Mystery needs an Ercoupe Guru...

James,

I haven't done a lot of flying yet but I just finished up an extensive restoration that included all of my coupe's flight controls. This involved a LOT of discussion with experienced mechanics about what would happen if certain parts failed, or if certain things were out of spec, misadjusted, etc., so take whatever I have to say with a healthy dose of skepticism but I have a few ideas.

This doesn't sound like an aileron problem, and if you had a bent wing I can only imagine that it wouldn't get better after takeoff as you are experiencing. If I were dealing with this, I think I'd go through it in this order. Not necessarily from most likely to least likely... sometimes it's worth checking the stuff that's easier to access first.

1. Visually inspect the rubber engine mount bushings and then engine mount itself to make sure you don't have a misaligned engine, or an engine that's moving out of alignment when thrust is applied.

2. With the nosewheel on the ground (i.e. steering more or less locked straight ahead) wiggle each rudder side to side gently. You're checking for looseness in the rudder cables and rods. The rudder cables in an Ercoupe are supposed to be MUCH tighter than conventional aircraft. Occasionally this gets overlooked and you end up with flutter or adverse yaw issues.

3. Give the rudders a little more forceful push (about 15-20 pounds worth) and make sure there's no flexing or popping. You're checking for internal damage to the rudder that can cause flexing or oil canning, and also damage to the rudder horns.
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4. Raise the nosewheel off the ground, either by hoisting the engine or by pressing down on the tail. Proper procedures are in the Ercoupe service manual . Have someone turn the yoke fully back and forth and observe rudder movement plus feel for resistance or binding. You're checking for integrity and freedom-of-movement in the rudder bellcrank where the rudder cables transfer motion to the rudder rods.
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5. Look under the center of the elevator for three inspection ports from Service Bulletin 34 . If they're not present, you should consider purchasing the kit from Univair and having them installed. The elevator control horn (steel) in bolted and riveted to the aluminum skin and aluminum elevator spar. Over time, dissimilar metal corrosion can damage this connection. Installation is easiest if you remove the tail and flip it over on a bench, but this isn't actually very difficult (I've done it twice now) and then it easy to fully inspect everything in the rudder & elevator controls.  I can imagine a failure mode where the horn settles into a new position at the beginning of each flight as aerodynamic forces come into effect. Sooner or later it could separate completely.

6. If everything above checks out, I'd make sure that the A&P has a copy of the Rigging Guide at annual time because Ercoupe empennage rigging is unique.  

C85-12... SMOH 60

This 1946 415-C has a tail section from 1966 Alon A2 with an STC on it.
So I have split elevator.

The "slop" you're referring is one of the the few reasonable explanation we're trying to explain this issue with as a reason. But we're not sure at the moment. Again, the plane will go into the annual on 25th March and we will check everything to figure this out.

P factor alone can't be this extreme as couple other Ercoupe owners/pilots flying this specific plane expressed that they never experienced this extreme head swing and wing drop and scared the crap out of them when it happened.
On a dead calm day, liftoff over the centerline and in 3 seconds you're out of the left side of the runway under you...

If you provide me your email, I'll send you the video to see how extreme it is.
But the head sway to the left and the amount of right wing drop is being consistently the same all the time tells me something wrong with the setup that effects the plane at that moment.
But no idea what it may be at this point!

The only thing I can think off logically "What is being done differently at the moment of takeoff compared to the rest of the flight?"
Answer is : "Applying more back pressure to the yoke!"
The next logical question is: "What is the outside effect airplane endures between 0-25' during the moment of takeoff?"
That answer is the "Ground Effect"...

Since when airplane reaches 30' AGL following this head sway and wing drop, at that point this movement disappears and corrects itself with a little input by the pilot and it never shows this or any type of awkward behavior again until next takeoff moment.. That is the confusing part to everyone so far! Climbs, flies and lands all ok with no issues.

Simple answer is: No... What I meant as other stages of flight is the normal pattern flight stages.
Imagine a 1000 ft pattern flight. The symptom shows itself only at the moment of liftoff to 20'-25' of the runway.
Same degree turn to the left, same amount of right wing drop and when that is corrected with yoke input by the pilot, then climbs straight, turns straight, level flight straight, descent straight and controlled and lands straight without any other symptoms.
If you try touch and go again same thing repeats at the moment of the lift off...
Nobody could come up with a certainty what may cause this?
This plane supposed to be highly modified and very well taken care of by a very experienced owner and was advertised here...
First ferry pilot notified me this behavior.
Then I noticed myself.
Then a friend with over 820 hrs on his Ercoupe tried and it scared the heck out of him.
Plane will go in for its annual in a week and we will check everything and make sure all is at where and how they supposed to be.
I was just wondering if anybody had a similar issue and hold a light to possible deficiency may cause this move?
Thank you for your response, I appreciate.

This is interesting. Just to clarify, when you say "never again at any other stages of a flight.." does that include slow flight and power on stalls and power off stalls?

I have a video to send to those of you interested to show what my newly purchased Ercoupe is doing during takeoff...

On a dead calm day, not a leaf moving, almost at sea level runway (220'MSL)  65F...
- Normal takeoff run-
- At 65/70 mph leaves the runway
- at 5' AGL nose sways to the left at drastically and drops the right wing a ft or two and almost floats in a crabbing position
- if takeoff process continued this move is corrected with a right input on the yoke and then left to level the wings... this happens in 10-15 seconds of time and by that time plane is back at runway heading and climbs perfectly straight
- level flight is straight
- no issues on turns to the right or left
- descent is stable
- touchdown without any issues
- braking ok, slow down to stop without any other problematic behavior.

hit the throttle to take off again and same weird move repeats itself at same degree, same intensity, same time period and then the rest of the pattern flight is back to normal again...

What kind of a problem only shows itself and cause a move like this only between runway and 25' AGL and only at during takeoff and never again at any other stages of a flight.?
Discussion at another Ercoupe forum is going on between many people but so far nobody can figure it out the issue in a definitive way...

I have the video to show the behavior to those who are interested to see. please email me at This email address is being protected from spambots. You need JavaScript enabled to view it. address so I can send you the video.
Who knows maybe someone can figure it out what I need to do to correct this issue.
I am scared to fly the darn thing as it is now.
God Bless you all and fly safe!