Dr. Purcell has spent the last 10 years working on pure vestibular controlled aerospace platforms to better understand vestibular and somatosensory integration in the brain stem. He believes that understanding sensory integration in the brain stem is very important when recommending phyusical therpy and vestibular rehab for his "dizzy" patients. He has pushed aggressively in the physical therapy communtiy for the implementation of high end balance devices such as the zero gravity or alter-g treadmills. This allows the patient while on an unstable platform to perform passive VOR exercises. This has turned out to be similar groundbreaking stride in vestibular rehab to his recommendation for patients to use the Force Dynamics 301 device. He has used the Jetpack and Rocketbelt to record VOR responses in a pure yaw and pure translational environment. "This device takes away somatosensory input to the brain stem and forces limited visual integration while trying to move through a complex 3D space" says Purcell. He uses this to better understand Vestibular control in the patients with somatosensory deficits in spinal cord injuries. He has flown his Jetpack for several physicians at hospitals here in San Diego not to mention venues as well known as the Olympics. Dr. Purcell also utilizes Jetpacks and rocketbelts for community awareness worldwide for his balance patients. He is known as the "DizzyDoc", "DizzyDoctor", or "Doc Rocket" by his fellow physicians and patients. He has used the Jetpack to gain entry into several business meetings throughout China where he is promoting Vestibular clinics in over 500 hospitals. He plans to jump his Jetpack over the Great Wall of China in early 2017 to promote his unique vestibular protocols transitioning into China and subsequnetially worldwide.

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Visual-Vestibular integration training protocols to increase pilot proficiency during Rocketbelt and Jet Pack training. 




With the development of newer lightweight aerospace materials and higher thrust producing micro-turbine engines there is increased interest in re-developing the jet pack as a means of personal transportation.  Pilots typically train on the rocketbelt prior to graduating to the jet pack platform.  The Rocketbelt has a longstanding reputation as a complex flight vehicle being very difficult to master with regards to pilot training and proficiency.  Five pilots with different aviation backgrounds were selected and placed in a specialized multi-sensory integration training program for one month prior to beginning their training on the rocketbelt platform.  All pilots completed the training program with each one achieving untethered flight proficiency status on the rocketbelt in thirteen to thirty-six training flights.  On average the pilots achieved free flight status with seventy-six percent (76%) fewer training flights compared to the previously reported training flights required by the Bell Aerospace pilots over four decades ago.  This proposed program substantially decreases training costs and makes training on the rocketbelt and jet pack more accessible to the general aviation pilot.


The early development of the first rocketbelt was pioneered by Bell Aerospace Systems for the purpose of creating a portable platform to move a pilot through a complex three-dimensional environment based solely on rocket propulsion.  The rocketbelt has been known in the aerospace community over the last fifty years as one of the most difficult and dangerous to master from a pilot training and proficiency standpoint.  With updated space-age technology, groups have utilized new lightweight metals and materials as well as higher performance catalyst pack reaction materials to increase the flight time of the original Bell flight platform from approximately eighteen seconds to thirty-two seconds.  Although with an almost doubling of the flight time duration, the realistic functional application of the device has still fallen short from gaining interest from both civilian and military contractors.  Development teams have recently increased the flight duration of the original Bell Rocketbelt platform to approximately four minutes duration utilizing micro-turbine technology.  This advance in flight duration as well as a switch in fuel from difficult to obtain hydrogen peroxide to more readily available kerosene has greatly increased interest in this device as a more viable flight platform.  There was initial concern with the large number of training flights required to transition a pilot from a training trapeze safety-wired flight to free flight and then to progress to an experience level required to perform advanced flight maneuvers.  With a twenty to thirty second training flight in a rocketbelt costing up to one hundred and seventy thousand dollars per hour to support, it became paramount to design a series of new and innovative training protocols to decrease the number of flight seconds required to obtain an acceptable pilot proficiency to status for transition to free flight status.  

Prior OtoNeurological studies have shown that there are three dominant afferent sensory inputs required for humans to maintain balance in complex three-dimensional environments.  They are:

1) Vision and how the visual system perceives the body's orientation to earth horizontal or a fixed point in space.  

2) Vestibular input from the inner ear balance organs regarding how the head is rotating in a pitch, yaw, or roll component or translating in space in both a vertical and horizontal fashion.  

3) Somatosensory input from upper and lower extremities utilizing touch, pressure and joint proprioception regarding how the body is making contact with a perceived earth stable surface and how the head is moving in reference to the body.  

