question on airplane balance
12-27-2012, 09:01 PM
#1
question on airplane balance
i have a 40% scale Extra 330 s
it weighs 46 pounds dry.
the engine is a DA 170, which has 18 hp. the thrust calcualtions with a 32 x 10 prop at 6000 rpm is about 108 pounds of static thrust
the recommended cg is center of wing tube.
on the first flight, i noted airplane kept wanting to climb. i used elevator trim to get her level, and she flew very well.
today was the second flight, she flew even better (cause i was less nervous and not shaking as much as 1st flight)
i flew her today inverted, and it required very little down elevator to keep her flying level.
i flew her inverted at 45 degrees from horizon, and she kept going in same trajectory, did not arc up or down.
my question is, i wonder if she is just slightly tail heavy.
today she landed just perfectly, 3 point landing, no bounce.
it weighs 46 pounds dry.
the engine is a DA 170, which has 18 hp. the thrust calcualtions with a 32 x 10 prop at 6000 rpm is about 108 pounds of static thrust
the recommended cg is center of wing tube.
on the first flight, i noted airplane kept wanting to climb. i used elevator trim to get her level, and she flew very well.
today was the second flight, she flew even better (cause i was less nervous and not shaking as much as 1st flight)
i flew her today inverted, and it required very little down elevator to keep her flying level.
i flew her inverted at 45 degrees from horizon, and she kept going in same trajectory, did not arc up or down.
my question is, i wonder if she is just slightly tail heavy.
today she landed just perfectly, 3 point landing, no bounce.
12-28-2012, 12:50 AM
#2
Senior Member
RE: question on airplane balance
Does she have any characteristic that you don't like? It sounds like she flies like a dream.
Whatever you decide about how to describe her CG, are you going to move it?
What I would do is change the description to remove whatever word bothers you. Sounds like the CG is 'just about perfect'.
Whatever you decide about how to describe her CG, are you going to move it?
What I would do is change the description to remove whatever word bothers you. Sounds like the CG is 'just about perfect'.
12-28-2012, 11:41 AM
#4
RE: question on airplane balance
If an elevator is very far from neutral, it could mean some trim issues. How much down trim did you add? Does the down trim manifest itself in too steep of a landing glide slope (is power on/off trim the same)? Another helpful test is knife edge to note if there is a pitch couple. Does the down trim cause a tuck to the gear? Remember, in knife edge, the elevator is gravity neutral and if it is trimmed to compensate for out of balance in level flight, it might display an unwanted characteristic in knife edge.
12-28-2012, 05:40 PM
#5
RE: question on airplane balance
All of the Extra's that I have had tuck to the gear in knife edge even with the CG set a tad forward. CGis one of those pwersonal preference things. This one sounds pretty close to being nuetral. The only downside is that it may end up being more pilot workload in a breeze. What I would do is carefully measure the stab and elevators to see if there is in fact downward deflection of the elevators or have then just been centered. Then the coice has to be made on weather to move the CG forward or to leave it alone. IMO that would depend on what type of flying is to be done. If you plan to fly IMAC the I would move it forward about .5" or so. If you are going to sport 3D fly then I would leave it alone and simply adjust the stab incedence so it flys with no visible elevator trim. If the tuck to the gear is excessive moving the CG forward will help but I have never seen it completly cure the tucking. I usually have to employ a mix for that one.
12-28-2012, 07:40 PM
#6
RE: question on airplane balance
hello
thank you all for the comments,
i did notice that with knife edge, that she started to go to left, when going away from me.
so she probably is tail heavy.
i still think she is doing well. it would probably be good idea to try to see what i can do to further move CG forward. so far, short of adding weights, i've done everything else.
might just leave as is, and keep flying her to get to know her better.
I do believe that both AA5BY and speedracer know their stuff, you guys, i think, hit nail on the head with the diagnosis.
12-29-2012, 01:31 AM
#7
RE: question on airplane balance
If the down trim is causing a power off trim problem with too steep of a glide slope, that can be dealt with by a mix. Just mix up trim to kick in when coming off the throttle. Modern radios are a wonder... eh.
12-29-2012, 11:21 AM
#9
RE: question on airplane balance
Sounds like it is in pretty good trim. Knife edge tuck is more often caused by drag imbalance than CG so given that the upline inverted test was good, inverted flight is good, and power on/off trim is the same... your good... enjoy.
