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Piper Comanche

 

TO ALL COMANCHE OWNERS:

If you own a Piper-Comanche, certainly you will be interested in improving its stability and aerodynamic efficiency.  If your craft is a Single or Twin no doubt you will be equally interested in obtaining additional fuel for extending your range, and in obtaining additional payload allowance of 150 lbs. on most models.  Even on short flights for example from point A to point B and returning without ever having to take precious time to refuel at point B, not to mention the fuel savings when topping off with low priced fuel.

 

 

GENERAL INFORMATION:
  J.L. OSBORNE, formerly Brittain Industries, pioneered the development of wing tip tanks for civilian aircraft many years ago.  Developing and completely redesigning the wind tip tank (20 gallons each) for Navions, Twin Navions, and Beechcraft Bonanzas, we are now marketing our FAA approved 15 gallon wing tip tank for the Comanches, providing for 30 gallons additional fuel.  The motivating factors in engineering this wing tip tank installation on a Comanche were two-fold: (1) to obtain an efficient means of carrying additional fuel, and (2) to obtain the desirable changes in the aircraft’s flight characteristics and performance that have been observed on all other makes of airplanes to which wing tip tanks have been added.  These changes are mainly in the improvement in stability of the aircraft and increases in both rate of climb and speed, and a decrease in stalling speed.

 

 

AUXILLARY FUEL:
  Obviously, there are two approaches to obtaining auxiliary fuel capability.  The first is internally mounted cells, such as in the baggage compartment or under the rear seat or internally mounted fuel cells within the wing panel outboard of the main tank.  Regardless of where these internally mounted fuel cells may be located, the net result is the addition of just so much non-supporting dead weight to the aircraft, diminishing its performance and “breaking its spirit” in the same manner as an equivalent amount of dead weight baggage or additional passengers.  In direct contrast the second method of obtaining auxiliary fuel facilities is to use eternally mounted wing tip tanks.  Here, we find that with a wing tip tank that is designed to be aerodynamically efficient, the tip load is self-supporting: that is, carries its own weight and actually improves the performance.

 

 

RATE OF CLIMB AND GROSS WEIGHT INCREASE:
  By the addition of wing tip tanks, the burble of air, or the vortex at the wing tip, is eliminated as a result of the “end plate” effect that the tip tank provides.  One actually obtains an increase of overall performance that is related to the rate of climb and speed.  Utilizing this aerodynamic benefit and by means of correlative engineering and drop tests to substantiate structural integrity, J. L. OSBORNE Incorporated affords gross weight allowances with installation of Wing Tip Tanks (gross weight may vary with serial number designation).  Carefully controlled flight test wherein many sawtooth climbs were made, establishing this increase in rate of climb to be a fact, leaving nothing to guesswork.  Further proof of the existence of additional lift lies in the fact that by adding Osborne Wing Tip Tanks, most owners find that Comanches equipped with stall warning devices required relocation of the actuator on leading edge of the wing to compensate for the increased angle of attack of the wing required to produce a stall with the tanks in place of the tip. This eliminated all guesswork and leaves nothing to an individual’s impression or biased interpretation of what has been accomplished toward improving the aerodynamic efficiency of the aircraft.

 

 

SPEED:
 
At sea level there is neither a measurable increase or decrease in cruising speed.  However, at higher altitudes: i.e., above 4,000 feet, one begins to note a definite increase in cruising speed, with this increase being 4-6 mph at 9,000 feet.  This is a result of increasing the lift of the wind where at high altitudes in thinner air, on-the-step performance is obtained, even at the lower indicated air speeds.  The weight of the fuel in the tip tanks is precisely on the center of gravity and does not interfere with on-the-step performance by rearward loading.  Owners who have installed the OSBORNE Wing Tip Tanks will attest to this increase in cruising speed. 

 

 

ENDINEERING AND TEST:
First, of course, it was necessary to establish the structural integrity of the aircraft itself, and mainly the wing.  The now OSBORNE Wing Tip Tanks were installed and static loads applied to the tanks to test the wing for resistance and strength in bending.  On this score, successful static tests were conducted, using 40% more weight than required by FAA.  Next, the aircraft was dropped, measuring with FAA equipment, the forces that developed in the landing gear and the wing tip.  In addition, complicated vibrations tests were performed by FAA Flight Test engineers in which all types of maneuvers were involved.

 

 

TANK:
  The OSBORNE tank is streamlined and smooth, with a flush filler well and drain.  By means of drop hammer dies, the shells are formed of heat treated aluminum which is hardened to resist dents and distortion.  The tank is assembled with flush welds, eliminating any raw edges or flanges protruding into the line of flight.  The workmanship is of the highest quality, with production being under is such that Princeton University Research Center chose our tank (formerly Brittain Industries) for external fuel cells on a “ground effect” vehicle that was under development.

 

 

INSTALLATION:
 
Installation is extremely simple and straight forward. Attachment of the tank is by means of nut plates installed on the outer flange of the end rib.  There is no major rework or modification of the wing structure required.  Fuel lines are readily routed on the external surface of the rear spar in the aileron and flap bay.  There is no re-balancing of the ailerons required.  The Single engine existing fuel selector valve is replaced with a pre-assembled fuel selector system.  Each tank contains a fuel quantity indicator.  The latter is mounted on the instrument panel where a toggle switch is employed to read the fuel quantity in the right or left wing tip tank.  The Single and Twin engine installations may be readily completed in the field by the average mechanic.

 

STABILITY:
  The most noticeable change in the flight characteristics of the Comanche is the increased stability in respect to roll and yaw.  This can best be compared with a tightrope walker who carries a long pole that is weighted at either end.  Without it, he will surely topple from one side to the other.  Although the Comanche is a remarkably stable aircraft, this increase in stability and the “feel” that results from the addition of tip tanks gives the plane the feeling of a light Twin and can only be fully appreciated by flying a Comanche so equipped.  As illogical as it may seem, several owner commented that they have installed the OSBORNE Tip Tanks on a Comanche mainly for the increased performance and improved stability and not primarily for the additional fuel capacity.  

FUEL SYSTEM:
SINGLE ENGINE

  The Single engine system is of the direct feed type and does not involve any transfer of fuel (See drawing 4017).  There are two selector valves mounted side by side, each with three positions.  By means of positioning the handles, one may draw fuel from both main tanks or both wing tip tanks simultaneously, providing automatically for a cross-feed system.  One may also position the valves to draw fuel from either tip tank or either main tank.  The wing aux equipped models also have the same selector capabilities making for the ultimate in versatility.  There are no electric solenoid valves or check valves to complicate the installation or restrict the flow of fuel. 

TWIN ENGINE

This fuel system is used in the same way as the factory wing auxiliary tanks (Drawing Reference 55031).  The installation of our solenoid valves permits fuel management of either wing auxiliary or for tip tank usage.  This is accomplished by our electrical selector switch system, placarded Aux Tip (See Drawing Reference). All in all, you will find the installation of the J.L. OSBORNE Incorporated Wing Tip Tanks is a great step in the improvement of the performance an utilization of the Comanche.  The increase in resale value of the Comanches so equipped makes it obvious that this modification is an investment and rather than an expenditure.

 

 

 

For more information, write or call:
J.L. OSBORNE Incorporated
18173 OSBORNE Road
 Victorville, California
  92394

Telephone Number: 800.963.8477
760.245.8477

Fax Number: 760.245.5735