Author Topic: The Reaction Engines Skylon/SABRE Master Thread (6) (Read 448506 times)

john smith 19 · « **Reply #140 on:** 09/14/2016 10:34 am »

Quote from: 93143 on 09/13/2016 10:17 pm

If one assumes that (a) Skylon D1 goes through exactly the same delta-V before transition as C1, and (b) my calculation of said delta-V (3657 m/s) from the C1 spreadsheet is correct, SABRE 4's average Isp can be calculated from the data in the NISSIG presentation as approximately 4889 s. The value I got for SABRE 2/3 was 2274 s. This yields an equivalence ratio for SABRE 4 of about 1.25.

Not bad... of course that's not constant during the trajectory...

With those caveats that means you can safely increase the mass growth margins on the designs. Exciting times.

john smith 19 · « **Reply #141 on:** 09/16/2016 09:30 pm »

Does anyone have any further information on the SABRE presentation the USAFRL gave last week?

Matthew Ak43 · « **Reply #142 on:** 09/16/2016 09:32 pm »

Conclusion of AFRL paper:
'This paper presented TSTO vehicle designs based on a first stage powered by REL’s SABRE. The first design
presented is a partially reusable vehicle sized for 5,000 lbm to orbit. The second is a scaled up version with an reusable upper stage for 20,000 lbm to orbit. These designs were developed as part of a CRADA between AFRL and REL to understand the scale of TSTO launch systems based on the SABRE. REL's vehicle design effort had originally focused on the Skylon SSTO vehicle concept. The present study sized two TSTO vehicle point designs to evaluate what a potentially lower risk approach to a SABRE-based space access system could be.
These designs have shown that if the SABRE designs performs as predicted, TSTO vehicle options of reasonable
size and scale could be fielded. For the partially reusable stage, the payload fraction is about 1.5% which is typical of vertical launch systems. The PMF of the booster stage is very low compared to traditional launch vehicles but that will allow pleny of flexibility in designing the vehicle. It also is shorter in length then the XB-70 (188ft long) and has a lower takeoff weight as the Concorde (412klbm). The flight loads (dynamic pressure and aeroheating) are in the range of near-term technology. Of course the SABRE is a unqiue cycle that will require significant development to mature. The conformal LH2 tanks used in the nose and aft body sections of the booster are also in need of technology maturation and represent a risk item. This type of tank construction has not been worked significantly since the failed X-33 program. The fully reusable system is still shorter than the Concorde and has a gross weight less on the order of a 747 or A380.
While the options in the paper show potential designs for how the SABRE could be used in a TSTO configuration,
an apples-to-apples comparison to other TSTO concepts is needed. This includes all rocket concepts, turbine based
and rocket based scramjet concepts, and other combined cycle engines. Another interesting trade to consider is using the SABRE cycle with methane or other high endothermic hydrocarbon fuel. For a TSTO system, these fuels could provide a smaller system in physical size and lower empty weight than LH2. These fuels could also simplify ground operations. This however would require some changes to the SABRE thermodynamic cycle that need to be modeled and verified.'

Matthew Ak43 · « **Reply #143 on:** 09/16/2016 09:41 pm »

Quote from: john smith 19 on 09/16/2016 09:30 pm

Does anyone have any further information on the SABRE presentation the USAFRL gave last week?

Of the two Sabre vehicles that the AFRL proposed. I found the reusable first stage/ expendable upper stage quite interesting. The expendable stage is in a compartment at the front of the vehicle, and is released from the base of the craft. I agree with ARFL that it is a good route to develop this less ambitious craft to start with, which in itself would be a game changer.

Unfortunately, according to Jeff Faust, the AIAA talk was not filmed so we are unlikely to see it on YouTube. There was no indication on what AFRL's plans are, if they are going to proceed with either vehicle. I guess they are sensibly waiting for the engine prototype, which REL and BAE say will be around 2020.

t43562 · « **Reply #144 on:** 09/17/2016 08:09 am »

(Thanks Matthew!)

Star One · « **Reply #145 on:** 09/17/2016 08:24 am »

Is there any particular reason that design has more than passing resemblance to the SR-71.

By the way can this paper be found online anywhere?

Matthew Ak43 · « **Reply #146 on:** 09/17/2016 10:32 am »

On the AIAA website. But you have to pay $25, for a 15 page PDF.

Star One · « **Reply #147 on:** 09/17/2016 12:03 pm »

Quote from: Matthew Ak43 on 09/17/2016 10:32 am

On the AIAA website. But you have to pay $25, for a 15 page PDF.

Thank you. Be interesting to see if it will accept out of US payment.

john smith 19 · « **Reply #148 on:** 09/17/2016 12:27 pm »

Quote from: Matthew Ak43 on 09/16/2016 09:41 pm

Quote from: john smith 19 on 09/16/2016 09:30 pm
Does anyone have any further information on the SABRE presentation the USAFRL gave last week?

