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Keil Craft Ajax

Balance point?

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Mike Hardy13/02/2013 10:07:48
405 forum posts
72 photos

Hi has anybody on here built the Ajax, Can you tell me where the balance point is? It is not given on the plan? How is the wing attached to the fuselage? Again no info on the plan.

Mike.

Martyn K13/02/2013 10:51:41
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5084 forum posts
3678 photos

Hi Mike,

Are you building it for Free flight or R/C?. If free flight it will be about 50% of chord, R/C, it will be much further forward suggest 25%. There is Vintage Rubber build section on Hip Pocket Aeronautics where you will probably get a definitive answer for F/F

Good luck, I am building a KK Senator for F/F at the moment.

Martyn

Mike Hardy13/02/2013 11:09:01
405 forum posts
72 photos

Hi Martyn, Yes its free flight I am also building a KK Auster Arrow with info - wing spar

Mike.

Erfolg13/02/2013 12:13:02
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11749 forum posts
1337 photos

I have in the past built the KK Ajax. From what I remember there is no CG position on the plan,although it may have had something in the text.

With respect to trimming FF models, there are two conditions you are attempting to satisfy. The first, is that FF models are trimmed for one speed of glide. The second, the model has to cope with a burst of power, which tails off, and climb, rather than stall or spiral in.

When I trimmed my model, from memory, I adjusted the glide by packing the wing or tailplane.

For the climb, the nose block was adjusted to give a lot of down thrust, as well as side thrust, to achieve a wide spiral climb, from memory to the right. The objective is to have a controlled climb, where the model settles out into a glide when the power runs out, rather than stall. With this type of model stalls are unpredictable in what happens later.

Mike Hardy13/02/2013 12:19:12
405 forum posts
72 photos

Thanks Erfolg.

Mike Rolls13/02/2013 12:39:00
500 forum posts
22 photos

The KK beginners' kits showed the cg at 1/3 back, but could, in fact, be trimmed out with it further back - my Cadet flew much better balanced at the rear spar (about 2/3) rather than the 1/3 shown

HTH

Mike

Simon Chaddock13/02/2013 12:58:40
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5716 forum posts
3034 photos

I have just checked on my original 1958 Ajax plan and you are quite right there is no CofG marked!

It would however be reasonable to initially balance on the spar which at 1.5" from the leading edge is at 37% chord.

Not quite sure what you meant by "I am also building a KK Auster Arrow with info - wing spar".

For a scale type the Arrow flies quite well.

Mike Hardy13/02/2013 13:04:27
405 forum posts
72 photos

.

Thanks Mike and Simon, The Arrow plan shows the balance point to be along the wing spar.

PatMc13/02/2013 14:08:10
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4407 forum posts
530 photos

Lot's more info here plus rc & electric conversion.

Erfolg13/02/2013 14:43:07
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11749 forum posts
1337 photos

This is an electric version.

As you know the requirements are a bit different. Having to have a speed range, and being guided to maintain stable flight.

Whereas a FF model, is a one speed device on the glide, normally, trimmed near the stall, and trimmed to self correct for the speed differences at climb out and the glide.

Interesting though.

Mike Hardy14/02/2013 09:33:42
405 forum posts
72 photos

Another Question - what gauge of wire is used on the undercarriage? I notice the undercarriage stubs fit into tube which makes the Assembly removable? The Ajax meant to be flown with or without undercarriage? Does anyone have a copy of the tnstruction sheet that went with the plan?

Mike.

Erfolg14/02/2013 11:06:32
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11749 forum posts
1337 photos

I thought on my model the UC was bound onto the airframe, though I could be wrong.

It is worth noting the UC function, was primarily to take landing shocks, rather than the airframe. That is why many were so springy, not just to save weight. The landings being uncontrolled onto anything, anywhere arrivals.

Even when ROG, the rubber power, dragged them of the ground immediately.

jack lackmaker14/02/2013 11:53:19
96 forum posts
1 photos

hi from what i remember most of kk rubber powerd kits had the c/g on the main wing spar

PatMc14/02/2013 12:29:25
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4407 forum posts
530 photos

The purpose of the UC on rubber models like the Ajax was to save the prop from breaking &/or the prop shaft from being bent on landing. Some people just took a chance & used free-wheeling props without any UC. They also usually carried a couple of spare nose block/prop assemblies with them.
Carving a wooden prop is quite time consuming, KK supplied plastic props with a lot of their later rubber kits (not refering to the scale range). The orange slow fly plastic props for electric models would make decent substitutes with the centre bushed to take piano wire.

