With the Lark project now completed, time to turn back to the DS-22. This has been on hold for a while, due to an awkward problem!
The tail-rotor drive on these machines is like a big speedometer drive cable (5mm), which also happens to be left-hand wound. I'm told they originally were manufactured for Amsterdam trams! Whatever, this means they are very difficult to replace! 5mm is a bit of overkill, and there are German suppliers offering 3mm replacements. However, these mean replacing the outer part of the cable as well as the inner, and since this winds its way up through the fuselage, is a last ditch option!
The new gearbox casings have an extra lug, which makes accessing the grub screws that hold the adapter to the gearbox output shaft difficult. Also the new, one-piece chassis further obstructs access to said grub-screws!
The easy solution is to attach the adapter to the gearbox prior to installation, and then tightening the grub screws on the wire drive after everything is in place.
This is great in theory! Unfortunately, my adapter hadn't been disturbed in over 30 years! The original metric grub screws had all been replace by BA ones (presumably someone stripped the threads!) and one of them that gripped the wire drive had had its head turned off!
I bought a set of left-handed drill bits, and finally managed to get the offending grub-screw out - without damaging the wire - only to find the wire drive thoroughly corroded into the adapter! Neither Plus Gas nor heat would shift it! In the end, I very carefully cut it in half with a Dremel cutting disc!
adapter by
Peter Christy, on Flickr
Again, by being very careful, I was able to finally get it off without damaging the wire drive! PHEW!
Once this was over, reassembly went very quickly, and the DS-22 is now awaiting first test hops!
Finished by
Peter Christy, on Flickr
The battery sits neatly in the space previously occupied by the fuel tank:
interior_1 by
Peter Christy, on Flickr
I've run it up in the back garden, just enough to get it light on its skids, and all appears well so far!
Since this is such a major change in the mechanics, I'll be doing a lot of low-level hovering for a while, until I'm certain nothing is going to shake loose or break!
Both the DS-22 and the Lark have been fitted with FrSky Neuron ESCs, and the amount of telemetry this provides is staggering! On the Lark, the telemetry logs clearly indicate that I've got the motor type and gearing pretty much spot-on, and I'm hoping the DS-22 will be the same.
On an aeroplane, its quite easy to change the prop size to suit! On a heli, you are mostly stuck with the "prop" size and gearing, and have to "guesstimate" the motor and battery requirements. The run-up in the garden looked promising. First proper tests will either be tomorrow (Sunday) or Monday.
Watch this space!
--
Pete