Just wondering if anyone has tips/links/experience installing elevator servos in the tail of a plane. I want to modify my Venus 40 by putting two mini servos in the tail, instead of the two 30" 2-56 rods linked to one servo in the fuse. Goal is to reduce elevator movement due to rod flex, allow for independent travel adjustment of each elevator half, reduce overall weight and help balance the .55 in the nose.

I'm sure it's not that complicated but not sure of the best way to add reinforcement, or if there are any rules of thumb on servo placement. Oh, and how much torque would be needed for each servo?

Probably the easiest way is to cut a hole in the side of the fuse..laminate some GOOD 1/8th ply in front and back of the holes to the wood,It needs to be the 5 or more ply, not that light cheap 3 ply... remove the covering where you glue the ply on. Place servo in hole,drill the screw holes..take out ...harden holes with thin ca, plug servo in to extended wires from reciever..buld your pushrod setup..THIS ROUTE WILL ADD TAIL WEIGHT, so be sure to balance...

This type of setup is good for the rare plane that builds nose heavy. There are trickier more complicated ways it can be done..mainly to hide the servo....

personally I would never go smaller than a standard servo on the elevator of a 40 size bird. I would place the servo in the fuse so that I have about 5-6 inches of pushrod ...it can be done shorter....

Thanks, sounds pretty straight forward.

Thinking about doing two mini servos - one for each elevator half.

gaRCfield
I have a set up like this on an Edge, I have 2- HS225MG in the tail

Its really a sweet way to go if it doesn't force you to add nose weight. Just make sure you have enough power and durability in those elevator servos.
An elevator is a terrible thing to waste, or was that lose?

Hopefully there is a enough area of solid ply toward the back to make a servo cut-out. Then all you have to do is make some doublers where the screws go from ply or hardwood. If there isn't a god enough area then you'll have to fill in a lightening hole with plywood or make some sort of frame from hardwood stick. Either way is really no big deal.

. Sorry double post

Suggest you stick with a simple surface mount (servo lugs on top of the fuse skin) rather than any attempt to sink them with only a portion of the servo or servo arm sticking out. Its far more functional and and looks better.

As far as servos go as ohno mentioned definately the HS 225mg would also be my choice.

The whole point of using aft servos in most cases is to as you noted minimise blow back and wet noodle pushrods there fore do position them for the shortest possible pushrod that your CG and possibly as noted above fuselage cutouts will allow.

With an airplane of this size I by far prefer single piece elevators but you really don,t have a choice. Since you will be positioning your own servo positions and if fuse cutouts allow there is a simple way to avoid the need for a reversing Y harness or using two elevator channels with an appropriate mix.

That is to have the servo arm below the servo on one side and above on the opposite side. The trick is to position them so the servo arms hole that you are going to use is directly in a horizontal line in front of the hole on the elevator horn that you are going to use. In other words the pushrods on both sides will be relatively level and the one servo will be above and the other below.

This works perfectly with no differentials introduced or other problems. A very simple way to simplifiy things when you are deciding your own servo positioning and a simple Y harness can be used.

John

I'm assuming since the manual suggests only a single, 45oz-in servo for both elevator halves, two servos with 30oz-in each should be enough...?

The HS82MG would be cool just because the size is good and the weight is good; just over a half-ounce each would probably be perfect for my balance issues. I am not thrilled with the way this plane flies so I want to add as little weight as possible, and the HS82's would actually not be adding weight, just moving it back. The battery is strapped to the rearmost former in the (cabin?) and there is lead on the tail, so plenty of room to shift weight forward if need be, when the job is done.

So my plan is to cutout two servo mounts from ply/hardwood - a solid piece with the servo hole cut from the center, and glue it to the balsa sheeting. Should I bother with trying to taper the servo mount? Probably more effort than it's worth if I'm going to use ball links.

I have two 1 3/4" titanium rods to use. If I stagger the servos so one is just on top of the other (but on opposite side) the ends of the servo arms should pretty much line up perfectly. This would put the arms positioned with one on top and one on the bottom (however I have a SICK new radio so that part doesn't really matter).

Yes your absolutely correct and doing so is fine. I am not familiar with the 82 but have used many 80, 81 and 85's and those are two screw mounts. I don,t know if the 82 is two screw or not but if it is then that is the root of my concern not the torque rating of the servo.

The problem arises when useing the torque values near their upper limits when used with a single sided output such as an elevator pushrod and worse if a fairly long output arm is used a rocking motion will be set up with the two screw mounts. The result will be mount screws constantly backing out. A few years back I tried using 85's in Q-500 pylon ships but the result was a lot of difficulty keeping servos in the airplane and a lot of missing screws.

John

Go to Central Hobbies web site and click on control linkage. you will see  a elevator bell crank .
I use them in 120 size IMAC planes.
You only need  1 servo. and you can put in as highest torque you want, and it  weights less than 2 servos <br type="_moz"/>

It's pretty much the same thing as the 81; it's a 2-screw mount. I'll keep looking...

All advise good so far, but I have a comment and a suggestion...

The comment - I installed tail servos on a few of my Ultra Sports and all I did was to add lite ply under the surface balsa and harden the holes with thin CA.

A suggestion: Make sure both servos will FIT side by side in the tail before you make any cuts! That is, make sure that once they are in place, the bottoms won't touch preventing the second one from seating correctly because it's hitting the first.

Thanks MinnFlyer. Still trying to find the 'right' mini servo w/4 screw holes. The HS81/2's fit nicely.

Just some concideration for you to think about. The Venus is a pattern plane aerodynamically designed to perform a certain way. Servos bulging out of the sides may effect the aerodynamics. Can a single servo be mounted in the tail inside the fuse? I too have relocated servos to the tail of a plane to eliminate rod flex and assist in ballance of generally too large of an engine installed on most of my planes. A lot of 3D planes come with tail mounted servos but they generally fly slower and the drag induced by the externally mounted servos have little effect on the desired performance.

The Venus II has tail mounted servos, and the Venus 40 really doesn't fly like a patter plane so I'm not too worried about it It is a good thought though...

Joe,

I'm sure you've already thought about this, but make sure you have enough channels in your receiver. I know you can use a reversing Y harness, but I've found them not as dependable or consistent as I like. The two servo's never seem to travel the same amount, even when I used the type adjustable type of reversing Y harness.[:'(] I've also found the reversing Y harnesses will change the servo travel depending on weather.[:'(]

David