A Kadet pushrod problem...
 

I've finally finished covering my Kadet Seniorita. :D Last night I installed the CA hinges, rudder and elevator. My next step was to hook up the servos and the tail feathers. I built the kit as per the plans. I used 1/4sq balsa for the pushrods, DuBro ball link at the servos and Dubro clevis at the tail. The rudder seems to be working fine, but I have a problem with the elevator. When I move the elevator I see the pushrod vibrating and bending a lot! I tried to pick the straightest, hardest balsa for the push-rods. Also, I'm worried about the bending push-rod because the servo has to push to make UP elevator. I'm worried that some day when I am flying and I really need to get the nose up and I yank back on the stick, but there is so much pressure on the elevator that it would just continue on straight down. Not good. [:o] I'm sure there are other Kadet flyers out there who have had a similar problem. Your advise is appreciated, and thank you in advance.

RE: A Kadet pushrod problem...
 

I use a dowel for the elevator pushrod my Senior. I't a bit portly at about 10 pounds as I have alot of extra goodies on it. Pushrod is holding up just fine. Just couldn't bring myself to use balsa for this.

I've also seen guys using braces for the balsa pushrods. May distrct from the transparent covering.

RE: A Kadet pushrod problem...
 

Goboto, your concern is very pertinent. A smart idea is to change to the dowel as suggested above.

RE: A Kadet pushrod problem...
 

Thanx guys... I just came back from a walk, thinking about this. Internal braces would be a pain to install now that it is covered. I think what I'll do is replace the balsa with carbon fibre rods. Any ideas what diameter I should use?

RE: A Kadet pushrod problem...
 

YOu can get away with a rather small carbon rod I think I am using 1/8" on my Kougar. Much more stress than the Kadet :) Just be careful about where you route the antenna. I've heard of some guys having problems with the antenna close to carbon rods. On my Kougar I have the antenna running inside the fuse near the pushrods, and haven't had a problem, but just thought I'd mention it as other have.

RE: A Kadet pushrod problem...
 

Another club member in our club did have his elevator push rod break while in flight causing a crash. I just put together a kadet senior ARF and used a composit pushrod and it works great and I fly with peace of mind!

RE: A Kadet pushrod problem...
 

I built a Senorita several years ago (still have it) using 1/4" hard balsa push rods. I don't know how many times its been flown with absolutely no problems.
Goboto- Surely your push rod is binding somewhere. The elevator rod exits right out the rear of the fuse, supported only by the servo arm and the elevator control horn. Have you tried moving the clevis out to the last hole in the horn? I can't remember what the elevator travel is, but it isn't much. When you get it ironed out, you'll have one great flying airplane- Jim

RE: A Kadet pushrod problem...
 

When I first showed up at the flying field many years ago with my Senior I used balsa pushrods as per the instruction booklet. The instructors wouldn't let it maiden without me first changing them for dowels. It probably would have worked fine, but them dowels have now lasted nearly two decades.

RE: A Kadet pushrod problem...
 

I have a Kadet Sr. and a Mark II. Used Goldenrods on both supported at each former. Never a problem with binding or anything else. Replaced the originals after the model was built and covered on the Sr. Just drilled the supports, slid them down the outer rod and used a piece of wire to hold them in place for the glue to set. The Sr. is in a pile after I tired to land it floating backwards in a 10mph headwind (worked so mnay times before.) The MkII is still one of my favorites for relaxing flying.

Jim

RE: A Kadet pushrod problem...
 

I have a Kadet and have had the SAME problem. This is how I fiexed it. I junked the original pushrods and went with Gold-N-Rod push-rods/tubes. After that I realized that I was still getting the bind, so I rehinged the surface (elevator, like yours.) After that I only had minimal bend, so I moved the rod to where it was as linear with the servo as possible (no curves.) All fixed!

All in all, the main reason why I was bending the original pushrod and causing the servo to work very very hard was I USED TOO MUCH CA ON THE SIG EASY HINGES! That in turn caused the elevator to be hard to move even by hand.

