A flyer in a can

The WASP (Wide Area Surveillance Projectile) is a folded UAV (unmanned aerial vehicle) that a standard, 155-mm artillery round, the M-483A, deploys as cargo (Reference 1, Picture). A unique load-mitigation approach protects the WASP from extreme gunfire environments (12,000g, 177 revolutions per second), enabling it to use the gun's energy rather than its own to quickly reach a target. The WASP uses the 155-mm infrastructure for handling, loading, and transportation; requires no special handling; is organic at the platoon level; and does not have to be recovered. You can also use it for multiple zero- and low-g applications. Phase I of the development program testing demonstrated that the flyer could be packaged and would fly. Phase II demonstrated g-hardness.

The convenience of WASP's packaging and electric propulsion begs applications beyond artillery launch. When you view a WASP as a "flyer in a can," you can envision many applications from multiple platforms that are extensions of the core design. The container serves as a multifunctional assembly for integrating UAV capabilities into various platforms. Its cylindrical form makes it relatively easy to retrofit into weapons or vehicles. Designs are available now for these applications.

The WASP is an autonomous vehicle. In a combat application, it would follow a mission plan that personnel at a UAV GCS (ground-control station) would prepare. Troops then could load the plan at the gun or directly from the GCS on the fly after WASP metamorphoses into its unfolded configuration. It flies between targets or clusters of targets at an altitude of about 4000 ft with 1-ft imaging resolution. An onboard, mechanically hardened electro-optical system sends images to the ground. Draper Laboratory currently is designing a chemical/biological microelectromechanical sensor that also could act as the payload. WASP is congruent with the DARPA (Defense Advanced Research Projects Agency)/Army Future Combat Systems development goal of multimission, rapidly deployed, light-logistics systems.

Scenarios change during the time it takes to get a UAV into the air and to the potential target. Trucks move, mobile rocket launchers disappear, tanks scurry for cover. One remedy is to position a strategic UAV, such as a Predator, over a region of interest. These expensive assets require flat areas for takeoff and recovery. Additional time is required to fuel, launch, and then fly the UAV to the target. This extra time may be acceptable at the theater level for such assets. However, at the platoon level, flexibility, short response time, and logistical simplicity are desirable. A WASP's time to target is essentially the same as its host platform. For the M-483A, the time to target is approximately 1 minute to travel 22 km; WASP's on-station time is 0.5 hours for the 20-in. fuselage under study. Once a WASP is deployed and operating as a UAV, you can redirect it with uplinked commands to revise the mission plan.

Availability means having the right asset where and when it is required. Cost, maintenance, planning time, number of assets, and the assets' basing location all contribute to availability. Allocation of most UAVs and their support systems is required well in advance of their need because current UAVs are relatively large and cumbersome to transport, and they require a small, specialized platoon for "care and feeding" that you must preposition for response. WASPs are prepackaged UAVs with the logistics base of artillery shells.

UAVs that you launch in a traditional manner and that fly to the area of interest suffer an unfavorable energy trade-off. To reach the target, the UAV expends stored energy, whether it is in the form of liquid fuel or batteries; however, you want to maximize the energy available over the target for endurance or function. WASPs use gun energy to reach areas of interest and use stored energy over only their targets, where it counts.

A shroud houses the WASP and serves as a handling container and load-mitigation structure. The container has a simple cylindrical configuration that makes it amenable to under-wing deployment from an aircraft, integration into a weapon-carrying canister, and other low-g applications. You can scale the same design for 5-in. naval guns, enabling you to deploy UAVs far inland at high speeds without the need for ponderous recovery systems.

The objective of Phase I of the WASP project was to design, fabricate, and fly a g-credible test flyer. Axial acceleration (12,000g); spin-up acceleration (110,000 rad/sec²); steady-state spin (177 revolutions/sec); balloting, or lateral acceleration (4000g); and negative linear acceleration (4000g) cause inertial loads on the vehicle. Range is insensitive to weight from approximately 80 to 140 lbs, which allows a trade-off between the flyer and shroud weights. Linear-acceleration load decreases with projectile weight for a standard propellant charge, and it is desirable to decrease g loading on the flyer. You should therefore minimize wing loading for the available propulsion power. The total projectile weight is the sum of the shell, flyer, and shroud weights. So, a light flyer and heavy shroud benefit both the flyer and the shroud. The approach for the components is to select devices with high-g pedigrees and, therefore, a controllable risk of not achieving complete g-hardness when funding becomes available in later development stages.

