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LTV / Scaled Composites SOFTA (Special Ops Forces Transport Aircraft) proposals

Stargazer2006

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The Vought Archive at the University of Texas in Dallas contains quite a strange series of entries:

Scaled Composites Report: Special Operations Forces Transport Aircraft (SOFTA) Rapid Prototyping Plan. 1991 August 1
Design study for the XC-142 for Special Operations Forces, Volumes 1 and 2, Report No. SCIR 91-009.
Original VAHF identification number: 141-424.
Scaled Composites Report: SOFTA Rapid Prototyping Plan. 1991 August 27
Design study for the XC-142 for Special Operations Forces, Report No. SCIR 91-010.
Original VAHF identification number: 141-423.
Scaled Composites Report: SOFTA Rapid Prototyping Plan. 1991 October 15
Design study for the XC-142 for Special Operations Forces, Report No. SCIR 91-012.
Original VAHF identification number: 141-425.
This clearly indicates that Scaled Composites conducted a study in 1991 for the rapid prototyping of a SOFTA aircraft.

Strange is the way the XC-142 seems to be associated to the same report. I first thought that the designation "XC-142" might have been a cover-up to conceal the nature of a secret SOFTA prototype built by Scaled Composites... but then why would the inhouse Scaled reports have ended up in Vought's archives?

Reversely, if the plan was to build a brand new Vought XC-142 as a SOFTA aircraft, would it have been adequate for that type of mission, and in what way could it have been a "rapid prototyping" program, knowing the size and inherent difficulties of a tilt-wing aircraft, a type of aircraft which Scaled had no previous experience of? And why go and dig up a 30-year-old design anyway?

Any thoughts would be appreciated! And if these reports are readily accessible to reviewers (as the mention "Note to the Researcher" appeared before each VAHF identification number) it would be fantastic is some forum member could go and ask to go through them!
 

sublight is back

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Wasn't Vought doing primarily missile development at the time?
 
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Ian33

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This clearly indicates that Scaled Composites conducted a study in 1991 for the rapid prototyping of a SOFTA aircraft.

Strange is the way the XC-142 seems to be associated to the same report. I first thought that the designation "XC-142" might have been a cover-up to conceal the nature of a secret SOFTA prototype built by Scaled Composites... but then why would the inhouse Scaled reports have ended up in Vought's archives?

Reversely, if the plan was to build a brand new Vought XC-142 as a SOFTA aircraft, would it have been adequate for that type of mission, and in what way could it have been a "rapid prototyping" program, knowing the size and inherent difficulties of a tilt-wing aircraft, a type of aircraft which Scaled had no previous experience of? And why go and dig up a 30-year-old design anyway?
Burt Rutans first major job was as the stability and control flight test engineer for...The XC-142. He even built an RC model of it in 1965.

He spoke of it once, and he poked fun at the V-22 as the 142 was faster, higher flying, heavier payload and longer ranged. I'm not surprised Mr Rutan took it on for a Special Forces Infiltrator airframe.
 

Stargazer2006

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Ian33 said:
Burt Rutans first major job was as the stability and control flight test engineer for...The XC-142. He even built an RC model of it in 1965.

He spoke of it once, and he poked fun at the V-22 as the 142 was faster, higher flying, heavier payload and longer ranged. I'm not surprised Mr Rutan took it on for a Special Forces Infiltrator airframe.
I knew someone was going to bring up Burt Rutan's involvement in the XC-142 program during the 1960s.

The point here is that this is work done 1°) by SCALED COMPOSITES (an entity which obviously didn't exist in the mid-sixties), 2°) in 1991, and 3°) under the SOFTA program (precisely an early 1990s program). Consequently this mention in the Vought Archives can IN NO WAY correspond to Burt Rutan's individual involvement in the original XC-142A program during the 1960s.

The SOFTA proposal COULD be a take on the original XC-142 design, OR it may also have been something totally different hiding under that same designation as a means to cover up the aircraft's nature and purpose. Having a new highly classified VTO transport program disguising as a cancelled tilt-wing type and choosing the same company to do the work (recently revived as an aircraft manufacturer per se, and therefore subcontracting for Northrop, which had acquired it at the time) would have been a very good way to conceal it in report titles I guess...

