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Old Apr 06, 2012, 10:10 AM
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Originally Posted by eflightray View Post
I still can't get my head around the need for all that weight up front to get the CG reasonable.

Models like the Sky Surfer have very similar proportions to yours, yet have no problem with the motor at the T.E.

What flight battery are you using ?

What is the wing chord ?

What dimension are you using for the CG location ?

What is the extension that sticks out the rear of the fuselage in your photo ?

Sky Surfer picture.
Yeah, I know, I was surprised by how tail heavy. I'm using a Dunlop carbon golf shaft. One option I considered is to cut that boom down further and remake the tail lighter.

Believe it or not, I dont have a measuring tape to get the chord. I lost a bunch of tools when I moved.

As for the CG, there is a spar which I'm guessing is around 25-30% and I'm trying to get it on the spar. From memory, my tail is intentionally a bit bigger than the aerobird xtreme which is where I got the wing. I think I tried for a 25% bigger tail and same length, but lost my notes too.

The extension beyond the tail is the pushrods before I trimmed them and hooked them up.

Interestingly, I took it to the hobbyshop and used their scale and it is at 2.4 pounds which is exactly what the aerobird xtreme weighs. If I get it to balance, the wing loading shoud be about 14 oz/sq ft. I'm using a 2200 3s
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Old Apr 06, 2012, 11:00 AM
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I dont know, now I look at it and compared to that sky surfer, mine has a long tail moment. That makes me think there is room to cut the boom and lose some tail weight.
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Last edited by HELModels; Apr 06, 2012 at 11:27 AM. Reason: add the modified tail pic
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Old Apr 06, 2012, 11:31 AM
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Cut it that much again, and make a larger horizontal. The tail moment on the original is way too long!
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Old Apr 06, 2012, 02:36 PM
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Thanks, Sparky. I increased it 15%
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Old Apr 11, 2012, 01:56 AM
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I finished the new tail. I need to cut the boom down and connect the pushrods. With the bigger tail, I dont think I lost enough weight to get the motor on the TE but the shaft extension would be much much shorter.
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Old Apr 11, 2012, 02:52 PM
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Here's where the motor goes now. I'm going with it. I need to make a bearing holder which will tie into the motor mount and attach at the wing hold down bolts.
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Old Apr 11, 2012, 06:19 PM
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I made the bearing(s) holder. I took 2 pieces of basswood, gouged out where the bearings would go with plenty of extra space for epoxy, wood glued the pieces together and then sunk the bearings in epoxy with a piece of shaft through the 2 bearings for alignment.
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Old Apr 13, 2012, 08:08 AM
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I hate to be a spoilsport but your setup as shown-has a good possibility of exploding when running.
you must support the prop as close to the bearing as possible
I will add a pic of my present pusher setup as an example
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Old Apr 13, 2012, 02:02 PM
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Originally Posted by richard hanson View Post
I hate to be a spoilsport but your setup as shown-has a good possibility of exploding when running.
you must support the prop as close to the bearing as possible
I will add a pic of my present pusher setup as an example
Yes, I do appreciate the warning. I flew it today!! At low RPM, static on the ground, it's smooth as butter. It gets dangerous looking when the prop kicks in. The shaft I'm using was originally a super thin archery arrow which I think is made to handle some serious flexing and loading.

I probably should redo the mount and get that bearing further back, but I wanted to fly - famous last words.

Anyway, the flight went perfect and it seemed quiet at high RPM like the flexing in the air is less maybe. It didnt blow up and CG was right on, very stable, and the bigger tail had plenty of control
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Old Apr 13, 2012, 06:13 PM
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I just went out and flew it again. I was able to get it to sound like it wanted to rip itself apart in one area, going from slow and no or low throttle to bam full throttle. It didnt like that and I could hear it go from a nice hum to a rattle. As soon as speed built, it went back to smooth sounding hum. I really should rework the mount and get the bearing as far back as possible, but it flies very nice and I'm happy about that.
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Old Apr 13, 2012, 11:47 PM
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Originally Posted by villapilote View Post
Hi HELModels
When struggling to get the CG correct, many of us forget that moving the wing is also a possibility. A small movement can have big results.
Yea, I dont understand why the wing cant be moved, it would be a much
quicker fix.
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Old Apr 14, 2012, 04:09 AM
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Originally Posted by The_RattleSnake View Post
Yea, I dont understand why the wing cant be moved, it would be a much
quicker fix.
I didnt move the wing because it sits in a molded saddle that is only as deep as the root chord. The wing is undercambered and to slide it back even an inch would change the incidence - moving the wing means remake the pod. The real problem though, I used a piece of lead for the boom. I have one more option, replace the boom. As it is, dangerous and heretical, it works - just dont slam the throttle. 50% bearing location is convenient, but it is why it vibrates when the prop is loaded. All vibration is between the prop and the bearing while between the bearing and motor is solid at all RPM's.
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Last edited by HELModels; Apr 14, 2012 at 12:41 PM. Reason: Cant move wing and why
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Old Apr 14, 2012, 01:31 PM
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Wilson, NC
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Hi HELModels
A lead pipe for the boom? No wonder it is tail heavy. I have seen similar planes that used a carbon fiber hollow "arrow shaft" for the boom. Very light weight and very strong. Once you make that change, you can move the motor back and mount the prop directly to the motor, eliminating other potential prop drive problems. The end result will be more reliable and lighter in weight, two items air plane designers are always looking for.
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Last edited by villapilote; Apr 14, 2012 at 01:39 PM.
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Old Apr 14, 2012, 04:13 PM
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Quote:
Originally Posted by villapilote View Post
Hi HELModels
A lead pipe for the boom? No wonder it is tail heavy. I have seen similar planes that used a carbon fiber hollow "arrow shaft" for the boom. Very light weight and very strong. Once you make that change, you can move the motor back and mount the prop directly to the motor, eliminating other potential prop drive problems. The end result will be more reliable and lighter in weight, two items air plane designers are always looking for.
My pusher used a .060 wall boom -too heavy!
so -I said -forget the idea and made a tractor out of it
The model is a mule -for testing various radio stuf (inc telemetry) and as it sits completed now- inc a 3300 ma e cell -it is just under 4 lbs at 800 square inches. If I kept the pusher config -Iwould need another 8 to10 ounces up front - I can still mount motor at rear and remove the front setup if I decide it is light enough.
The radio has a setup for flapperons and I have it setup for both ailerons up - centered or down
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Old Apr 14, 2012, 07:02 PM
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Looks like a reliable machine you got there.

Everybody can tell me I told you so. I flew again today and it seemed to be losing power and I figured it was the end of the battery so I landed without incident. I get it home and decided to move the bearing back and when I hacked the bearing holder off, the motor bearings were shot, all kinds of slop. The local hobby shop can probably help there, but still stinks.

I have one more idea for a motor extension and that's to use an idea from rubber power.

Edit: I checked the motor over again and it was just a loose grub screw, but I'll take it as a warning as to what is going on in there.
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Last edited by HELModels; Apr 14, 2012 at 10:28 PM. Reason: loose set screw this time
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