REPORT SA4000DS, REV. IR COMPLIANCE CHECKLIST FOR FIELD APPROVAL TSO’d 31” DESSER TUNDRA ON STC’d 10” ABI WHEELS FOR CESSNA 180 & 185

Prepared by: Melvin W. Stene Date: July 1, 2017

1 Report SA4000DS Revision: IR July 01, 2017

Compliance Checklist

• ABI STC SA01015SE • Desser TSO-62e Approved 31” Tundra , rated at 2,225lbs, speed rated 120mph • FAA Advisory Circular AC23-17C

Following the guidance of FAA advisory circular AC23-17C in showing compliance for the installation of “tundra tires” on light airplanes that have a certification basis of CAR 3 the following report has been assembled to insure compliance with the applicable CAR’s.

Table #1 below outlines the specific regulations identified in AC23-17C, Appendix 2, “A Compliance Checklist to CAR part 3, as amended Nov. 1, 1949. Both the Cessna 185 and 180 were certified under CAR Part 3 as per TCDS’s, 5A6 and 3A24.

The wheels already meet the regulatory requirements by having STC approval under ABI STC SA01765SE for the Cessna 185 and 180 incorporating the installation of 8.50x10 and 29x10 tires.

The 31” Desser tires have TSO-62e approval, rated at 2,225lbs and 120mph, and meet the requirements of ABI 10” wheel STC SA01765SE for the tire being rated at, or above, the weight and speed rating of the aircraft. The 29” ABI Bushwheel is STC approved for the Cessna 180 and 185 but does not have TSO approval and its speed rating is reduced to 70mph.

Instructions for continued airworthiness will follow the requirements of STC SA01765SE for the ABI wheel assemblies and AC43.13-1b, Chapter 9, sections 9-13 thru 9-19 for the 31” Desser Tires. Recommended tire pressure ranges for the 31” Desser Tires are minimum 8psi and maximum of 20psi.

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COMPLIANCE CHECKLIST

CAR Subject Evaluation Means of Compliance 3.71 Weight & Balance Original W&B: EW 1899.00 CG: 39.16 Moment: Analysis 74373.45 • Remove 8.50x6 Wheels & Tires; -52lbs @ 17in • Add 31” Tires & 10” Wheels; 102lbs @ 17in

New W&B: EW 1949.0 CG: 38.60 Moment: 75223.45

3.72 Use of Ballast Not Required: Per TCDS CG range; Analysis (+41.9) to (+46.5) at 3350 lb. (+34.5) to (+46.5) at 2100 lb. or less

3.73 Empty Weight No Change Analysis 3.74 Maximum Weight No Change Analysis 3.75 Minimum Weight No Change Analysis 3.76 CG Position No Change Analysis 3.81 Performance Appendix A Analysis, Similarity 3.82 Definition of Appendix A Analysis, stalling speeds Similarity 3.83 Stalling Speed Appendix A Analysis, Similarity 3.84 Takeoff Appendix A Analysis, Similarity 3.85 Climb Appendix A Analysis, Similarity 3.86 Landing Appendix A Analysis, Similarity 3.105 Flight Appendix A Analysis, Characteristics - Similarity Requirements 3.143 Ground and Water Upon installation of the wheel and tire combination Design Characteristics - ground handling characteristics will be evaluated to insure Evaluation, Requirements there are no tendencies to 1) Nose Over 2) Brakes Similarity Operate Smoothly with no nose over tendencies 3) No uncontrollable looping tendencies

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3.159 Flutter & Vibration Upon installation of the wheel and tire combination, Design (vibration only) vibration will be evaluated to insure the aircraft does not Evaluation, exhibit excessive vibration. Similarity 3.189 Airplane No Change N/A equilibrium 3.190 Flaps extended No Change N/A flight conditions 3.191 Unsymmetrical No Change N/A flight conditions 3.211 General No Change N/A 3.212 Pilot Effort No Change N/A 3.213 effects No Change N/A 3.214 Horizontal tail No Change N/A surfaces 3.219 Maneuvering No Change N/A Loads 3.231 Primary flight No Change N/A controls and systems 3.241 Ground Loads STC’d Wheels for model of aircraft & TSO’d tires for Analysis, applicable load and speed. Similarity 3.242 Design Weight STC’d Wheels for model of aircraft & TSO’d tires for Analysis, applicable load and speed. Similarity 3.243 Load factor for STC’d Wheels for model of aircraft & TSO’d tires for Analysis, landing conditions applicable load and speed. Similarity 3.244 Landing cases and STC’d Wheels for model of aircraft & TSO’d tires for Analysis, attitudes applicable load and speed. Similarity 3.248 Braked roll STC’d Wheels for model of aircraft & TSO’d tires for Analysis, applicable load and speed. Similarity 3.249 Side load STC’d Wheels for model of aircraft & TSO’d tires for Analysis, applicable load and speed. Similarity 3.342 Proof of Strength STC’d Wheels for model of aircraft & TSO’d tires for Analysis, applicable load and speed. Similarity 3.351 Tests STC’d Wheels for model of aircraft & TSO’d tires for Analysis, applicable load and speed. Similarity 3.353 Shock Absorption STC’d Wheels for model of aircraft & TSO’d tires for Analysis, Tests applicable load and speed. Similarity

