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Old 10-03-2019, 09:36 AM
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Question
CG or thrust angle

I maiden flew my xtreme flight 35cc laser last night. It calls for the CG to be between 5 & 6 Inches, I set it up to balance at 5.5 inches. When I put in in the air it need just a couple tics of up trim to fly level. Did the 45% up line test and when I went inverted in fell toward the nose drastic. Moved the battery back a couple inches, was better but still fell of like crazy in the test. If it balanced perfect on the bench, what is causing this? Should I change the thrust angle a bit? The amount of up elevator I had to add for level flight wasn't enough in my opinion to cause such a dramatic drop when testing inverted. If I keep moving the batter back I'm going to get pitch sensitive. Any suggestions. It has a DLE35 RA with a 20x9 prop as they recommend at xtreme flight.
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Old 10-03-2019, 10:28 AM
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http://www.flyinggiants.com/forums/s...2&d=1218140174
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Old 10-03-2019, 10:41 AM
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Yeah, but why does it balance perfect on the balancer then show nose heavy when test is done?
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Old 10-03-2019, 12:40 PM
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You can't go by manufactures CG.They do that so you have a safer maiden flight.After that you just keep moving weight back till your happy.I just maiden a 30% Aeroplus Sbach,to hit their CG I needed a pound of weight up front.I went back 5/8" of a inch for the CG for maiden and it flew hands off inverted.
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Old 10-03-2019, 01:07 PM
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Quote:
Originally Posted by jersey flyer View Post
Yeah, but why does it balance perfect on the balancer then show nose heavy when test is done?
So you don't crash on maiden and blame them for it being tail heavy. I don't know of any manufacture that doesn't state to start with their suggestion and adjust to your tastes.

Your plane is an EF. If it has an incidence or thrust angle problem, you caused it. Now get back out there and sneak up on that setup you like but don't get too focused on just hands off inverted. That works for many people but it might make it a bit touchier if you're not up for it.
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Old 10-03-2019, 01:46 PM
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Quote:
Originally Posted by KMatch View Post
So you don't crash on maiden and blame them for it being tail heavy. I don't know of any manufacture that doesn't state to start with their suggestion and adjust to your tastes.

Your plane is an EF. If it has an incidence or thrust angle problem, you caused it. Now get back out there and sneak up on that setup you like but don't get too focused on just hands off inverted. That works for many people but it might make it a bit touchier if you're not up for it.
OK, My ass is on it, I'll take a couple bricks with me, that should do it
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Old 10-03-2019, 08:33 PM
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I agree the better plan is to sneak up on the perfect CG/balance for you and the plane. Depending on the plane, it's often a compromise consisting of how the plane reacts in several flight modes, and if that's not enough to keep you busy thinking, you can add wind speed and direction to complicate things further. Point being, you can't just make changes in a knee jerk reaction mode. As you get closer to perfect the plane should be flown several times, in different conditions to confirm your suspicions.

The dropping nose on a 45 degree inverted climb is just one test. How does it track on KE? If it's pulling towards the canopy, that might reinforce your experience on the 45 degree inverted climb out for instance. Here, the elevator is trimmed up to maintain level flight. It's trimmed that way to hold a too heavy nose up.

When the plane is rolled inverted, depending on how much up trim is required, that up trim is now dropping the nose. That same up trim, when the plane is on it's side, is turning the plane toward it's canopy.....

Down trim bites your butt the same way, only opposite. That's likely a tail heavy plane that will climb on the inverted test, and turn towards the gear on KE......

So get out there and get some stick time on it, but watch it closely for hints that will make it handle better!
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Old 10-04-2019, 06:39 AM
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I think I'll try a smaller gas tank as well, I used the 24oz tank that extreme flight recommended for it. But I think I'll drop down to a 18oz instead. Usually when I fill it, then land and check it, I hardly used any fuel. Usually I only fly about ten minute's or so anyway then land, see if that helps. Balanced on bench with the battery on the wing tube, after trim flight I moved it in back of the wing tube. Then back to just in front of the pull pull rudder servo, still was nose heavy, moved it back last night to behind the servo which puts it about at the end of the turtle deck, I'll see how that goes. Using a single Ion 5200 battery in it. Like I said, Don't want it to get pitch sensitive .
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Old 10-04-2019, 07:20 AM
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Don't worry about pitch sensitive. You likely have a long way to go to get that, IF it ever gets there. The plane will tell you what's going on if you watch it.

If setting up for 3D for instance, which requires a CG that's quite a ways back, you'll notice that as the plane slows, the tail will loose enough lift to allow the rear of the plane to settle. This will tell you you're getting close. If you continue moving it back (maybe too far), the plane will still fly fine at speed, but when slowing down to land, you may have to give it down elevator to hold the tail up to get the plane's nose down. It's trying to go into a Harrier by itself! These newer designs will still fly fine like that IF you continue flying the plane! It's not going to fall out of the sky on you! If you see it going into an unexpected Harrier like that, add some throttle and give it some down elevator - keep flying it!

It's true though, that many are not going to want a CG back this far as they are not interested in what the plane can do when messing with low and slow 3D. That's what guys are talking about when mentioning the right CG is about what YOU want. My point is, don't be afraid to push the limits when experimenting (if YOU are up for that!). There are a LOT of old wives tales floating around....

Last, you can experiment with props a little as you get further into this. Don't be afraid to experiment there either. For instance, some are flying with a 20x6. A prop like that will have outstanding vertical acceleration (like accelerating out of the top of a hover), it will help control the plane's speed on down lines, and it will stop like it's got air brakes when you chop the throttle. It also slows down very nicely when landing....


And a 16oz tank is plenty......
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Old 10-04-2019, 10:44 AM
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OK, I'll see where it goes, Thanks everyone for the input.
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Old 10-04-2019, 12:11 PM
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Lastly, make your balance tests as well as all other level style tests around half power. Full throttle can force the plane into more of a straight line fooling you on any of the tests. Being over powered does have this one trait many don't pay attention to.
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