful takeoff.  (This also means that if they have to abort after a successful takeoff, they need to dump the propellant before attempting to land.)

Skylon's predecessor HOTOL had a rocket trolley.  It was a huge pain, so REL got rid of it.
« Last Edit: 01/16/2013 09:31 AM by 93143 »

Offline grondilu

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #51 on: 01/16/2013 09:35 AM »
The undercarriage is expected to be about 1.5% of the total mass, IIRC - so about 4 tonnes for C1, and maybe 5 for D1.

Oh, that's much less than I thought.  Well,  it seems totally fine, then.

Quote
Skylon's predecessor HOTOL had a rocket trolley.  It was a huge pain, so REL got rid of it.

Indeed I was thinking about something like that and now that you mention it, I remember having heard that indeed HOTOL was supposed to use this.
Space is pretty much literally an astronomically-high hanging fruit.

Offline john smith 19

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #52 on: 01/16/2013 11:19 AM »
The undercarriage is expected to be about 1.5% of the total mass, IIRC - so about 4 tonnes for C1, and maybe 5 for D1.
Oh, that's much less than I thought.  Well,  it seems totally fine, then.

The usual rule of thumb for aircraft undercarriages is 3-3.5% of gross landing weight.
The B58 demonstrated that you can do much better if its a priority. Apparently water cooled brakes are a feature of heavy truck racing  :o so there is experience in using it.

For extra sneakiness you would inject the water into the nacelle exhausts  :) Water injection is an old jet engine trick from the 1950's to increase takeoff thrust. IIRC It was also used in the Ariane 4 turbopumps to get more flow in the drive gases at a slightly lower temperature.

However while giving a short thrust boost at a point where you want it the complexity would probably outweigh the benefits.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline simonbp

Re: The Reaction Engines Skylon Master Thread (2)
« Reply #53 on: 01/16/2013 05:21 PM »
It's about the under-carriage:  how much will it weight and does Skylon really need one?

The loads are pretty significant; as measured for the closest flown aircraft:

www.nasa.gov/centers/dryden/pdf/87742main_H-471.pdf

Offline grondilu

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #54 on: 01/16/2013 11:21 PM »
It's about the under-carriage:  how much will it weight and does Skylon really need one?

The loads are pretty significant; as measured for the closest flown aircraft:

www.nasa.gov/centers/dryden/pdf/87742main_H-471.pdf

From this document about the landing loads of the X-70-1, I can read in the first paragraph:
Landing weights vary from 419,000 pounds (190,400 kilograms) to 274,000 pounds (124,000 kilograms).

Skylon is not supposed to weigh more than 55,000 kilograms at landing IIRC.  So I'm not sure the comparison with X-70-1 is of much use.
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Offline Lar

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #55 on: 01/17/2013 12:50 AM »
The loads are pretty significant; as measured for the closest flown aircraft:

www.nasa.gov/centers/dryden/pdf/87742main_H-471.pdf

From this document about the landing loads of the X-70-1, I can read in the first paragraph:
Landing weights vary from 419,000 pounds (190,400 kilograms) to 274,000 pounds (124,000 kilograms).

Skylon is not supposed to weigh more than 55,000 kilograms at landing IIRC.  So I'm not sure the comparison with X-70-1 is of much use.

Perhaps proportionality could be used to draw some useful conclusions? I would expect the accelerations to be about the same, but the forces to scale linearly, and the predicted minimum size for struts in gear and the like to also scale linearly.
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Offline 93143

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #56 on: 01/17/2013 01:28 AM »
Skylon's landing gear is sized for a takeoff abort.  Full tanks.  The water cooling saves something like four tonnes of heat sink mass.

Offline grondilu

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #57 on: 01/17/2013 01:50 AM »
Perhaps proportionality could be used to draw some useful conclusions? I would expect the accelerations to be about the same, but the forces to scale linearly, and the predicted minimum size for struts in gear and the like to also scale linearly.

I'm no expert but from what I know a landing gear is basically a piston.  And I'm pretty sure the mechanical behavior of a piston does not scale linearly (very few things do anyway).
« Last Edit: 01/17/2013 01:54 AM by grondilu »
Space is pretty much literally an astronomically-high hanging fruit.

Offline veedriver22

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #58 on: 01/17/2013 05:03 PM »
 The cool thing about water cooling the brakes, is once you are at a reasonable altitude you can dump a portion of that water.

Offline Rugoz

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Re: The Reaction Engines Skylon Master Thread (2)
« Reply #59 on: 01/17/2013 11:24 PM »
Quote from: 93143
Skylon's landing gear is sized for a takeoff abort.  Full tanks.  The water cooling saves something like four tonnes of heat sink mass.

They could also start on passive sleds with brakes. You'll need rails, sure, but with stronger brakes you could probably make them shorter than a strengthened runway. Maybe too complicated but if you save a ton or so...
« Last Edit: 01/17/2013 11:27 PM by Rugoz »

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