The main thing I would like to tell you gentlemen is something I guess you know already: that the modern propeller has become a very complex and at the same time highly refined mechanism as it has progressed from the original wooden slab, through controllable pitch and through feathering and through reversing, with electric heaters contained in the blades for throwing off ice as it is formed. All of these are progressive contributions to aircraft safety, improving performance, and catering to the problems of all-weather flying as they have arisen.

The propeller itself is a hydraulic mechanism which uses oil from the engine-oil supply, that is pumped up to a proper working pressure and valved by a governor to control engine speed at the will of the pilot. There are subsidiary control systems which enable_the propeller to be feathered very rapidly, so as to cut down the drag which would arise after an engine failure if the blades were not turned into a feathered position.

One of the features that we worked very hard on has been the speed of feathering, since when an emergency arises you want to cut the drag right down. This propeller can feather in 2 or 3 seconds.

Mr. KLEIN. Of course, I think Mr. Hinshaw is the only engineer on this committee, and would you tell us in simple language just what feathering is?

Mr. KEARNS. I can show you very simply, if you would like, right here.

In normal flight, a propeller blade is at an angle. The propeller rotates in this direction, so that in effect, the air is pushed behind it and thrust is developed. It takes force, applied by the engine, to produce the thrust. When all goes well, the propeller varies its angle 'over about a 20° range from something like 20° more than flat pitch to about 40° or 45°. However, if the engine power were suddenly to cease, then the airstream advancing on this propeller would produce forces on the blade which cause the propeller to continue rotation, and it continues to rotate the engine, which perhaps has a failed part, let us say. The energy that is taken from the airstream to cause this rotation results in a drag on the airplane.

It is in order to eliminate that drag at the time when you have a loss of positive thrust, to prevent it from becoming negative, that the propeller is feathered. We will feather this propeller. The blade angle is increased, so that now the air approaches through the sharp edge of the blade, and the propeller remains stationary, and the drag is a negligible quantity.

Mr. KLEIN. When it is in that position, the force of the air on it does not make it turn around as it would if it were flat?

Mr. KEARNS. And moreover, the force is reduced to a minimum because of the small area that the blade presents to the approaching

stream.

Mr. KLEIN. Is that what you call feathering, when you get it in this position?

Mr. KEARNS. Yes.

Mr. KLEIN. Does that require some manual operation by the pilot in order to get it in that position?

Mr. KEARNS. The pilot has a series of push buttons, red buttons, prominently displayed.

Mr. KLEIN. We went over that before, but I would like to have that on the record.

Mr. KEARNS. He simply presses a button once, and an automatic system takes over from there. He needs to do nothing further, and the propeller feathers and stops.

Mr. KLEIN. Regardless of what may be happening in the moto you could still press that button and make the propeller of this plane be in a feathered position, is that right?

Mr. KEARNS. That is right.

Mr. KLEIN. All right; will you proceed, please?

Mr. KEARNS. That is certainly a most important feature of the propeller.

Then as an additional contribution to maneuvering the airplane, such as on an icy runway when the brakes are ineffective even though they may be mechanically sound, the additional feature of reversing has been supplied. The blades, instead of being in what is now this positive thrust and positive pitch position, can be rotated, as we will show you, so that a continued supply of power from the motor now produces a thrust force and pushes the air back or a thrust to the rear, which acts to slow down the airplane.

if

Mr. KLEIN. When you reverse it, you have the same effect, and you want to use it as a brake you reverse the propeller? Mr. KEARNS. That is right.

Now, there are a number of other features about a modern propeller in the interests of passenger comfort and aircraft efficiency. With a multiengine airplane, it is desirable to get all of the propellers running at exactly the same speed across the airplane. If they are not at quite the same speed, there is a throbbing and humming, undulating sound.

Mr. KLEIN. Does it have any effect on the motion of the plane? Mr. KEARNS. No; it is not discernible in that way. It is largely an audible impression that you get.

Mr. KLEIN. Your division makes just this propeller, and so you have nothing to do with the engine manufacture?

Mr. KEARNS. That is right. We make propellers that are used on all of the principal aircraft engines in the world, really, except for those of Russia; there, so far as we know, many of our designs have been copied.