Also, stating at some point in his bios that "Burt Rutan worked on the XC-142" would not be a lie in that context, but would not necessarily describe a 1960s involvement...

What I can't quite explain is that these documents would be available today in a public archive accessible to any researcher, considering the technology used in the SOFTA article (whether it was actually built or not) would probably still be pretty sensitive today.
 

Stargazer2006

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More on SOFA, SOFTA and such from the Vought Archive:

Special Operations Aircraft Correspondence & Reports.
1987-1991
Original VAHF identification number: 141-422 & 141-423.
Paper: Technology & Design Considerations For An Advanced Theater Transport.
Unknown
A paper by Richard Wible about design and technology implications for the VSTOL.
Original VAHF identification number: 141-409.
Special Operations Forces Aircraft (SOFA) Candidate Aircraft Comparison Charts.
1989 February 9
Original VAHF identification number: 141-412.
Advanced Theater Transport Contracts & Presentation.
1990
XC-142A aero database application to ATT Technology contract and presentation.
Original VAHF identification number: 141-406.
XC-142 Program Employees.
1990 February 9
A list of employees who worked on the XC-142 program in 1990.
Original VAHF identification number: 141-1.
XC-142 Program American Defense Preparedness Association (ADPA) Conference Presentation Correspondence.
1991 October-December
Original VAHF identification number: 141-334.
XC-142 Airplane No. 2 Flight Data Graphs and Charts. Unknown
Original VAHF identification number: 141-89, 141-90, and 141-91.
What we learn here:
  • Program started circa 1987-1989 as the Special Operations Forces Aircraft (SOFA) candidate.
  • It was selected circa 1990 as the Advanced Theater Transport (ATT).
  • It was designated the XC-142A (and rechristened the SOFTA somewhere along the way).
  • There must have been at least two prototypes built since a document talks about the "Flight Data" of "the XC-142 Airplane No. 2".
 

SOC

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Part of me wants to use my new powers and call the Pentagon's PAO, but that might have the unintended effect of getting the good stuff hidden away again ;D

I can't think of anybody I know of in the Dallas area, or I'd see about getting someone into the archives. I'd strongly consider rooting around down there myself but I won't have the kind of time needed to go anywhere until January.
 

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Not sure if all of those assertions are supportable. It sounds to me like they dug up historical data from the XC-142A program and analysed it for information relevant to ATT/SOFA/SOFTA. That would take a team of data entry specialists and technical people to covert analog records into digital formats. References to XC-142A Aircraft No.2 are consistent with this, since there were five original XC-142 airframes and #2 is the only known survivor, I believe.
 

yasotay

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McDonnell Douglas also did considerable work on SOF aircraft, however all of the data remains unreleasable. :(
 

quellish

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It remains unclear if there is any relation between the program that resulted in the Scaled ATT and the SENIOR CITIZEN requirements. Infrastructure to support clandestine testing of vertical lift systems for a transport-sized aircraft was put in place during 1993-1994 at a sensitive location. Parts of this program filled in space that had just become vacant with the departure of a large program.

It seems likely, though, that ATT and what what we know as SENIOR CITIZEN were different sets of requirements. I believe ATT requirements are available on DTIC but I would have to go looking for them.

DARPA/SRS summary of ATT:
http://www.dtic.mil/dtic/tr/fulltext/u2/a227498.pdf
 

Stargazer2006

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Great reminder, Ian33, thanks! For some reason that passage had slipped my mind.

TomS said:
Not sure if all of those assertions are supportable. It sounds to me like they dug up historical data from the XC-142A program and analysed it for information relevant to ATT/SOFA/SOFTA. That would take a team of data entry specialists and technical people to covert analog records into digital formats. References to XC-142A Aircraft No.2 are consistent with this, since there were five original XC-142 airframes and #2 is the only known survivor, I believe.
In the light of this video it does make some sense. I might have got a little carried away... :-[

This being said, some questions remain:
  • "A list of employees who worked on the XC-142 program in 1990." — Sounds like a little more involvement than just compiling old data to me, but then, maybe it was just that.
  • "Candidate Aircraft Comparison Charts" — It sounds like this document would contain, not only the names of the companies involved in the ATT program, but also the planned performance data for their submittals and maybe even the designations thereof.
  • If ATT and SOFA/SOFTA are different, why would they be dealt with in the same batch of reports?
 

