AeroTech Pitts Python 50cc

A short story sort of. Many years ago, I say that because I cannot remember when exactly but at the time I think Dave B was still a teenager Anyway he introduced me to his friend Mark. Drawing out a fair amount of cash one fine Sunday I went round to Mark's house and returned home with a CAP232 (you may have already seen it at Cashmoor infrequently) and a Pitts Bipe. They were new in box except there may be some small parts missing and no build manuals. During a quick rummage through the boxes, Mark gave me some parts that were obviously missing. Anyway these boxes sat idling away at the back of the garage for a few more years.

With the necessity to have a hip replacement just over three years ago, and unable to go out I was allowed to bring in the CAP and start building it, making mods as I went along. (Do away with CA hinges and use Robarts for one thing) A few more years have passed and the Bipe in a large box was still filling out a corner of the garage taking up valuable space. BUT not anymore! With Camping weekend cancelled due to high winds and boredom setting in. The large box is in the recycle bin and the plane parts are spread out in my backroom.

First job I chose was to fit the cabanes and centre wing section. I have spent most of the morning running taps through the upper wings where the cabanes locate. Corrosion in the captured nuts I think. First I thought I was using the wrong screws, I assumed they were 6/32s. But later I discovered that they are quite possibly 4mm and corrosion of the threads was confusing me. However, I can confirm they are 4mm and the Centre wing section is now fitted and secured. There was a small build blog on RC groups back in 2010 where Americans were talking of fitting 4/40 and 6/32 screws and captured nuts, removing the Metric ones Aha! A clue... I wish these Yanks would get on board with the rest of the world but with Trump in power maybe not for some time yet. :lol:

Next job is a bit of slog, modding wings to take 3/16 Robart hinges, all four of them, 5 per surface. :ohmy: The flat stab will use 1/8th, 5 per elevator. The rudder I plan to use Great Planes flat hinges with the pins pulled out so I can fit a 1mm wire in. This will give the option of removing the rudder whilst in transit if need be.

Have you got a Robart drill jig Phil?

Brian wrote: Have you got a Robart drill jig Phil?

Yes I have Brian. All I need now is the desire to get on with it. :lol:

Before I move on to the wings I just wanted to verify the engine mounting. The plane was designed to take a DA50 which has virtually the same footprint as the DLE55. Using the DLE template on to the pre-marked lines and checking engine alignment by dry fitting cowl I made some small pilot holes. Looking into the inside of the box the holes line up with some internal balsa fillets. These fillets will have to chiselled out! Originally I thought I would use large washers to spread the bolt down load but as the holes will be close to the edges it now means a trip down to B&Q for some 15mm aluminium angle acting as load bearers and fillets. (Using metal angle in the engine box appears to be the norm for Extreme Flight planes too and probably many others in the giant scale class) These angles will then be bolted on. Glass the rest of the engine box?

Example I am following is Extreme Flight with a DA50 - last image

Aluminium angle installed and bolted to engine box sides. Engine stand-offs installed with load spreading washers where necessary. Taken most of a morning as I keep getting diverted to go and do other general home stuff.

Rudder finally fitted along with Horizontal stab.

A bit of a quandary now. The two elevator halves each have three 25mm Mylar hinges. I was thinking maybe add two per elevator (easiest mod) or fit three Kavan hinges. The stab is 11mm thick and so is the leading edge of the elevators which is bevelled. There is not much balsa depth on the elevators which is why I am discarding the plan of 1/8th Robarts, especially after the frigging about hinging the rudder with Robarts. Although using stock components these planes were used successfully at IMAC some years ago according to reports.

Am I being concerned to much? Just use what was supplied?

I personally wouldn't use normal mylar hinges on a 50cc Phil, I wouldn't trust them to be strong enough. For that thickness of surface I think flat pinned hinges like the Kavan ones would be the way to go, minimum of 3 per surface.

JonTappin wrote: I personally wouldn't use normal mylar hinges on a 50cc Phil, I wouldn't trust them to be strong enough.

That was my line of thinking Jon but asked for those with more knowledge. Kavans it will be with pinning.

Best method of slotting other than scapels and craft knives?

Use a dedicated slotting tool and guide. The tool looks like a flat blade with a "V" cut out of the front edge. The guide centralises the slot. A second tool is slightly hook shaped and is used for picking out the material removed by the slotting tool. When fitting flat hinges, I drill a 1/8" hole on the centre line of the slot, then cut the slot. The hole is to enable glue to be squeezed in. I prefer to use canopy glue when fitting flat hinges, quick, and easy to clean up. I have slotting tools in two sizes, you're welcome to borrow them Phil.