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Fun Cub Gyro

A simple Fun Cub conversion to Autogyro yet maintaining fixed wing operation.

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Tom Wright 202/06/2014 14:27:59
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3908 forum posts
297 photos

Hi All

Down at the field this weekend I was offered a complete Fun Cub for free as the owner had moved on to more challenging projects, my thoughts immediately turned to the possibility of a Auto gyro conversion.

The model is larger than than the E Flight Cub conversion I did a couple of weeks ago and yet light and tough enough to make a great medium sized hack trainer so following an inspection an a few very minor tidy up repairs I will make a start today .

The first job was to predict the AUW which will enable a simple calculation to ascertain the rotor blade area needed for nice light flying and low sink rate.

The motor power can now be derived using around `125 Watts per pound of so it's off to search the draws for a suitable motor that will comfortably return 350 watts on a 2.2 A three cell and with a KV between 850 and 1100 as lower KV would eat up to much ground clearance, more after sorting out a motor.

Tom.

Tom Wright 202/06/2014 15:22:42
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3908 forum posts
297 photos

The Fun Cub quaking in its boots in anticipation of getting a rotary conversion.

fun cub gyro.jpg

Tom Wright 202/06/2014 16:53:22
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3908 forum posts
297 photos

Found a motor that fitted nicely and should have a good power reserve as the Fun Cub has a very easy motor mount system it was fitted in no time at all .

fun cub gyro 002.jpg

Tom Wright 202/06/2014 16:58:54
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3908 forum posts
297 photos

fun cub gyro 001.jpg

Richard Elliot02/06/2014 17:01:00
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180 forum posts
118 photos

Nice cub fuz there Tom, I imagine it's quite light so hopefully you can have blades that finish short of the fin again.

You sure those wheels will be big enough?devil

Tom Wright 202/06/2014 18:02:42
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3908 forum posts
297 photos

At first sight Rich it should tick most of the boxes necessary to succeed as a gyro. The fus is super light even with a hefty motor and lipo in place, will have it easily finished and test flown in time for Winterton so may be I can pass you the TX again without telling you its mode one surprise not that a small matter of opposite controls is likely to phase you wink 2. Had thought of putting on proper wheels but it would not be a Fun Cub .

Tom.

Tom Wright 202/06/2014 18:06:02
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3908 forum posts
297 photos

OK now to make a start on the whirly bits, the first job is to fashion a 1/8 ply plate held in place by the original nylon bolts, this will enable conversion back to fixed wing at the field .

fun cub gyro mast mount.jpg

Tom Wright 202/06/2014 18:15:17
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3908 forum posts
297 photos

That's a bit of luck a search though the rotor box revealed a set with plate that just clear the rudder .

fun cub gyro rotors.jpg

Tom Wright 202/06/2014 19:36:57
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3908 forum posts
297 photos

The next job was to fabricate the mast pivot supports which have a 1/4 x 1/2 spruce base screwed and glued to the platform.

The photo shows a quick mock up to check rotor clearance and anticipated lift vector relative to the cog.

fun cub gyro mast.jpg

Tom Wright 202/06/2014 23:00:30
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3908 forum posts
297 photos

Built the control mech this evening and fitted the roll control servo ,just need to find a suitable ESC and it should be ready for the trim flights tomorrow.

I have made the mast angle field adjustable within the range predicted of 3 - 9 degrees so if all goes well I can then do some cosmetic work on the mast and anchor plate. The AUW came out at 2.25 pounds which is pretty light for a model of this size and only 8oz more than the smaller Cub conversion.The small Cub has AJ 450 blades so its possible the Fun Cub would also fly on the same blades .....we will see?

Tom.

Tom Wright 203/06/2014 15:10:56
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3908 forum posts
297 photos

The first attempt from a hand launch was successful with plenty of lift from the old set of rotors, just off to the field again but this time I fitted the model with a set of AJ 450 Blades just to see if they will lift 2.25 lbs....more later.

Tom.

Handyman03/06/2014 15:21:49
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210 forum posts
1 photos

Hi Tom. Just a quick observation, I always thought you had your blades turning anti-clockwise, If my old eyes do not deceive me, yours on the "Fun Cub" are turning clockwise. ?????? Any reason for that, and does that mean that it will try and roll to the right as opposed to your CFL which always seemed to roll to the left. Just wondering.