Stargazer2006

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quellish said:
It seems likely, though, that ATT and what what we know as SENIOR CITIZEN were different sets of requirements. I believe ATT requirements are available on DTIC but I would have to go looking for them.

DARPA/SRS summary of ATT:
http://www.dtic.mil/dtic/tr/fulltext/u2/a227498.pdf
Great PDF file I had never seen before!! Thanks a lot for this link.

I doubt however that ATT (Advanced Theater Transport) and ATTT (Advanced Technology Tactical Transport — also known as AT3) were one and the same requirement.
 

quellish

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Stargazer2006 said:
Great PDF file I had never seen before!! Thanks a lot for this link.

I doubt however that ATT (Advanced Theater Transport) and ATTT (Advanced Technology Tactical Transport — also known as AT3) were one and the same requirement.
This should be relevant to the current discussion:

Advanced Tactical Transport
Concept no. 900664 is a VTOL aircraft capable of carrying large payloads to nations that have limited airfields. SAF will need an extremely agile, large cargo transport for both intratheater and intertheater transport. A solution may be the tiltwing, super-short-takeoff and landing, advanced theater transport (Tlltwing SSTOL ATT). The Tiltwlng SSTOL combines extreme short-field capability with autonomous cargo handling to enable deliveries to unprepared landing areas on short notice. The propulsion system may use turboprop or jet engines. Minimum flight speed would be approximately 50 knots, with a field length requirement in excess of 750 feet at high-altitude, hot temperature conditions.
This was actually part of one of the "Air Force in 2025" type studies done in 1996 by the Air War College, but the concept apparently had it's roots in another study done earlier.
 

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Sundog

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Was the Northrop MUVR related to any of these programs? Reading about the automated STOL cargo delivery system reminded me of it.
 

AeroFranz

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Stargazer2006 said:
I doubt however that ATT (Advanced Theater Transport) and ATTT (Advanced Technology Tactical Transport — also known as AT3) were one and the same requirement.

ATT is/was Boeing's Super Frog/ Super Lobster.


Sundog, I think MUVR was a smaller unmanned delivery system (few thousand pounds fractionated payload) designed to similar specs orat least CONOPS to what is now the Lockheed KMAX.
 

Stargazer2006

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One distinguished forum member (whom I cannot thank enough) has dug up the Scaled Composites documents on SOFTA from the University of Texas library (see my list in previous page), and though it's going all to be posted later this week, I can already tell you this much:
  • Studies by Scaled of the XC-142A were conducted circa 1990 merely as a starting point for new Special Ops transport studies.
  • Scaled was acting as a subcontractor for LTV, which is surprising because the company had long ceased to produce aircraft as a prime contractor (though it was the major subcontractor on the B-2 for Northrop).
  • Scaled made a series of very original and highly varied design proposals.
  • The reports list and depict in high detail every one of these proposals, notably the three that LTV singled out of the lot (a tandem wing, a VTOL and a flying wing design — none of which being exactly what you'd expect!).
To be continued... ;D
 

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Awesome news Stargazer, thanks for updating us and to whomever, and I have a pretty good guess, that dug up the info. :)
 

Stargazer2006

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From SCIR 91-012 Scaled Composites, Inc. 15 October 1991:

On May 23, 1991, LTV Aircraft Products Group of Dallas, Texas (LTV) contracted with Scaled Composites to prepare a preliminary design study and a prototyping plan for a proposed Special Operations Forces Transport Aircraft (SOFTA). The requirements for the SOFFA transport were stated as follows:

Need: the capability to penetrate unfriendly territory in a clandestine manner and to infiltrate/exfiltrate/resupply Special Forces teams or equipment at an unprepared site.

