A return to model building and flying. Part 44

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October 2007

Early Morning Landing


Couldn't resist using this atmospheric shot of my F8 Crusader after finally making a successful landing on a wet carrier deck: after a few fights to get the hook to function properly and find the basic settings on the newly fitted MDS.25 engine and throttle. 

Although it's the most attractive to look at, it's also the most awkward and perverse model to fly I have ever owned; but I might get some use out of this model yet? If I ever built another one it would have to have some radical redesigning of everything to make it practical as a competition model. It's already had the bellcrank moved externally and changed in several ways., the hook modified, the undercarriage altered, and several changes of engine from .25 to .36 and everything in between, and had so many holes drilled in it, it is starting to resemble a certain Swiss cheese. 

The trike' U/C has an inherent disadvantage. When the nose rotates for take off, the tail is pushed into the ground. The whole design of the rear end and hook being mounted where it is, means that it is pushed into the ground before any speed can be built up. This is deadly on grass, as there is not really much clearance on this design. The original kit model has a short nose leg, no doubt to imitate the real aircraft; unfortunately this aggravates the rotation and take off problem necessitating the fitting of a longer nose leg to help get a shorter take off run.

The worst engine has been a OS.25 AX. it's performance has been no better than the MDS.25 I have in at present, and the throttle linkage arm on the carb is a really bad design, It makes me wonder if they gave the job to the new work experience recruit. The most remarkable was the MDS.28 that had a 90° misaligned cylinder liner that not only ran OK, but still ran OK when it was corrected.

This was also a test of how the 2 litre milk bottle drag weights perform. Being stored for a few months they had lost about half their contents, but instead of filling them up again, I decided to see just how they would work at half the weight. Answer: with no problem at all. They pull further and sometimes two lines are hooked instead of the normal one, but this is a somewhat heavy and fast model to land, and it still pulled up well before it got any where near to the end of the deck, even with the last wire hooked.

The standard old style MDS silencer is a bit raucous at high revs, so back home I attempted to find out how they where put together. Maybe I could modify it if I could find out how to dismantle it. 

I had an old one so so I was prepared to break one if necessary to find out.

mds silecer internals

Well the bad news is, I did have to saw off the end to get into it, (picture above) It is pressed together and it it also looks as if some sort of bonding has been done as well. Trying to take one apart is not something I would recommend to anyone now I know this. The noise is produced because the internal baffle is too small, but there is no way of dismantling the thing easily to get at it. Now I have sawn off the end, fixing it back is also something of a problem. If I have this noise problem in future I will attempt to fit an extension silencer onto the existing one.

However, searching around in my box of engine bits, I found an Irvine mini pipe, which has as near as damn it the same fixing holes as the MDS, so on it went. It has a bigger volume and a smaller outlet which I hoped would keep the bark to reasonable limits.

irvine pipe

The engine goes well at full throttle and feels like something much bigger than a .25. it also throttles well, not quite as responsive as when fitted with the normal silencer but very even through the whole rev range. It's still a bit more noisy than I would like, but I can afford to lose a bit off the top end with some additional silencing.

The scary thing was all the endless messing about with this model has worked, not just the engine, but every thing else as well. For the fist time I stood there after the landing and tried to think of something that needed modifying, or repairing, and couldn't come up with anything. Now that's really scary!

Self Launch

After spending a couple of years and a lot of brain ache on and off, trying to work out a way of self launching my throttled carrier models and coming up with nothing workable, or if it did, introduced some other problem; finally, by accident, I stumbled upon a way that is so simple it beggars belief. The following would not work on a hard surface, but some sort of weight might be employed to achieve the same end. This solution is only meant for my simple handle and a keyring throttle pull. How, or if, it would work with anything else, is for you find out.

The screwdriver is driven into the ground to stop the handle pulling toward the model and as an extra precaution pushed in all the way to pin the handle to the ground. There is no reason why a hole couldn't be drilled through the handle so the screwdriver or whatever skewer you decide to use, could be pushed through it. adding to the safety aspect. For now I am just testing the workability of the idea. I have also started to put the safety strap over the screwdriver as well when unattended, as an extra precaution.

A side effect of doing this, is that moving the model sideways toward the handle allows the bias spring in the carb to open the throttle, pulling away from the handle does the opposite. This produces a neat way of setting the tick over speed of the engine whilst setting the model ready to be left unattended just before take off.

three line release

Carrying the screwdriver  whilst flying also enables the model to be landed and the handle pinned to the ground so that engine adjustments, or other adjustments, can be carried out without stopping the engine.

This simple idea has revolutionised the way I fly, and what I can do on my own, and so far has worked flawlessly for more than a month of fairly regular flying.

Next thing when I get round to it, is to work how to self launch from the carrier deck? The above would not work because there is no grass acting as a brake on the wheels.

Tutor Trainer - Carrier Conversion

Some time ago I decided after refitting my own design Tutor three-line trainer, it would be a good idea to add a hook so that it could also be used as a carrier trainer. My first attempts to try it out on the Scuttle Bucket can be seen on this short not brilliant quality video. the first attempt actually came off the deck side and the prop chopped a hole in one of the buckets, you can hear the sawing sound on the audio. Must remember to place the buckets, all, the way beneath the deck in future.

1.4MB .wmv

I am still impressed by the way the SC carb woks on the Thunder Tiger .15. the only drawback is the close proximity of the needle assembly to the prop, which means it is frequently knocked whilst starting. However it's performance is flawless.

Well after the last few days of nice weather it now looks and feels like Autumn is turning into Winter now, so I will have to pull my finger out and get some building done.

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