De Havilland Gypsy Moth Wing-Rib Question

I got my Gypsy Moth plans yesterday. Even though they were presented as “a very small set” in all there are 270 drawings. At a first look the airframe appears complete. Thanks for your input everybody.

Peter

There are 20 rib part numbers, each needing a different jig. I know ‘cos I have all 20 jigs and have made the “odd few” sets.
Props are also not a mystery, having “carved” 62 so far.
Ref Janics Magnificent book; the actual lineage of the “Moth” was the DH60 Cirrus Moth–DH60X Moth- DH60G Gipsy Moth-which was then fitted with a metal fuselage to become the DH60M Metal Gipsy Moth. The 60G was fitted with the inverted Gipsy III ,which engine was developed into the Gipsy Major and so the type then became the DH60GIII Moth Major. The DH60M was developed as the DH60T Moth Trainer with dropped front cockpit top longerons with deeper doors and the wing bracing wires shifted to the front spar, both of which were to facilitate entry in to the front cockpit whilst wearing a “bumpack” parachute. These mods were not enough to satisfy the Ministry so, as all the books tell us, the 60T was taken to the back shed and modified per P & Ps quotation above to become the now new model, the DH82 Tiger Moth. Here there is a divergence of opinion. The good books state that the DH82 was modified by shortening the interplane struts, fitting a plywood turtle decking to the rear fuselage and deleting the longer front cockpit door to become the DH82a. Research has disclosed that there is reference on many DH drawings to a DH60MIII or Metal Moth Major, but this model does not get mentioned as being produced. The Moth Major is recognised as wooden fuselage, straight wing with Gipsy Major, not as metal fuselage. The fuselage assembly drawing shows that the DH60MIII and the DH82a are the same assembly number and the contention is that the 60MIII fuselage was used for the 82a. Many years ago Bob Ogden found a Moth Major in Switzerland which “seems to have acquired a metal fuselage?” and I have been told of a similar example in, if I remember rightly, Sweden.
One of my current projects is converting a DH82a Tiger Moth back to a DH60MIII Metal Moth Major, strictly according to the relevant DH drawings. Will post a few piccies shortly.

I don’t know what the difference is but the drawing numbers are different.

DH.60G & G III Main Rib, H.18729
DH.82, A, C Main Rib, H.34187

Anne

[QUOTE=Peter Garner;2043492][QUOTE=powerandpassion;2043477]

Peter,
Thank you, a generous reply. One day you should stick these photos and descriptions into the Historical Aviation University, I suspect you have a whole course available, Herr Professor. I have always regarded the making of wooden propellors to be the ultimate expression of wooden wizardry. I understand in mass production in the 1930s a steel template was made and used in a pantograph type arrangement to control the routing of timber copies.

I guess your next step was to create a 1:1 sectional drawing based on tracing out the templates, but then you are back to the tradition of hand making a prop with steel test templates as guides. I am utterly perplexed how folk achieved blade symmetry all those years ago, but I guess practice makes perfect. I think you need a walrus mustache and a pipe in your mouth to really succeed in this. I do not have the talent for this and am attracted to 3D laser scanning as it can output an electronic file that can be loaded into a modern routing machine which can then free me to wander off to a cappuccino machine to try and figure out how to operate the little breech lock mechanism to insert ground coffee, again another struggle….3D scanning was quoted at 3K by a scanning mob, so it is not cheap, but I guess this can be amortized across a number of props.

I feel like a talentless fraud doing it this way but it means that the file can be emailed across the world to serve other folks needs or ten identical props can be made in one production run, achieving some of the production efficiencies enjoyed by the pantograph approach.

I will shamelessly copy your prop cardboard template method though to create a drawing for a wishbone section inserted into the spar end of Hawker Hind/Demon wings and in fact to copy some ribs in situ within a wing that I was struggling to conjure a system to handle. I will call this the Von Garner method to apply sufficient gravitas when some kid wanders over to ask me what I am doing. I am much obliged. In your photos I am also amazed at the fraulein that just keeps staring at you with those loving, never shifting eyes, an aviation buff’s ideal woman, silent and uncomplaining !

[QUOTE=powerandpassion;2043477]

Thanks for your reply powerandpassion,

The reverse engineering of the prop is something I would love to learn more about.

The jig for taking off the sections was prepared in my workshop. All I needed to know at the time was the diameter of the airscrew. Wooden strips were attached
to the board in equal distances into which the templates were be slotted when the measuring was carried out. Once in the museum things were set up and the propeller was secured to the table. The outline of the propeller was transferred onto the board using a square and a pencil. The outline can just be made out between templates F-G and G-H.

Each template consists of two pieces – the top and lower part. Here the lower halfs are slotted onto the jig and small cardboard squares are being used to fill out the gaps between the airscrew and the template thus recreating the exact section at that given station.

Here the top parts have been attached to the outer templates at the tip pf the propeller. The thickish cardboard rectangles are where the upper part slots onto the lower part. Here too work has progressed in taking off each section by filling out the spaces with cardboard pieces.