Design Mission: penetrate 1000 NM into unfriendly territory (no payload) and exflltrate clandestinely an Army Special Forces “A” team of 12 personnel and 500 pounds of equipment, 4,500 pound total payload, and return 1000 NM to the Forward Operating Location.

Design Reguirements:
  • STOL required - 1000 to 1500 foot over 50 foot obstacle at an unprepared site.
  • VTOL desired — at objective area, 4000 density altitude, 95° day, 4500 pound payload.
  • Payload — 4500 pound (design), 10,000 pound (overload).
  • Combat Radius — 1000 NM, 100 to 500 foot altitude, 300 to 400 knots.
  • Self—deployment Range - 2400 NM, best cruise altitude/Mach.
  • Signatures - low to moderate
The first three months’ activity for the design study consisted of development of configurations that could satisfy the mission requirements. This portion of the study was intended to allow the maximum freedom to explore new methods to meet the mission. Working with a minimum number of constraints, a large variety of configurations were explored. Twelve concepts were presented during a Mid-Term presentation at LTV on 1 August 1991. Those preliminary configurations included
the following:

MODEL DESCRIPTION
  • Model 208 Plenum fuselage, blown slot lip, tandem wing
  • Model 209 Advanced, two-rotor tiltwing
  • Model 212 Tandem stopped rotor, turbofan for cruise
  • Model 213 Single stopped rotor, turbofan for cruise
  • Model 215 Tandem wing, skirt for Super-STOL, rocket assist
  • Model 216 Tilt tri-rotor
  • Model 217 Counter-rotating rotor, tail sitter
  • Model 218 Dual aft rotor, tail sitter
  • Model 219 Single rotor, X-wing, tail sitter
  • Model 220 Dual rotor, tail sitter
  • Model 222 Direct lift engine turbofan
  • Model 223 Capsule-delivery/recovery turbofan
On 7 August 1991, LTV provided a downselect to six of the twelve configurations. Scaled responded with a second preliminary design study report including further refinement and performance estimates on the following six configurations:

MODEL DESCRIPTION
  • Model 209 Advanced, two-rotor tiltwing
  • Model 213 Single, stopped rotor, turbofan for cruise
  • Model 215 Tandem wing, skirt for Super-STOL, rocket assist
  • Model 216 Tilt tri-rotor
  • Model 220 Dual rotor, tail sitter
  • Model 223 Capsule-delivery/recovery turbofan
The presentation of those six configurations, including refined performance and weight estimates was provided in a report to LTV on 27 August 1991.

On 16 September 1991, LTV requested that the remaining portion of the design study consider only Models 215, 220 and 223.
 

Stargazer2006

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From Scaled Composites, Inc. Report # SCIR 91-009 (1 August 1991):

The following paragraphs provide a brief summary of the general features of 12 different configurations. All configurations address the accomplishment of a long range infil/exfil mission requiring a mid-mission hover. Payload is 5,000 pounds consisting of 14 fully-equipped troops or other small package size containers. The mission radius of action is 1,000 nautical miles. Low observability is desired. The configurations are illustrated in the separately bound 3-view drawings. Drawing scale is either 1/140 or 1/100 for all 3-views. Also included is a summary of weight, size, performance and selection criteria for the 12 configurations as well as for the V-22 and XC-142A. A more detailed discussion of the various tradeoffs will be provided in an oral presentation.

