Dactyl (oz1567)


Dactyl (oz1567) by CM Holden 1949 - plan thumbnail

About this Plan

Dactyl. Free flight sailplane. Flying wing glider. July 1949 Aeromodeller.

Quote: "THE number of 'built-up' tailless models to my credit (or otherwise) is some 12, not including several solid chuck-glider types of widely varying shape, and some of the information thus gathered the hard way may be of use to other designers.

My first was a 3 feet span glider with swept-back tips, no dihedral, tip fins, and a reflex wing section, which just managed to fly. The next, a converted pair of wings taken off an orthodox glider. These wings were given about 20° sweep-back, tip fins and flaps, and about 6° washout warped into the tips. Wing section was RAF.32 and test flights were very encouraging, the model behaving perfectly on the tow-line.

A gull-winged model followed later, without fins but with a small fuselage and centre pylon. About 3 ft 5 in span, it was very stable on the line but had a rather high sinking speed (this model holds the local club tailless record of 3 mins. 28 secs.).

'Gull-hedral' was used again on the next project with small fins and rudders at the breaks, small sheet flaps and a six-sided fuselage pod. Sinking speed was fairly high, but towline stability was perfect, giving overhead launches in very gusty weather. The model placed third against orthodox models in a local meet under such conditions.

The next design was a step in the right direction. This model was just a pair of wings, with small flaps for trimming purposes, and a piece of thin ply with hooks attached for a fuselage. Washout was practically nil, although the wing section had slight under camber, and the model flew very fast. Side slipping occurred in gusty weather, but soon stopped when slight dihedral was incorporated and several fly-aways followed aided by overhead tows. The glide was extremely flat, even allowing for the high speed, and sinking speed was very low.

Knowing that larger models possess greater inherent stability I decided that an enlarged version would result in improved performance, especially in poor weather, so I built 'Dactyl' - a similar model of 5 feet span. My estimations were correct. I doubt if I can improve on its performance, except by further increasing the span. Alterations to the original 3 ft 6 in model included slight increase in sweepback, more undercamber to wing section, extremely small tip fins and stronger construction.

This model won the tailless event at the 'Daily Despatch' Northern Area Rally last season, and was later lost after a 20 min flight and recovered from 8 miles away. An important thing to note about this flight is that the model was entirely devoid of fins - having been extensively damaged when it hit a fence during the previous flight!

This model is very reliable, even more so than the orthodox type when on the towline, and is fairly consistent as regards duration. Construction is very simple and needs no explanation.

With regard to general design I believe that under-cambered sections are necessary for high-performance, and tailless models are no exception. Mr. Guilmant's note about too much area at the tip destroying central control is only too true, and I have found that tapering everything, ie spars, ribs, etc, towards the tips helps very much to stabilize the model. I think that some dihedral is necessary..."

Replaced this plan with a clearer copy (patterned background removed) thanks to TonyP.

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