Almost done. I arrived at the museum first thing in the morning to get the job done in one day. I only just managed to complete the work shortly after the museum closed for the day. This was done in Hannover-Laatzen and staff was extremely helpful. (That girl is still sitting in the back seat of that car watching me)

The distances between the templates narrowed as I approached the spinner. The edge of each template had the correspond exactly with the edge of the jig to ensure that everything lined up when redesigning the airscrew.

A selection of completed templates lined up on the museum floor.

Here I’m producing the template of the spinner. Only one was needed as the spinner is (usually) circular.

I have already drawn the plan of the propeller and it is pretty spectacular. I should have it scanned one day so I can show it to you. These are all the pictures I have but should you require further information, let me know.

The Heinkel project is still here. However I have given up my business as a professional modelmaker and I’m taking on a full-time job after the holidays. So instead of having to redesign an airframe before I build it I’m hoping to embark on a project for which hopefully (most of) the plans already exist. This is where either the Gypsy Moth or the Tiger Moth steps in. I had been in touch with a Tiger Moth clubs etc. a few years ago but they don’t sell plans to amateur aircraft builders (do they have to know?) so I’ll have to locate another source.

Anyway – for the time being this is just an idea. Should I only get as far as building a few wing-ribs I’m sure I’ll love every minute of it.

Peter

[QUOTE=Peter Garner;2043419]Thanks for your reply powerandpassion,

Peter,
On your previous posts on Ha51, a remarkable project, how has this progressed ? I would love to tap into your knowledge of tube supply. The reverse engineering of the prop is something I would love to learn more about. One thought was to use 3D laser scanning, but you seem to have worked out a traditional approach. I often wish that this knowledge could be either recorded on video or by written word and lodged in an internet based ‘historical aviation university’ for posterity. The use of 3D paper templates on the fuselage is a fantastic idea, I’ll copy it and call it a ‘Garner’ ! I am interested in 1930’s British metal aircraft – Hawker biplane- the parallel development of the Ha51 is interesting in how different designers evolved their ideas.

There is rather more to the wings than just spruce!!! A large amount of metal fittings are also required.

If you’re seriously planning on building one, whether static or flying, you really need to dig a bit deeper than Wikipedia as your primary reference source.

May I suggest de Havilland Support Ltd at Duxford as your first port of call. http://www.dhsupport.com/contact.php

You should also consider joining the de Havilland Moth Club. http://www.dhmothclub.co.uk/membership/apply.htm

Thanks for your reply powerandpassion,

there are a number of plans that are available from all sorts of sources but most of them are not official. The Tiger Moth plans appear to be reasonably complete but the Gypsy Moth plans are listed as a “small set” so I don’t know what to expect. After I had read your reply I was able to do further research in the web and came across the Wikipedia site which states that the wings were made of spruce – I have huge amounts of well seasoned spruce in my workshop right now! I’ll have to do some load-testing on some samples just to see what it is like.
What I also find very intriguing is the wooden fuselage. I hope that there are sufficient plans around to build one of these.

Regards
Pete

Hi all,

can someone here telll me if the Gypsy Moth and the Tiger Moth had identical wing ribs or the same profile?

Thanks
Pete

From ‘Magnificent Enterprise” by Janic Geelen ,pg 60 (NB, get this book from NZ Aviation Press, well worth it) :

How the Tiger Moth was Born.

The Moth Trainer (DH60GIII) was modified to satisfy the RAF…they wanted better access from the front cockpit. The problem lay with the wing struts that surrounded it. …they could solve the problem by moving the centre section of the wing forward…so that all four struts were now in front of the cockpit. By now, the upper wing was so far forward that the centre of lift was in front of the centre of gravity, which would make the plane uncontrollable. The solution was to move the centre of lift back…the wings were swept back..by 9 inches, 2 inches more on the upper wings. The test pilots criticised the small gound clearance of the wingtips, for with every degree of sweepback, the wingtips came closer to the ground. The solution was shorter interplane struts, which raised the lower wings. (They) produced a biplane that was not only distinctive, but also superior to any of the Moths that preceded it. The Tiger Moth was born.”

So essentially a Tiger Moth has Gipsy Moth wings swept back. An existing set of wings had the rear spar cut down and the wing was re-attached. The ribs on a Tiger Moth are therefore at 9 and 11 degrees to the direction of travel, which costs some airspeed, but cheaper solution than re-engineering entirely new wings. So the wing ribs are identical. (NB – Get a second opinion.)

A very lovely old gentleman in Bendigo, Australia made up some ribs that allowed one set of unique Tiger Moth wings to have ribs at 90 degrees to the direction of travel, giving an extra 10mph of airspeed. Rib formers are sitting in an old shed, waiting for a lover. Old bloke tore up his LAME qualifications when he got sick and tired of annual paperwork requirements. Didn’t know how to change the door on a Boeing, but could build Tiger Moth wings standing on his head. Now in heaven arguing with Angel Ministry for more sweepback on Gabriel.