Sperry Messenger (oz1281)


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

About this Plan

Sperry Messenger. Scale biplane for .010 power, and radio control. June 1969, Model Airplane News.

Quote: "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 manu-factured 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 Aerofred, 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.

Supplementary file notes



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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

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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
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  • Sperry Messenger (oz1281)
  • Plan File Filesize: 524KB Filename: Sperry_Messenger_oz1281.pdf
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  • Supplement Filesize: 1864KB Filename: Sperry_Messenger_oz1281_article.pdf
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