A few remarks before we get to the heart of the matter...
  • This is clearly the first detailed insight we get of Scaled's process of design submission as a subcontractor and how they did things. I'm only attaching key documents from the reports, but a detailed inspection of the reports provide great understanding of that process.
  • All drawings are signed ELR, which means Elbert L. Rutan ("Burt" Rutan himself).
  • All designs done for LTV for the SOFTA requirement carry the name "TIDDS", obviously the inhouse name for the program.
    We know Scaled had a habit of allocating funny acronyms to its programs (TUNA, SCAT, etc.) and so one can assume that TIDDS (the meaning of which is not explicited anywhere in the documents) must have been an acronym too, possibly made from the initials of some funny sentence. Ideas, anyone?
  • The first set of drawings (dated July 1991) carry only the basic model numbers: 208, 209, 211, etc.
    The second set of drawings (dated August 1991) carry a "-1" sub-type number: 208-1, 209-1, 211-1, etc.
    The third set of drawings (dated October 1991) carry a "-3" sub-type number: 215-3, 220-3, 223-3.
    The dash number could indicate that these were the 1st or 3rd modification of the initial design. However, there is a possibility from the above that the dash number could also indicate the month after program launch (July +1, July +3).
  • Two bits of info appear in Report 91-009 that do not show up in 91-012 (at least directly, since 91-009 is included as an Appendix): "Low observability is desired" and "Payload is 5,000 pounds consisting of 14 fully-equipped troops or other small package size containers."
  • Though LTV singled out three designs (215, 220 and 223) and though Scaled fixed a calendar for the rapid prototyping and delivery of a demonstrator (see attachments) there is no guarantee that a demonstrator was actually built.
  • Connection between SOFTA and "Senior Citizen" cannot be established at this stage, hence the fact I split this from the "Senior Citizen" topic. Of interest however is the fact that both "Senior Citizen" and Scaled Composites have the initials "S. C." and that several details seem to coincide.
 

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sublight is back

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A couple things,

has anybody other than Paul McGinnis said that Senior Citizen was a tactical airlift aircraft?

And this msg by Sundog is relevant....

Sundog said:
I would tend to think of this program as Senior Citizen as well. But I do recall that for a while, Steve Douglass used to have a picture of a "stealthy" transport plane on his site that sort of looked like a jet powered C-130. It's engines were mounted in the fuselage, but on top of it and the intakes, IIRC, were just around the wing trailing edge. Another way of llooking at it, the engines were sort of a dorsal mounted pod that was blended with the fuselage. The tail was mounted above it.

I think I downloaded the drawing, but I don't know if I can find it now. I'll look.
That sounds like a description of several of the Rutan drawings....
 

Stargazer2006

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MODEL 208 PLENUM FUSELAGE CONCEPT
Plenum fuselage, blown slot lip, tandem wing

The Model 208 concept consists of a tandem wing configuration with high aspect ratio wings optimized for cruise efficiency. The wings are not equipped with high lift devices or conventional control surfaces. The inclined mid-span hinge line for the rear wing provides outer panel twisting via internal actuation. The twisting provides roll and pitch control for cruise. Twin verticals provide yaw stability and control. The embedded aft engine is used for cruise. The other three engines‘ ducts are valved closed for cruise. For transition and hover operations, all four engines are running, providing pressurization for the plenum which occupies approximately half the fuselage volume. For hover, the aft thrust duct is closed. Control vanes and valves in the longitudinal slots on the fuselage sides provide a Coanda effect resulting in enhanced hover lift. The plenum side slots extend from just aft of the canard trailing edge to the leading edge of the main wing.
 

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Stargazer2006

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MODEL 209 TILT ROTOR/WING CONCEPT
Advanced, two-rotor tiltwing

The Model 209 is a concept which combines the features of the V-22 Osprey and the XC-142A tilt wing transport. The payload is packaged in a very compact, small fuselage. The entire wing tilts with the transition angle in a manner which eliminates the open fuselage top. The wing is extended beyond the nacelle for improved span loading (induced drag) during cruise. The tip extensions also provide roll control in cruise and yaw control in hover, thus eliminating the need for rotor swash plates. The rotors are large scimitar variable pitch, no-cyclic propellers. Pitch control during hover is provided by a horizontal “fan tail” which is covered for cruise RCS. The props turn top-in, so that the inboard wing is in downwash during transition. The outboard wing panels are varied to optimize their local angle of attack during all stages of transition providing the proper control power. The configuration does not require wing flaps. The scimitar shape of the large, 2-blade rotors is designed to aerolastically vary the twist distribution in order to reduce the compromise in blade twist between hover and cruise. The result is a compact, simple aircraft compared to the conventional tilt-wing/tilt-rotor configuration. The wing download during hover is eliminated, resulting in improved hover power required with a positive ground effect due to the fuselage shape.
 

