A return to model building and flying. Part 71


June 2011

Corsair Modifications


Well the weather has been so Bloody! awful wind wise this year, I have done almost no flying at all, and the one comp I did enter I nearly lost my Class One Corsair carrier model when it was suddenly caught be by a very strong gust and I lost control. Fortunately it was over grass and  only dinted a wing tip and sprung a wing mount, but it was enough to make me take the hint and give up flying for that day and pray for a less windy day at the next comp. The modifications I have been working on do look like they might have some potential, if I can manage to sort out a really basic problem without resorting to electronics.

Because I have been doing a lot of staying in since last year, for the reasons stated above. all I have managed to do is have fits and starts at modifying models, interspersed with long periods of thinking, which is always a dangerous thing. Most of this is just trying to work out one seemingly insoluble problem after another with the modelling. The in-flight line rake release was one such problem and only took nearly six months to come up with an answer. I wanted a design that would  transfer to other models so that I don't have to keep reinventing the wheel with each new model

lr-f    lr-bk

The pictures show the results. What I came up with is very versatile, as the line rake position and travel can be all be adjusted just by moving the brass wheel collets. It's triggered by a short wire attached to the up line. I now have line rake and rudder offset triggered by full up and the hook by full down. Ii works fine, as long as I don't forget and give full up at launch. I would like some more precise way of setting the point of release,

in fact it was so smooth the first time I activated it in flight I didn't know it had happened. In case anyone is wondering, the slider bar does not need to be strong as it bears very little force. If you want to use it as as a carrying handle as I sometimes do, it does really need to be a bit thicker. I didn't notice the wild the trim change because I was jerking the lines very hard on the first flight as I was unsure about how much movement I would need to trigger said device. I didn't realise at the time that the excessive trim change had cause the bumpy landing that sheared off an elevator. So that was that for one day, point proven and repairs needed.

Until I had the chance to fly the corsair again on a rare fine day, I was surprised I managed to fly it at all in the strength of wind I had flown it in at the comp, The trim change from full forward line rake to to full back is so great I can barely control it for landing. This will take a lot of thought and ingenuity to sort out. The only good thing to come out of this is  that my idea for a release mechanism is remarkably good, and the rudder offset trigger works too. The whole thing is a bit of a mess as it's all retro fitted, but if I can at least get the ideas to work they can be refined when I build the next model. Hopefully by next year I will have flaps working on the Corsair too, barring accidents? Sometimes I wonder why I do all this?

It is an modified ARTF RC model after all, so not quite as strong in the right places as it should be for my purposes, I was fed up with the elevator weakness anyway, and it was easier to make a new tailplane and elevators than repair the originals. A lot of work followed, only to nearly wreck the results at the comp.

Next up was an engine change in the bearcat from a Magnum 36 which expired with a death rattle last year, with a Super Custom 32, as they are the same sized engine externally (and internaly). I have yet to fly it in anger.

Then out of pure boredom and the hope of generating some enthusiasm in myself, I swapped out a SC 40 for an Irvine 40 that I had inherited. Of course that little exercise had to be fraught with problems too, mainly because the Irvine carb has no throttle stop (this will be written on my grave). So it was a case of trying to fit an SC carb, and while I was at it an SC rear needle valve assembly. This  should have been easy...., but no, the Irvine has a carb spigot hole that would not disgrace a manhole, so another afternoon was spent with my limited resources trying to make a sleeve . One day I must get a better tabletop lathe. It looks pretty now and I am curious to see how it performs.

irvine40




Engine Building Down Under


Bernard Smith in Oz (at least hope he's in Oz, or I will have a red face!) wrote to me with some examples of replica engines he builds. I was so impressed I had to share with you all.



spary 5.0    Taipan 2.5

Spary 5cc diesel                                                                           Taipan 2.5cc diesel



Casting

by Bernard Smith


The purists probably won't agree but it works. A wooden pattern is probably worthwhile as you can see what you are trying to achieve



spary



The mould is made from four pieces of bright mild steel bolted together(make sure the bolts will miss the boring & cut outs you need to do)

Chuck in four jaw chuck & bore from what will be rear of crankcase plus some extra depth to allow for wastage to be turned off at rear of crankcase(say 10mm)




spary spary

Mold spread open to show internals                                                         Mold in halves to mill lugs & gussets in top half



spary spary


More detail of top halves



Start with a car induction manifold which is gravity cast ( pistons are pressure die cast & will result in a coarser finish externally, the casting photos are of piston material which were my first attempts which is not too bad but the manifold works better)



carb man


spary spary

Piston aluminium material rougher finish on external of case


spary spaty

casting

Later versions from manifold material & finer external finish  (taipan 2.5 & K Vulture)

   

The mold is bolted together and coated with canola oil (from supermarket) aluminium is heated for required time (½ hour for my oven), at about ¼ hour put mold into oven to pre heat it to very close to aluminium temperature. Take mold out & sit in a bed of dry sand (in case if spillage) then pour the aluminium, while it is all still fluid tap the side of the mold to settle the molten metal into all the detail.

Let cool & unbolt mold.

I know that the lost wax method is ok also, but takes a lot of time & if the result is not perfect you have to start all over again. For the little bit of extra work to make the metal mold & if you have a “dud” in ½ hour you can have another one made.



Part 70left        right Part 72

Back to the beginning of the saga

Home