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Old Nov 11, 2012, 02:49 PM
MountainMike is offline
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Well finally picked one up with power combo, got it all built and now 20mph winds. Waiting for a maiden soon.
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Old Nov 11, 2012, 02:57 PM
TBone08 is offline
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I hear you. all I do the weekend in build, didnt get to fly yet...
Old Nov 11, 2012, 04:08 PM
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Finally nice out here in PA after Sandy. Flew another 4 batteries this afternoon. Was a bit windier then this morning. Had one tree incident where it took a bite out of the wing. I decided to keep flying and performance didn't seem to be hurt.

Found the chunk and just glued it back in place.

Just have to say it again, I love this plane!!!!
Old Nov 11, 2012, 07:30 PM
Chris Arena is offline
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Warm vs cold weather foam expansion.


I went to fly my Crack Yak yesterday and when I turned it on to fly, I noticed that my elevator had about 1/8" of downtrim, the rudder and ailerons were also out of trim slightly. We have had a change in the weather over the last week and the temperature has dropped from about 60 degrees down to around 40. Could the weather have caused some expansion in the EPP foam? I have had a DW Hobbies 9 mm 40" extra for about the past year and a half and have never had this problem. This is my first EPP plane. Is this normal? No bigge, I love the model, but have never encountered this problem before.
Old Nov 11, 2012, 07:43 PM
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where do I place the battery ?
I read that it suppose to be 8.5 cm from the leading edge but the photos show it on top of the wooden bar that crosses the wing ? maybe I missed something. your 2 cents appreciated.
also, does the number refer to the front part of the battery or the middle part ??
Old Nov 11, 2012, 07:50 PM
JC Spohr is offline
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Quote:
Originally Posted by Chris Arena View Post
I went to fly my Crack Yak yesterday and when I turned it on to fly, I noticed that my elevator had about 1/8" of downtrim, the rudder and ailerons were also out of trim slightly. We have had a change in the weather over the last week and the temperature has dropped from about 60 degrees down to around 40. Could the weather have caused some expansion in the EPP foam? I have had a DW Hobbies 9 mm 40" extra for about the past year and a half and have never had this problem. This is my first EPP plane. Is this normal? No bigge, I love the model, but have never encountered this problem before.
This is normal for an EPP plane with long CF rods for Elevator and Rudder. Typically the ailerons are not affected do to the shorter control rods.

First flight of the day - check and readjust.

JC

ps - Make sure you always store the plane hanging from its prop in order to prevent warpage.
Old Nov 11, 2012, 07:52 PM
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Quote:
Originally Posted by TBone08 View Post
where do I place the battery ?
I read that it suppose to be 8.5 cm from the leading edge but the photos show it on top of the wooden bar that crosses the wing ? maybe I missed something. your 2 cents appreciated.
also, does the number refer to the front part of the battery or the middle part ??
81.5 mm is the CG for this plane.

Put your plane on a balnce stand at that measurement and then place the battery on top of the wing next the fuselage to adjust CG. Mark the outline of the battery. Cut the hole about 2-3 mm smaller than the outline so it holds the battery in tight.

JC
Old Nov 11, 2012, 07:55 PM
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thanks. you mentioned 81.5: what are your thoughts about the written: "For totally neutral it is 3.25" or 82.55mm from the leading edge of the wing " ?
also, - backwards (from the place the front and inner part of the wing meets the fuselage) ?
Old Nov 11, 2012, 08:41 PM
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Quote:
Originally Posted by TBone08 View Post
thanks. you mentioned 81.5: what are your thoughts about the written: "For totally neutral it is 3.25" or 82.55mm from the leading edge of the wing " ?
also, - backwards (from the place the front and inner part of the wing meets the fuselage) ?
Herc (Chris Jewett) designed the plane and I'd listen to him. I did. I'm flying the CY lite and he told me 81.5. My understanding is that this is the same CG for the non-lite version.

I doubt you will notice 1mm difference.

BTW - that measure is from the LE of the wing where it meets the horizontal fuselage.

JC
Old Nov 11, 2012, 09:23 PM
KamikazePilot is offline
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What better source than the designer of the plane himself. I have my Yak setup at the recommended cg like JC and most other guys I know. Battery placement would be where the plane would be level at the cg mark. On mine I have it just ahead of the aileron servo. That’s with the standard power combo and no landing gear. Though I’ve seen others have it there or where Chris has his at the beginning of the build post.

Been awhile since I got a video here. So here's one from last weekend where the weather was playing nice with me. Unlike this weekend where the wind was throwing everything around.
Crack Yak (4 min 7 sec)
Last edited by KamikazePilot; Nov 11, 2012 at 09:54 PM. Reason: Added video link.
Old Nov 11, 2012, 11:08 PM
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there's actualy over a CM between the two. the issue I'm having is that with the combo setup and no gear- the written CG (8.5) is bit behind the wooden wings enforcment, while on the CG machine with my setup, its balanced out when the battery is bit front of the ailerons (like mentioned earlier). there's like good 9 CM of difference.
Old Nov 11, 2012, 11:14 PM
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Quote:
Originally Posted by TBone08 View Post
there's actualy over a CM between the two. the issue I'm having is that with the combo setup and no gear- the written CG (8.5) is bit behind the wooden wings enforcment, while on the CG machine with my setup, its balanced out when the battery is bit front of the ailerons (like mentioned earlier). there's like good 9 CM of difference.
Some people have had to put there battery ahead of the aileron servo while others ended up with the battery over the spar throughout the thread. It's a common thing. I guess it's the differences in the EPP between kits as well as how much glue is used.


Basically it doesn't matter where the battery actually ends up as long as the CG on the plane is correct.





Nice video Kamikaze. Is that a keychain cam?
Old Nov 11, 2012, 11:18 PM
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thanks for the pointers guys. I guess then I'll just go by the CG machine set to designers recommendation - and place it where the plane keeps balance.
Old Nov 11, 2012, 11:33 PM
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Quote:
Originally Posted by hone1er View Post
Some people have had to put there battery ahead of the aileron servo while others ended up with the battery over the spar throughout the thread. It's a common thing. I guess it's the differences in the EPP between kits as well as how much glue is used.


Basically it doesn't matter where the battery actually ends up as long as the CG on the plane is correct.





Nice video Kamikaze. Is that a keychain cam?
Thanks, yeah it's the 808 #16 cam that Avie and Cdee mentioned on the Pitts thread, I got it after I was dissapointed with the Dicecam I got from Hobbypartz.

Quote:
Originally Posted by TBone08 View Post
thanks for the pointers guys. I guess then I'll just go by the CG machine set to designers recommendation - and place it where the plane keeps balance.
That's the best route to go. My cg machine is either my two index fingers or two dowels drilled into a block of wood with eraser caps on them. I'm cheap I know, but it works.
Old Nov 11, 2012, 11:41 PM
ROLLING CIRCLE is offline
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GET YOUR CRACK YAK LIT UP INDOOR STYLE (2 min 57 sec)


fwiw....this plane on 3S has the batt on top of the wing with about 3/4 of the batt in front of the spar... 450 mah gens ace 30c
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