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MODEL 212 TANDEM STOPPED ROTOR CONCEPT
Tandem stopped rotor, turbofan for cruise

Model 212 is a high disc-loaded tandem rotor helicopter that brakes its rotors to a stop for cruise, resulting in a fixed tandem wing aircraft with an unusual wing configuration. The aircraft is equipped with small turbofan engines for cruise that also provide yaw control in hover. The turboshaft engines that power the rotors for hover are shut down during cruise. The small rotors are staggered laterally to provide additional span for cruise induced drag improvement. The stagger also functions to improve the lift distribution of the asymmetrical wing airfoils during cruise. All four wing panels (rotor blades) are all-flying surfaces, controllable by the rigid swash plates. The swash plates act conventionally during hovering flight. In cruise, the swash plates adjust incidence to optimize each panel’s lift coefficient to provide roll and pitch control as well as limit the lift of the panels that are aligned trailing edge forward. The lateral offset of the rotor allows more spanwise overlap of the less efiicient panels whose trailing edges are aligned forward. The panels are adjusted for approximately twice the lift coefficient on outboard versus inboard panels. The wings/rotors are rigidly attached at the hub to allow transmittal of asymmetric wing bending to the airframe. Large rotor brakes provide prompt rotor deceleration. Overpowered turboshaft engines provide a prompt spinup. As shown in the accompanying time histories, the stop or start cycle of the rotor occurs during a parabolic coast after the aircraft performs apullup maneuver. This allows a time period of approximately 15 seconds in which the rotor CL is near zero and airspeed is less than 60 knots. The time histories are for a first estimate maneuver in which the angle of attack remains constant after the initial pullup. A more optimized maneuver could be developed to provide a longer rotor spin up/spin down interval. The resulting configuration is apoor helicopter. However, the hover efficiency is not important due to the short time (5 minutes per flight) required for rotor borne flight. The high wing loaded stopped rotor provides a solid turbulence ride and a low wetted area. Risks involve the dynamics of the rotor at low RPM, the stiffness requirements of the trailing edge – forward wing panels and the drive shaft structural loads during rotor braking asymmetries.
 

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MODEL 213 STOPPED/FLIPPED ROTOR CONCEPT
Single stopped rotor, turbofan for cruise

Model 213 configuration also requires the pullup maneuver described for Model 212 in order to transition between rotor borne and wing borne flight. The asymmetry in cruise due to the left wing trailing edge forward is addressed by a 180° twisting “flip” in one win g panel outboard of Buttline 60. The wing flip is accomplished at the portion of the pullup—coast maneuver in which the lift is near zero and the speed is less than 50 knots. Small all-flying auxiliary wings are positioned on the fuselage to allow roll control during the low speed portions of the transition. The cruise thrust engine and the hover yaw control are similar to Model 212.
 

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MODEL 215 SKIRT TANDEM SUPERSTOL
Tandem wing, skirt for Super-STOL, rocket assist

Model 215 is a conventional tandem wing configuration for cruise that is optimized for a high cruise L/D using high aspect ratio sailplane-like wings. The aft wing outer panels can be hinged similar to Model 208 for pitch and roll control during cruise. As shown in the section view, the entire fuselage between the canard and main wing contains a drum in which a sail-like “skirt” is rolled up and stowed for cruise. Where runway length allows, the aircraft makes conventional takeoffs and landings without the skirt high lift device. For SuperSTOL operations, the aircraft is slowed to near the stall speed, then is continuously slowed as the skirt is unfurled laterally between the canard and wing. The skirt edges are retained in tracks similar to that used on high performance racing sail boats using a continuous root-to-tip cable loop at the canard and the wing. This geometry transition results in a three-fold increase in aircraft wing area and a significant reduction in aspect ratio, allowing a steep, slow descent into the landing zone using conventional fixed wing aerodynamics. In this configuration, the aircraft is actually a cross between a rigid conventional transport and a rag-wing type ultralight aircraft. When the aircraft is in the flare several feet in the air before touchdown, rocket engines are fired facing forward at the nose. A rocket burn of approximately 2.5 seconds provides a 1.0 G deceleration and reduces the speed to 35 knots within a 75-foot ground roll. Wheel brakes are used for the remaining 50 foot ground roll, providing a total ground distance of 125 feet. Thus, the several minute noise signature of the conventional vertical landing craft is replaced by a very loud 2.5 second “What was that?” type of signature. For takeoff, aft-facing rockets provide acceleration in addition to the turbofan engines and the landing transition is reversed. Total rocket fuel, using a specific impulse of 200 seconds results in a fuel weight of approximately 850 pounds, an excellent tradeoff compared to most vertical landing systems. The rockets are used, of course, only when SuperSTOL performance is mandatory.
 

