IS IT REALLY TORQUE? Part 4 of a series, this one suggesting instruction manuals should be clarified.

By George B. Collinge, EAA 67 5037 Marlin Way

Oxnard, Calif. 93030 Illustrations by the author

It is a personal opinion but I do think that some of the blame for incorrect explanations of torque in this country must be laid to the FAA. Correction and updating of some of their basic flying instruction manuals would seem to be long overdue. Is it irreverent to suggest that our all-powerful government is not 100 percent correct? You be the judge. Let's look at a section of one of their publications, piece by piece. "Flight Instructor's Handbook" was written by the Flight Standards Service, FAA, and dated 1964. On page 53 under the heading "Torque and 'P' factor" it starts off by saying that the reason an airplane has a tendency to turn on take-off and climb is "most controversial." To print this right at the beginning appears to admit confusion within the FAA would it

FIG.

29

Take-off, FAA style.

This statement completely ignores the fact that the airplane can be turning immediately it starts to roll and before there is any effective flow over the ailerons. Also, they say, the added apparent load imposed on the left landing gear (guess "right aileron" didn't stop torque after all) causes a turn to the left. If this really happened to any extent, the airplane would be leaning over to the left and it isn't! If it is leaning at all it is most likely to the opposite side of the turn, the starboard side, and is heeling due to an unfortunate combination of centrifugal and centripetal forces. However that may be, the FAA then says — because the left wing (or wings) is causing more drag, the counteraction for this is to offset the fin! How's that for government logic? They claim everything is balanced out at cruising speed though. The proof? Disturb the airplane with elevator trim only, from a cruising condition. Trim nose up, the airplane rolls, turns left. Down, it rolls and turns right. The FAA should say, the airplane yaws, THEN rolls,

because that's what really would happen. The yaw is due to slipstream rotation, and the rolling due only to the yaw going unchecked. The FAA book continues, "during flight operations with high power settings it is necessary to use SOME FORCE on the aileron controls to maintain flight." After this statement you may wonder why, in the above demonstration of detecting torque reaction they advised hands off the controls using only elevator trim. Could it be because this "force" is, in normal flying, so slight, if at all, that one might not notice or detect such a slight pressure otherwise? And if "some force" was necessary (and we don't all have bulging biceps) how come every airplane doesn't require aileron trim? To continue the FAA, and it is though a new writer

has taken charge, because it now says that you must hold right rudder during take-off and climb "to take care of torque." After all the funny explanations already given it

is though they are starting over again. Then comes another switch and next it says that

not? It next gives a weak primary reason for the left

torque is not the entire picture anyway, and that "P fac-

turning tendency followed by what I think is a fantastic explanation as proof. "It is common practice" it says "to rig a slightly higher angle of incidence in the left wing", and which in turn creates a drag. This old wives tale has already been commented upon earlier. Also, our modern airplanes obviously do not have this cockeyed rigging, yet they still turn. To continue, the FAA says that on take-off, one counters torque by putting on right aileron. "This application of aileron control, usually to the right, adds to the

tor" has a great influence! First you have to have a tailwheeled airplane, in the three-point attitude. Then, the descending prop blade, at a higher angle of attack than the ascending blade, pulls more. Being on the starboard side it supposedly pulls the airplane to the left. This is the way the slipstream would have to look

drag on the left wing, and the tendency of the airplane

to turn left during take-off and climb." (Never heard of differential ailerons, I guess). 36

MAY 1969

to abide by the FAA explanation of P factor. If the descending blade actually did have more thrust, it would deflect more or faster air than the rising blade. The slipstream would bend to the left and have the same effect as offset thrust! It would tend to cancel the left-turn tendency. One cannot think only about one isolated portion of the whole picture and ignore the rest. This would be

FIG. 30.

FAA "P" factor airflow, as it would have to look.

like the people who think all lift comes from the upper

curved part of a wing or from a cabin windshield or roof. They fail to realize that lift is not a magnetic-like occurrence where a section of a body is attracted or sucked up. Lift is derived from air being PUSHED DOWN and a cabin roof or a wing upper leading edge is only an integral and inseparable part of the entire mechanical

process.

Anyway, wind tunnel data differs from the FAA. Actually the propeller induces the flow some distance ahead of it, so that up to quite a high angle of yaw each blade is operating essentially at the same angle of attack. NACA reports on propellers in yaw and on analyses of effects of the resultant slipstream over the airplane reveal that P factor is not a factor. Further, and as one example only, page 531, Airplane Design and Performance by Warner describes that divergence of the propeller axis can be ignored for all calculations up to at least 15 degrees of misalignment, " . . . the effect of inclination should sim-

ply be disregarded." Helicopters, of course, are obviously

something else.

FIG. 32. If "P" factor was valid, there would be a larger angle on the lower blade.

other causes and any designer in his right mind would not want to add to it. Clearly, in this case, the entire slipstream-tube direction remains at 90 degrees to the propeller disc, in exactly the same manner and because of the same basic laws that apply to the airplane in the nose-high take-off mode. To close its interesting chapter on Torque, the Flight Instructor's Handbook offers a couple of meager paragraphs on two "lesser effects", that of gyroscopic precession and of the "spiral nature of the propeller blast." These, as you may have no doubt guessed, by actual demonstration can be shown to be the only two factors that have any genuine consistent influence on swinging or yawing. The other things previously described are possibly remnants of faulty handling techniques being justified or rationalized or are just bad theory. As the rotating slipstream has been covered in some detail, we now come to the gyroscope. Gyroscopic properties of the engine or propeller are something that affect every airplane, some to a lesser extent, but some to such a high degree that at times one actually has to modify basic control movements (or pressures) to compensate

for it. So don't miss the next exciting part of this series (and the last one) "Precession and what it means to you." ®

FIBERGLAS CUT-OFF WHEEL

By Michael A. Donnelly, EAA 40647 26183 Stanwood Ave., Hayward, Calif. FIG. 31.

Actual flow through a propeller.

This is how it really looks. The flow gains approximately half of its speed ahead of the pump (propeller)

and half behind it. It does not reach full velocity until it is some distance behind the prop disk.

If there really was such a thing as P factor, then off-

setting the thrust line would not produce the results desired by the designer, that of cancelling the left turn tendency. Using the P factor philosophy, the lower blade

because of its larger angle of attack, would merely make

the nose go up! And as recounted in part one of this series, this is something that already happens due to

I have found a cut-off wheel that I believe to have advantageous characteristics for the homebuilder. This

wheel is Norton's A60-OBNA-2, available in two sizes: 7 by .035 by % in., and 8 by .035 by % in. The important

aspects are that this wheel is fiberglas reinforced, flexible,

requires no lubrication, and will not break. It cuts through 4130 very easily. Mine is installed in a table

saw, and has been flexed while cutting 4130, and brought

to a dead stop from around 5,000-6,000 rpm. Price is about $4.00, and it can be ordered from S. L. Fusco, Inc. "House of Abrasives," 2807 Miller Ave., San,

Leandro, Calif. 94577. If in doubt about anything concern-

ing this wheel, contact William V. Nelson, abrasive specialist, at that address. He has been more than helpful in answering my questions. ® SPORT AVIATION

S7