About nine months ago, Ray Colelli sent me a pair of the first of his then-experimental molded nylon propellers, in the 18-6 size. I was immediately impressed with the appearance of the prop, it being of a shape that appeared to optimize the maximum benefits of propeller aerodynamics as I have learned to recognize them. I admit to a great deal of initial negative thinking. Nylon props in the smaller sizes have earned a reputation for being dangerous in certain situations if not properly cared for. Ray's props were at least three times the size of any of the smaller nylon jobs.

However, after careful consideration of all the factors surrounding these props, I have come to the tentative conclusion that these props are one of the best products of their type on the market today. I base that conclusion on several factors:

1. These props are almost universally going to be used on ignition engines that are basically incapable of extreme rpm. Most of these engines will not exceed 8,000 rpm, and at these speeds, the centrifugal forces that are primarily responsible for the destruction of the smaller props, run at the extreme speeds of the modern .60's, are not such a factor. This fact alone adds greatly to the safety factor of any prop.

2. These props are molded out of a very special, extremely stiff nylon material that seems much more ideally adapted to propeller construction than the softer nylon that most of the smaller props are made out of.

3. Ray has gone to a great deal of trouble to make the props come out of the mold as aerodynamically true and as closely balanced as he possibly can. This is proven by the very little work needed to finish off and balance the blade statically, and in the way the blades track when they are running. The Dynathrust props track more consistently, prop to prop, than any of the competitive brands.

4. The cross-section of Ray's props from about the midpoint on out to the tip becomes extremely thin. This has two effects. Out on the blade where the airspeed is highest, an extremely thin airfoi1 is very desirable from a drag standpoint. The thinner blade also then subjects the hub to greatly- reduced centrifugal forces, This thin blade would be impossible to achieve in wood; the resulting prop would be very limber and weak. Only the unique properties of the nylon Ray uses allows this technique.

Flight Testing

As far as I am concerned, the only place to test any item for a plane is on the plane, in the air. For props, I have heard just about every kind of off-the-wall testing procedure that the mind of man can dream up. Some of them were downright inventive.

Personally, I conduct only two kinds of tests, and pay attention only to the flight performance test. First, I run a ground RPM check, switching from prop to prop, without changing any other factors, just as quickly as this can be accomplished. Second, I fly all the props in the same manner; determining the performance of the plane in the air as quickly and as thoroughly as I can, then landing, changing props, and reduplicating the same maneuvers. I have other observers available while this is being done, to verify my observation.

The results obtained this way may not be scientific, but they are very practical. Those results, as apply to the Dynathrust props, are that the Dynathrust props allowed a little higher ground RPM than any of the competing props, (from 25 to as much a. 200 rpm difference), and they flew the plane BETTER in all maneuvers. Most of the pilots helping me with these tests also commented that the engines seemed to idle smoother. I would attribute that effect to the superior tip tracking of. the Dynathrusts, plus the slightly overall-heavier blade having a superior flywheel effect.

The Dynathrust props rate a superior review in one other area. That is their ability to withstand a minor brush with the ground without apparent damage, whereas the standard wood prop in these sizes is almost totally certain to be destroyed in a like situation. I give this review with some trepidation; I have personally seen this characteristic demonstrated, but I hate to mention it because any prop that has hit the ground is a potentially dangerous prop. Any contact with the ground or an object puts extreme stresses on a prop, and damage might then exist that isn't obvious.

This last factor is the one reason that I do state that any approval of the Dynathrust props is tenative. All tests and flying I have conducted with these props says that they are superior in every way. However, I would reserve total final judgment until. we have at least two years' experience with them.

Dynathrust Props are available only direct from the manufacturer, so that he may keep the price down. See the Dynathrust ad elsewhere in this issue for prices.

One last comment and I'll shut up. The Dynathrust props have extremely thin tips. These tips, when swinging on a running engine, make very efficient meat slicers!!! So do any prop tips, for that matter, but The Dynathrust will be more effective at s1icing you up than just about any other, though the end result is the same. Do not start up our size birds without someone else anchoring the plane. Be very careful of your forearms whenever you reach around the prop for any reason; these props are a heck of a lot bigger, than the smaller ones, and they are much harder to reach around. Stay away from them as much as humanly possib1e. Please don't let me hear that you pot all chopped up from one of our planes.