Flight Troubles?

Greg Doe
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Re: Flight Troubles?

Postby Greg Doe » March 11th, 2010, 10:17 pm

Krisharmaan
If the wing is still taped to the fuselage move it rearward until the Center of Gravity (CG) is 2cm.
in front of the rear wing post. To get this CG the front wing post is 6cm. from the prop thrust
bearing. I have the greatest respect for the Freedom Flight airplane, and its designer, but we
couldn't get them to fly consistantly with the recommended CG. All 5 of my students airplanes are ballanced within 2mm of this location. The two schools I coached each won their respective
regionals, with a best time of 2.05 in a gym size room.
Item # 2. You need to carefully eyeball the washin and washout in your wing. It sounds like you
do not have any right trim in the wing, or worse still you have left trim. If a fully wound airplane
dives into the ground in a left turn it usually indicates a lack of wash out in the right wing.
If your wing posts are still tapped to the fuselage you can introduce a small right twist with thin
balsa shims. I use 1/32" balsa and sand a bevel on a piece about 1/4" wide and 3/8" long. If your
wing post sockets are taped to the left side of the fuselage push your shim between the front
socket and the fuselage comming from the bottom of the airplane, or push your shim down from
the top at the rear wing post socket. What you are trying to accomplish is to slightely twist the
wing by twisting the wing mounting posts. If your wing posts are poorly aligned to begin with,
your washin and washout will change dramatically as you change the angle of attack of the wing!
This can cause unwanted trim changes, so check all your trim settings to be certain the airplane
is close to the recommended settings. Good luck.
Greg Doe
Smyrna, TN

mg
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Re: Flight Troubles?

Postby mg » March 12th, 2010, 11:05 am

My plane also crashes left with high winds. I crashed my first flight at State, but still won on the second flight with alot less winds.I think I have a wash in and was out problem, but am confused on the terms. When I built my freedom flght model the wings were glued level but now I notice the left wing tip is 1 cm lower than the right wing tip. Part of the problem is that the left wing is longer and weights more than the right. For wash in, the left wing tip should be higher, not lower? Should I reglue or shim in the opposite direction? In the FF instructions, the leading egde of the wings are level and the trailing egde of the right wing should be 1/8 " lower. I tried to do this but some how the left leading egde is lower. Any suggestions? Thanks, MG

Greg Doe
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Re: Flight Troubles?

Postby Greg Doe » March 12th, 2010, 11:46 pm

Mg,
I will try to help, but first we need to get our termonology straight. Right and left is determined
as if you are sitting in the airplane, and looking straight ahead over the nose.
I explained washin and washout before, but apparently I wasn't clear. Let's start with washout,
which is a twist in the wing from root to tip. If we jig up the wing so that the root rib is dead flat to the direction of air flow, then the tip rib will be at a negative angle. This means the leading edge will be twisted down, and the trailing edge will be twisted up. Washin is a twist in the opposit direction. If your left wing trailing edge is 1cm lower than than your right your wing, it is twisted in the correct direction, but WAY TOO MUCH! I'm guessing that you are experiencing an adverse yaw condition which can actually cause your airplane to turn in the opposit direction of what you would expect. Another problem is that if your left wing trailing edge is twisted down, so you have washin in that wing. Washin is generally an unstable trim technique, and should be avoided most of the
time. (There are exceptions to this rule) Most full size airplanes are built with washout in both
wings because it makes the airplane more stable when approaching a stall. As the angle of attack
of the wing increases in a steep climb the root (or center) of the wing will stall first, and the tip
of the wing won't stall until the nose is raised even higher. This helps maintain better control of the airplane through the stall, and recovery of control after the stall.
Your question that for "washin the left wing tip should be higher, not lower?" makes me think you
are confused. Washin and washout has to do with the the DIFFERENCE in the angle of attack from
the center of the wing to the tip of the wing.
I had to go check my Freedom Flight instructions to confirm what the recommendation was, and I
find it confusing. The picture on page 8 is a HEAD ON view. The notation is on the right hand side of the drawing, pointing at the LEFT wing, and says "Wing should have a small amount of 'twist' or
Wing Warp to keep wings level in turn (left wing down) THAT MIGHT BE CLEARER IF IT SAID "LEFT WING TRAILING EDGE DOWN"
The next thing you said is that the FF instructions say that "the leading edge of the wings are level,
and the trailing edge of the right wing should be 1/8" lower.(Or to put it another way the right wing
would have washin). I didn't want to take the time now to research the instructions, but one of two things are going on, you have misunderstood the instructions, or it's a misprint. You want the opposit twist. When viewing the airplane from the tail (looking in the direction of flight) you want
the trailing edge of the right wing to be 1/8" higher than the leading edge. The twist should be a gradual change from root to tip, with the 1/8" amount at the tip. If possible it's almost always best
to use washout instead of washin. Therefore, if possible, try to twist the right wing trailing edge
up, instead of twisting the left trailing edge down. Now in the real world this doesn't always work
out! Our wing structures are not very warp resistant so most of the time when you try to twist one
side of the wing one way, the other side tries to twist the other way.
Now if you are not totally confused I will put it in as few words as possible. When viewing your
airplane from the rear you want the right trailing edge at the tip of the wing slightely higher than the leading edge. Not quite as desirable is to have the left wing trailing edge at the tip to be slightely
lower than the leading edge. Good luck
Greg Doe
Smyrna, TN

