• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Bolivia 4-Place Build

Took way too long to fabricate these mounts but I finally have lights.20230911_175209.webp20230912_172539.webp
 

Attachments

  • 20230911_175209.webp
    20230911_175209.webp
    32.7 KB · Views: 88
  • 20230912_172539.webp
    20230912_172539.webp
    39.1 KB · Views: 98
First ride...hangar to gas pumps. Looking at the new task-based flight testing program. Anyone done that yet?20230921_164418.webp

Sent from my SM-G965U1 using SuperCub.Org mobile app
 

Attachments

  • 20230921_164418.webp
    20230921_164418.webp
    78.9 KB · Views: 134
Thanks for your help Bill!

That last 10% was a real eye opener. The 90% done, 90% to go saying is true!

The only significant squawk was lack of enough nose down trim to fly hands off at 110-115 mph that engine break-in requires. It has Javron's riser butt hinges, 3/8ths of an inch more AOI at the front spar. More-better disease. It probably needs to go back to stock which means pulling tanks, re-rigging, new weight and balance. I got a little greedy I guess. Live and learn. I also pointed the vertical stabilizer 2 inches off center at the top of the cabin. Probably fine for 80-90 mph but I'm holding left rudder all the time at 110 mph.

Sent from my SM-G965U1 using SuperCub.Org mobile app
 
The upper spring holds the elevator just above streamlined with the trim all the way nose up. Just what I'm used to. I don't have the lower spring. Could that be a fix???

Sent from my SM-G965U1 using SuperCub.Org mobile app
 
I am not a rigging expert but it sounds like the elevator is fighting the stabilizer. Adjust it so it is perfectly level or a bit down and see what that does for you. It is not uncommon when you change both trust line and wing incidence to have trim issues if you did not also adjust the tail to compensate. Adjust the spring if that don't work try some gap seal tape/foam. Lots of ways to adjust the tail. I have seen offset tubes that will shift the travel for more nose down. If you are flying currently flying with forward CG and having problems I would load it with max load and rear CG to see just how much change you need! Be careful on the takeoff in that condition do not fly it off in 3 point make sure you have tail authority to lift it as high as you want or you may just go into a nose high takeoff and not be able to recover.
DENNY
 
The only significant squawk was lack of enough nose down trim to fly hands off at 110-115 mph that engine break-in requires. It has Javron's riser butt hinges, 3/8ths of an inch more AOI at the front spar. More-better disease. It probably needs to go back to stock which means pulling tanks, re-rigging, new weight and balance. I got a little greedy I guess. Live and learn.
Did you check the actual mechanical position of the stabilizer after you landed? I had a similar issue and found the tension spring on the trim cable was too weak. So I made a bracket to tighten the cable which helped. Even then it appears the trim cable stretches slightly. Occasionally to trim at higher speeds I grab the trim cable with my hand, twist it to tighten. Only then will the trim move. The faster the Cub goes, the higher the loads on the stabilizer, the more the cable wants to slip. Even after making the cable a lot tighter, I still occasionally have it slip.

Fly it again at the higher speed, trim to max nose down, leave the trim alone and land. Look at it. Is it full nose down or not?
 
The loads are pretty high at high speeds. I was getting full travel and could feel it hit the stop. The cable would slip if i put more pressure on it. The handle also at times would try to unwind off the nose down stop.

Sent from my SM-G965U1 using SuperCub.Org mobile app
 
Was the horizontal indexed to compensate for the revised AOI?

Maybe try adjusting the CG a little to calm it down? A little weight can make a big difference.
 
Last edited:
Was the horizontal indexed to compensate for the revised AOI?

Maybe try adjusting the CG a little to calm it down? A little weight can make a big difference.
No, we thought we could cheat a little without raising the forward edge of the stabilizer. I guess that would be another path but I'm not eager to do it. I did have 20 lbs in the extended baggage for the first flight. I will fly it again without the weight and check the max speed that it will trim out at before I change anything.

Sent from my SM-G965U1 using SuperCub.Org mobile app
 
That is a good pic. Sorry I did not make myself more clear also a view of the entire tail from the side to see the stabilizer/elevator relationship at full nose up trim.
DENNY
 
A friend was getting a STC to install flaps on his J-3/PA-11. During the flight test, the FAA test pilot decided it needed more nose down trim. The FAA engineer (Gordan Mandell) suggested we take 1/2" out of each lower longeron under the tail. We did, and that solved the trim issue.

I know you didn't want to hear this, but it may be the easiest fix.

edit: I think I may still have a copy of the 337 with the dimensions on it, if you wish to go this way.
 
