I haven't been keeping up with this forum, so sorry if this has been covered before.

I have been flying and enjoying my 28% Extra 300 Special for about a year now, but it has always had a tendency to snap on a hard pull up. It will drop the right wind and flip right over if I let it. It will even do it at low rates in certain conditions. To balance it side to side I have had to add weight to the right wing but with or without weight it makes no difference, it will still snap. The hinges are sealed. Any Ideas?

My Edge would do that also, but on low rate, and never in the same
place twice. It was very scary and unpredictable. I was still working
on a solution when i crashed the other day... (I think it was related
to duel elevator servo setup)

This may have, and I say !QUOT!may!QUOT! have contributed to my crash,
but make no mistake... an incorrect rudder input by myself was
the overriding factor in the crash.

It happen so fast... in panic mode I pulled hard on the elevator
at low rate and it might have snapped, but I'm not sure if it did
or not, another Hare owner was watching and said it looked like it
snapped, but who knows...

It is nerve wracking not knowing when or under what circumstances it
will happen.

I was thinking about the Extra instead of the Edge for this very reason.

phmil1,

My special did that for awhile, but when I perfectly lateral balanced her and made sure the elevator throws both moved the same speed and distance, problem solved. I absolutely love the 300 special. I can pull hard on high rate (low power of course) and she just does a wall, no snap. So double check everything: incidence, throws, servos working together, lateral balance and heck, I don't know, maybe even CG. Tom, or somebody will help

The only thing I can add is to be sure the wing and stab incidences are the same and correct. This usually comes down to servos or balance.

TF

After checking your servo travel and speeds as suggested above, make sure you "dynamically balance" your aircraft. Your wings might weigh the same, but that doesn't mean your plane will be balanced under flight loads (G's).

Reference Peter Goldsmith's Trimming article in MA (Scale Aerobatics Feb and Apr 05) for details.

Reference Post #5: http://www.rcuniverse.com/forum/m_28...tm.htm#2819925

It is best to run the whole trimming sequence, in order, but here's one step.

Here's a quick overview: Climb to an altitude of 500 to 1000', go into a power-off dive, 3 to 4 seconds, then pull hard (on low rates, ~15 deg elev. travel) to the horizontal...your wings should be level when you reach horizontal, if not, add weight to the higher wing. Repeat until satisfied.

Good luck and keep us updated!

Lateral balance, possible nose heavyness, and incidence angles. All of the above fixed the problems with my edge, and it had a similar problem.

If you were in knife edge and gave rudder control and then hit hard elevator, I guarantee you snapped it into the crash. Don't see where there is any "may" about it. A lot of us have "dumb thumbed a plane into the ground. Just learn from your mistake instead of looking for some mysterious cause. I am sorry to see it go, though. It was a beautiful plane.

Thanks for all the pointers. I have been going through it today on the ground. Tomorrow I will try the trimming sequence and balance, and see how it goes.

A nose heavy plane snaps easily. A real good starting balance point for the 300S is 3-1/2" aft of the leading edge at the tips. The tail doesn't have to work too hard to keep things in shape there. Another factor is the speed at which the plane is pulled up at. Too slow and over it will go. I've seen too many people fly the larger planes like smaller glow aircraft and they have been dissapointed when the performance/reaction wasn't the same as with the smaller plane. Bigger flys differently, and you have to learn and adjust to the differences. As the planes become larger, the flight habits get closer and closer to full scale as the size increases. High power outputs negate this to some extent, but aerodynamics can only be "bent" so much.

Pat

Maybe you should reread what I typed....
I am not looking for any mysterios cause.

[X(]

Nose heavy. Just get the CG back a little more and she should stop snapping.

Also a quick CG check would be to fly a 45degree upline and flip it inverted. It should continue to climb for about 3-4 seconds before starting to drop.

So I have been fighting this problem all summer long with no success. I have tried everything that has been suggested here and much more. This is really not a hard snap - it's more of a quick barrel role. I have a short video of what is happening, just not sure how to post it. There are two very short clips on the video. The first is of a power-off dive with a hard pull (full up on low rates) it basically barrel roles to the right. No rudder or aileron except at the bottom of the loop to stop the role. The second clip is of level flight at half throttle with the same barrel role. The strange thing is that if I put 5 clicks left rudder, off of trim, it roles the other direction. It is very sensative to rudder. 3 clicks left and it almost stops the role and is close to acceptable (but then the rudder is out of trim). On an inverted push it actually stays flat with rudder trimmed. Any left or right rudder off of trim causes an inverted push to role over one way or the other. My flying buddies have all tried the same maneuvers with their planes (other brands), none of which behaved like this.

Here is what I have checked and tried so far.

