Insufficient nose up pitch trim in a CP-65

[Lance Fisher]

The pitch trim in my CP-65 (small crank turning a jackscrew attached to two springs, all on the interconnect tube between the two sticks) has never provided adequate nose up trim for solo flight.  With full nose up trim dialed in about a five pound pull is required to maintain final approach speed (around 45 mph indicated) power off with just me up front.  If there's someone in back the same speed requires about 20 turns CW.  Also if the trim is set within 5 turns of the full travel (either end but I never need to go full nose down) one of the two springs bottoms out.

I'm wondering if this is "normal" or if there's a fix available.  One option would be stiffer springs and another would be to change the incidence of the fixed portion of the horizontal stabilizer (I don't know if that's adjustable though).  I suppose I could also add some ballast but I'm not fond of that approach.  According to the last weighing the plane is well within the TCDS CG limits.

Anyone have any useful ideas?

[John Bentley]

I would check the Weight and balance, I am not sure the proceedure other than I believe the level is placed on the door sill, put the scales under the wheels and compare this weight with previous weight and balance checks. Alot of time old weight and balance checks are recorded in the log book or are found in the paper work some where, these will show wheel weights. look to see how they compare with the current weight and balance and what you see on the scales, where you are in the envlope, you may be forward, you may even want to weigh the aircraft with you in it. The springs may be weak as well. If you take the springs out and hang a 5 pound weight from the end of the spring and see how the two springs compare it might give you and idea how much a new spring would need to travel, then comes the hunt for new springs.

John

[John Bentley]

 According to the Maintenance and Inspection manual the leveling means is " Ship is in level postion when a bar is placed on the cross tube at the bottom of the instrument panel and the top of the rear seat is level", sounds a little weird and I have not tried it yet. Sometimes the leveling means is stated on the weight and balance.

 

                                 John
John Bentley said:

I would check the Weight and balance, I am not sure the proceedure other than I believe the level is placed on the door sill, put the scales under the wheels and compare this weight with previous weight and balance checks. Alot of time old weight and balance checks are recorded in the log book or are found in the paper work some where, these will show wheel weights. look to see how they compare with the current weight and balance and what you see on the scales, where you are in the envlope, you may be forward, you may even want to weigh the aircraft with you in it. The springs may be weak as well. If you take the springs out and hang a 5 pound weight from the end of the spring and see how the two springs compare it might give you and idea how much a new spring would need to travel, then comes the hunt for new springs.

John

[Lance Fisher]

While I haven't checked the logged W&B myself, I know it was weighed carefully by the folks who rebuilt the airplane in 1981 and I have no reason to distrust their results.  There is plenty of elevator authority in both directions with one or two people although it is difficult to keep the airplane in a spin when soloing from the front seat.   It does seem plausible that the 60+ year old trim springs are weak but I don't have anything to compare them with.

I was hoping that someone would respond by telling me if their CP-65 can be trimmed for a power off glide at 40-45 mph IAS with one person in the front seat so I could tell if this is "normal" or something that could be fixed.

[fredric matt koblenzer]

Lance,

I have a cp65 serial 660.  I have no problem trimming to 55 mph approach speed and little stick pressure during flair.  I believe I still have up trim left.  The next time I fly I will look close and check the full up trim speed.

Matt

[Lance Fisher]

Thanks Matt.  See if you can trim for a hands off descent at 45 mph while soloing from the front seat.

-lance

[fredric matt koblenzer]

Lance,

I flew yesterday with two of us, so did not check out trim to stall, but did look at the trim mechanism .

I was able to trim the stick all the way back to the aft seat and forward to the forward seat back.  At the extremes the relaxed spring is completely relax and slightly bent.  A thought, you should check your elevator rig,  should be 22 degress up and 15 degress down. This my best recolation, I am remembering these numbers in my plane info.  I will have to find and confirm those numbers and will also test the trim at stall. The stick can be centered on the trim rod by adjusting the turn buckles at the stick giving more or less trim travel for elevator position.

Matt