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3.354 Limit Drop Tests STC’d Wheels for model of aircraft & TSO’d tires for Analysis, applicable load and speed. Similarity 3.355 Reserve Energy STC’d Wheels for model of aircraft & TSO’d tires for Analysis, Absorption Drop applicable load and speed. Similarity Tests 3.361 Wheels STC’d Wheels for model of aircraft & TSO’d tires for Analysis, applicable load and speed. Similarity 3.362 Tires STC’d Wheels for model of aircraft & TSO’d tires for Analysis, applicable load and speed. Similarity 3.363 Brakes STC’d Wheels for model of aircraft & TSO’d tires for Analysis, applicable load and speed. Similarity 3.429 Fuel System Nearly identical physical dimensions as STC approved Similarity General Tundra tire which does not impose any Fuel System limitations. 3.437 Unusable Fuel Nearly identical physical dimensions as STC approved Similarity Tundra tire which does not impose any Fuel System limitations. 3.444 Sump No Change N/A 3.553 Fuel Tank Drains No Change N/A 3.583 Cooling Tests No Change N/A 3.605 Induction System No Change N/A General 3.606 Induction Systems No Change N/A de-icing and anti- icing provisions 3.699 Landing light Identical landing and taxi stance as the STC’d 29” Similarity installation Bushwheel and wheel configuration so lights would illuminate in an identical manner hence satisfying the regulatory requirements by similarity. 3.735 General No Change N/A 3.737 Limitations No Change N/A

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Revision History Revision Description Date Author IR Initial Release July 01, 2017 W. Stene

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Appendix A

Tire Evaluation and Calculations:

The 31” Desser tire is an FAA TSO’d tire with a load rating of 2,225lbs per tire and a speed rating to 120mph. The tire is mounted on an ABI 10” wheel assembly that are STC’d for the Cessna 180 & 185 airplanes and has approval for both 8.50x10 and 29x10 tires.

The load rating of 2,225lbs for the 31” Desser tundra tire meets the requirements for both the Cessna 180 and 185 series aircraft that have a maximum gross weight of 3350lbs.

The physical dimensions and weights of the 31” Desser tire was compared to the STC approved 29” AK Bushwheel. The dimensions measured from actual tires are shown in Table #1.

Tire Height (d) Width (w) Weight (Including Wheel Assembly) 31” Desser 30.25” 11.75” 50 lbs/ea. 29” Bushwheel 30.125” 11.75” 38 lbs/ea. Table #1: Tire Physical dimensions measured from actual tires and weights.

The ABI 29” Bushwheel are STC approved for both Cessna 180 and 185 aircraft models with physical dimensions similar to the 31” Desser. The ABI 29” Bushwheel is speed rated to 70mph while the 31” Desser tire is speed rated to 120mph.

The difference of weight and dimension of the STC’d 29” ABI Bushwheels and 31” Desser tundra tires will be evaluated to demonstrate compliance with CAR 3 via similarity to the approved Bushwheels. It will be shown that the differences are negligible and that the installation of the 31” Desser meet the regulatory requirements of CAR 3.

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Per reference [1], the additive drag coefficient of tire type, C, high floatation tundra tires is given by the following equation:

ΔCDtire = ((d x w)/Sref)*ΔCDs

ΔCDS = 0.23 For Type C Tires, Reference [1], page 718

Tire ΔCDtire 31” Desser 0.00326 29” Bushwheel 0.00325

Table #2: ΔCDtire calculations

Per Reference [1], CDmin for the Cessna 180/185 series of airplane is 0.0297. With the total CDmin of the aircraft known we can now evaluate the impact of the differences in ΔCDtire between the 31” Desser tire and the 29” Bushwheel tire on the aircraft.

The difference in ΔCDtire for the 31” Desser tire and 29” Bushwheel is virtually negligible; calculation 0.00326-0.00325 = 0.00001. This difference constitutes an impact of only 0.03% over the total CDmin of the aircraft of 0.0297. Such a small difference would not be measurable and validates the use of similarity of the STC’d 29” Bushwheel tire to the 31” Desser tire as a means of compliance.

The small difference in CDmin and nearly identical physical properties of the tires insures no measurable difference in the flight performance of the aircraft with respect to take-off, climb, and landing vs the STC’d 29” Bushwheels. Therefore the 31” Desser tires meet the regulatory requirements via similarity for CAR’s 3.81,3.84,3.85, & 3.86.

In evaluating the stall speed it would be expected the tires would not impact stall speed or balanced stall characteristics in a measurable manner. This matches the findings in FAA AC23-17C when evaluating the effects of tundra tires on Piper SuperCub type airplanes. The 29” Bushwheels already satisfies the FAA regulatory requirements and the 31” Desser tires are effectively identical in physical and aerodynamic properties hence they meet the regulatory requirements via similarity for CAR’s 3.82 & 3.83.

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In evaluating the ground handling characteristics of the 31” Desser Tundra tire a comparison of stiffness to STC approved tires is made. The 31” Desser tire is stiffer than the 29” ABI Bushwheel but slightly softer than the STC approved 29”x11-10 tundra tire. With the stiffness of the 31” Desser tire being in the middle of two STC approved designs it would be reasonable to expect that the tire would exhibit satisfactory ground handling characteristics. It is recognized by the FAA that “Tundra” tires adversely affect handling qualities of the airplane but the FAA has determined these effects not to be significant with regard to safety. To assure compliance it is recommended upon installation of the wheel and tire that ground tests be conducted to insure there are no tendencies to 1) Nose Over 2) Brakes operate smoothly with no nose over tendencies & 3) No uncontrollable looping tendencies exist. Therefore with evaluation to similar designs and ground testing the ground handling characteristics of the wheel and tires would satisfy CAR 3.143

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This report is available for use by aircraft owners obtaining a field approval for 31” Desser Tires on 10” AB wheels. This report is not to be used as documentation for submission to obtain an STC.

References 1) General Aviation Aircraft Design, Applied Methods and Procedures. Snorri Gudmundsson

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