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Old Jan 07, 2012, 11:44 PM
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United States, NE, Kearney
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You do some immaculate work!
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Old Jan 15, 2012, 09:43 PM
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Chicago, IL
Joined Dec 2006
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Almost done! I used inkjet decals for now, but still might replace them with vinyl from Callie. At least it's flyable at this point, but I still need to fair the wings struts and landing gear. We have about 8" of snow at the moment so I'll have to wait for dryer weather, which gives me a little more time for finishing touches.
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Old Jan 15, 2012, 10:12 PM
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Quote:
Originally Posted by warhead_71 View Post
Almost done! I used inkjet decals for now, but still might replace them with vinyl from Callie. At least it's flyable at this point, but I still need to fair the wings struts and landing gear. We have about 8" of snow at the moment so I'll have to wait for dryer weather, which gives me a little more time for finishing touches.
I love your fictitious name for the airfield.
I grew up on the northwest side of Chicago where streets got names like that!

You DO NOT have 8" of snow... I heard the weather forecast on AM-720 for the storm and the prediction was 1-3" of snow!
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Old Jan 15, 2012, 10:34 PM
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Chicago, IL
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Wunderground says 5", but that's measured out in the burbs. In the city where it's warmer we got a bit more snow -- it's up higher than my hiking boots:

http://www.wunderground.com/history/...q_statename=NA
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Old Jan 17, 2012, 10:13 PM
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Chicago, IL
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I ordered graphics from Callie - they should get here in a day or two. The inkjet decals just don't cut it. Except for putting little fairings on the struts, the plane weighs 3lbs-13oz without batteries. I planned to use 2x 2200mah 3S Lipos in parallel which weigh another 13oz... but I may get away with a single 3300mah 3S Lipo and that weighs only 10oz. So we're looking at 55oz-58oz AUW.

Wing area is Top Wing: 52"x9" (468) and Bottom Wing 46"x8" (368) for a total of 836sqin.

So wing loading is just a hair under 10oz/sf and cubic loading is 4.15oz/cubic ft.

Clark-Y wing has a Max Cl. of about 1.25, so stall speed will be around 15mph.


This will be a floater.

*** EDIT ***

Oops!!!! I just realized the math is off for my AUW. It's 74oz, not 58oz AUW -- seems I forgot to add the batteries, plus now the weight of the dummy pilots and other little details.

So that's about the exact same weight as the Eflite Stearman, but with a lot more wing area (PT17 = 608sqin, TA = 836sqin). A .25-size motor on 3S should suffice for scale flight. A .32-size motor on 4S would probably go vertical.

Wing loading is now 12.75oz/sf, not 10oz/sf.

Cubic loading is 5.29oz/cu.ft -- which is still at the low end of "sail plane/park flyer" category.

Stall speed is 16mph, not 15mph.
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Old Jan 20, 2012, 07:04 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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Wow- I've got this kit lying around as well- now I'm beginning to think that the AF 40G may be a bit of overkill- might be the AF 25G instead.

Thanks,

Sam
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Old Jan 20, 2012, 10:58 PM
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Wow, those are antiques. I'm sure the 25G is plenty of power at 500W but it would weigh a lot compared to a modern brushless outrunner and Lipos.
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Old Jan 21, 2012, 09:49 AM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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Actually, they're very nice motors and the weight differential isn't as bad as you might think. It'd probably take 7-8 oz of Axi to match the 25G at 12 oz which means that most of the weight difference is the gearbox. Plus they're very sturdy motors- the 25G took a plant that would have probably left an Axi in pieces. The real revolution in e-flight has been the batteries-lipolys have dropped the weight by roughly a third. This means that the performance of the airplane with an Astro versus a more modern brushless motor just isn't all that great- the batteries make a bigger difference. The distinctions in motor performance were always a lot smaller. The worse problem is ESCs- Castle quit making brushed ESCs and I've had to buy a Jeti for the AF 40G. I do look for airplanes that will need noseweight to use them, but most of my fleet are glow conversions anyhow.