Of the two Sabre vehicles that the AFRL proposed. I found the reusable first stage/ expendable upper stage quite interesting. The expendable stage is in a compartment at the front of the vehicle, and is released from the base of the craft. I agree with ARFL that it is a good route to develop this less ambitious craft to start with, which in itself would be a game changer.

Unfortunately, according to Jeff Faust, the AIAA talk was not filmed so we are unlikely to see it on YouTube. There was no indication on what AFRL's plans are, if they are going to proceed with either vehicle. I guess they are sensibly waiting for the engine prototype, which REL and BAE say will be around 2020.

Thanks for the conclusions and welcome to the forum.

john smith 19 · « **Reply #149 on:** 09/17/2016 01:03 pm »

I've attached a small spread sheet breaking down the figures in t43562's graphic in terms of dry and gross takeoff weights as percentages.

There are a few discrepancies. I calculated the Gross Dry Weight by summing the previous items. It comes up 10lbs short compared to the number on the graphic. Logically the sum should be the sum of the parts on this item. This looks like an error.

Likewise I derived GTOW from Weight at Staging plus the following 4 items. That came up 1380lb short to the stated figure. I'm guessing this is the propellant used between staging and RTLS. Presumably some part of this flight will be powered?

I'll leave others to comment if they think the figures they've given for other parts of the design seem sensible. I'm quite sure a payload of 1.58% is well below that of TSTO ELV's. They've also got a landing gear mass of 4% of GTOW for a start. I'll also note they've got an expendable LH2 upper stage. Given all the concern for "risk" this seems rather odd. People might like to check the figure for main propulsion versus GTOW.

I'd very much like to know what they plan for a TPS.

BTW the conclusions part of their paper talks about an "apples to apples" comparison. I'd like to see that with actual TRL's of those other systems they plan to judge against and wheather the actual hardware is off the shelf (IE existing engine design already built), being developed or just we-could-do-this-if-you-paid-us.

Archibald · « **Reply #150 on:** 09/17/2016 04:16 pm »

TSTO with expendable upper stage ? with a 5000 pounds payload ? Reminds me of the XS-1, which doesn't need sabre engines in any way. I vastly prefer the Skylon SSTO by itself.

t43562 · « **Reply #151 on:** 09/19/2016 01:31 pm »

Ravenger · « **Reply #152 on:** 09/19/2016 04:05 pm »

The whole point of Skylon was to learn from the mistakes of HOTOL, where the engines at the rear caused a huge pitching moment as the fuel supply was used up and the COG shifted. The measures used to correct this cut into the payload fraction so much that HOTOL became an 'expensive method of sending hydraulics into orbit'.

Surely the above SR71 style concept with the engines towards the rear of the fuselage could suffer from the same issue? Or is it not as big a problem as the booster is only sub-orbital?

It looks remarkably like the SR71/D21 drone system developed by the Skunk Works. In the end there were too many problems launching the drone at Mach 3 from the carrier aircraft (including the tragic loss of a SR71 and crew) so they resorted to launching off a B52 with a solid rocket booster to get it up to speed.

To be honest I can't easily see how this two stage concept would be more reliable or easier to achieve than a Skylon SSTO, especially as hypersonic staging is so risky.

RanulfC · « **Reply #153 on:** 09/19/2016 05:29 pm »

Quote from: Ravenger on 09/19/2016 04:05 pm

The whole point of Skylon was to learn from the mistakes of HOTOL, where the engines at the rear caused a huge pitching moment as the fuel supply was used up and the COG shifted. The measures used to correct this cut into the payload fraction so much that HOTOL became an 'expensive method of sending hydraulics into orbit'.

Surely the above SR71 style concept with the engines towards the rear of the fuselage could suffer from the same issue? Or is it not as big a problem as the booster is only sub-orbital?

"Shifts-happen"?

Seriously the SR-71 had similar shifts in transonic performance as well and the engines are actually located at what would be the COG/COP shift point. The larger wing area helps dampen out the shifts as well.

Additionally the engines here are placed to take some advantage of the body-nose compression from shockwaves unlike the Skylon which has the engines mounted so as to avoid any interaction with the body's slipstream.

Quote

It looks remarkably like the SR71/D21 drone system developed by the Skunk Works. In the end there were too many problems launching the drone at Mach 3 from the carrier aircraft (including the tragic loss of a SR71 and crew) so they resorted to launching off a B52 with a solid rocket booster to get it up to speed.