These three afferent sensory inputs are integrated in the brainstem and processed to create the complex program to maintain balance.  When ambulating, a human will always need two of those three sensory inputs to maintain acceptable balance and not become a fall risk .  Pilots instructed on complex aeronautical platforms do very well because they are trained to rely on primarily visual and vestibular integration and in certain cases fly instruments only when there may be abhorrent vestibular input.  Somatosensory information is utilized, but to a lesser degree in standard flight platforms.  

In our typical OtoNeurology clinic encounter, we often evaluate pilots with either vestibular or somatosensory integration deficits.  An example of a vestibular integration deficit being an acoustic neuroma or a viral vestibular neuronitis resulting in a loss or compromise of vestibular afferent inputs from the inner ear.  An example of a somatosensory integration deficit being a cervical central canal cord compression with or without myelopathy or a diabetic peripheral neuropathy of the lower extremities resulting in compromise of somatosensory afferent input from the arms or legs.  Both of these deficits may likely have the pilot present with balance complaints.  The former with chronic "disequilibrium" sitting and standing, and the latter typically symptomatic while standing and ambulating but more asymptomatic while sitting.  Pilots with somatosensory deficits typically can perform their flight requirements while those with compromise to their vestibular afferent input cannot.  

A rocketbelt pilot on the other hand utilizes a large component of all three sensory inputs to fly that platform.  The most obvious difference being that the rocketbelt pilot uses a predominance of mid thoracic and cervical somatosensory integration.  This requires a stiffened lower extremity posture to create a pendulum component to achieve an earth horizontal reference and then a compensatory series of cervical and thoracic musculoskeletal maneuvers to control the flight dynamics of the rocketbelt flight platform.  The rocketbelt pilot still requires visual and vestibular integration to an ever so slightly lesser degree.  This need to rely so much more heavily on somatosensory integration in order to fly a rocketbelt is why fixed and rotary wing pilots have a very difficult time with the platform transition.  There have been more men to walk on the moon than have flown an untethered rocketbelt.  Those that have performed the best had minimal to no formal prior flight training but still required upwards of seventy-five to one-hundred training flights prior to their first successful untethered flight as demonstrated by the Bell Aerospace team.  This proposed difference in multisensory integration deficits between a fixed wing and rocketbelt flight platform raised the question as to whether modified training protocols might decrease the training time to unteathered free flight for the rocketbelt.  We proposed a preflight training protocol for pilots that included aggressive training on a combination of three different physical therapy balance devices that are typically utilized in our OtoNeurology clinic for patients with different types of balance integration deficits.  Five pilots were chosen with different previous flight training backgrounds and ran through a multisensory integration balance program for one month prior to beginning training on the rocketbelt. They were then followed through their flight training on the tethered safety wire trapeze and graduation to untethered flight status with their flight numbers for each recorded.


Five pilots were selected for the single arm flight training program.  The small N was acceptable secondary to the excessive costs incurred for the actual rocketbelt flights and the extreme risk exposure to the pilots flying the device.  Pilot A was a 23 year old male, height 6'0", 178 pounds with no prior flight or skydiving experience.  Pilot B was a 48 year old male, height 5'9", 170 pounds with 900 hours of both reciprocal and jet engine fixed wing experience and twenty skydive training jumps.  Pilot C was a 60 year male, height 5'9", 167 pounds with over 2000 hours of high performance fixed wing experience.  Pilot D was a 16 year old female, height 5'8", 132 pounds with 38 hours of student pilot training in fixed wing tail-dragger.  Pilot E was a 13 year old male, height 5'5", 120 pounds with no prior flight experience.  Each pilot was instructed on the proper use of each of three training devices by an experienced physical therapist specializing in vestibular rehabilitation. 

The balance training devices and training protocols:

The first device was a Spine Force system developed by LPG, as seen in figure 1.  The Spine Force is a motorized orbiting platform with computerized resistance protocols for spinal stabilization and somatosensory integration.  Each pilot followed a series of six preset programs for a total of 30 minutes daily on the machine.

Figure 1. Two separate views of the Spine Force System developed by LPG, designed as to act on the muscles of the vertebral column to improve posture, equilibrium and coordination.

The second device was company Alter-G’s Anti-gravity treadmill model P200, as seen in figure 2. This piece of equipment was programmed to suspend the pilot at 75% of their normal weight on a cushion of air.  Each pilot ran a total of 30 minutes daily on the gravity assist treadmill at 3.5, 5.0, and 6.0 MPH for 10 minutes at each speed setting.  While running on the treadmill the pilots were asked to perform visual-vestibular stabilization protocols by stabilizing their vision on various targets placed strategically around the treadmill device.  The pilots typically visually tracked each target for one minute each prior to moving to the next target while continuing to run on the specialized treadmill.
