WASP's mechanical packaging was a challenge. The flyer airframe was designed to use nearly all composite materials, because composites significantly reduce system weight and have good tensile characteristics. Regardless of this advantage, it was clear that the flyer itself could not bear all the launch loads through the airframe because of buckling and other concerns. Therefore, the flyer is mechanically "hung" with most of it in tension in the shroud—a sabot-load-distribution strategy. A single wing-box "bulkhead" completes the coupling between the flyer and the shroud, giving a well-defined and manageable load path.

The shroud provides crucial radial support to the fuselage and folded flight surfaces during balloting. It also protects the flyer from the environment during the early stages of metamorphosis. Future refinements of the design will include supportive cavities machined into the shroud's inside surfaces that capture the flight surfaces to immobilize them during gunfire launching.

Phase I aimed to show that you could package the flyer within the 155-mm space constraints, and it would fly. Funding constraints precluded the full development of components. Therefore, testing used inexpensive commercial surrogates. However, the test flyer had the same aero configuration, power, weight, and center-of-gravity location as the intended final design.

Captive carry tests performed full dress rehearsals for glide and powered flight tests. Two WASP test flyers received a thorough shakedown of all sensors and systems while flown on a radio-controlled ultralight's mounting interface (Picture). This testing allowed developers to thoroughly evaluate the control surfaces, GPS navigator, air speed, and RF-communications downlink in a scaled-back flight environment. It also ensured that the aircraft was in radio-control and RF range at all times, that the pilot had good visibility, and that the time of flight was optimized. The team developed flight procedures and selected an optimum flight path. It also fixed a video recording and downlink system to the ultralight's structure to capture the entire WASP. In this manner, the team made it possible to observe flight-control inputs and the behavior of the WASP in real time from the ground to verify that the flyer properly receives and acts on commanded inputs. It is also useful for observing the vehicle's prerelease orientation.

The first drop test was a glide test to preview flight worthiness. The glider configuration used a dummy motor, a dummy battery, and no prop. The vehicle was ballasted as required to produce the proper center of gravity and included a Draper-designed stability-augmentation system. The ultralight dropped the WASP from approximately 250 ft, with a 1000-ft glide into a net. The conclusion was that the vehicle's nominal handling qualities were similar to the computer simulation previously studied. The WASP was stable and controllable.

Powered flight tests aimed to initiate several turns and determine the aircraft's handling qualities. After a clean separation from the ultralight, the pilot commanded a left turn, leveled out, and then commanded another gradual left turn. The WASP flew under powered flight and circled the field. It hardly could be heard due to the quiet electric propulsion.

The Phase II thrust was to design and fabricate a g-hard UAV based on the principles established in Phase I (preserving flight integrity) with rail-gun demonstrations. Draper built mass mockups of the major components, such as the imager and battery, to the interface requirements previously established. Given the inertial-loading approach, the major challenges were the bulkhead and the wing.

The flight tests demonstrated that roll control on the main wing is necessary, because the tail surfaces are inadequate. Hardening the conventional aileron mechanisms (bell crank, pushrod) used in Phase I is difficult. The approach selected for roll control was wing warping using active composites. The challenge was to design a wing that would be strong enough to tolerate the launch environments but "soft" enough about the major axis to be twisted by piezo or Nitinol actuators.

Draper designers examined multiple composite materials, including carbon fiber, fiberglass, and Kevlar. They assessed loading from axial acceleration, spin-up acceleration, and negative-linear-acceleration environments. After extensive finite-element analysis, they decided that the two-section wing would have one ply of 0.009-in.-thick, plain-weave fiberglass, oriented 0/90, and one 0.007-in.-thick unilayer, oriented along the wing axis. Researchers chose Nomex, a lightweight honeycomb, for the wing core. The team was careful when adding material for g-hardness. At the 12,000g design level, every additional ounce means 750 lbs of load.

Preliminary selection of the activation material was also interesting. Piezo actuators have a higher bandwidth but smaller stroke than those of Nitinol. Nitinol can consume noticeable power, because it relies on heating the actuator to its phase-change temperature. However, a piezo device would be excited at approximately 1500V dc, which could later present a shielding problem. The team reviewed the vehicle-bandwidth requirement and expected roll- duty cycle and estimated 13W for heating power. Draper funded two graduate students at the Massachusetts Institute of Technology to conduct thesis work on both alternatives. Piezo is the more promising approach, because Nitinol requires excessive power for heating.

The bulkhead is the keystone of the load-management strategy in that all vehicle loads pass through this part and are subsequently transferred to the shroud. During the gunfire event, the avionics section puts the bulkhead into compression, and the fuselage, wings, and tail section put it into tension. Multiple design iterations converged on Titanium 6Al4V for this critical part. A program of rail-gun testing of individual flight components was successful after sustaining approximately 11,200g. During rail-gun testing of the complete airframe at the same g level in April 2002, one of the dummy masses broke loose. However, examination of the test data revealed that the airframe and its components were successful.