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MODEL 216 THREE-SURFACE TRIPLE TILT ROTOR
Tilt tri-rotor

The Model 216 configuration is an attempt to provide an aircraft with a low span loading for cruise without the structural loads imposed on the main wing by a rotor system. The wing is a simple conventional sailplane-like low drag surface optimized for the cruise mode. It has conventional ailerons for cruise but no flaps. A forward rotor with a small canard wing is pivoted for the transition to hover. The canard wing is an all-flying surface used to control the pitch of the airplane in conventional flight. The surfaces can be aligned to avoid separation and provide control during transition. The two aft rotors are small (20 foot diameter) to minimize the gyroscopie loads on the aft horizontal tail structure. They are positioned to provide hover thrust without the penalty of win g download and with a strong rotor ground effect. This configuration might be controlled in hover without the need for swash plates on any of the rotors.
 

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MODEL 217 COUNTER-ROTATING TAIL SITTER
Counter-rotating rotor, tail sitter

Tail sitters, the basis of three experimental aircraft tested in the late 50’s, are inherently simple in that the rotor and wing are not adjusted off the body axis for transition. The 1950’s tail sitters were deemed unsuccessful for several reasons. The pilot's task of hovering and landing while looking over his shoulder at a backward environment was nearly impossible and control problems occurred during portions of transition due to stalling of the wing. The Model 217 configuration and other tail sitters discussed in this report provide unique solutions to those deficiencies. This configuration has high aspect ratio wing panels that are all-flying, thus can be adjusted to the proper angle of attack for stall suppression and control power during transition. The high aspect ratio provides the required L/D for long range cruise. Two unique features allow the pilot to make a conventional controlled excellent visibility, transition, hover and landing: (1) the pilot’s seat moves through an are of approximately 100° such that his seated position is approximately level to the horizon throughout all stages of the transition between cruise and hover. This allows excellent downward and sideward visibility during the approach to landing and hover. The pilot looks out of the aircraft’s bottom. (2) As the pilot’s seat moves within the airframe, control system mixers transition his flight controls such that he is always flying the stability axis rather than the body axis. For example, in cruise, at 300 knots, a left and right motion of the control stick provides conventional roll control and the foot pedals provide yaw control. During hover, a left and right motion of the control stick provides aircraft yaw control and the foot pedals roll the aircraft. Thus, from the pilot’s perspective during hover, he not only has an excellent view of the landing area, but controls the airplane in a very conventional helicopter mode. The cockpit controls also include a conventional helicopter collective lever. Translations done during hover can be accomplished via the flight control system commanding a stationery 90° pitch attitude and then using the all-flying wings in the rotor downwash to provide translation control. Thus, the aircraft can land vertically even into a wind. To further enhance landing safety, the control system and ground sensors can adjust the landing gear to allow a vertical touchdown on sloped terrain (a “smart” gear, similar to automotive active suspension systems). Cargo loading of the tail sitter involves a unique arrangement using a single lower surface door rotated 90° for loading operations. The door is less complex than the normal, multi-door configurations of the conventional cargo aircraft and since the payload is only 8% of gross weight, the loads imposed by hydraulically lifting the entire payload into the fuselage are manageable. In order to balance the tail sitter, a significant amount of its disposable systems (electrical, hydraulic, avionics, etc.) are located in the tail cone area along with a relatively heavy landing gear. This not only allows adequate balance, but provides easy access to systems. The pilots, however, need to get used to a long climb. Note that this configuration requires sharing of visibility duties left and right by the pilot and copilot due to the large intrusion of the center gearbox. Hover control can be via complete swash plates on both rotors or possibly pitch, yaw and roll from the four wash-induced flying surfaces. Anti-torque is provided via relative rotor collective pitch. An obvious disadvantage to the tail sitter is the inability to do an over-gross STOL takeoff.
 

