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Lynn Williams 88% Yakovlev UT-1

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cluttonfred

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I received this message last night from Lynn Williams of Flitzer biplane fame that he asked me to share with the HBA crowd. Great stuff!

Hello Matt,

I caught sight of some very recent posts on the Homebuilders' site which you contribute to, and among the topics was the possibility of building a Yakovlev UT-1.

The suggestion was, as with many such ideas tossed around, that the Bowers Fly Baby could be a good basis for such an endeavour.

In my opinion this is a waste of time and effort as you would never get near to a true impression of the real thing, especially with a wire-braced monoplane wing of whatever planform.

Years ago I began the design of a full-size UT-1 with a one-piece wooden wing and a fuselage in steel tube, much like the original but rigidly warren-braced rather than wire-braced. Wing section was the original Goettingen 387 but later modified to the 398 (from memory) to increase performance. At that time I had a Blackburn Cirrus II in-line motor of about 100 hp. and the idea was to replicate one of the special UT-1s powered by a copy of the Bengali in-line motor. I had designed several replica types around that engine but eventually parted with it and forgot about the UT-1 for some years. In any event, a full-size UT-1 with a relatively low-powered engine would not have done justice to that scintillating little aerobatic and fighter trainer.

However, I resurrected the design a while back, this time with an all-wood fuselage and scaled-down to around 88%, which is in my view the minimum scale to represent a (replica) low wing monoplane which (unlike biplanes such as the Flitzer) can look like toys when viewed up close. Equipped with, say, a Continental C-90 or bigger, the bilateral cylinder arrangement could be disguised effectively as a 5-cylinder M.11 radial, at least at 'stand off scale' distance. Of course the 85 hp. Verner 5Si direct-drive radial would be ideal and is capable of providing a suitable performance to a 21' span UT-1 and indeed my 80 hp. AeroVee motor might do the same.

I attach a GA of the UT-1 showing additional views with a flat-four installation to demonstrate how effective this could be, using 'cosmetic' cylinders to represent the M.11. Were I to use the Verner I would add extended (dummy) rocker covers to increase the diameter of the radial to the correct scale size.

About 3 years ago, Justin Adams, who had already 'flown' several of my Flitzer designs in X-Plane simulation as well as my Rat16 (down-scaled Polikarpov I-16) produced a basic UT-1 Vimeo of the UT-1. This utilised the same NACA 24xxx airfoil I used on the Rat16 (2416 on a/c centre-line and 2410 at the tipmost rib, wing tip being slimmed to 2409). Both the Rat and the UT-1 exhibited superlative handling with no pitch-trim change from take-off to maximum level speeds and a benign stall despite using a zero/zero wing. In the case of the Rat, that was zero incidence and zero washout, dihedral only due to underside thickness-taper and the same with the UT-1 except for greater dihedral.

This Vimeo is available here: Lowi-close-up

[video=vimeo;75426208]https://vimeo.com/75426208/[/video]

It shows a little of the manoeuvrability of the machine and a very gentle wing lowering at the stall. The Rat stalled straight ahead.

Although the original aeroplane featured a 'one-piece' wing, tapered and with swept-forward and swept-aft rear spars, with dihedral built-in, this makes wing design and attachment and also rib attachment fussy, so my reduced scale version featured separate wing panels bolted via fitch plates at the roots to a fixed carry-through system, like on the KRs, Taylor Monoplane and Flitzer types. This enables a maximum depth spar to be fitted on the thickest part of the airfoil to endow the wing with the greatest strength, all else being as original. The main undercarriage has to be attached on extended stirrup-blocks on the mainspar forward face to bring the front landing gear legs into the right geometrical position; but this is not a problem and does not affect the external appearance of the machine. Cockpit has been moved forwards very slightly to assist balance.

The later UT-1s had a longer nose, a bigger fin to compensate and clipped wingtips, but it is not quite as attractive.

I attach some CAD views (with manikins) of the reduced replica to provide an impression of its actual size.

Note some of the sketches are from the steel-tube fuselage version. Please feel free to share this.

best regards ,

Lynn
 

Attachments

  • Yak UT-1 Wingfus.2.jpg
    Yak UT-1 Wingfus.2.jpg
    26.9 KB · Views: 88
  • Yak UT-1 88% mod flat4 original  wscreen.jpg
    Yak UT-1 88% mod flat4 original wscreen.jpg
    62.3 KB · Views: 105
  • UT-1 STA-1 frame draft 2.jpg
    UT-1 STA-1 frame draft 2.jpg
    47.3 KB · Views: 67
  • UT-1 spar position.jpg
    UT-1 spar position.jpg
    35.9 KB · Views: 78
  • UT-1 88% r.3.4.jpg
    UT-1 88% r.3.4.jpg
    20.1 KB · Views: 61
  • UT-1 88% front 3.4.jpg
    UT-1 88% front 3.4.jpg
    23.9 KB · Views: 69
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