RPM Regulation
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III.  RPM Regulation

Adjustment of the Aeromatic propeller for control of engine speed is termed "regulation."  This regulation is accomplished as outlined in the following paragraphs.

1.  Static RPM

The ground (static) RPM of the engine is adjusted by the addition or removal of laminated shims between the head of the low-pitch stop bolt and the stop bolt boss on the side of the hub barrel.  These shims are laminated so that the thickness may be reduced in increments of .002 inch at a time.  The low-pitch stop bolts and bosses are stamped "1L" for the No. 1 blade and "2L" for the No. 2 blade.  Corresponding marks "1H" and "2H" indicate high-pitch stops for No. 1 and No. 2 blades.  These stops are located diagonally from each other on the same side of the hub.


For instance, a shim .030 inch thick will change the RPM approximately 100 when added or removed.  Correspondingly, thinner or thicker shims will cause proportionate speed changes.

Note:  On the geared Lycoming engine Model GO-435-C series all the RPM values will be approximately 1/2 of those given in this booklet.  This concerns regulation only.

2.  Flight RPM

This flight RPM of the engine is adjusted by the addition or removal of counterweights on the counterweight arms.


To Pick Up Remove Counterweight
25 RPM (1) No. 2965-1
50 RPM (1) No. 2965-2
100 RPM (1) No. 2965-3

For instance, removal of counterweight No. 2965-1 will cause an increase of approximately 25 RPM, while removal of counterweight No. 2965-2 will effect a change of 50 RPM.  Determination of flight RPM is conducted with full throttle at level flight position with maximum air speed as close to field elevation as practical.

Note:  Always add or remove the same amount of weights from both counterweight arms.

When the Hi-Cruise control is installed on either Model 220-1 or 220H, the following additional flight test should be made after the propeller is completely adjusted as an Aeromatic:

  1. All Aeromatic regulation should be made with the pitch control handle in full aft position.
  2. With the control handle full forward, make a flight holding best climb speed immediately after take off.  At this airspeed the engine RPM should be the manufacturer's full throttle rated RPM.  The full throttle climb RPM should be adjusted to maximum RPM regardless of the field elevation at point of take-off.

If the climb RPM is too low, the thrust button screws located on the counterweight arm should be lengthened - that is, screwed outward from the bracket and toward the engine.  If the RPM is too high with control handle full forward at best climb speed, shorten the thrust button adjustment.

One complete turn of this thrust button screw will make approximately 100 RPM change.

3.  Caution

Your Aeromatic propeller is a precise and well-made mechanism and should be treated as such to insure long life and high performance.  Its makers, in cooperation with your aircraft manufacturer, have determined the correct adjustments to provide you maximum performance.  These adjustments must not be altered except for certain minor RPM changes.  When these adjustments are necessary, follow instructions carefully.  Remember:

Static RPM is adjusted by stop bolt shims
Flight RPM is adjusted by counterweights.

Shims and counterweights may be obtained from your local dealer or distributor or by writing directly to the Aeromatic Service Section in Baltimore, Maryland.

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