Bracing baffle using the pushrod tube

bullojm1 · #1 12-01-2008, 08:31 PM

Is there any issue bracing the baffles using an adel clamp on a pushrod tube? Scott Will referenced he did this on his RV-7A (reference thread: http://www.vansairforce.com/communit...90&postcount=5)

His setup:

Ironflight · #2 12-01-2008, 08:56 PM

Mike,

I personally would have to see some good evidence from others that this wouldn't' cause any harm over the long term. My experience with pushrod tubes on previous airplanes is that they can be pretty delicate, easily dented (around spark plugs, by careless mechanics), and can fatigue to produce leaks. Maybe none of this will happen if you attach a brace, but if it does, you have ruined a tube (at best). But....you can easily attach the brace to a bolt on the case or the end of the cylinder (I like the case, because it is more rigid) and not have to find out if he tubes will be damaged....

Paul

Walt · #3 12-01-2008, 09:06 PM

The push rod tubes are not designed to support the baffles, I would definately recommend against this. As paul said use the case, there is an available bolt location between the cyls that is perfect for this.

jrs14855 · #4 12-01-2008, 09:13 PM

A better way: remove the top rocker screw and replace with a screw that protrudes thru the cylinder at lease 1/2". Run a tube brace with flat fittings welded to each end from the long screw to the baffle. Lock nut or plain nut and star washer on inboard end of long screw, machine screw and nut on baffle end.

bullojm1 · #5 12-01-2008, 09:28 PM

Thanks guys for your opinions and suggestions. Perhaps I should expand on my particular problem. I am using the James cowl (round inlets) and not his plenum. So I have a round-to-square adapter I fabbed up to interface to the Van's baffles. Its pretty solid, except the top inboard corner which needs to be braced. It would be a piece of cake to run some 063 angle to a adel clamp on the pushrod tube. Going to the bolts on the engine case might be possible, but the pushrod is in such a prime location!

Here is a pic of my adapter. It's the upper right corner of the round-to-square adapter I am needing to brace.

Rick_A · #6 12-01-2008, 09:40 PM

Not the best picture but you can see how I did mine.

I was not able to get the geometry of the bend right using a single piece of angle, so I have a long brace from the engine to the rear baffle then riveted a 1" piece to the brace to get the correct angle to attach to the rear baffle.

L.Adamson · #7 12-01-2008, 09:52 PM

Mine. It's an ex aileron tube.

kiwipete · #8 12-02-2008, 02:34 AM

Mike

Just looking at your round to square adapter. I think you could suffer cooling problems if you don't allow the air to have a smooth transition. I think you'll need some sort of diffuser stop the airflow becoming too turbulent.

Why aren't you using the plenum?

Cheers

Peter

Captain Avgas · #9 12-02-2008, 08:19 PM

Quote:

Originally Posted by bullojm1

Is there any issue bracing the baffles using an adel clamp on a pushrod tube?

Pushrod shrouds have very light walls and they are obviously not designed to withstand any bending moment at all. If you induce bending moment onto the shroud it could induce failure of the oil seals at the top and bottom of the shroud resulting in oil loss. It could also result in bending of the internal pushrod leading to loss of power.

No licenced aircraft maintenance engineer would approve this practice.

scsmith · #10 12-03-2008, 02:21 PM

Quote:

Originally Posted by kiwipete

Mike

Just looking at your round to square adapter. I think you could suffer cooling problems if you don't allow the air to have a smooth transition. I think you'll need some sort of diffuser stop the airflow becoming too turbulent.

Why aren't you using the plenum?

Cheers

Peter

I second this comment. The reason that SJ can use such small inlets is partly because of the smooth flow contour into his plenum. With the abrupt round-to-square transition, you will loose a lot of recovery pressure. You should consider molding some fairly smooth transition pieces from fiberglass, so that the transition occurs over at least a diameter (about 4"?) if you can.

Another choice would be to modify the cowl itself to have rectangular cooling intets. The primary reason for the round inlet is to provide an easy flexible connection to the plenum with the rings. Otherwise there is nothing magic about the round inlets.