Sikorsky S-51 (oz9620)


Sikorsky S-51 (oz9620) by Roy Clough 1953 - plan thumbnail

About this Plan

Sikorsky S-51. Free flight helicopter model, for K&B .049 power.

Quote: "Probably the most famous design of pioneer helicopter builder Igor Sikorsky, the S-51 helicopter has racked up an impressive record in life-saving and rescue operations, both at home and abroad. It is the standard unit of Los Angeles Airways, first airline with scheduled helicopter operation, and has been manufactured in England by Westland under license from the parent company. In addition to its performance record, it is generally agreed to be the most beautiful rotary wing craft ever built, with clean flowing lines that adapt themselves readily to scale model practice.

The big ship uses a three-bladed rotor of the type known in the trade as the 'flapping blade' or articulated system. This rotor type has an extreme degree of maneuverability with rapid control reactions and is quite stable in normal cruising flight. The torque effect of the rotor is nullified by a small rotor attached to the tail boom which produces a counteractive side thrust and is used as a heading control. This arrangement is fine for a full-scale craft, but the unstable hovering characteristics of an articulated rotor limits its usefulness to piloted craft - it is not the best system to use on a model which must fly independently and has no pilot aboard to correct disturbances due to gusts or roughness in the air which are present under even the most ideal conditions. Therefore we must use a rotor, which has a degree of automatic stability if we wish our model to fly for more than a few seconds without skating wildly in all directions and finally crashing.

Our first S-51 model, therefore, used a dynamically stabilized rotor of the so-called 'feathering' type. That is, the blades did not flap up and down, but rotated within limits in a span-wise plane, allowing flight deflections to register as pitch changes instead of flapping movements. The pitch changes served to maintain the stability of the machine by adjusting the lift of the rotor from sideto- side as required, since the blades were independent of each other and, to a limited extent, of the rotor shaft. Pitch was determined by rotational speed (centrifugal force) and the model used a rear torque correcting propeller. The power was rubber and thrust was transmitted through a bevel gear drive to the main rotor and by pulley to the tail rotor. This model flew very well, was stable and able to cope with rough air without upsetting or going into a wild dance. However, the duration was very limited and the altitude attained was not very great, due to the complexity of the machinery required and the rather sharply limited output of twisted rubber bands.

We decided to scrap this design in favor of something that could be powered by a 1/2A engine, on the theory that builders would rather have a much simpler model with greater performance, and would be willing to sacrifice a bit of scale appearance to get it. By using the torque-reaction drive, we eliminated gearing and clutches and the need for a torque prop.

The dynamic stabilizers, which govern individual blade pitch, were retained, giving a good, positive and fully automatic auto-rotational let-down when the motor quit—an important factor in models having any considerable weight and power. The torque prop, an outstanding feature of the original, was replaced with a clear disk of plastic, which serves as a fin. The result is a model which is quite realistic in flight, more rugged in construction, and actually much simpler to build than the original rubber-powered version.

Construction: The fuselage is a straightforward semi-monocoque keel-type affair. Build one side over the keel on a flat surface to insure good alignment, then put on the half-bulkheads on the other side..."

Quote: "Hi Steve & Mary, Here is another Roy Clough free flight helicopter that I don't think that you have. Merry Christmas! Gene"

Direct submission to Outerzone.

Supplementary file notes

Article pages.


Did we get something wrong with these details about this plan (especially the datafile)? That happens sometimes. You can help us fix it.
Add a correction

Sikorsky S-51 (oz9620) by Roy Clough 1953 - model pic

  • (oz9620)
    Sikorsky S-51
    by Roy Clough
    from Flying Models
    February 1953 
    27in span
    Scale IC F/F
    clean :)
    all formers complete :)
    got article :)
  • Submitted: 22/12/2017
    Filesize: 232KB
    Format: • PDFbitmap
    Credit*: rchopper56
    Downloads: 749

  • Sikorsky_H-5 | help
    see Wikipedia | search Outerzone
    Test link:
    search RCLibrary 3views (opens in new window)

    ScaleType: This (oz9620) is a scale plan. Where possible we link scale plans to Wikipedia, using a text string called ScaleType.

    If we got this right, you now have a couple of direct links (above) to 1. see the Wikipedia page, and 2. search Oz for more plans of this type. If we didn't, then see below.

    ScaleType is formed from the last part of the Wikipedia page address, which here is
    Wikipedia page addresses may well change over time.
    For more obscure types, there currently will be no Wiki page found. We tag these cases as ScaleType = NotFound. These will change over time.
    Corrections? Use the correction form to tell us the new/better ScaleType link we should be using. Thanks.

Do you have a photo you'd like to submit for this page? Then email

User comments

No comments yet for this plan. Got something to say about this one?
Add a comment



Download File(s):


* Credit field

The Credit field in the Outerzone database is designed to recognise and credit the hard work done in scanning and digitally cleaning these vintage and old timer model aircraft plans to get them into a usable format. Currently, it is also used to credit people simply for uploading the plan to a forum on the internet. Which is not quite the same thing. This will change soon. Probably.


This model plan (like all plans on Outerzone) is supposedly scaled correctly and supposedly will print out nicely at the right size. But that doesn't always happen. If you are about to start building a model plane using this free plan, you are strongly advised to check the scaling very, very carefully before cutting any balsa wood.


Terms of Use

© Outerzone, 2011-2024.

All content is free to download for personal use.

For non-personal use and/or publication: plans, photos, excerpts, links etc may be used, provided that full and clear credit is given to Outerzone with appropriate and specific direction to the original content i.e. a direct hyperlink back to the Outerzone source page.

Unauthorized use and/or duplication of this material without express and written permission from this site's owner is strictly prohibited. If we discover that content is being stolen, we will consider filing a formal DMCA notice.