KISTEX,

Did you have any idea where the CG should be instead? I'm a little confused, especially after that I have seen that I have to add about 500 g ballast in the tail. Engine is a OS 120 Surpass II.
To all the guys who has this thing in the air: What did you think? Is the CG correct? Mine is "grounded" so long[>:]. No maiden flight before I have figured this out.

//Peter

snap snap thats all it does if i do a loop it snaps sometime it will snap when i make a turn landing is insane YS 110 where do you guys have yours balanced

I balanced mine right in the middle of the range and it took some tail weight to balance it. I have a Saito 100 in the nose. I haven't had any snapping tendencies with mine, except when I get to slow on landing.

rc-sport-RCU, what do your manual say about the CG. I have a german translation that says 135-145mm from the leading edge. Maybe there are translation misses?

//Peter

its the same balance point but it wants to snap very bad i think i will make it a little nose heavy and try it

Peter,

i just called up the german distibution for China Models. The guy said that they flew and tested this EXTRA only with .91 FS and didnt need much weight to balance it at the suggest CG. They have NO experience with the much more heavy 1.20 FS motor, they even say that the 1.20 FS is not suitable for this plane. In case the customer choses a 1.20 FS he has to find the right CG by test flying. Great Info!

KISTEX,

This answer from the distributor is very useless! Not suitable? I don't believe that.

For all:
I discussed this problem with the most experienced pilot in our club (a guy who has build a couple of Extra's in different scales).
His anwser was that the CG shall absolutely not be more than 30% from the leading edge (in this case 123mm). For the first flight maybe little more nose heavy. Longer back and it will snap...[X(]
However I will try this with a CG 120 mm from the leading edge. If the weather allow it, I plan the first flight this weekend.[8D]

//Peter

Of course 30% from the leading edge is the correct amount but that is 100% right IF the wing is a straight one. If you have a tapered wing (leading or trailing edge or both) then the 30% is not at the same point as the straight wing. For a tapered leading edge then the CG is farther back than a straight wing and for the tapered trailing edge the CG is farther forwards. I hope I studied my physics right!

Always maiden your plane slightly nose heavy. If the recommended CG is 100-120 I will usually set it at 105 level or 110 about 5-10 degrees nose down. When you do this the plane will always not surprise you. Then as you get comfortable with the plane just shift the CG farther back.

Peter

120mm sounds much better than 145mm. The thing wont be tailheavy then. Tell me how it flies please.

balanced in the middle you mean 140MM

come on fellas we need more response on this balance thing i know they sold more planes than this

Sorry for the delay in my response. Yes I balanced mine right at 140 mm along the fuse. I used the space behind the rudder servo to hold the lead ballast.

Hi guys,

Sorry for the late answer. I have had only a very short first flight on Saturday afternoon. About 15 sec. after lift off (in the first turn) I've got a very strange flame out[&o].
And this with an unknown plane that I have to land with the "wind in the rear" and almost no altitude[X(]. OK, it was a hard landing and the prop was broken (on a Saturday afternoon[:@]).

A little bit off topic but I will tell the story:

Coming to the field I double checked (almost) everything, fired upp the engine for the first time (bought on a swap market) and after a very little adjustment it works very fine.
After a couple of minutes of "test driving" I made a lift off (straight and fine) and a left turn (also fine). Then I recognized that the engine has no power anymore. Understand me, I heard it running
but no reaction on the trottle and no power for anything. So after a few seconds confusion I decided to handle this as a dead stick[>:]. Hard landing with a broken prop,
some scratch on the cowl and the landing gear was off (no damage, I use nylon bults and didn't mounted the pants).
What has happened? The "after crash" check showed it -> no glow plug int the engine! The only thing I didn't check, it was not screwed in correctly and the engine fired out the plug after a few seconds in the air!

BTW I balanced on 120mm from the leading edge, it seems to be a little nose heavy but looked fine?! no it doesn't snap even when I was to slow. Only falling over the nose (2 meters over ground).

Hopefully next weekend!