Greg Doe
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Re: Flight Troubles?

Postby Greg Doe » March 13th, 2010, 11:19 am

Mg
I was half asleep last night, and I failed to answere one of your questions. "How to correct the
unwanted warp?" The instructions in the Freedom Flight kit suggest that you gently stroke curved
sticks between your thumb and forfinger. It can be done on the assembled wing too. You might
take a piece of scrap wood of similar size and practice on that first. Then try your new "skill" on
the wing trailing edge (unless the leading edge is bent). A little moisture from your breath might help. I like the method of twisting the wing posts in relation to one another (front to rear). You could loosen and reglue one or the other post, but be sure you figure out which way to offset the post to get the desired results. It's easy to get it backwards. (Don't ask how I know that). Lastly (and I have used this method) crack the trailing edge at the center rib, and raise each trailing edge slightely, and reglue. I like to see anywhere from zero washout to 1mm in the left wing, and 3 to 4 mm washout in the right wing. Good luck.
Greg Doe
Smyrna, TN

mg
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Re: Flight Troubles?

Postby mg » March 13th, 2010, 5:26 pm

Thanks Greg for all your help!
MG

krisharmaan
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Re: Flight Troubles?

Postby krisharmaan » March 16th, 2010, 6:34 pm

Thanks for your help Greg. I did what you suggested somewhat and got it to fly pretty good. We could've beaten the 1st place time if it had not crashed into an under hanging net. What made it even worse was that our motor snapped as we were winding for our 2nd official run so our backup motor wasnt very good and give as a terrible time. We still settled for 4th place so it wasn't that bad.
2010 Regionals:

Elevated Bridge- 1st
Bio-Blitz- 3rd

2010 States:

Battery buggy- 1st
Wright Stuff- 4th
Elevated Bridge- 5th

Overall, 2nd place in states. Nationals maybe depending on invitation.

Greg Doe
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Re: Flight Troubles?

Postby Greg Doe » March 16th, 2010, 8:48 pm

Krisharmaan,
Are you done, or are you going to the state competition? Sometimes you learn more from your
failures, than from your successes! It looks like you were involved in a number of building events,
all of which are time consuming. A little more preparation in WS might paid off in a higher finish.
On the other hand it might have cost you in one of your other events.
Of the three WS teams I coached, two had back up airplanes. Like Jeff Anderson I believe in
prepration. That means knowing your equipment, and having as much back up equipment as the
rules allow. Your back up motor should be as good as, or better, than your first line motor. The reason for this is that on your first flight you want to wind and fly on the conservative side. In
other words you don't gamble. If the first flight goes as planned, and you get a decent time, you
can "push your luck" a little on the second flight. If you have problems on the first flight, like
hitting a net, you go conservative on your second attempt.
Considering the problems you had getting your airplane to fly right, and then a bad first flight,
the fact that you salvaged a 4th place finish is a testament to your perserverance. I hope my
limited knowledge was of some help. Congratulations on all your SO placings.
Greg Doe
Smyrna, TN

Greg Doe
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Posts: 81
Joined: December 13th, 2008, 4:49 pm

Re: Flight Troubles?

Postby Greg Doe » March 16th, 2010, 8:57 pm

Krisharmaan,
I didn't read all the way to the end of your post. I see this last competition was your state event.
I hope your team gets an invitation to the Nationals, and if I can be of further help, don't hesitate
to ask. The teams I'm coaching are a real long shot to win overall at the state, but I would like to
find an excuse to go to Illinois State for the Nationals, if only to spectate. Good luck
Greg Doe
Smyrna, TN


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