Sperry Messenger (oz1281)


Sperry Messenger (oz1281) by Dave Robelen 1969 - plan thumbnail

About this Plan

Sperry Messenger. Radio control scale model biplane for .010 power. Wingspan 11-5/8 in.

Quote: "We've watched, and listened, as this little R/C scaler performs. It's still hard to believe. You won't either, until you try it. Sperry Messenger, by Dave Robelen.

Top contender for the all-time title of 'Cutest Airplane in the US Army' is the Sperry Messenger of 1920. No other military US airplane has ever matched its tiny 20 ft wing span or extremely low gross weight. No freak however, the Sperry Messenger was a thoroughly practical airplane designed to operate out of small unprepared fields and from country roads.

Much of the foregoing could apply to the model presented here, as it also is extremely tiny for an R/C model with a very low gross weight. It too, is a completely practical performer with an ability to operate out of the smallest unprepared fields and, due to its rugged all-balsa construction, is very resistant to damage.

With such a tiny size and comparatively large engine, one would expect the model to be a swift, violent little hornet that would require an expert to handle. Let me assure you nothing is farther from the truth; that this model is actually an extremely gentle flyer with a slow scale-like speed and stability which must be seen to be appreciated.

Wherever I fly the little Sperry people are continually amazed at its abilities, as the tiny bird maneuvers about at altitudes as low as 1 foot with complete safety, roaring (?) along at its top speed of about 15 mph.

With all of the features mentioned above you would expect that I have made many alterations in the airplane's design to obtain such remarkable performance in a tiny model; well, hang on. The only alterations are down and right thrust, and a slight increase in dihedral. That's right, all of the surface areas as well as the outlines are exact scale to the best of my abilities; even the incidence angles and wing airfoils are approximately scale.

To obtain all of this performance in a model so close to true scale and as tiny as this one requires just a few unusual approaches to the problems. The main problem is what to do with all of the excess power available in the Cox .010, for it would pull this tiny model straight up if run wide open and unchecked. The answer here is a special restrictor manufactured by Carl Vogt and sold through Ace R/C Inc. This unit wraps around the exhaust ports of the engine and can be instantly adjusted to the proper level before flying.

An interesting thing here is the muffling effect of this restrictor; it cuts the engine noise down to an amazingly low purr that cannot be heard 50ft away. The use of a 4-1/2in Cox nylon propeller greatly aids easy hand starting and smoothness of running without harming the engine in any way.

The other factor that contributes to the gentle performance of this model is the use of extremely small, light radio control equipment. The maximum payload that can be carried is about one ounce, with less preferred if possible. The original model uses a radio of German manufacture that has a total airborne weight of less than 3/4 ounce. This is the Bentert receiver and magnetic pulse actuator that is available from Polk's in New York. Although a super-regenerative receiver, the Bentert rejects most interference through the use of a high (3400 cps) tone filter circuit. A special transmitter is required to match the tone and this also is available through Polk's.

The Albin receiver from ACE R/C is also suitable and can be used with most American pulse transmitters including the R/O Commander sold by ACE. At this writing the only other actuator that is suitable is the ADAMS Baby AR model which requires a switcher to operate with the currently available receivers.

As for batteries, I have found the S76E hearing aid cell manufactured by Eveready to be most suitable in this application; with a voltage of 1.5v per cell, all of the afore-mentioned equipment will operate fine on a pair of these. They weigh only 14 ounce for a pair and are widely available wherever hearing aid batteries are sold - large drug stores, etc. These cells are non-rechargeable, however, I get as many as 30-40 3 minute flights on a pair with a Bentert actuator... "

Update 20/12/2017: Added an alternate version of the same plan, thanks to jkexpress. This one shows some further detail. This was posted as a raw scan on the AF site, I have cleaned and straightened it out, stitched the two parts together. This plan was published in "Radio Control Manual no.4"

Update 21/12/2017: Added article, thanks to RFJ.

Update 17/5/2024: Replaced this plan with a clearer copy. This has been corrected for scaling and cleaned up, also edited to fill the missing central band.

Supplementary file notes

Previous scan version.


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Sperry Messenger (oz1281) by Dave Robelen 1969 - model pic


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    ScaleType: This (oz1281) is a scale plan. Where possible we link scale plans to Wikipedia, using a text string called ScaleType.

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Sperry Messenger (oz1281) by Dave Robelen 1969 - pic 003.jpg
Sperry Messenger (oz1281) by Dave Robelen 1969 - pic 004.jpg
Sperry Messenger (oz1281) by Dave Robelen 1969 - pic 005.jpg

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User comments

A careful examination of the lower rudder will show the actuating rod for the single channel, pulse proportional radio that was used. This is, for its time, a very advanced R/C model.
anon - 12/09/2016
Aha, good point. Have tagged this as RC now, Thanks.
SteveWMD - 12/09/2016
I think this is the same model, as built by David, it's now in the AMA museum
Madhukar - 17/05/2024
Nice find. Fascinating to see the original model, and in colour. They've labelled it as an 'indoor' model, which seems a mistake - the 1969 article says nothing about indoor flying, but does describe taking it out to the flying field, and includes a headline photo of it being launched in the great outdoors.
SteveWMD - 17/05/2024
Agreed, i think this would be too fast and squirrelly to fly indoors.
Madhukar - 19/05/2024
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  • Plan File Filesize: 343KB Filename: Sperry_Messenger_oz1281_.pdf
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