Mr. KLEIN. Do you make them for military planes, also?

Mr. KEARNS. We do.

Now, as I say, the principal points are that these propellers have refined functions, lightweight, rapid action, and reliable mechanical mechanisms, and, as Mr. Martin pointed out, a lot of engineering effort which simply can't be seen in looking at the final article-in making sure that all the vibratory stresses throughout the whole blade, the hub, and the assembly-all of those vibratory stresses which could result in a fatigue failure-crystallization after a long period of time-are controlled to prevent such failures.

Mr. KLEIN. Is the propeller installed by your company?

Mr. KEARNS. We sell the propellers to the aircraft manufacturers, usually, who install them.

Mr. KLEIN. In other words, your effort ceases as soon as you sell the propeller, after you have finished with its manufacture?

Mr. KEARNS. Actually, our effort truly doesn't cease, because we are vitally interested in the subsequent performance of the product, and we follow it quite closely. But there is a sharp line of responsibility; you are quite correct..

Mr. KLEIN. Do your people maintain or do you have a maintenance department which repairs these propellers if they should go wrong? Mr. KEARNS. That is done in two ways. For example, if we sell a propeller for an airline's airplane, and if it is a large, established airline, they will take care of its subsequent overhaul and maintenance. However, many private operators-commercial concerns who own one or two airplanes and want to have them serviced-send them around to us and we take care of them.

Mr. MARTIN. We have a service organization that works with the airlines, to help them do their maintenance.

Mr. KLEIN. If you should receive a complaint from one of the airlines, do you send a man over to look at it, or do they have to disassemble the propeller and send it back to you, and then you examine it at your plant?

Mr. KEARNS. We have regional servicemen who are often stationed with a major airline at its overhaul base, or if he isn't there at the time, he is on call. So they are spotted all over the world and available for help.

Mr. WOLVERTON. With that exhibit before us as an illustration, would you point out to us what part your company is engaged in? Is it just in the propeller, or does it come down into that mechanism that may be spoken of as the dome? Just where does it end?

Mr. KEARNS. I will point out the parts that we supply.

Within the center of this propeller is a shaft which is a standardthere are a series of sizes, but agreed upon by industry and the Government, so that engines in a given power class have a certain standard size of shaft, and this is a 60 size. There the engine ends. All of the parts surrounding that shaft, including this brush housing for transfer of electric current for the electric heaters that are inside the blade, are supplied by us.

We also supply this element which mounts on the engine nose; that is the governor that can be set to control propeller speed at the pilot's will. The speed of that governor is changed or established by setting a certain spring tension inside of it, which can be done manually; and it is done in certain aircraft designs by a cable and pulley system, which we do not supply; or it can be set as here, with a small electric motor and reduction gear, which part we do supply as in this particular illustration.

Also, we supply a pump and auxiliary motor which can be used to aid the governor in feathering the propeller rapidly, or reversing it rapidly, or in controlling the propeller pitch when the engine is not rotating. That may be desirable for one reason or another.

Then, in addition to these elements, there are certain other control components throughout the airplane, including certain relays that contact various electric currents to perform the feathering function and the reversing function, and so on.

There is a control box for the electric heater system, which cycles one propeller on, and then another, and another, and then another; and then it comes back and repeats the process, to economize on electricity.

And then we supply usually just one other component in the cockpit, which is the feathering push button.

In other words, those parts, those elements of the control system which have a really vital function, we supply ourselves, although others could supply them if they wished.

Mr. WOLVERTON. Will you point out what is referred to as the dome?
Mr. KEARNS. This is the dome of the propeller [indicating].
Mr. WOLVERTON. Do you manufacture that?

Mr. KEARNS. We do.

Mr. WOLVERTON. How far are you able to express an opinion with respect to the possibility of corrosion in the dome or any of the parts that you have referred to as being connected with the operation of the propeller?

Mr. KEARNS. Well, I think that I can express an opinion. We proect these parts in general with a plating, either zinc or cadmium, to ninimize, first. anv tendency to corrosion.

Then secondly, being bathed in the lubricating oil under pressure at all times, the system remains quite clean.