Tony Bamford.

Tom Wright 203/06/2014 17:02:16
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3908 forum posts
297 photos

Hi Tony

Nice to hear from you again , and top marks for spotting the CW rotors thumbs up.

All my blades are now ACW but this old set was from my early Auto gyro days and the only set that was not in use,. CW blades will roll the model to the right if not up to speed , and slow turning ACW will roll left , it just a matter of setting the roll trim the opposite way with CW rotors.

This afternoon I robbed a set of AJ 450 blades from a CFL and fitted them to the Fun Cub Gyro ,the results were truly surprising as the fixed wing Cub is quite a large 60" model and in gyro mode weighs more than twice as much as a CFL . the narrower and shorter AJ blades performed better than the longer wider blades which backs up the theory that higher AR blades turn faster and as the lift increases by the square of the blade speed more lift is obtainable from less blade area .

The first try with the AJ 450 blades was a ROG in nill wind which was absolutely straight forward as it was just a matter of a few tweaks on the rudder and progressively increasing the power , the model would fly in circles hands off and performed very tidy loops with no effort.

One days work has turned this freebie model into nice sized club gyro trainer so thanks to Richard Gill for generously donating it for the Auto gyro conversion........sorry Rich you can't have it back I like it wink 2.

Tom.

Tom Wright 203/06/2014 19:05:47
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3908 forum posts
297 photos

Forgot to mention that the model is returning 5 mins flight time from a 2.2 A three cell and with the AJ 450 blades fitted. Looks like it's about to rain so might spend some time this evening to do some cosmetic work on the mast and mounting plate.

Tom.

Richard Elliot03/06/2014 19:18:48
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180 forum posts
118 photos

Tom

You made very short work of that conversion, nice one. Hope you can shoe horn it into the Tardis for Winterton so we can see it goyes

Rich

Tom Wright 203/06/2014 19:39:02
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3908 forum posts
297 photos

Rich

I must now get some cosmetic work done on the model so it can hold it's head up against the great looking models that will be at Winterton. No probs getting it into the "Tardis" as the mast and rotors are easily detachable.

The quick conversion was made easy by making the mast angle field adjustable, and the fact that the single axis head is so simple to build from scratch, I believe Cali has ordered perfect weather for Winterton. smile d.

Tom.

Tom Wright 203/06/2014 20:56:10
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3908 forum posts
297 photos

Got one more flight after the rain stopped this evening and found if I opened her up, raised the nose up 20 degrees, and then applied full roll stick ,the model rolled through 360 without effort or white knuckles, it will also roll off the top of a loop without any ill effects that can occur as rotor speed drops......I returned well pleased with the models versatility smile.

Tom.

Tom Wright 204/06/2014 15:00:41
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3908 forum posts
297 photos

The first step to consolidate the model was taken last night by building a wider stiffer U/C and in doing so taking care to end up with the ground sit angle combined with the mast angle that added up to a value of between 18 -20 degrees. This has proved to be a worthwhile exercise as the spin up / ROG performance is optimised along with the ground handling stability .The stock u/c was very floppy narrow track and generally ungainly so the new one will now allow operation from very rough patches ,the huge stock wheels were used as they are the defining Fun Cub feature and make orientation easy.

The model was test flown again this morning and returned impeccable performance, the new U/C lowered the drag center and the COG which was of further benefit as the motor has very little down thrust , it also brought the drag vector datum closer to the COG which all makes for a sweeter flying model.

Tom.

Tom Wright 204/06/2014 18:42:36
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3908 forum posts
297 photos

After testing the new undercarriage this morning , I managed to tidy the mast and plate.

cub gyro improved mast 001.jpg

Tom Wright 204/06/2014 20:38:06
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3908 forum posts
297 photos

More flying with the Fun Cub Gyro this evening but this time with a 3 A three cell , would those small blades object to the extra weight ? ......not at all she took off in "dead air" with no fuss or running all over the place to get the rotors up to speed ,the only thing to do now is recover the rotors in white as the yellow looks all wrong.

Tom.

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