Sam
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Old Jan 21, 2012, 10:55 AM
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This bipe has a pretty long nose and mine might actually be a tad nose-heavy.
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Old Jan 30, 2012, 09:49 AM
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Chicago, IL
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She's almost ready for maiden. I went over the whole plane to double-check all the flying surfaces, linkages, and electrical connections... she seems solid. One thing though... I think there's a bit of flex in the elevator pushrods. When I installed the pushrods (2 pushrods, one to each elevator half) I didn't use any guides in the middle and now I'm getting some "bounce" when I manually push against the elevator in the "up" position. I don't think it would flex in flight at slower speeds or just cruising, but pulling out of a steep dive or loop and it might flutter -- so I need to do something. Now that the plane is covered, it will be a PITA. I might be able to add some bracing using forceps and a mirror to reach inside the fuselage. Sort of like building a ship in a bottle
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Old Feb 03, 2012, 09:00 PM
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Chicago, IL
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Holy Ground-loop Batman!!!

I just took her out to a soccer field to do some taxi tests and could not get her to go straight. I know the tailwheel and rudder are perfectly aligned, but as soon as the tail gets light she starts wagging all over the place. I made about 20 runs into the wind and not a single one went straight. Then as soon as I chop the throttle and the tail settles back in she snakes all over the place... first one direction, then the next.

I brought her back home and put the axles in a vise to bend a little toe-in. Not sure what else I can do... maybe it needs some right-thrust. I'll recheck the balance and try again this weekend.
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Old Feb 03, 2012, 09:31 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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Check that your wheels aren't binding and that they both roll freely. This catches some folks out. Other than that- yeah- some toe in should help as well as bending the gear back a little. Check your cg again too- if it's too far back, that can lead to nasty ground handling.

Sam
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Old Feb 03, 2012, 10:25 PM
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Chicago, IL
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I did some reading... seems that I need to roll out with up-elevator to keep the tail-wheel pushed into the ground until I have enough air-speed that the rudder is effective. Sounds a bit like getting up on step with a seaplane... up elevator until you get your speed up then ease off.

I thought maybe the wheels are too far forward as well... probably to prevent nose-overs. But I can't simply bend them back because they are braced/triangulated. Maybe I could mount them backwards? -- but that would look weird.

Both wheels roll freely... the wheels are plastic hubs and the axles are brass-sleeved. I could smear some graphite on it just to be sure but they already spin like roller skates.

As a last resort, I could always add a gyro to the rudder, but I'll try a few tweaks first and see how it goes.

And yes, I'll triple-check the CG.

Knock on wood... I hope to get her in the air this weekend.
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Old Feb 03, 2012, 10:55 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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The guy who set up a taildragger well was Dave Robelen- I still miss my Playmate. His comment- consider a vehicle on the ground- not an airplane and a couple of things become clear.

It sounds like you've done the right stuff on the wheels with respect to the friction issue.

1) Wheels need to be back towards the cg for stability- the further forward in front of the cg- the more the incentive for the back of the vehicle to be leading.
2) The tailwheel only supplies minimal force.
3) Move the tailwheel back- the further back the better. Plus- get the tail higher in the air- this helps move the cg further forward.

Summary- the closer the airplane is to the takeoff angle- the better. Wheels need to be close to the cg.

I'd try toe in- and I might try a smaller, skinnier main tire- as well as using a taller tailwheel setup.

HTH

Sam
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Old Feb 04, 2012, 11:42 AM
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Chicago, IL
Joined Dec 2006
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Yeah, I think the mains might be too far forward... probably designed that way to prevent nose-overs... so maybe I'll turn them backwards and give it a try. Also, I'll swap out the 4" wheels for 3" and see if that helps the AOA. But it's built exactly to spec as far as incidences and tailwheel height and CG... so I can't be far off.
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