Model Autogyro Flight Prediction Chart

Jim Baxter, 1997

The angling red line on this chart represents the seemingly magic rotor disk loading of 5.0 ounces per square foot.   Experience tells us that a model with a disk load of 5.0 or less should perform fairly well, providing of course the blades & rotor are of good design, and using a proven airfoil such as the flat bottomed "Clark Y".   Simply enter with one or two arguments and find the other.   As an example if you want to design a model with a 48" rotor, enter at 48" on the left, go across to the 5.0 line, then by proceeding down you find that the model ideally should weigh no more than aproximately 65 ounces.   If you enter with both the weight and disk size of your model and the plot of the two lines falls  below the line, then the performance will be less than desirable, and directly proportional to the distance from the line.   Conversely, the opposite is true if your plot falls above the line, which is where most all top performing models will plot...

Should you have a model with a 48" rotor, and it weighs 4 1/2 # (72 ounces),  you will probably find it`s lift performance will be only fair, particularly at low airspeeds.   That model may fly, but would not hover in anything less than a strong wind.    Models with disk loads which fall below the line will tend to fly faster and require a higher take-off and landing speed.  A typical example of this is the Whistler  which will plot below the line, and in fact does require a higher takeoff and landing speed, and will not hover without a reasonably strong headwind..

Please note that much depends on the design of the model and it`s rotor hub and blades,  This chart was developed with experience gained from small models utilizing free flapping rotors with 3 to 4 blades.  Ideally, you want the lowest disk loading possible with your model.  if you are able to build a model with a disk load of 2.5, for example, you can expect an absolute superb lift performance.

Another chart is being developed to aid in the determination of weight & rotor size versus power required for the model.  However until this is completed, If you can calculate the thrust power of your engine, the model weight must not exceed twice that amount.   In otherwords, if your model has an engine with 4# thrust, the model may weigh up to 8# and still be able to fly.

Note: This chart applys to rotors having various numbers of blades...  Rotor solidity is not considered highly significant for our general prediction purposes.   The more blades you install the slower the rotor will autorotate, thus the difference in lift is not significant enough for the purposes of this guidance chart..

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rev 02-26-01.. jb