Quote from: ChefPat on 12/28/2012 02:48 pmWhere is Stratolaunch on the modifications to their carrier aircraft? It would certainly be large enough to handle a Dreamchaser.A long way from even being constructed.
Where is Stratolaunch on the modifications to their carrier aircraft? It would certainly be large enough to handle a Dreamchaser.
Quote from: john smith 19 on 12/28/2012 03:24 pmQuote from: ChefPat on 12/28/2012 02:48 pmWhere is Stratolaunch on the modifications to their carrier aircraft? It would certainly be large enough to handle a Dreamchaser.A long way from even being constructed. Are they? They've had the 2 jets for more than ten months now. How long does it take to modify them?
Based on what I'm hearing, it looks like there will be no drop test until late 2013- 2014. It takes time to adapt out a system and look at all possibilities.
Attaching a jettisonable parachute to DC's tail, and dropping from high altitude by helicopter doesn't sound like the sort of thing that would take till late 2013, or does it?
There are definately some low altitude / low speed tests they can do with the helicopter, including the first free-flight and landing tests.
I think so. But if that's the case, what test(s) will a helicopter be insufficient for?
The "issue" here is "dropping from high altitude" with a helicopter. Especially with the DC lifting body.We've got several "facts" to work with already:The stats for the Skycrane can be found here:http://www.ericksonaircrane.com/Note: Maxium "hook" weight is the important figure here. The S-64E can lift up to 9,072kg (20,000lbs) while the S-64F can lift up to 11,340kg (25,000lbs) with a "maxium" cruise speed of 115-knots (212kph/132mph) for the former and 104-knots (192kph/119mph) with the latter. This is important for several reasons but the "biggie" is that these figures (for the Skycrane(s)) is for rather LOW altitude, well below 20,000ft. (As a comparison you can see the Shuttle A-and-L tests here, ya "wikipedia" I know but the general data is accurate, http://en.wikipedia.org/wiki/Approach_and_Landing_Tests )The "highest" altitude recorded for the "type" for the S-64 is held by an earlier version for the US Army the "CH-54" which reached a maxium altitude of 36,000ft but this was with NO load, limited fuel/crew, no forward speed, etc so that it COULD reach that high. "Typical" maximum operational altitude is listed as a bit over 18,000ft but again that's NOT going to be with a full load, nor at "high" speed. Helicopters like all "active" lift vehicles have a limit of what they can lift that goes DOWN with altitude, as does speed. (You have to trade "lift" power for speed power) So in general we're looking at a "probable" release at or around 10,000ft at most."Assuming" the DC-ETV mass' somewhat close to the "operational" launch mass of around 11,340kg the Helo flying it must be the F model which means a lower intial speed to start off with. If it's below 9,000kg they could use the E model but then the "flying" characteristics will be a lot different than the "actual" DC orbiter vehicle.
It could very easily be MORE than a year or two to get all the data needed to even see if they actually CAN use a helo to do "free-flight" drop tests for the DC-ETV. In general the DC-ETV has to "fall" fast enough, from high enough to generate a viable speed of almost 200-knots, (370kph/230mph) from a possible "maximum" drop speed of between 104 to 115-knots,(192kph/119mph to 212kph/132mph) and that's non-trivial.As an example I'd point to the fact that NASA did this testing type mission when evaluating the low-speed handling characteristics of the "staight-wing" versus the "delta-wing" versions of the Shuttle. Most of them still ended up "pranging" the nose of the model pretty good because they simply couldn't generate enough lift from a zero-speed drop IIRC.And that's a WINGED vehicle and not a lifting body
They really need a "carrier" aircraft for flight testing both to give it the intial minimum speed and a better altitude to work from. Which brings me to the idea of "hanging" the DC-ETV from a "normal" airliner mounting station. My take is its do-able as long as the station can be configured (a mounting pylon/bracket) and is able to handle the load. Which points to a particular issue; mass. Most of the engine weights I'm seeing do not exceed 4,000kg to 5000kg which is far below even the "low" estimated mass of the DC-ETV of 9,000kg. And that doesn't take into effect the mass of the "pylon" and mounting system. It's possible they could make a mount that would "span" say an inboard engine mount and the ferry engine mount but even then the total "weight" capacity of the mounts probably won't be enough to carry the load.
Now if the overall mass of the DC-ETV IS lower than anything listed they could very well use such an arrangment to test fly the vehicle HOWEVER the "tests" will be very far off the mark for any comparision to the "real-thing" because of the lift/drag/mass-ratio of the test vehicle.(A low mass test vehicle will glide and generally fly much better than something that is close to the actual planned vehicle mass which would throw off any results)
On the subject of dropping lifting bodies from helicopters...It's not like we have no experience doing this. Anyone remember Project Parawing? Hyper-X? X-40A? All dropped from helicopters at rather modest altitudes - all landed without incident (In the case of the X-40A multiple times). We (the metaphysical we) know how to do this.IMNSHO, much ado about nothing.
In a DC thread some time ago people expressed doubt that one nozzle design could be chosen that would work in vacuum and the atmosphere. I'm not sure if this is in fact that big a problem (shuttle SRM nozzle operated from 0-146K ft without trouble) but if it is, then the hybrids couldn't be used for drop tests
...If the RCS can also operate at all altitudes, then technically DC doesn't need any carrier aircraft at all for low altitude test: back it up to the end of a long runway, fire the hybrids, then at ~200mph fire the down RCS jets to pick the nose up, fly for a few seconds, cut the hybrids and land. Note: this is not a a serious suggestion, but it certainly would be fun to see tried!
It sounds like the best guess is a helicopter will be used for low speed low altitude tests. For higher speed tests, we may have wait quite a while until SNC is ready to install/fire the hybrids or design/qualify mounts for an as yet unknown carrier aircraft.
Quote from: adrianwyard on 12/30/2012 06:55 amIt sounds like the best guess is a helicopter will be used for low speed low altitude tests. For higher speed tests, we may have wait quite a while until SNC is ready to install/fire the hybrids or design/qualify mounts for an as yet unknown carrier aircraft. Well the hybrids are a fairly well characterized system and SNC have a relationship with the suppliers. The high altitude balloon drop is starting to look almost sensible.
Quote from: john smith 19 on 12/30/2012 11:03 amQuote from: adrianwyard on 12/30/2012 06:55 amIt sounds like the best guess is a helicopter will be used for low speed low altitude tests. For higher speed tests, we may have wait quite a while until SNC is ready to install/fire the hybrids or design/qualify mounts for an as yet unknown carrier aircraft. Well the hybrids are a fairly well characterized system and SNC have a relationship with the suppliers. The high altitude balloon drop is starting to look almost sensible. Aren't SNC themselves the developers of the hybrids? It sounds cavalier to suggest hybrids be fired early on in the test program (see SS2's large number of unpowered flights) but if the DC motor is as ready for flight testing as the airframe and avionics, then I guess it wouldn't be insane.
I'm not sure if this is in fact that big a problem (shuttle SRM nozzle operated from 0-146K ft without trouble)
I don’t buy that... SS1 Flew just fine and SS2 will use a similar motor to DC...
If the RCS can also operate at all altitudes,
Quote from: Rocket Science on 12/29/2012 10:23 pmI don’t buy that... SS1 Flew just fine and SS2 will use a similar motor to DC...Not relevant or applicable.