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Flying indoors (or in the garden on a windless day)


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mikef

To warm up for lighter models, I put a BMFA Gyminnie Cricket together. ¬†Too big and heavy to turn in my lounge, I flew it outside in the calm, ¬†drifted about 15 metres in 30 seconds. ¬†385 mm span, porky 7.4 gram airframe ūüė≥. ¬†Rubber 1 x 1.9 mm. 1.1 grams 280 mm. loop. ¬†500 turns ish. ¬†Could take more power but it tried to get on the roof on ¬†2.5 mm wide strip.... ¬†Kept it lower for safety.

Now for something lighter and smaller.

Edit 20:08,  got braver.... 38 seconds....

 

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Edited by mikef
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mikef

Maybe this one?  Full size plan on a sheet of A4...   177mm span (7in.)

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PeterT

Well done Mike, it's good to see models that can be flown in the back garden!

Peter

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mikef

Another perfect evening.  Knackered the original motor on 750 winds but got 43 secs.  BMFA Gyminnie Cricket.

26 May.  Did 49 seconds - went high (exciting) and glided down on freewheel.  Longer piece of same rubber needed.

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Kyri

Mike that looks great - the propeller looks just like the ones I had on "sleek streek" rubber powered models that were great fun as a child I had lots of them,

 

Where might I get such a propeller so I can recreate this?

 

Thanks!
Kyri

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mikef

The supplied black prop is 152mm dia. and is 3.7gm.  The complete kit is £3.50 + postage from BMFA.  https://education.bmfa.org/products/gymminie-cricket

I needed less nose weight so I swapped to the lighter red prop - it also was made for a thicker motor stick so I was able to pack it to fit giving a little left thrust to cure a power stall.  It's actually the prop from the Sleek Streak's big brother, Star Flyer 174 mm dia. and 3.3 gm.

BMFA sell the smaller red ¬†‚ÄúDart‚Ä̬†prop units at 138mm dia. 2.8 gm. ¬†(That might be the same as Sleek Streak! I have a prop that size in my bits box - but no nose bearing)

Bad news - the 138 mm. red props are  £14 for 35!  https://education.bmfa.org/products/accessories

Good news!  SAMS has both the red Dart and black Gyminnie Cricket props at £1.40 each + postage.  http://www.samsmodels.com/products/propellors/plastic-propellers-with-hub-assembly
 

 

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mikef

The 7 inch (177.8 mm) span-limited class is called 'Living Room Stick'.  Mine is from the Jiri Kalina  TOM kit.  A challenging build for me, not having handled light balsa in such small sizes for many years.  The structure is mainly 0.04 inch square wood.  (1 mm ).

Some of Jiri's kits are listed on the Flitehook site but I haven't checked stock with them.  

I waited to post until I had succeeded in building the model - just in case.  I have now started to sort the model out and have broken the minute in a flight that brushed a light fitting once and hit the sofa about a foot up at the end!  62 seconds!

Airframe 0.67 grams, rubber 0.31 grams 230mm loop 0.8x1.0 mm.  Flying weight 0.98 grams (0.035oz.)

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mikef

The kit contents.  Condenser paper covering included and laid across the left side of the picture.  Wonderfull attention to detail from Jiri and good quality materials.  Pre sliced wood and pre-fab prop hub etc.

The rubber had perished - I've had this kit nearly 30 years....

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mikef

Ready to start...

 

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mikef

It's a constant chord wing and I decided to build the leading and trailing edges flat on the board.

A close-up shows tailplane and fin joints the scale is millimetres...

 

 

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mikef

Wing assembly...

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mikef

Add tip ribs..

 

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mikef

The prop blades are formed on a 500ml bottle.  These are fun to empty.

 

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mikef

Final assembly.  Tail tilt, fin offset, 5mm wing offset and wing warps are all intentional!

 

 

 

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Kyri

Mike, fantastic, thanks a lot for the information, links  and pictures.

In the meantime, I got hold of this, the plane I used to look forward to getting at christmas or birthdays as a child. 

With some old balsa, I had just enough to make a copy, but need props and the plastic part to attach the wings so will have to sort that out. 

Makes a nice change from soldering and composites! 

Cheers

Kyri

 

sleek streek old.JPG

sleek copy.JPG

sleek copy built.JPG

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mikef

Spares from my 'bits box'....

The 135mm red prop (no bearing)¬†¬†is probably ‚ÄėSleek¬†Streek‚Äô‚Äô as are the wheels and legs. ¬†The black prop is Gyminnie Cricket. ¬†Sams do a prop that looks like the one you want - details above. ¬†The small red prop and¬†clips are ‚ÄėSpirit‚Äô¬†parts. ¬†I think you could cut 1 and a bit Spirit clips to make a Sleek Streek equivalent. ¬†The nylon bearing bits seem the same on all the props, Spirit, Gyminnie¬†Cricket, Sleek Streek ¬†and Star Flyer. ¬†Let me know if you can use any of this....

 

 

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CTR
On 02/05/2020 at 11:37, mikef said:

Final assembly.  Tail tilt, fin offset, 5mm wing offset and wing warps are all intentional!

 

 

 

DBF85334-89D2-4C9A-A93D-DF2DF6312D6E.jpeg

 

Hi Mike, 

How about some details as to the purpose of each of the non-symmetrical trimming aspects of the build?

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mikef

The model turns left and flies without excessive bank in a 2.5 meter ish diameter tight circle to avoid the walls. The relatively large prop turns clockwise looking from the back so the torque from the rubber causes a left rolling tendency.

Wing offset and twist (more incidence on the left) are there to distribute lift to resist motor torque.  The twist also ’holds up the inside wing' in the turn and causes the drag to be offset left to encourage the left turn.  Remember, in a tight flat turn, the inner wing tip  is moving more slowly through the air than the outer wing tip.  The twist also means that, approaching a stall, the drag will rise faster on the inboard wing and tighten the turn, helping to avoid the stall.

The fin is offset to yaw the model left.

The tail tilt, tip higher on the inside of the turn, also induces a yaw into the turn (lifting tail)  and, approaching the stall, this effect increases giving some stall avoidance effect.  (Watch Red Kites using this as their main yaw control in the absence of a vertical tail fin.)

There is also about three degrees ‚Äėleft thrust‚Äô in the prop bearing - you know why.....

Sorry if you just wanted a sip of water and I turned the fire hose on you!

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mikef

I was telling someone that the TOM 7 inch model weighs just less than a gram with its rubber when I remembered  that a sheet of standard (80 gsm) A4 paper weighs 5 grams - that gives a context.

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