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Grumman Airplane Performance

Except for two brief attempts at revival, the AA-5* airplanes are 35-40 years old. So are their Owners' Manuals ("POH").

When those manuals were written, electronic calculators cost over $200, in 1970s dollars (over $1000 in 2015) – an expensive addition to anyone's flight bag. So the manuals have performance listed in tables that help the pilot avoid having to calculate density altitude. The information was always there, just cloaked a little bit.

The charts here are based on density altitude[1], which is easy to calculate these days. They are graphic, so that intermediate values are available without the need to use that (now cheap) electronic calculator for interpolation. They are derived directly from POH data. The tables from the manual were simply entered into a spreadsheet and plotted.

Data are given for the airplane at maximum gross weight. For lighter weights, performance is better in all parameters. Shorter takeoff and landing distances, faster airspeeds, etc. These charts were compiled from data for the 1972-79 series only. Data for the 1990's and 2000's should not be substantially different. For the Traveler, the POH takeoff and landing charts are so sparse that they are not graphed here. It wouldn't be much of a graph.

One parameter that is not usually addressed is best range. Melville Byington and Russ Erb wrote articles on this topic over twenty years ago, and David Rogers more recently, but their results still don't seem to be widely used.

The manufacturer's tables give figures for airspeed (miles per hour) and fuel burn (gallons per hour). It's a simple task to divide one number by the other, so the charts include graphs for specific range (miles per gallon). The curves peak at a power setting that's lower than we usually use to cruise, but there isn't a lot of variation below 65% power.

Byington's article states that the calibrated airspeed[2] for maximum specific range is independent of altitude. Rogers makes the same point in his excellent series on technical flying. The manufacturer's data for the AA-5* series do not exactly agree with this statement[3]. I have contacted a few "experts" about the discrepancy, but nobody has come up with an explanation for it.

 

[1] Look at the center column in the cruise performance tables. Those parameters are given at the standard temperature for each pressure altitude; i.e., for density altitude.

[2] Rogers cites equivalent airspeed. At Grumman speeds, this is the same as calibrated airspeed.

[3] It takes a bit more work with the spreadsheet to get this relationship, using standard formulas to convert true airspeed back to calibrated airspeed. Once this number is known, the pilot can easily get the required indicated airspeed, and fly that speed at any altitude to maximize his range.

Maj. Russell E. Erb, "A Low Cost Method for Generating Takeoff Ground Roll Charts from Flight Test Data," Society of Flight Test Engineers (SFTE) 27th Annual Symposium, Fort Worth, Texas, November, 1966, http://www.eaa1000.av.org/technicl/takeoff/topaper.htm A Sample Atmosphere Table (US Units) http://www.pdas.com/e2.htm Harvard Holmes, "Using a Spreadsheet to Construct a Takeoff Chart," Dec. 2002, http://www.eaa393.org/Cleco/Cleco03/to-m20e_3.htm

 

AA5 Traveler

Cruise Performance

 

 

AA5A Cheetah

Takeoff Distance

Max. power, flaps up.
Runway: hard surface, level and dry.
Lift off: 56 KIAS
Clear 50 feet: 63 KIAS
Distances apply from the point where maximum power is attained.

Decrease by 4% for each 5 knots headwind.
Increase by 10% for each 2.5 knots tailwind, up to 10 knots.

Landing Distance

61 KIAS at 50 feet, full flaps.

Decrease by 4% for each 5 knots headwind.
Increase by 9% for each 2.5 knots tailwind, up to 10 knots.

 

Cruise Performance

 

 

AA5B Tiger

Takeoff Distance

Max. power, flaps up.
Runway: hard surface, level and dry.
Lift off: 57 KIAS
Clear 50 feet: 65 KIAS
Distances apply from the point where maximum power is attained.

Decrease by 4% for each 5 knots headwind.
Increase by 8% for each 2.5 knots tailwind, up to 10 knots.

Landing Distance

Short field: 63 KIAS at 50 feet, full flaps.
Normal: 69 KIAS at 50 feet, full flaps.

Decrease by 3% for each 5 knots headwind.
Increase by 9% for each 2.5 knots tailwind, up to 10 knots.

 

Cruise Performance