//Peter

Hi guys,

Some updates:

Two weeks ago I've got it airborne. But with a very strange behaviour! Flying around works fine, but if I tried to loop it rolls to the right!
But not only if I try to loop, everytime when i pull the elevator more than a few millimeter it rolls to the right!
Ok, first theory was that the music wire between the two halfs is too weak, so I installed a second servo on the left half of the elevator, mixed in the radio.
Better? No, worse! Now it snaps in a loop and it is almost impossible to fly. But, accidently I shut of the mixer in the radio (the music wire is still in the elevator), so the right half
of the elevator moved much more than the left and it flied almost perfect! Strange?!

Everybody on the field checked everything on this plane but with no result. Everything is straight and looks like it should!
I was flying with low rates on the elevator with about 40% of the recommended control throws, so this should not be an issue.

Any ideas?

mine still snaps to the left comeing out of a loop every time lucky the plane was high in the air im to scared to fly it now i checked everything can find nothing wrong

This post in reference where to locate your CG. Do a Goggle Search for (MAC+rc models), read the information provided. It has been my experience that the manufactures reccomended CG is very conservative. Normally between 22-27 percent of MAC. This is fine for your first test flight but not flying acrobatics.
The longer I stay in this hobby it astounds me to see the lack of aerodynamic knowledge. I once assisted what I though was an experienced modeler prep his new 1/3 scale Cap for its' maiden flight. Ever thing on the plane was perfect from engine run-up to range checking the radio. All set and ready to go he proceeded his takeoff run. Upon rotating the tail went down and the model rocketed almost vertical skyward. His excellent flying skills saved his airplane from disaster and upon landing that inevideable question arose. Did you balance the Cap per the plans? His answer was yes. Well, it comes to find out the plans were wrong and if was not for his skills the plane would have been history.

If you plane snaps when you pull the elevator then there might be too much throw or its just that the plane has bad flying characteristic. Try to put in some EXPO (30%-40%) and tame the plane down by making it a little nose heavy until you are used with the plane. Also try adding some washout on the ailerons ... 1/8". Try and then see ... also ... loops faster to try and eliminate the tip stall. Happy huntin'

it has a lot of expo the throw is not to much a friend with good touch flew it and noticed when its looped fast its ok but slow loops it snaps and trys to snap in just regaler flying we checked everything im ready to sell in i cant handle it

See it is tip stalling ... that happens as the plane has a relatively high wing loading or just an air foil that is not that efficient. Looks like the plane was designed badly. Try to add washout on the ailerons ... raise BOTH by 1/8".

thank you for that fast responce i will try that i fly high cause i know its shakey did a loop up high one time and it snaped and i had to fight like hell to get it out came very close to goinging in i will try the ailerons up 1/8

Let me know what happens! Happy huntin'

Folks, I am running this plane with an OS 90 FX. I had the snap issue that the answer was::: get rid of the right thrust that the directions has you induce with washers. As soon as I got rid of the right thrust...it flew straight and true with on-line loops.

I HAVE HAD 2 OF THE EXTRAS AND THEY BOTH FLEW AT THE RECOMENDED BALANCE POINTS WITH THE 120 OS I PUT IN THEM. BOTH PLANES FLEW WITH 2 CLICKS OF RIGHT TRIM PERFICT. IF THERE IS TO MUCH THROW IN THE ELEVATOR YOU WILL GET A HIGH SPEED SNAP IF YOU PULL TOO MUCH ELEVATOR. I SET MY DUEL RATES AT 50% FOR THE ELEVATOR THE SAME FOR THE REST OF THE PLANE. THIS IS MORE THAN ENOUGH TO SCARE THE SH-- OUT OF YOU IF YOU NEED TOO. AT 100% THE PLANE WILL ROLL AT 720 DEGREES PER SECOND. AND BY THE WAY I LOST THE FIRST ONE BECAUSE A BRAND NEW CYCLED BATTERY PACK SHORTED OUT ABOUT 5 MIN. INTO MY FIRST FLIGHT. GOOD LUCK

I just built the 65" extra and also have the snap proplem. It has a 120ax and needed alot af tail weight so I left it a little nose heavy (120 mm from l.e) and it is scarry to fly snaps everywhere. has anybody figured out this problem. should I move c.g. fore or aft.

Double check your elevator throws. Some planes are very sensitive to Elevator. Cut it down and use your dual rates for your aerbatic settings.