ALSO, by making your control surfaces as easy to move as possbile, you SAVE BATTERY POWER!

Hope this helps.

RE: A Kadet pushrod problem...
 

GOBOTO;

To me; this indicates that you have the Elevator servo set up incorrectly.

From your description here it is travelling too far, the elevator cannot accomodate the amount of movement. Once it reaches it's maximum travel the rod keeps pushing and you get the bending and vibration.

Before you do anything drastic, if you have a computer radio adjust your End Point Adjustment. Reduce it to the point that you still have maximum deflection and no bending of the rod.

If you have a regular radio you are going to have to start playing with the control horns at both the servo as well as the elevator to reduce the effect of the movement. Basically, you need to move the ball link into the centre of the servo wheel, this will reduce the travel of the rod. Then you can put the control rod on the top of the Elevator control horn. As a last point of interest have a look at the elevator itself, is it free wheeling? or it it binding ? If you didn't shape the hinge points properly you could have reduced the amount of motion possible to the Elevator.

As they say; "The Devil is in the Details!"

RE: A Kadet pushrod problem...
 

I use carbon arrow shafts. They work perfectly. Be sure that your elevator and stab don't have a slight bow after hinging. This also causes a bind.

RE: A Kadet pushrod problem...
 

Ditto on Biper/Piper's suggestion.

RE: A Kadet pushrod problem...
 

I have Kadet Senior with balsa pushrods as the kit describes. Everything works just fine.

It works because mine flies really slow. Slow speed means much less pressure on the control surfaces. The same setup might be a bad idea on a faster plane?

Unless you're flattening out the wings, adding weight, clipping the wing a few bays and/or putting twice the engine in it, it will continue to fly as slow as it was designed.

The pushrod tubes are often easier to install, but the Kadet doesn't have any bulkheads in the tail to mount them through.

If you're worried, the dowels sound like a good idea, but if it makes the model tail heavy, you may be adding a lot more weight than you realize.

RE: A Kadet pushrod problem...
 

It is usually better to pull up elevator, rather than push it. This way the push rod won't flex when pulling out of a dive or loop, etc. However, this requires having the horn on the top of the surface.

Set all of your EPA's to 100% travel. Then, make sure your push rods are connected to the INNERMOST holes on your servo arms/wheels and connected to the OUTERMOST holes on your control horns.

This does two very important things. One, it gives you maximum resolution so that your surfaces travel smoothly, precisely and proportionally to your tx stick movement. When you move your tx stick 1/4 of the way, the control surface should also move 1/4 of it's total travel, and so on. Second, it allows you to use more of the servos' torque. And, third, it will decrease control surface travel mechanically, which is a thousand times better than using EPA to decrease travel. You can use EPA to make fine adjustments to your travel, but the closer it's set to 100% the smoother your plane will fly.

Nine times out of ten when a pilot has a twitchy, sensitive new plane it is because they have the push rods hooked up wrong. By hooking them up as I described you will use all or most of your servos' travel which will always give you the smoothest and most precise control of your plane. It makes a night and day difference in how your plane will fly.

David

RE: A Kadet pushrod problem...
 

I scratch built a very sturdy Kadet and, since I've powered it with a G23 (with reinforced firewall and tail dragger landing gear) I wanted something more foolproof for the elevator and rudder so went with pull-pull on both. Big advantage as no slop, no mass of heavy pushrods to be adversely effective under high G's and no friction anywhere.

RE: A Kadet pushrod problem...
 

I converted a Senior ARF to a taildragger. I used 2-56 pull-pull from the rudder servo to control the tail wheel. I used the SIG-provided balsa dowel for the pushrods.

On the Senior kit that I just completed (8 1/2 lbs) I used arrow shafts for the pushrods and a Hitec HS81 servo mounted immediately in front of the tail wheel assembly. As this Senior will see floats the servo will easily double for controlling the float rudder. If not for the float mod I would have used the pull-pull technique again.