Most Competition rubber models used folding props, single or two bladed. These are not difficult to make & there were a number of articles in the Aeromodeller Mag over the years showing how.

PS if you do intend to make an UC have a look at some other similar size designs on the Outerzone for the wire sizes. Avoid the American ones as they are usually quoted in fractions of an inch.

Edited By PatMc on 14/02/2013 12:32:12

Simon Chaddock14/02/2013 12:46:21
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5716 forum posts
3034 photos

If you hand launch you can certainly fly a rubber power Ajax with the undercarriage removed. When the rubber unwinds the nose block is quite loose so it saves the prop - or rather the fuselage nose!

The U/C was really only needed for take off. At the time a ROG was considered the ultimate test but as landings could be anywhere the U/C probably did as much harm as good!

Erfolg14/02/2013 13:41:36
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11749 forum posts
1337 photos

Do agree that the UC is by no means essential.

I am not sure that the Ajax was ever, or just briefly a competition model. I do believe the reason they were so bendy, was as shock absorber rather than a UC. I can also believe they saved the prop, to some extent.

I would not dispute that without the UC the flying performance will be far better.

There are however 2 issues. The model would not be quite an Ajax, probably more important, is that obtaining the maximum performance could have the model exceeding the flying space and a lost or damaged model.

So other than a freewheeling propeller, which I think my own came with (although you made it, via the plastic propeller supplied), I am not sure I would consider that route, unless the flying space could cope.

Simon Chaddock14/02/2013 23:00:01
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5716 forum posts
3034 photos

Mike

Out of interest I looked up the Auster Arrow.

Rather surprisingly the Auster Arrow that Mr Hatfull drew is incorrect. All the Arrows produced by Auster had 75hp Continentals in a 'narrow' cowling with the cylinder heads sticking out like this.

One Arrow was converted in Australia to a 'Super' Arrow with a 105hp Continental in a fully enclosed cowling.

So the KK Arrow is not wrong just very rare! wink 2

Edited By Simon Chaddock on 14/02/2013 23:00:37

Mike Hardy15/02/2013 09:28:31
405 forum posts
72 photos

Thanks All, I have now got a copy of the instructions from another forum, no mention of CofG though but a lot of trim info.  The prop supplied with the kit is 8" dia but I have heard talk that the original Kit had 10" wood or 12" plastic not sure what a smaller prop will have on flight performance? Can anyone confirm the prop dia?

Mike.

Edited By Mike Hardy on 15/02/2013 09:29:37

Erfolg15/02/2013 11:42:17
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11749 forum posts
1337 photos

Mike

My model had a large propeller (plastic). I do not know if i still have it, just stuck away somewhere, i will go and have a look.

My model had a lot of rubber, the amount was decided by others. From what I have seen with FF in my club, it was probably far more than necessary, they can get a lot of height and duration from very little. Then again they know what they are doing. I did not, and still don't.

I do remember a real performance in lubricating the rubber, I think with lanolin, where I got it from is another matter, seem to remember a tube, though not certain. Then there was a real performance again, in winding the rubber, of stretching the rubber whilst winding, and slowly shortening the effective length as the tension rose.

I do remember that I corrected one of my mistakes, at that time. I saw no need to have a load of rear motor dowel sticking out. So shortened it, to make it look pretty. It was only when trying to wind, that it became apparent, that a much longer motor dowel was required to hold onto.

The model was built for the kids to watch and follow. The set up, meant that the proper wind up procedure could not be used. You cannot expect to have kids hold onto a model just by a dowel. The obvious solution, of making a FF holding frame, was to much work, given that I was not a modeller at the time, being in my late 20's had much more to worry about and little time, certainly not for modelling.

Erfolg16/02/2013 15:02:06
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11749 forum posts
1337 photos

I have had a look today for the KK prop. So far I have not found it.

But as with most things, when it is to late to be a help, it will be there, right in front of me.

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