Repairing a concealed elevator snake

[Hydeflyer]

I've just repaired my RCRCM Tomcat fuselage after a partial twist fracture midway along the boom behind the wing. Sadly, now I've tested everything I find the elevator snake is not operating the bellcrank in the tail fin so it must be broken internally. Can anyone advise how to get at this element to effect a repair? Clearly some cutting out will be required around the base of the fin but I'm not sure of the connection or how much to cut out to get access. The push-rod is solid carbon inside a plastic outer tube so I'm assuming the carbon rod has snapped inside the tube. has anyone done a similar repair... the RCRCM Typhoon is exactly the same I believe.

[kc]

Well nobody has commented so far and I don't know this model so cannot help. Suggest you show a photo of the area concerned which may get some help.

Generally I would suggest that if you cannot get the pushrod out to fit a new one the only other way would be to put a snake there instead or fix a servo near the tail with a direct pushrod. However I suspect your problem is more how to get inside to couple things up - possibly you need to be brave and do some surgery!

[kc]

Well nobody has commented so far and I don't know this model so cannot help. Suggest you show a photo of the area concerned which may get some help.

Generally I would suggest that if you cannot get the pushrod out to fit a new one the only other way would be to put a snake there instead or fix a servo near the tail with a direct pushrod. However I suspect your problem is more how to get inside to couple things up - possibly you need to be brave and do some surgery!

[Keith Berriman]

Sorry for my late response do you have the space to withdraw the broken rod from both ends and then look at a new rod inserted in one piece down the easiest access maybe with one end ready with clevis attached and work on second fixing

As said a picture saves a thousand words

[Guest]

Looking at the RCRCM Tomcat picture on their website...

I would expect the connection to the "All moving Tail" is immediately below/slightly behind the forward pivot. Its right at the front of the fin and the boom at that point is very narrow.

You could make an exploritary hole in the bottom fuselage not too large to confirm clevis/ball link say 6-8mm dia.

Pair of snipe nosed pliers might be able to open/pop off clevis to the actuator. Either way you need to do something to actually find out.

Once it is off you might be able to slide it out of the fuselage through the hole (which probably will need elongating towards rear.) Bear in mind this will be a high stress area holding flight loading and would need some subsequent C/F applied externally as reinforcement after repair.

Once slid out you might be able to find suitable replacement CF rod to make a new inner. You would need to plan how to get that back in.

Make up the clevis end but not fix it. feed rod in via canopy hatch end pull a working length out at rear of fuselage. Bond clevis etc to rod then pull back into hole and reattach to bellcrank.

Alternatively if the "outer" is severely damaged. Make a pushrod from 6mm CF tube with clevis and screwed rod epoxied in pass into fuselage and fix to bellcrank with your exploratory hole. Space at the fin end will limit diameter especially since there is Rudder actuation down there as well

I expect its going to be a bit tricky.

N

[John Wagg]

Can you move the rod by hand?

If just the rod/snake is severed then I would expect some part of it to move.

[Rod Parsons 1]

Hello

I think a better reply might come from the BARCS ( gliders) Forum.

However, the elevator Linkage in my minivec came off at the bellcrank.

Access to the bellcrank is a nightmare.

If the pushrod is detached or snapped your will need to access the bellcrank in the tail.

You have two options:

Cut an access hole In the tail fin/ rear fuz near the crank ( not a good idea)

Gain acces from behind by moving the rudder out the way. Space will be very limited, but this is how I did it. You might have to remove part of a rudder post to get to it.

The rudder will be on a live hinge, so undo the rudder clevis and hold it over as far as you dare until you get the access. 

It’s a good couple of years since I did it, so can’t remember exactly.

 

Rod

 

 

Edited By Rod Parsons 1 on 07/08/2020 11:35:51

[Hydeflyer]

Thanks for the replies... I've realised that the elevator pushrod is probably not broken but has come away from the clevis at the bellcrank. Of course this is enclosed and inaccessible and as Nigel suggests it pivots close to the leading edge of the fin. I will have to cut a hole in the fus near the base of the bellcrank to see what's happened and then try a repair. I've just remembered I have the remains an old Typhoon tail end and have opened it up to see the arrangement of the clevis. (photos below). It will help me to decide the best way forward.

[Guest]

And....

If you do a very neat cut on the Tomcat then you can stick that back on like a hatch. Especially if you have that rarity these days called "Diamond Tape"

They should do that by default so you can do maintenance.

N