Cooling on a pipe

[Chris Fretz]

Do you guys put vent holes on the cowl or just let it vent out where the pipe comes out the bottom?

[Howard Rush]

I put a hole about 1” x 2” toward the back of the cowl on the bottom. I didn’t know whether air went in or out that hole, so I put a tuft on it to see. Air went in. Thus I put an NACA inlet there so it would look cool.

[dale gleason]

Does the NACA hole allow flight in known icing? I have a sorta orange Impcat and sometimes it gets quite cold in these parts...

Thank you.

[Chris Fretz]

Does the NACA hole allow flight in known icing? I have a sorta orange Impcat and sometimes it gets quite cold in these parts...

Thank you.

This is the second time I've heard of a NACA, what is a NACA hole?

[Carl Cisneros]

Chris
please see the following pics buddy of the NACA DUCT (not hole)

Carl

the measurements on the bottom pic can be scaled down for our use.

also, looks like I will not be able to go to Brodaks this year. I could not get the time off scheduled for annual leave.    sucks

[Dave_Trible]

I prefer to let them breath.  Especially during hot weather I think the pipe needs to stay cool as possible for stability and to simply last longer.  I’ve only burned one pipe out but that took years.  The first pic is about my minimum,  the second my preference.  It’s also a lot easier for maintenance and assembly/ disasembly.

[Dave_Trible]

...

[Steve Helmick]

Dave's 2nd picture is pretty close to what I've got going on for almost 10 years. More is good! Mine allow a good view of the header from the bottom. Every mod I've made has been to make bigger openings aft of the engine. Designing the fuselage and cowl structure/tiedowns takes some pondering.

I've not had any pipe problems and seldom need to get at the engine, but I like to make that less difficult...and quicker, just in case. If you can remove the cowl and pull the engine/header/pipe out in one piece, I think you done good! That's my goal, anyway.  Steve

[frank williams]

This is internal pipe temperature measured with a thermocouple run up the pipe of a system running at normal operating conditions.  The hottest part of the system is the first 8-10 inches of the header and pipe.  These temps are internal.

[John Leidle]

    I had no idea they were running at that temp.
             John

[Chris Fretz]

Chris
please see the following pics buddy of the NACA DUCT (not hole)

Carl

the measurements on the bottom pic can be scaled down for our use.

also, looks like I will not be able to go to Brodaks this year. I could not get the time off scheduled for annual leave.    sucks

Thanks Carl! I was wondering what the heck it was!  That is a bummer about Brodaks for sure,  however with this Virus I have to wonder if Brodaks or many other contests will even happen this year!

Chris

[Carl Cisneros]

I know Chris
and Brodaks is only 3 months out

Carl

[Brett Buck]

Do you guys put vent holes on the cowl or just let it vent out where the pipe comes out the bottom?

    You don't want to put vent holes in the cowl at all. The hot air off the engine will exit the system, and leave no air going over the rest of it. We have learned that the hard way over the years. Several of Teds airplanes and my first Infinity all had cowl exit holes, one flight at Muncie was all for that plan, we had to block them to keep the air in the tunnel to at least past the coupler. Other people have gotten away with it.

   Dave's example only has vents starting at the coupler, which is a bit less-than-ideal, but it *usually* works. The danger area is the front end of the pipe, near the coupler. Ideally you want the air to go all the way from the intake near the cylinder and all the way to the back of the pipe, or at least to the constant-diameter section.  Letting it out earlier causes temperature gradients across the pipe, because the air leaves, so the top of the pipe gets little cooling.

   There is little concern over the engine itself getting too hot. The same case/the same cooling effects happen on these engines, and their pylon racing older brothers, some of which run 5x the power and in some cases, *the glow plug glows a dull red* when it's running. Put enough air across it to keep the pipe alive, and the engine will be fine.

    Brett

[Doug Moisuk]

Just as a add on, Randy Smith told me to never cut the header to shorten the pipe. Cut the pipe. I cut my first header and the front of the pipe started to burn over a short time. I then used a full header and cut the pipe and have no trouble with the pipe since.

[Steve Helmick]

Just as a add on, Randy Smith told me to never cut the header to shorten the pipe. Cut the pipe. I cut my first header and the front of the pipe started to burn over a short time. I then used a full header and cut the pipe and have no trouble with the pipe since.

True dat. Maybe worthwhile noting that there is a slip-in aluminum sleeve in the front of the pipe. Pull that out before  you shorten the pipe and then re-insert the aluminum sleeve.  Steve

[Doug Moisuk]

True dat. Maybe worthwhile noting that there is a slip-in aluminum sleeve in the front of the pipe. Pull that out before  you shorten the pipe and then re-insert the aluminum sleeve.  Steve

Good point I should have added that.

[Chris Fretz]

    You don't want to put vent holes in the cowl at all. The hot air off the engine will exit the system, and leave no air going over the rest of it. We have learned that the hard way over the years. Several of Teds airplanes and my first Infinity all had cowl exit holes, one flight at Muncie was all for that plan, we had to block them to keep the air in the tunnel to at least past the coupler. Other people have gotten away with it.