Ran through several different trimming sequences. This plane is now very well trimmed.
Moved CG up to 1" up and back with no change to behavior
added weight to wing tips - no change
added trip on wing - no change
Swapped wings, left to right upside down (very confusing) No change
Checked all incedences, all are right on and same left and right
Checked and matched all throws and travel on control surfaces
Changed throws on right-side elevator, plus and minus to left side - no change
Closely inspected the airfoil - All looks very good. it appears that this is a NACA-12 Airfoil. Does anyone have info on what airfoil was used when this plane was designed? I would like to do a closer check on the leading edge curve.
I believe the power off dive with a pull rules out any p-factor, torque or gyro.
There is a slight twist to the airframe, maybe 2deg. I have fixed the horizontal stab to be parrallel with the wings, but the rudder is still slightly off.

I fly this plane either fairly fast or completley stalled. It does a great elevator and harrier starting with a dive and a full high-rate pull. On a gradual pull it tracks perfectly straignt. It's the in-detween that drives me crazy (and gets the heart pumping real fast). It's a handfull landing if it gets too slow. It will always drop the right wing, unless I am very quick with the left rudder (strange as it sounds it will do this regardless of which wing I put on the right side :<o ).

Why is it sooo sensitive to the rudder?
Any other ideas?? I'm running out.

I snapped my LX a few weeks ago and now need a new fuse

My question to you guys is how or what is the best way to laterally balance these large birds?


matt

You know, aerobatic planes with symmetrical wings will snap when too much elevator is applied, and it doesn't take very much elevator to be too much. Maybe it's just doing what id does?

Balancing laterally is just supporting the plane on its centerline and balancing the plane from side to side. I don't know if there is a BEST way to do it.

TF

What does the airplane weigh? Sounds like a possible wing loading issue to me.


Shawn Berkheimer

R/C Blimp Productions.com

I have the same problem with my 300 Special. I had 1 1/2 oz in the right wing to lat. balance, and the plane would snap to the right. I removed the weight started to add weight to left wing just to experiment. It took 2 oz's to take care of the snap on a hard pull-up. The lat. balance is being done by putting a string under the next to the last hinge on the bottom of the vert. fin and holding the crankshaft on the motor. With the right thrust built in is this affecting the lat. balance, or should this be done by finding the centerline of the plane??????

Try reducing your elevator throws as Tom mentioned. 2 much and itl will snap even if perfectly set up. Will onlt take a few seconds to setup and try

I just came back to this thread after a long departure from it, and reading it all again has provided a forgotten perspective. Has anyone stopped to consider the need for a small amount of rudder input for both sides of the power curve? Increasing and decreasing throttle? Pulling a sharp elevator input at any rate acts like a brake and is the same as a change in power setting, with the appropriate propeller and torque effects.

A symmetrical airfoil generates lift in part based upon incidence angles and angles of attack. If one wing is "higher" than the other in any attitude one wing will generate more lift than the other wing. Without the proper rudder input the plane begins to "skid" opposite the bank. This can happen at any attitude and airspeed and is a part of an "accelerated stall". We need to all not be so lazy with our left thumbs.

Regarding the question about why the rudder is so effective? It's because it has to be for the plane to fly correctly with the positive rudder response we all like so much.

I do agree with Tom that all aerobatic planes may do this to some degree. I am just wondering why the other similar planes that I fly with do it too a much lesser degree.

I think rcblimppro may be on to it. The biggest difference between the other planes I fly with and this WH Extra is wing loading. My plane comes in just under 17lbs with a DA50 (I need to check it again). With the 1365 sq in wing area - this puts the wing loading at about .2 oz/sq in. One of the other planes I fly with is an Extreme Flight Yak-54. It has a wing area of 1450 and weighs in at about 16lbs with .17 oz/sq in. It has very little tendency to role over on a hard pull.

Based on some crud measurements it seems that the EF Yak and the WH Extra have the exact same airfoil, from end to end. The Yak has about 85 sq in more area on the wing and weighs about a pound less then my Extra. I believe the higher the wing loading the more precise the setup needs to be.

I have done a fair amount of weight reduction to the plane - carbon fiber gear, took off the wheel pants, eliminated the redundant battery, regulator, switch and remove material in the canopy and firewall area. I have the light-weight aluminum wing tube, but could save a few more oz with carbon fiber. What else can I do to get weight out of it?

So, for now I will reduce the throws on the elevator, maybe put 1 or 2 clicks in on left rudder, and just fly it. I really do enjoy flying this plane. It is very capable of precise aerobatics and 3Ds very well. I'll just keep looking for ways to get more weight out of it.

Oh and one more thing - not be so "lazy" with the left thumb as Silversurfer states. That is very true. With a little attention to the rudder - this all goes away.

Hey PHAMIL1 my thread which is only about 14 post down in this forum could be helpful,, you are facing the same problem I am,, my plane came in at 20lb 3oz's on the scale,, so I am putting it on a major diet (engine and all carbon),, I would love to get it down to 17ish, I think my problem is wing loading,, is to high, any way read there is some good comments in my post,, hope this helps
http://www.rcuniverse.com/forum/m_3541968/tm.htm