There are a number of stainless steel parts; there are certain rings hat are bronze, and so on.

So as a matter of practice now, we have learned which parts need to be corrosion-protected, and in what way, and have carefully taken care of the requirement.

Mr. WOLVERTON. Are we attaching too much importance to the corrosion effect of tetraethyl lead in the quantity that is now provided by order No. 4?

Mr. KEARNS. Well, I haven't been following the proceedings of your committee closely enough to be sure exactly what importance you lo attach to it, but I would say this, that we have

Mr. WOLVERTON. What, if any, importance would you attach to it, which is more importance than what we would attach to it?

Mr. KEARNS. I will give you my opinion. It is that as the lead content is increased we do find that more frequent maintenance of the dome region is required than formerly, but that that seems to be a perfectly straightforward situation, if you will, and proper maintenance measures do quite adequately take care of it. So I can say that I observe no critical effect.

Mr. WOLVERTON. Is that answer based upon the assumption that there is a proper examination at appropriate times for the presence. of corrosion?

Mr. KEARNS. That is quite so.

Mr. WOLVERTON. In the event that there was not that care observed, how would that find expression in the operation of the propeller or any of its parts? Have I made it clear?"

Mr. KEARNS. Yes; I think I understand what you mean. I think the principal effect that you would find would be a sluggish operation which would become noticeable to the pilot. It would call for finding out what is wrong with No. 4 propeller.

Mr. WOLVERTON. Would that create the possibility of accident from any standpoint whatsoever?

Mr. KEARNS. I think surely that if sludge and other accumulations were permitted to go completley uncared for that after a while the propeller would cease to function.

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Mr. KLEIN. Could it happen suddenly?

Mr. KEARNS. I think not. It is a very gradual accumulation. Mr. KLEIN. There would come a point where you might have some bad effect from the fact that it has gotten so bad and nobody discovered it; I think that that is what you are getting at, is it not, Mr. Wolverton?

Mr. WOLVERTON. Yes.

Mr. MARTIN. I think that I might help you there. The airlines, by taking off the dome and looking at it, learn how many hours it takes to form a deposit of any consequence, and then they schedule the removal of the dome at some lesser time than that and wash it out and put it back on again. That length of time is still quite long, and it is not a real maintenance headache. It is something like every 1,000 hours they must take the dome off and wash it out and put back on again.

Mr. WOLVERTON. Is that fixation of time the result of experiments or resulting from practical operation?

Mr. MARTIN. Well, the general overhaul practice is to start off with a short period and examine the article, then increase that period as time goes on, and as your experience indicates it may safely be increased, and that is done on the recommendation of the airlines, with the manufacturer's concurrence and with the approval of the CAA. So it is quite a methodical procedure.

Mr. WOLVERTON. Has the Hamilton Co. or the airline or the CAA, either individually or working together, determined a fixed time when there should be an examination or a take-down or a cleaning process, whatever you may term it?

Mr. MARTIN. Yes. For every airline and every propeller, there is a stipulated time, and it varies with the type of airplane and the type of engine and the type of propeller and the type of operation. It is not uniform.

Mr. WOLVERTON. When you speak of type of operation, do you refer to climatic conditions, or otherwise?

Mr. MARTIN. Principally the difference between a transcontinental operation and a transoceanic operation.

Mr. WOLVERTON. Is that based on distance or climatic conditions! Mr. MARTIN. I think it is probably a difference in cruising condi tions that they use. In one case it is relatively high power, and in the other case it is a lower powered condition.

Mr. WOLVERTON. In what way has that experience been put into orders, advice, or what not, as a guide to when this operation should be done?

Mr. MARTIN. As I said, each airline has a formally approved schedule which has been recommended by them and approved by the CAA, usually with our concurrence.

Mr. WOLVERTON. Are such in effect at the present time?

Mr. MARTIN. Yes, sir.

Mr. WOLVERTON. If you have knowledge of the subject, what inspection is made to ascertain that those orders or advice, or whatever character they take, are carried out?

Mr. MARTIN. Well, our service people that visit all of these airlines report to us as to the method employed by the individual airlines, and their compliance with their rules and regulations; and also, the CAA inspectors check up on it.