Not there are two different launch methods with the expendable being dropped from in internal bay while the reusable is supposedly mounted on the back. There were few problems launching the D21 from the M21 (SR71 derived) other than the one failure of a D21 autopilot which dove the D21 back down into the M21 a few seconds after release from the M21. Continued un-reliability of the D21 autopilot system precluded the higher risk launches using the M21 as well as the cost of the M21 and flight operations over the "simpler" and "safer" rocket powered launch. Later studies by both the Air Force and NASA again suggested using the SR-71 as a launch platform and determined that the back of a super/hypersonic-platform had a very stable and benign environment for launch compared to any other placement as the launched vehicle would remain behind and inside the carrier vehicle shock-cone and allowing it to attain stable flight with little outside influencing factors.

Of course really none of that matters as the proposed concept doesn't stage in the effective atmosphere.

Quote

To be honest I can't easily see how this two stage concept would be more reliable or easier to achieve than a Skylon SSTO, especially as hypersonic staging is so risky.

Hypersonic staging is only risky if you do it too deep in the atmosphere. Since the staging takes place around Mach-8 and 265,000ft/50miles/80km the drag and interactions are going to be minimal.

Randy

lkm · « **Reply #154 on:** 09/19/2016 05:55 pm »

So I'm confused. Either l'm reading this stuff wrong or not much of this makes sense.
If the reusable first stage is 57m long then we should be able to guesstimate the tank volume from the design, and when I do that I make it over 1000m3 or over three the volume required by the reusable first stage mission. In fact it likely has enough tankage to put the entire 16mt second stage in orbit by itself ( it's actually short on oxygen and long on hydrogen tankage). The entire payload section seems mass inefficient when that tankage could more efficiently be added to the fore and aft tanks. The need to include a very long payload bay seems to have created a very unoptimisable design.
Perhaps the tankage is scaled so because that's the tank volume required by the fully reusable mission but that vehicle has a higher dry weight.
Or perhaps the USAF has a need for a very long narrow downward dropping payload bay on a Mach 8 capable vehicle with a range requirement which has driven the tankage volume and has called this vehicle a reusable booster to spare our blushes.

john smith 19 · « **Reply #155 on:** 09/19/2016 09:17 pm »

I'll note a few points about that fully reusable 20Klb system

Excluding the 20Klb payload from the upper stage gross mass gives a dry weight that's 17% of propellant. considerably lower than Skylon, which remember is considered too risky as a concept, partly because it's structural mass is so low. Including the payload puts the structural fraction about 15%. So how are they going to build this structure ?

Kelly Johnson considered the M21/D21 drone project too dangerous to continue with but IIRC part of that was due to the (relatively) narrow clearance between the drone and inward canted twin tails on the SR71. Obviously without needing stealth that would not be a problem for the design and of course modern autopilots are much better at this stuff than they were. Staging at an altitude where atmospheric pressure is measured in pounds per foot also reduces issues but logically implies you'll be needing an RCS since control surfaces won't be very effective.

If you're going for full reusability then you'll need full orbital TPS and I'm still not clear what they have in mind for this.

momerathe · « **Reply #156 on:** 09/21/2016 07:05 am »

can anyone see behind this paywall?
http://aviationweek.com/new-space/reaction-engines-refines-hypersonic-engine-demonstrator-plan

francesco nicoli · « **Reply #157 on:** 09/21/2016 11:39 am »

Quote from: momerathe on 09/21/2016 07:05 am

can anyone see behind this paywall?
http://aviationweek.com/new-space/reaction-engines-refines-hypersonic-engine-demonstrator-plan

nope... but if anyone does, please recall the main points OR the original source, so we can identify it!

best,

Francesco

Star One · « **Reply #158 on:** 09/21/2016 04:09 pm »

Quote from: momerathe on 09/21/2016 07:05 am

can anyone see behind this paywall?
http://aviationweek.com/new-space/reaction-engines-refines-hypersonic-engine-demonstrator-plan

Try this link instead.

http://www.nextbigfuture.com/2016/09/fighter-engine-size-hypersonic-ground.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+blogspot/advancednano+(nextbigfuture)&utm_content=FaceBook&m=1

Paul451 · « **Reply #159 on:** 09/21/2016 11:13 pm »

Quote from: Star One on 09/21/2016 04:09 pm

Quote from: momerathe on 09/21/2016 07:05 am
can anyone see behind this paywall?
http://aviationweek.com/new-space/reaction-engines-refines-hypersonic-engine-demonstrator-plan
Try this link instead.
http://www.nextbigfuture.com/2016/09/fighter-engine-size-hypersonic-ground.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+blogspot/advancednano+(nextbigfuture)&utm_content=FaceBook&m=1

The NBF article includes nothing about the single-engine demonstrator, it just regurgitates general decade old info about Skylon/SABRE.

[Edit: The key phrase in the pre-Paywalled summary would be "fighter engine-size ground demonstrator" I suspect. In other words, nothing to see here, we already knew they'd do this. The only new info would be an estimated date.]