Sport scale sprung u/c for 58" DB DH60 Moth

[Geoff S]

Some time ago Gordon Whitehead posted some details of the sport/scale undercarriage he'd designed and built for his beautiful 1/5th scale Tiger Moth. I was building a DB 58" Cirrus Moth but as a the Gypsy Moth flown in the film 'Out of Africa' by Robert Redford's character. The main reason being the distinctive yellow and black colour scheme.

The fact that another forumite chose the same scheme is totally coincidental

The DB Cirrus kit provides the straight through undercarriage of early DH60s but this Gypsy Moth has the later Tiger Moth type so I decided to build a version of Gordon's design.

Unfortunately, his otherwise excellent drawing is undimensioned so I had to make a few guesses aided by my Pound Shop scientific calculator (I couldn't believe it was only a quid but it works!). I've had a few headaches because I seemed to working in imperial and metric units as well as calculating ratios from my print-out all at the same time and went wrong somewhere.

Anyway, I bought the brass tube and strip needed and the piano wire (some from stock), fired up my trusty 125 watt Henley Solon soldering iron and set to work.

The tricky bit I found was making the wrap around lugs. After buying the excellent wire bender from darkest Norfolk the piano wire part was relatively easy.

Here's Gordon's original drawing:

Eventually I'd assembled a set of parts:

The springs I found on eBay and are 6mm diameter with 1mm wire and are 40mm long and have proved ideal. The thought of winding my own horrifies me!

The wooden blocks were cut from a really heavy plank of 1/2" balsa I acquired from somewhere. Anyone who disputes that balsa is a hard wood should feel the weight of that plank. I drilled a 7.3mm (I have few imperial drill bits) hole down the length and glued them to the 9/32 tube oleo outers as farings and planed them to shape.

I ordered some 2.5mm nuts, bolts and washers from Modelfixings (it cost me a fortune because I always seem to find lots of other stuff I'm 'short of' to make the order worthwhile. I love Modelfixings) and assembled my parts:

There proved to be a few dimensional issues. I'll post this now and continue with my tale of woe in another episode.

Geoff

[Geoff S]

continued:

Somehow the oleo legs are too long though I'd deliberately made the sliding (1/4" part over long because cutting metal always worries me in case I cut too much off. Also the u/c was too wide and too high despite that I though I'd allowed for everything. My brain began to hurt a lot more!

There were several factors.

1: The top mounting brackets are screwed to a piece of 3mm ply the same length as the hardwood mount on the bottom wing intended to support the undercarriage. That's just 90 mm. On Gordon't model he mounts the undercarriage directly on the fuselage because his wings fit differently. So the mounts on my undercarriage, even allowing for the smaller scale are closer together which makes the wire parts extend downwards further.

2: Somehow I'd made the 4mm piano wire too long (115mm/side rather than the 105 mm I ended up with).

3: I also realised I'd made the angle a little bigger on the main 4mm piano wire which also made the axle lower.

After much though and a little re-engineering (ie unsoldering and re-soldering - which is harder than using new parts!) I ended up with these dimensions:

This looks a lot better and more or less as it should:

And with the top wing on just to admire it:

The front strut was child's play by comparison. Rather than using the stitch method to a fuselage former I'd installed a piece of 6mm ply because the former is almost completely cut away for the battery compartment. I use conventional saddle clamps to hold it. I used the model itself as a jig to get it the right length and soldered the end fittings in situ.

The main undercarriage 3mm ply plate bolts to the usual hardwood block under the bottom wing with 2 4mm bolts screwed in threaded inserts supplied by Modelfixings again:

which will make it quick and easy to remove the wing for storage and transport.

I've posted this here rather than on my somewhat neglected build blog because it may help anyone who wishes to add a sprung undercarriage to either of the excellent DB 58" Moth kits. I was a bit nervous of tackling the job myself and without Gordon's drawing to encourage I never would have attempted it. It certainly seems to be strong and springy. Whether it will survive the arrivals I jokingly call landing remains to be seen.

Geoff

[Eamonn Fahey]

That looks brilliant Geoff. Are Gordons drawings in the forum or in his excellent book? Thanks.

[Geoff S]

Thanks. Gordon's drawing and some description are on the forum on the 1/4 scale Stampe thread.

Geoff

[Eamonn Fahey]

Thanks Geoff, I'll start reading the 124 pages tomorrow.

[Geoff S]

No need. Just click in the link and it takes you to the relevant page (119 IIRC).

Geoff

[Manish Chandrayan]

And may more such suggestions and drawings in his excellent book.

[Bob Cotsford]

Nicely done Geoff. I made an articulated U/C for my Jungmeister, unfortunately I think I over-engineered it by using commercial vehicle steel bundy tube brake pipes for the oleos as the model wound up incredibly nose heavy. It will withstand some pretty heavy landings though

[Tim Hooper]

Hi Geoff,

Your struts look great!

I used a similar method on my 65" Blackburn B2. The struts were made of brass tube and rod, with an enclosed spring. Still working well!

Tim

[Geoff S]

Thanks, Tim (and all). I was showing my u/c to a very knowledgeable club mate at the field to day and he opined they were too stiff and might not work better than a rigid set up. I've used a 40mm long spring in 1mm wire (the thinnest the supplier did). I'm thinking of cutting off 10mm and seeing what the effect is. I may need to make longer sliders.

I've never though that K&S brass tube would be strong enough. Perhaps it isn't if some of my arrivals today are anything to go by!

Has some lovely flights with my Tiggie today btw. First time out with it since we flew together at Ashbourne last October.

Geoff