   Dave's example only has vents starting at the coupler, which is a bit less-than-ideal, but it *usually* works. The danger area is the front end of the pipe, near the coupler. Ideally you want the air to go all the way from the intake near the cylinder and all the way to the back of the pipe, or at least to the constant-diameter section.  Letting it out earlier causes temperature gradients across the pipe, because the air leaves, so the top of the pipe gets little cooling.

   There is little concern over the engine itself getting too hot. The same case/the same cooling effects happen on these engines, and their pylon racing older brothers, some of which run 5x the power and in some cases, *the glow plug glows a dull red* when it's running. Put enough air across it to keep the pipe alive, and the engine will be fine.

    Brett

Thanks for chiming in!  That info was much appreciated. Half the guys said put holes half the guys said don't.

[Chris Fretz]

Just as a add on, Randy Smith told me to never cut the header to shorten the pipe. Cut the pipe. I cut my first header and the front of the pipe started to burn over a short time. I then used a full header and cut the pipe and have no trouble with the pipe since.

When I first started messing with a pipe last year a guy told me to cut the header. Luckily I asked Randy Smith before I did fo that.  Makes sense if you think about it, aluminum will withstand the heat better than the pipe. Unfortunately one of my second hand header is already cut, and they are darn near impossible to obtain!

[Chris Fretz]

I prefer to let them breath.  Especially during hot weather I think the pipe needs to stay cool as possible for stability and to simply last longer.  I’ve only burned one pipe out but that took years.  The first pic is about my minimum,  the second my preference.  It’s also a lot easier for maintenance and assembly/ disasembly.

Thanks for the pictures Dave! You never get to see the bottom of peoples airplanes. Only ever the top!

[Dave_Trible]

Very welcome!  When I first started using pipes maybe 20 years ago I know I sort of over-thought the whole thing pertaining to the airplane.  I thought I'd have to glass the inside or otherwise put down some heat shielding or something.  All that got me was very heavy airplanes.  None of that is necessary as long as you get enough space and air around the pipe.  As far as cutting the pipe-my setups these day don't require I cut anything due to length but back when:  we sort of went the other way.  Pipes were $110.  Headers were $30...   we cut headers if it wasn't too drastic.  Once you cut the pipe then want to go longer at some point you must use a very long coupler.  In one case I grafted back on a length of carbon pipe sawn off a junk one....just sayin'

Dave

[Chris Fretz]

Very welcome!  When I first started using pipes maybe 20 years ago I know I sort of over-thought the whole thing pertaining to the airplane.  I thought I'd have to glass the inside or otherwise put down some heat shielding or something.  All that got me was very heavy airplanes.  None of that is necessary as long as you get enough space and air around the pipe.  As far as cutting the pipe-my setups these day don't require I cut anything due to length but back when:  we sort of went the other way.  Pipes were $110.  Headers were $30...   we cut headers if it wasn't too drastic.  Once you cut the pipe then want to go longer at some point you must use a very long coupler.  In one case I grafted back on a length of carbon pipe sawn off a junk one....just sayin'

Dave

Do you zpoxy  the tunnel or anything now?

What happens when you burn up a pipe?  Does it melt or deteriorate?

[Dave_Trible]

Nothing but a few coats of dope to fuel proof the tunnel.  I might put a piece of aluminum foil duct tape anywhere the pipe touches.   My experience with burning a pipe was large flakes of resin would break loose inside and plug the exit holes,  shutting the engine off like a switch.

Dave

[Chris Fretz]

My experience with burning a pipe was large flakes of resin would break loose inside and plug the exit holes,  shutting the engine off like a switch.

Dave

Yikes!

[Brett Buck]

Do you zpoxy  the tunnel or anything now?

What happens when you burn up a pipe?  Does it melt or deteriorate?

   Typically it collapses, where the coupler is pressing on it, right behind whatever you put in there to keep it from collapsing.

    Brett

[RandySmith]

Do you guys put vent holes on the cowl or just let it vent out where the pipe comes out the bottom?

Chris    do not  use  any holes  in the cowling,  Just let the  air  go past the  pipe  to cool the  system,  Think  sewer pipe  from the  engine  to the  rear of the pipe,  You just want as much air as you  can  to get  past to the  middle rear part of the pipe

Randy

[Alan Buck]

Chris    make sure the pipe does not touch the tunnel but the mount

[Chris Fretz]

Chris    do not  use  any holes  in the cowling,  Just let the  air  go past the  pipe  to cool the  system,  Think  sewer pipe  from the  engine  to the  rear of the pipe,  You just want as much air as you  can  to get  past to the  middle rear part of the pipe

Randy

Thanks Randy will do!

Chris    make sure the pipe does not touch the tunnel but the mount

Ok I'll keep an eye out for that too.