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Enstrom F28A Instrument Panel

This is a picture of an Enstrom F28A instrument panel:

In the upper left corner we currently have a clock mounted. Previously this panel position held an EGT. Below and to the left of the clock you can see a red light. This is a warning light that the clutch is not engaged. The clutch on the Enstrom is mechanical and takes quite a strong pull to engage.

Flight Instruments

All flight instruments are clustered on the upper instrument panel.

Dual Tachometer

The dual tachometer in the Enstrom is a mechanical instrument, connected to the main rotor and engine by cables.

The outer scale displays to engine RPM (revolutions per minute), while the inner scale displays rotor RPM. The red lines show the legal range: the engine must be operated between 2750 and 2900 RPM while in flight. The main rotor must be operated between 313 and 385 RPM while in flight. The higher upper rotor limit allows the pilot to build RPM during the autorotation flare, giving him a massive amount of energy available for touchdown without an engine.


This instrument senses barometric pressure and indicates height above sea level based on that pressure. Most altimeters (including this one) are sensitive altimeters in that the pilot can turn an adjusting knob to compensate for non-standard pressure. The little window on the right side of the instrument (partially obscured by the large indicator hand) tells the pilot what pressure the altimeter is set for. In this case, it's set for about 29.94 inches of mercury.

The altimeter looks a lot like a clock, with a long arrow shaped indicator and a short arrow shaped indicator. The short indicator indicates thousands of feet. Here it is about 1/4 of the way from 0 to 1 because we are about 250 feet above sea level. The long indicator indicates in hundreds of feet. It is pointing halfway between the 2 and the 3, so we are at about 250 feet. Each mark between numbers is 20 feet, so we are indicating about 260 feet here. If you compare this altimeter with the ones in our Robinsons and JetRanger, you'll notice that this one does not have a 10,000 foot pointer. Enstrom is being realistic about how high this helicopter can go!


This instrument displays airspeed as measured by the pitot tube. The pitot tube is just a piece of tubing on the front of the helicopter pointing directly forward. As the helicopter moves forward, air is rammed into the tube. The air being rammed in increases the pressure inside the instrument and the pressure moves the indicator:

This indicator is calibrated in MPH (miles per hour). The VNE (never exceed speed) is indicated by the red line at 112 miles per hour. However, there is a chart the pilot uses to calculate VNE given temperature and pressure and on a typical summer day the VNE will be lower than 112.

Vertical Speed Indicator

The vertical speed indicator is like an altimeter, but shows how rapidly altitude is changing. Each mark above the "0" indicates 100 feet per minute of climb rate. Each mark below "0" indicates 100 feet per minute of descent rate. This particular gauge can show a maximum climb or descent rate of 3,500 feet per minute.

You may notice that this gauge is marked "IVSI" which stands for "Instantaneous Vertical Speed Indicator". When we first got this aircraft, it had no VSI at all. Students requested that it be fitted with one. At first, a normal airplane VSI was fitted (by mistake). The problem is that normal VSIs have a great deal of lag, i.e. it takes several seconds for them to adjust to changes in climb or descent rate. This causes a problem for a helicopter because the descent rate is constantly changing on approach, and if the lag is too long (which it was in the particular instrument we had) the gauge is essentially useless because it is displaying information that is out of date.

An instantaneous VSI has extra mechanical linkages to sense a change in the rate of altitude change, and it moves the indicator in response to that change. The result is a faster indication that the pilot has changed his rate of climb or descent.

Manifold Pressure and Fuel Flow

This is a dual instrument, displaying manifold pressure on the left side and fuel flow on the right side. Below the gauge is the inclinometer, which is used to determine whether the aircraft is in trim. In this case, the position of the ball directly above "0" means we are in trim.

The manifold pressure gauge indicates the atmospheric pressure inside the intake manifold. The engine is not running in this photograph, therefore the guage is indicating ambient pressure, slightly below 29.00 inches of mercury. Normally we use about 15 inches of manifold pressure to descend, 23 inches of manifold pressure to cruise, and 25-27 inches of manifold pressure to hover and takeoff.

The fuel flow gauge shows the fuel flow rate going into the engine. This will depend on the throttle setting. Typically at cruise power settings, we burn about 90 pounds per hour. During hover and climb we burn about 105 pounds per hour. Because the fuel quantity gauge is calibrated in pounds, it's very simple for the pilot to use the fuel flow gauge and fuel quantity gauge to estimate how long he can fly at the current power setting.

Engine Instrument Cluster


This gauge shows total fuel in the two (interconnected) fuel tanks. It is marked in pounds of fuel. Fuel weighs 6 pounds per gallon, so 240 pounds divided by 6 gives us 40 gallons of fuel maximum in this aircraft.


This gauge shows the temperature of the main rotor gearbox (as opposed to a simple warning light in the Robinson and the Bell). Right now it's indicating ambient temperature. During flights at high power settings it will read substantially higher, but never gets near the top of the green arc. Seeing the temperature that high would indicate a problem with the gearbox, and the pilot would land immediately to investigate.


This gauge shows the charge or discharge rate of the battery. If the alternator was to fail, the ammeter would indicate a discharge rate.


This shows the oil pressure within the engine. Normal operating range is 60 to 90 PSI. Oil performs both a lubricating and a cooling function in piston aircraft engines.


This gauge displays the oil temperature. On a hot day, excessive hovering might cause the temperature to reach the red line, in which case the pilot would reduce the power demands on the engine. High temperature coupled with low oil pressure might indicate oil starvation.


This gauge displays the temperature of the (air cooled) engine cylinder heads. Typically it is connected ot a single cylinder which is known to be the hottest of the cylinders in the helicopter. High cylinder temperatures will result from high power settings, too lean a fuel mixture, or problems with the cooling fan.


This helicopter is fuel injected. It has an engine driven fuel pump, and an electric fuel pump (the boost pump). If fuel pressure is normal, the green light is illuminated. If fuel pressure is low, the red light illuminates. If the boost pump was not putting out sufficient pressure and the engine driven pump failed, the engine could potentially quit.
Paul Cantrell paul at copters.com

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