Last edited:
That looks normal as far as the stabilizer to elevator relationship is concerned. So a simple spring/cable change is most likely not the answer.
DENNY
 
Thanks for your help Bill!

That last 10% was a real eye opener. The 90% done, 90% to go saying is true!

The only significant squawk was lack of enough nose down trim to fly hands off at 110-115 mph that engine break-in requires. It has Javron's riser butt hinges, 3/8ths of an inch more AOI at the front spar. More-better disease. It probably needs to go back to stock which means pulling tanks, re-rigging, new weight and balance. I got a little greedy I guess. Live and learn. I also pointed the vertical stabilizer 2 inches off center at the top of the cabin. Probably fine for 80-90 mph but I'm holding left rudder all the time at 110 mph.

Sent from my SM-G965U1 using SuperCub.Org mobile app

Do you have a picture of the butt hinge? 3/8 does not sound like much. This is a picture of mine it is around 1 1/2 inch center to center. Jay said 3 degree change.
DENNY
 

Attachments

  • IMG_8808.webp
    IMG_8808.webp
    42.7 KB · Views: 39
I had my fuselage built with the upper longeron tubes attached to the tail post 1 inch lower than stock to change the tail angles and account for the added wing incidence. Shorting the lower longeron will have the same effect and is a semi common fix for issues/or mods in Alaska I would finish breaking in the motor and just think about things for a bit. I think skywagon8a has the right answer. For the mission you have vis over the nose is very important!! You may have to fly a bit to find the skill for the job but other than paint it does not take that long. Just keep flying and see if it is not some other simple issue.
DENNY
 
Fly it at designed operating weight and power settings before adjusting anything. The plane has a purpose and it may serve it very well as-is. Hopping into a new exp Cub with light loads and full power isn’t the best time to make major change decisions. That opinion is one from my own experience. Welcome to being a test pilot, and expect it to remain true for every flight as you shake it out.
 
I had my fuselage built with the upper longeron tubes attached to the tail post 1 inch lower than stock to change the tail angles and account for the added wing incidence. Shorting the lower longeron will have the same effect and is a semi common fix for issues/or mods in Alaska I would finish breaking in the motor and just think about things for a bit. I think skywagon8a has the right answer. For the mission you have vis over the nose is very important!! You may have to fly a bit to find the skill for the job but other than paint it does not take that long. Just keep flying and see if it is not some other simple issue.
DENNY

Denny, is this airplane with the changes flying or are you still building? I did not follow close enough I guess. If flying how do you like it?
Thanks, Mark
 
Still building, hope to be done by July of some time before I die. I called Talked with Dan Default/Jay/Mitch/Kirt/few others in an effort to avoid problems down the line. Dan said he used to lower them 1 1/2 inch but has found 1 inch works fine. I think Randy of Carbon Concepts has adjusted the front of the stabilizer with offset tubes if I remember correctly. I also have a lowered engine mount with 7 degrees of thrust line correction from stock because I am adding 3 degrees of incidence to the wing. Soooooo Hopefully the front angles would mimic a stock cub with thrust line mod. I think it will help improve speed. I make up the tail correction by lowering the rear of the stabilizer. It is going to be one of them fly it and see if I was right things. I am tempted to do metal instead of fabric from the lift handle back from right above the stabilizer/elevator. This would make inspection/matinance /airframe tubing adjustment a simple process if needed. Right now the upper longerns are only tack welded at the rudder post. Once I fit and rig everything else I can adjust the longerons as needed. I will also try to make the cowling adjustable in case I need to change engine thrust line down the road. Any input on the project is appreciated.
DENNY
 
Thanks guys...I'm going to take a conservative approach on this. The 3/8th AOI change lowers the nose 1 inch on approach. While that is nice it doesn't seem like enough to start changing other stuff. Our last Cub had 1.25 inch risers added which should have lowered the nose about 3.7 inches. It landed nice and slow on the mains and got off short which I liked.. With low power output at high altitude and rear CG the raised stab leading edge helped get the tail up. I shouldn't have that combination too often with this plane.

A disadvantage was that it had less downforce for braking after landing. Kirk says this model approaches really flat compared with a stock Cub so I think it will be fine with stock AOI. Keeps everything simple.

I could raise the stabilizer like Dan and Randy have but I'm not wild about going down that road for this small gain. To go more than 3/8ths involves other stuff that I know I don't want to get into.20220714_151337.webp
 

Attachments

  • 20220714_151337.webp
    20220714_151337.webp
    39.8 KB · Views: 58
Back
Top