Never Forget (oz9096)

 

Never Forget (oz9096) by John Pool 1980 - plan thumbnail

About this Plan

Never Forget. Rubber tailless competition model.

Quote: "Regular winner of the Lady Shelley Trophy John Pool's 50 in wingspan rubber driven tailless. Never Forget.

Twenty years of rubber powered unaccompanied wings. My series of Tailless models began in 1958 with a small 120sq inches wing model largely inspired by the writings of George Woolls and Josh Marshall. By 1962 my design had grown to a 288sq inch wing which won the Lady Shelley Cup for me for the first time. The 1963 model grew further to 300sq inches with a relatively high aspect ratio and geodetic construction. All models to this date had featured wings swept back 30° and twisted continuously along the span to give 5-6 degrees nominal washout at the tips. The model I flew most between 1964 and 1968 was the 1963 wing on a square fuselage, 4 oz air-frame and 3 oz Dunlop rubber made into 16 strands driving a 22 x 30 in featherer. Although it had a short run of about 60 secs it was very stable and had a fine glide for a 2.20-2.30 still air total. The model presented here was developed between 1968-78 as my series named 'Never Forget'.

DESIGN HINTS FOR RUBBER POWERED TAILLESS The main problem with designing tailless models is being economical with stability compared with orthodox models. The cost of stability is inefficiency. Efficiency only matters with tailless models when they are put into competition with orthodox models, or to a lesser extent, other tailless models. Without the need to cut corners for extra seconds they can be made into super stable and attractive fliers. In fact the tailless model is so tolerant that little attention need be given to lateral or directional stability, the emphasis being on longitudinal stability - which is the main function of the missing tailplane. The tailplane's effectiveness depends mainly on its area, the distance it is set away from the wing and an angular setting which is usu-ally negative to the wing. These three factors are interdependent, more of one can call for less of the others.

With most tailless models the angular difference between centre wing panels and the tips (which effectively do the job of the tail) is produced by twisting the wing or washing out the tips. Alternatively what becomes a separate surface altogether is stuck on the end of the wing as an elevon at a negative angle. The distance between wing and tips (acting as the tail) is produced by sweep-back (or sweep forward) and the area fac-tor is simply the area of that part of the tip which is rigged at a different angle to the rest of the wing.

NEVER FORGET 1979 No 2 Mk 14: It is worth working to weights shown because a light airframe gives you the option of local beefing up, extra rubber, or trim ballast later, and of course if you get near to my weights a model which should fly off the board. If you don't have any lightweight scales make up an Easy Weigher as described; the wood weights to be looking for are:

1/32 sheets x 3 x 36 in about .25 to .3oz
1/16 sheets x 3 x 36 in about .35 to .4oz
3/32 sheets x 3 x 36 in about .5 to .6oz and about .8 to 1oz
1/8 sheets x 3 x36 in about 1oz to 1.25oz

I strip most of my wood on the device shown, the Easy Stripper described on the plan.

The motor when required, should be made up, lubricated, tensioned and fitted with bobbins as chosen. The motor is split into two eight strand skeins if Pirelli, or six strands if using FAI Supplies rubber. Install motor in fuselage and fit prop. Wind some turns on and allow to tension up. Fit the fin and cone with bands from the hooks on the cone corners round the rear motor peg. Put a drop of cement on each end of the wing mount spine and fix in place with the rear of the wing mount just forward of the spacer "Inn back from the nose. Stick a temporary pin in the rear of the wing mount spine and fit wing to spine using this for the band, hooked also to front peg in rearmost hole. The wing TE should be lined up with the rear of the TE support.

Now check for balance. The aim is to balance initially with the CG at the apex of the trailing edge and to achieve this balance with fingers under the LE. If needed, move the wing mount until this is achieved. (Or you can settle for this setting and ballast for CG later.) When satisfied, remove wing mount finally, and glue firmly in place along the top longeron. No need to reinforce, it might sheer off and save something else breaking in a really bad landing. When dry, cut to size and glue in the side supports. The advantages of my particular wing fixing and DT arrangement are as follows:

(1) it allows for a large span light wing in two parts without hefty dihedral bracing and joiners
(2) the wing is flexible down-wards if the model gets on its back
(3) the wing is moveable; a little with no effortand moving it a lot doesn't involve a workshop session
(4) the D/T is superb though I must admit it is a long time since I had to extricate one from a tree!

TRIMMING: This is only slightly different from trim-ming an orthodox Open Rubber model. The elevons are multi-function. They can be used as a tailplane would be, increasing the elevon angle has the same effect as packing up the tailplane trailing edge, it will raise the nose in flight to cure a dive. This works on both power and glide stages, to the extent that it can cause stalling or looping on high power. The same effect can be attained by moving the wing forward (or ballasting at the rear) and this will have negligible effect on the power flight. The aim must be to use as little elevon angle as possible but enough to give a reasonably quick recovery after a disturbance.

Using a differential elevon has been frowned on by others but it has two desirable effects. With the port elevon at a higher angle than the starboard a wing will have a natural left turn when gliding because these elevons have a drag as well as elevator effect. Under power and using right sidethrust the differential elevons have a banking effect, cancelling the sometimes worrying bank, starboard wing down, induced by sidethrust and sometimes turning into a spiral dive. The general effect of elevon angle changes is rather gentle, probably because they are away from the prop blast but the effect is proportioned to speed of the model and they can be very powerful controls on full turns.

Fin offset is also much more effective under high power and can appear to have almost negligible effect on the glide circle even in coarse settings..."

Scan from DBHL, cleanup by theshadow.

ref DBHL-5984.

Direct submission to Outerzone.

Update 21/08/2017: added article, thanks to Pit.

Supplementary file notes

Article.

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Never Forget (oz9096) by John Pool 1980 - model pic

Datafile:
  • (oz9096)
    Never Forget
    by John Pool
    from Aeromodeller (ref:D/1388)
    March 1980 
    59in span
    Rubber F/F
    clean :)
    all formers complete :)
    got article :)
  • Submitted: 15/08/2017
    Filesize: 483KB
    Format: • PDFbitmap
    Credit*: DBHL, theshadow
    Downloads: 657

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Notes

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Scaling

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