BM-1/2 (oz14171)

About this Plan

BM-1/2 (BM Half). Radio control sport model.

Note (with thanks to Zdenek for clarification, see comments) the original BM-1 design was by Adriano Bacchetti, and was first published in Dec 1941. This here is a later, smaller, version re-designed by Geoff Northmore for 1/2A engines in 1998.

Direct submission to Outerzone.

Quote: "1/2 size version of the popular BM1 vintage design, for 3 function R/C and .049 - .061 engines.

BM 1/2. No matter how sophisticated aeromodelling gets, there'll always be a place for tissue and dope, as Geoff Northmore proves with his classic vintage cruiser.

The subject of this feature is a half sized radio controlled version of the BM-1. The designer is unknown to me but as far as I can make out, it is a 1941 (Italian?) design. The drawing I worked from appeared in the May 1992 'Sam Speaks' magazine and was useful in as much as it gave outlines, rib positions, the general construction as well as wingspan, length and dihedral angle. I had to invent a rib section as nothing usable was shown, otherwise the model is as close to the original as hand enlarging permits. In the power department I used a Russian BigMIG .049 R/C engine which I've found is just about perfect.

Radio is a Fleet Micro Rx, 3 Hitec micro servo's with closed loop on rudder, pushrod for elevator and a wire pushrod for the throttle. Initially I used 130 mA batteries but have now changed to 200 mA as these install slightly more confidence, especially towards the end of a flying session. The .049 and the 35 mm film canister tank, featured on page 61 in issue 11, is a satisfactory combination giving a staggering 23 minutes endurance with normal usage, so I'm more than happy in that department.

Hitec servos are fine with Fleet radio providing you change the red and black leads over at the servo plug - just lift the plastic tags with a pin and withdraw the wires - swap over - click tags back and Bob's your uncle! Just make sure you plug into the receiver the correct way i.e. red lead upper most. I put red paint on plug and Rx to avoid mistakes. For your interest, the new 'Super Naro' micro servos from J. Perkins need the same treatment if they are to be used with Fleet gear, the choice is yours - why, you could even use the Fleet servos if you fancy, I'm sure they wouldn't mind!

Totally Traditional: This is a fairly simple model to build but like all aircraft, careful and accurate construction will pay dividends with looks and performance. The following notes may assist those with only one or two conventional construction models under their belt.

Fuselage: Cut out all ply formers and while the fret saw is in use, hell, you may as well cut the rib template and dihedral braces. Bend up the main undercarriage leg from good quality piano wire, stitch it to its former but don't epoxy yet. Leave the forward undercarriage leg until later. Using hard balsa for longerons, pin down over the protected plan and build the first side, noting the grain direction of the balsa sheeting and leaving gaps for ply formers along the way. I use scrap ply as spacers. When dry, cover the frame with cling film and build the second side over the first..."

Update 4/11/2022: Added (older, original BM-1) article from l'Aquilone n.11, Mar 1942, thanks to Pit. This is useful background and seems to be the original first publication of the original BM-1 design, at wingspan 2100 mm. If anyone can find us a full-size plan of the original BM-1, we'll split this into 2 listings :)

Note Pit's 1942 article includes a small 3view-style plan of the original BM-1 design [see pic 006] which is probably the drawing Geoff Northmore worked from, as mentioned in his article.

Supplementary file notes

Article.
Article (1942, l'Aquilone).

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