Figure 2. Alter G anti-gravity treadmill, with inflatable apparatus (black) which lifts runner/pilot and can be adjusted to varying difficulties. The display, as shown in both pictures in front of the runner, will allow for manipulation of the speeds as needed for the study, as well as provide a stable platform to place a variety of visual vestibular stabilization protocol points for the pilot to lock on to. 


The third device was a high performance Force Dynamics Corporation motion simulator model 301 (figure 3).  Each pilot ran a series of 3 difficult preset simulated racing courses 30 minutes daily while simultaneously performing visual saccade tasking to a preset pattern of random laser targets on the race course screen.













Figure 3. Force Dynamics motion simulator model 301(FD 301).  The first picture shows some of the range of motion that the device is capable of, while the second depicts how the display will look when in use. 



Prior to training on the balance devices, baseline benchmark balance testing was performed on each pilot and again repeated at the end of the one month training program prior to beginning tethered flights on the rocketbelt.  Benchmark balance evaluation included computerized dynamic posturography testing (CDP), dynamic visual acuity testing, dynamic gait index testing, and course lap times on the FD 301 device.  A five to twenty percent improvement was expected in average post treatment testing scores in a normal patient population from prior clinical experience.  If a pilot met testing expectation improvements they were advanced to tethered flight training in the rocketbelt.  


The rocketbelt: The rocketbelt (refer to figure 4) utilized in this study is a close design to the original Bell belt platform with design modifications in the aluminum frame, fluid systems, jet nozzles, and tanks to decrease weight and therefore flight duration.  The belt consists of a 6061 vertical aluminum spine that holds a horizontally aligned tank rack and housing for a Mity Mite dome type nitrogen pressure regulator and multiple segments of 316 stainless steel tubing and needle, pressure relief, and check valves.  Two D2 stainless steel hydrogen peroxide tanks holding 2.4 gallons each are attached to the tank racks with stainless steel bands.  Centering the D2tanks is an Air Hog carbon fiber reinforced light weight aluminum bladder nitrogen tank rated to 4000 PSI.  A carbon fiber corset custom molded to the pilot is attached to the aluminum spine and the pilot secured by means of a five point quick release harness.  A 316 stainless steel motor chamber housing ninety silver plated nickel alloy catalyst screens and two propulsion tubes with exhaust nozzles and bilateral thrust jetavator rings is attached to the top of the aluminum spine with a gimbling device and anti-yaw coupler.  Two aluminum control arms are attached to the gimble and allow the pilot to control the thrust from the motor nozzles in a pitch and roll fashion by adjusting upper body position in reference to his stationary and pendular leg position.  Two control handles are positioned on arm assembly.  On the right is a cable type throttle control handle that opens and closes a hydrogen peroxide valve that is a similar design as the Waterworks valve used in the Bell belt.  This valve regulates the amount of thrust created by limiting the volume of hydrogen peroxide passed across the silver catalyst screens in the motor chamber.  On the left is a cable type control handle that attaches to both thrust vectoring jetavators that provide isolated pilot yaw control.  The liquid fuel used in this study is a double pass resin deionized 90 percent hydrogen peroxide supplied by XL-Space Systems Corp. There are two gauges to allow pilot monitoring of the Air Hog pre-regulated nitrogen pressure and D2 post-regulated hydrogen peroxide tank pressure after passing through the Mity Mite regulator.  There is also a digital timer located on the throttle valve to provide the pilot with flight duration information allowing termination of the flight prior to exhaustion of fuel reserve.





















Figure 4. Back, side and front views of the Rocketbelt, as described above, supported on tripod



Tethered flight training:  The tether cable trapeze system consists of a 2800 pound tensile strength stainless steel aircraft cable suspended twenty-five feet above the ground in an earth horizontal fashion.  This cable is called the support cable.  Another independent cable called the catch cable is attached to the rocketbelt spine with a fastening device and directed upwards and over a single pulley attached to a trolley system located on the support cable.  The trolley system, via independent pulleys, travels freely in either direction horizontally along the support cable staying directly above the rocketbelt pilot. The catch cable, after passing up and over the trolley pulley, is directed downwards and attached to a handlebar with a fastening device.  During a rocketbelt training flight an assistant called the catcher holds the handlebar. The catcher positions himself, the catch cable, and the handlebar to keep the trolley located above the rocketbelt pilot during flight and provides rapid  resistance to the catch cable should the pilot fall or lose flight control. This is done to reduce the risk of pilot injury or damage to the rocketbelt during practice flight.  Figure 5 shows a pilot completing a tethered flight.


















Figure 5. A pilot completing a tethered flight with harness and pulleys shown.  The catcher can be seen in the first picture furthest to the left.



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