Sunday, October 22, 2017
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Digitize Your Robart Incidence Meter

Making A Great Tool Even Better

These are the items needed for this simple upgrade: the original Robart Incidence Meter, a Cen-Tech digital angle finder, contact cement and, in this case, an old trophy plate.

If you are an avid model builder, you most likely have an important instrument in the toolbox called an Incidence Meter. For you newcomers, this device allows you to measure the alignment angles of your wing, tailplane engine thrustline and fin to the fuselage itself, so that the aircraft will fly correctly. On high-performance models, these incidence angles are critical to attaining top performance. Mostly used when building models from a kit, plans or scratch-built, an incidence meter is also very handy while setting up most ARFs. One of the most popular incidence meters of all time has got to be the Robart Incidence Meter. It is simple yet very effective, using a pendulum type pointer set against a printed gauge face to provide you with the measured wing angle in degrees.

I depend on my incidence meter constantly, and after more than 20 years of service, I started to wonder if my meter could be upgraded with a digital readout for more flexible and easier reading. I found the answer in a compact yet robust digital angle gauge from Harbor Freight Tools.

Here we see the bottom of the incidence meter with the trimmed trophy plate glued in place.
 

MODIFYING AN OLD FAVORITE

I did not want to abandon the original tools functionality as made by Robart, but instead, I would augment it by adding the digital capability. After all, the original tool is sinfully simple and easy to use, and would prove to be a good check for my modification. Augmenting the original tool turned out to be quite easy and effective. You will need the Robart Incidence Meter of course, a strong but permanent contact adhesive and some scrap materials from around the shop and a digital angle gauge. I used the Cen-Tech Digital Angle Gauge (P/N 95998) from Harbor Freight. There are many such gauges available now. Looking in any woodworking catalog should turn up a similar device.

We have adhered some thin hook and loop fabric to the back of the angle finder and the front of the incidence meter to hold the two together.
 

The Robart Incidence Meter is precision made and readily lends itself to this modification. I decided to make the digital gauge removable, but still wanted to be able to mount it with a consistent alignment to the meter face. The bottom of the digital gauge is magnetic and I wanted to mount the gauge on a magnetically-attractive base to take advantage of this. I found an old, engraved steel trophy-plate and cut it down to match the bottom of the Robart meter body and the digital gauge. I attached this plate to the bottom edge of the meter body with Household Goop adhesive, a very aggressive adhesive found at most craft and hardware stores. If you are looking at your local hobby shop, reach for the Zap Goo.

Once the plate was attached and the adhesive fully cured, I wanted to make sure the meter would not slide sideways, despite the magnetic attachment. Nothing worse than to have a tool flop onto your new model wing by accident! To prevent any movement, I used a thin strip of a hook and loop material glued to the back of the gauge and the front of the Robart meter. Thats it! Your incidence meter is now analog and digital capable!

Our upgraded incidence meter is at work on a Tri-Squire wing. Note that the incidence meter and angle finder show the same relative angle.
 

IN USE

With the digital meter in place, mount the incidence gauge to the reference datum on your model and press the zero button. Now when you mount the gauge on your wing, stabilizer or engine shaft, you will immediately be presented with an easy-to-read digital readout of any angular difference. Checking the wing washout, for instance, couldnt be easier. Mount the gauge to the wing root and zero it out. Now move to both tips and read off the twist to be sure they are the same and correct.

There are several advantages with this modification. Not only can you read the angle faster, but you can also have the gauge hold the angle reading for you, or you may compare two angle readings with the press of a button. Note that the digital gauge is going to add significant weight to the original meter, and this is the main reason I wanted to make the meter removable. By removing the digital gauge, I can still use the meter in its original configuration on my very lightly constructed models without harm to more fragile structures.

This is the completed upgrade—nice and tidy, ready to go to work. Using the hook and loop material makes removal of the angle finder quick and easy.
 

CONCLUSION

I am very pleased with the results of this modification and I am looking forward to using it on many upcoming projects! It has already confirmed my good workmanship on my most recent model, a 50-year old Midwest Tri-Squire kit that called for 2.5 degrees of positive incidence to the stab. It was spot on! And, by the way, Robarts original pendulum meter showed the exact same reading as the digital gauge did. Thats outstanding for a meter that has spent 20 years kicking around my shop! Thanks, Robart, for a great tool design!

Links

Robart Mfg.

www.robart.com, (630) 584-7616

ZAP Goo is manufactured by Pacer Technology

www.zapglue.com