Posted: February 16th, 2017

Landing Performance

For this last part of this week’s assignment you will continue with your reciprocating engine (i.e. prop) powered aircraft and its reduced weight. Let’s first collect some of the data that we already know:

- Stall Speed for 90% of Maximum Gross Weight (i.e. the stall speed for 10% decreased weight from above, which we already calculated in Exercise 4, problem B.):

- Find the Approach Speed [kts] for your 90% max gross weight aircraft trying to land at a standard sea level airport. Approach speed is usually some safety margin above stall speed -.let’s assume for our case a factor of 1.2, i.e. multiply your stall speed from number 3. with a factor of 1.2 to find the approach speed:

- Determine the drag [lbs] on the aircraft during landing roll.

- I) For simplification, start by using the total drag value [lbs] for stall speed (for the full weight aircraft) from your module 4 table:

- II) Adjust the total drag (from I) above) for the new weight (from H. I) above) by using the textbook Equation 7.1 relationship: D
_{2}/D_{1}= W_{2}/W_{1}

III) Find the average drag [lbs] on the aircraft during landing roll. A commonly used simplification for the dynamics at play is to use 70% of the total drag at touchdown as the average value. Therefore, find 70% of your II) result above.

- Find the frictional forces during landing roll. The Total Friction is comprised of Braking Friction at the main wheels and Rolling Friction at the nose/tail wheel. For this example, let’s assume that, in average, there is 75% of aircraft weight on the main wheels and 25% on the nose/tail wheel over the course of the landing roll. The Average Friction Force is then the product of respective friction coefficient and effective weight at the wheel/wheels (see p. 209 textbook):

F = m*N

- I) If the rolling friction coefficient is 0.02, what is the Rolling Friction [lbs] on the nose/tail wheel? (Remember that only 25% of total weight are on that wheel and that the weight was reduced by 10% from maximum gross weight – see H I)):

- II) If the main wheel brakes are applied for an optimum 10% wheel slippage (as discussed on textbook pp. 209/210), what is the Braking Friction [lbs] on the main wheels during landing roll on a dry concrete runway? Use textbook figure 13.9 to determine the friction coefficient. (Remember that the weight on the main wheels is only 75% of total aircraft weight).

III) Find the total Average Friction [lbs] during landing by building the sum of I) and II):

- Find the Average Deceleration [ft/s
^{2}] during landing roll. Use the same rectilinear relationships as in module 1, applying the decelerating forces of friction and drag from J. III) & K. III) above. Assume that residual thrust is zero. (Keep again in mind that for application of Newton’s second law, mass is not the same as weight. Your result should be a negative acceleration value since the aircraft decelerates in this case.):

- Find the Landing Distance [ft] (Remember that we start from a V0 at approach speed and want to slow the aircraft to a complete stop, applying the negative acceleration that we found in L. Also, remember to convert approach speed from I. above into a consistent unit of ft/s.):

- If your aircraft was to land at a higher than sea level airport (e.g. at Aspen, Co) what factors would change and how would it affect your previous calculations, especially your landing distance. Explain principles and relationships at work and support your answer with applicable formula/equations from the textbook. You can include example calculations to support your answer:

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