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MODEL 218 MID POSITIONED DUAL ROTOR TAIL SITTER
Dual aft rotor, tail sitter

Since hover efficiencies are related to disc-loading, a more efficient hover can be achieved by separating the counter-rotating rotors of the Model 217. This configuration provides a relatively high aspect ratio wing for efficient cruise, control power for hover roll and yaw control is enhanced, however, hover pitch control is marginal. Hover visibility forward and laterally is unrestricted.
 

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MODEL 219 SINGLE ROTOR TAIL SITTER
Single rotor, X-wing, tail sitter

The Model 219 addresses the problem of the complex counter-rotating rotor of the Model 217. By using four wings rather than two in the downwash and by using wing camber, adequate hover anti-torque can be provided by the fixed wing flying surfaces. Thus, the rotor becomes a single two- or three-blade constant speed prop rather than a complex counter rotating system that relies on relative collective pitch for yaw control in hover. The configuration has higher span loading and more wet» ted area than the Model 217, however. All six flying surfaces are pivoted at their roots for maximum control effectiveness. Two or four of the main wings may require adjustable camber for hover. This configuration would allow fore/aft and left/right translation while the aircraft axis remains vertical during hover operations by adjusting the relative wing positions.
 

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MODEL 220 TWIN ROTOR TAIL SITTER
Dual rotor, tail sitter

This configuration combines the simple wing configuration of Model 217 with the two rotor anti-torque shared disc-loading of the Model 218. As compared to the Model 218, the Model 220 provides improved hover pitch control and a reduced-complexity cross-shaft system.
 

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MODEL 222 LIFT FAN VSTOL
Direct lift engine turbofan

In general, a direct lift fan configuration is unsatisfactory due to the high downwash velocities. This results in ground erosion and an inability to conduct ground operations in the downwash wake. The Model 222 configuration uses a single large cruise engine that can be vectored down for hover. Its lift is supplanted by four direct lift turbofan engines which are used only for transition and hover operations with the direct lift engines inclined outward, the split-nose loading is intended to provide protection for loading and unloading during ground operations with lift engines powered up. Blast deflectors near the main landing gear and fuselage nose provide protection of the high velocity ground wash to the loading and unloading crews. This configuration results in an extremely heavy powerplant installation. However, its long, efficient wing provides excellent cruise range.
 

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MODEL 223 CAPSULE DELIVERY/RECOVERY SYSTEM
Capsule-delivery/recovery turbofan

The Model 223 system, illustrated in two separate three-views, (one for delivery and one for recovery) shows a different approach to the basic problem of sneaking in and sneaking out unobserved. Instead of attempting to hover and infil with the entire aircraft and the return fuel. Only the payload is delivered to the landing zone. The payload delivery system is different from a standard airdrop scenario, however. A large (approximately 4 foot deep) airbag shock attenuation system allows the payload capsule with six passengers to be dropped at a sink rate of approximately 50 feet per second while limiting the impact accelerations to less than l2Gs. This can be further reduced to approximately 9Gs using stroking seats. The high sink rate delivery allows the capsule to be targeted with precision similar to the precision delivery of a smart bomb. Position designators or GPS is used to provide a landing area reference and the descent parachute is steerable in any lateral direction in order to position the payload into a small area. The “bomber” comprises its low observable shape only for the extraction, then can orbit undetected or return for refueling during ground operations of the infil crew. For recovery, the ground crew deploys a lanyard with a helium balloon, similar to the C-130 rescue system developed for the Vietnam era personnel recovery system. The mother ship picks up the payload lanyard and hauls it onboard for the high altitude stealthy cruise home. Thus, only the payload plus approximately 2,000 pounds is delivered to the high intensity area.
 

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Avimimus

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These are certainly some great finds! Thanks!
 

AeroFranz

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I had never seen an analysis of alternatives from Scaled. This shows configurations that even they thought were too extreme, or at least were not downselected.
Top post, Stephane! :)
 
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