Ionosphere Mk21 (oz15469)

About this Plan

Ionosphere Mk21. Free flight twin model, with push-pull layout. Wingspan 60 in.

Direct submission to Outerzone.

Quote: "Hi Mary, please find attached a plan for the Ionosphere Mk21, a large 60 in wingspan flying wing, which was the subject of an Aero Modeller article by (Peter) OFW Fisher in December 1993, see attached. The article was supposed to contain a reduced image of the plans, and there were details of where it could be purchased. However, the wrong plan was included in the article, a mistake that was never corrected. As far as I am aware the Ionosphere Mk21 was never marketed as a kit, although I believe the plan will have been available through Peter’s company Performance Kits until his death in 2005. I have recently managed to find a copy of the plans for this flying wing, which had until now proved to be rather elusive.

So many of Peter Fisher’s designs are still hard to find, or simply unavailable, so it's great to locate this plan and make it available on Outerzone. Really appreciate all the hard work you and Steve do running the site, it’s such a hugely valuable resource. All the best, Mark Robinson"

Quote: "Peter Fisher has put in much development work to produce this interesting model. A fine flyer but be careful how you launch it.

The 'Ionosphere Mk 21' is the 21st in a line of progressively developed flying wings, dating back to the Mk 1 model in 1950. The Mk 21 first flew on 14/12/1986; and since that time has had a vast number of excellent flights, mainly on Jurby aerodrome, on the Isle of Man. Most flights have been rise-off-ground (ROG), but should a hand-launch become mandatory, due to a lack of a suitable runway, I strongly recommend an underarm launch, holding to top of the fuselage. The usual type of overarm launch will risk the unfortunate likelihood of feeding the launch hand's digits through the rear propeller!

The prototype Mk 21 flew, exactly as designed, and no trim
adjustments were required. It used two original Mills .75 diesels, fitted with DC 7x4 props.

Design and development: The tandem engine layout of the Mk 21, well tried and tested in the Ionosphere line of models, has the advantage that both torque and gyroscopic effects being on the same thrust axis tend to neutralize; and their effects are further reduced by the relative damping effect of the flying-wing layout. It is not necessary to utilize identical or matched engines, or even ones of the same capacity, and the early prototypes were fitted with engines of differing capacities. If you use different capacity motors, the heavier one should be mounted in the nose.

The Mk 21 is ideal for engines of 0.44 - 0.8 cc, with identical engines the synchronized note is of course an added bonus. A second Mk 21 has been built by Don Knight and this has been flying well with a PAW 80 and a PK 86. The Mk 21 is exceedingly stable under all weather conditions and has often been flown in strong winds. Span is 59.6 in and weight, with nylon covering and twin Mills 75 engines 1 lb 11 oz.

Construction: The wing is built up from four sections, two inner and two outer ones. It features centre dihedral ar R1 to give 0.6 in at R8..."

Supplementary file notes

Article.

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