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Old Jun 03, 2009, 12:26 AM
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Combat Gremlin....EP


Building my first combat plane....a Gremlin. I would never have been turned on to it but a "buddy of a buddy"s uncle or dad or something cuts the wings and puts together "short kits". My buddy got two 'kits" and one ended up in my garage. Anyways...having never seen a Gremlin before I had to go online to see WHT the thing was supposed to look like. Well....I'm intrigued....got 'er about 1/2 to 3/4 done and she's going to have electric power. Going to run a Turnigy 42-40B 900kv with a Turnigy 60A Plush speed control with on 4s (3200 or 3700). This combo pulled 670watts with a 13x6.5 and flew a 6.5 lb Hanger9 Cherokee conversion....hope I have to skills to fly it!

Motor mount is built, but still needs to be boxed in.....thrust line is the same as a slimer engine. Went with goofy pink just because. LOL. (oh, and covering does stick to drainpipe)
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Old Jun 05, 2009, 06:40 PM
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Finished the vertical stabilizers and elevons today. Marked the CG and just kinda dropped all the gear in place to see where I'll be....should work out nicely. Going to run a Turnigy Plush60 and HS225s with an AR6200. Coming along OK...
Old Jun 06, 2009, 01:57 AM
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OK...servos mounted, motor mounted....CG is very close to what it's supposed to be.
Question: since the advised CG is 1.7" from leading edge with a fuel engine....this is assumed empty gas tank, right? Is it logical to allow a bit further rear for an electric model since we don't have a tank to fill? Ive converted a few gas models to EP before and always set things for the recommended CG, but in this case, it is sooooo touchy that I'm wondering if I can go a bit back.
Old Jun 06, 2009, 02:01 PM
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Quote:
Originally Posted by HMX Dave
OK...servos mounted, motor mounted....CG is very close to what it's supposed to be.
Question: since the advised CG is 1.7" from leading edge with a fuel engine....this is assumed empty gas tank, right? Is it logical to allow a bit further rear for an electric model since we don't have a tank to fill? Ive converted a few gas models to EP before and always set things for the recommended CG, but in this case, it is sooooo touchy that I'm wondering if I can go a bit back.
Yes that's correct on the CG with a empty fuel tank.

Generally it's like that so when you fly, you wouldn't be coming in for landing unless you were either low on fuel or ran out.

Engine flame outs or shutdowns will be a bit nose heavy but this helps in keeping the airspeed up to compensate for the added weight from the fuel.

I would start with the CG where it should be at with a empty tank, do one flight and see how it feels.
Then strap on a weight or tape it on to balance the aircraft to the CG you want to try (more rearward in your case) and see how it feels.

That should make it easy to pick which one you like.

BTW the color scheme on your plane reminds me of victoria secret PINK lineup
Old Jun 09, 2009, 04:10 PM
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This is great, my club loves combat and I fly only electric. I have always thought of doing a electric gremlin.
Old Jun 11, 2009, 10:49 AM
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Lookin good Dave. Mine is pretty much the same as yours except I cut off the plastic nose vertically where your firewall is and put wood screws into the edges of the firewall, through the plastic. Just another means of accomplishing the same thing. I also put a landing gear on it to help save props. Very fast and will outloop just about anything. Have fun

Gord.
Old Jun 12, 2009, 09:40 AM
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Sounds neat Gord! I've been waiting for calmer winds for the maiden still....

Post a few pics of yours if you get the time. I'm interested to see the differences and your landing gear.
Old Jun 12, 2009, 10:10 AM
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I'm afraid it's out in the garage somewhere Dave. Couldn't get anybody to do battle except for a club member with the same plane with a 25 FX glow. He had trouble getting the motor to run right so I could walk circles around him. Using a Himax HC 3516-1130. For the landing gear, I put a 3/32 ply plate on the bottom up against the firewall right where yours is. The wire is W shaped and screwed on with sheet metal screws and straps made from 1/16 aluminum.
Old Jun 15, 2009, 08:37 PM
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Well....two unsuccessful hand launches....two big arcs into the ground and two broken props. I attributed the first one to launching at 1/2 throttle, so the second one was a nice full throttle smash into the ground. LOL! Tough plane! Got prop #3 on there now and I reset the battery location so the CG is back at 2" from 1.6". I'll keep tryin'....hahaha.
Old Jun 15, 2009, 10:23 PM
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Try raising the trailing edge of the ailerons about 1/8 in. Should follow the contour of the bottom airfoil. Acts like decalage. CG should be around 15 to 20 % of the wing chord. This might help.

Gord.
Old Jun 15, 2009, 10:32 PM
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Thanks for the tip....I'll reset the elevons. The instructions are not clear on how to set them, so I set them dead down the center of the wing since it's a symmetrical wing. Kinda going at this blind since nobody at our club has one...few of the fellas remember them, but never flew one.
Old Jun 15, 2009, 10:53 PM
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Better tell them to pull up their shorts Dave. This is one quick little sucker. I'd figure 60 to 70 mph. For a slick finish, I covered mine with plastic shelf liner, you know, peel the backing off and stick it on. Great for a disposable plane.

Gord.
Old Jun 15, 2009, 11:48 PM
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Quote:
Originally Posted by HMX Dave
Well....two unsuccessful hand launches....two big arcs into the ground and two broken props. I attributed the first one to launching at 1/2 throttle, so the second one was a nice full throttle smash into the ground. LOL! Tough plane! Got prop #3 on there now and I reset the battery location so the CG is back at 2" from 1.6". I'll keep tryin'....hahaha.
Always launch at full throttle, you need to get the airspeed build up quick to get a effective control.

If that doesn't work, let's call the U.S. Navy and borrow their aircraft carrier
Old Jun 16, 2009, 11:21 PM
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SUCCESS! She flies! I pulled the CG back to about 1.9-2 inches...then I adjusted the elevons up about 1/16...then launched with my LEFT hand...up she went. Wanted to climb all the time, so I skidded 'er in and put the elevons back to a neutral position and let 'er rip again. FUN! One thing I noticed: I have no trim control for the elevator. (DX7 with AR6200) I screwed around with about 75 different settings and still no dice. Anyways....it flys so good after I manually trimmed it that it's not really an issue. She's pretty FAST with a 12x6....which is waaaay low on the prop numbers I want to run....just all I had left in the proper size range after two successive failed hand launches. Gonna be fun!


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