FenderBean

I was pondering my f-15 today and I noticed these two setups. The half bipass they are using comes with the jet and they have connected it to the bell mouth on one and the other is straight to the pipe. The bypass is just fiberglass, will this not degrade from the heat and eventually crumble from the extreme heat? Just wondering for when I install mine. Thanks

http://flyeaglejet.com/f15e/1aa11%20%283%29.jpg

http://flyeaglejet.com/f15e/IMG_3324.JPG

David Jackson

My Feedback: (15)

Usually coat the inside of mine with BVM heat shield.

FenderBean

yeah I thought about that as well, but didn't know if that would last for long periods of time in such close contact with such high heat.

Greg Wright

My Feedback: (6)

The bypasses should be carbon fibre if they are black like that. There just not as good of quality as you would find in a BVM Product. But as David has said you should paint the last three to four inches of the back end with at least three coats of the BVM heat shield and they should be just fine. Make sure you sand the inside real good and wipe them out with isopropyl alcohol before you apply the Heat shield.

dubd

I have used similar set ups in CARF planes without any problems.

wojtek

My Feedback: (73)

the bellmouths in the 2nd photo are unnecessary, and don't serve much of a function ( amusing the carbon lip fits into the pipe as it looks it does )

~V~

dubd

Agreed. It's redundant.

FenderBean

k thanks for the info, yeah I wouldn't use the bellmouth. Just for info, the fact its not a full bypass matter?

rhklenke

My Feedback: (24)

As dubd said, CARF supplies basically the same thing and it seems to hold up well as long as its painted with BVM heat shield. It may hold up OK without it, but I also painted the one in my Flash with heat shield to be sure.

This thing is basically just a large bell mouth. The bell mouth serves two purposes. The first is to smooth the airflow from inside the airframe into the pipe. Without the bell mouth, the air passing around the sharp leading edge of the pipe would be very turbulent, which would severely restrict the amount of air that gets into the pipe - robbing thrust and increasing airframe drag (from ram air backing up into the inlets). The second purpose is to support the front end of the pipe. The bell mouth greatly increases the rigidity of the front of the pipe and also reduces the vibration from the turbulence, which can damage or collapse the pipe.

You have to have either a full bypass, or a bell mouth. Which one each model has is a choice of the aircraft designer and/or builder...

Bob

FenderBean

Okay so this type of setup is just a fancy bell mouth, so would you still use the recommended distance from turbine cone to the start of bell mouth?

rhklenke

My Feedback: (24)

No, in this setup, I use the distance (the typical 3/4" to 1") from the end of the engine tail pipe to the start of the pipe itself - not the bell mouth. With this "big bell mouth" the tail cone of the engine will actually be partly inside the bell mouth - as your pictures show.

BTW, my Skymaster F-4 came with a "big bell mouth" that is close to the size of the carbon ones in your pictures, but this one is actually made of spin aluminum. I use the same placement method as with the carbon bell mouths.

Bob

ron Sweeney

Take a look at the Wren pipes, hardly any bell mouth, just the end turned out slightly, makes you wonder??? Ron.

FenderBean

I got it locked in now, thanks for the info Bob

rhklenke

My Feedback: (24)

I'd be willing to bet that the "turned out slightly" end is much stiffer than an end that is not turned out at all. I'd be really worried about a pipe that did not have *something* to stiffen the end near the turbine.

I've not seen a Wren pipe first-hand, I'd also be curious to see if they use thicker material in their pipes.

Bob

FenderBean

so maybe adding the bell mouth like the one picture is still a good idea?

rhklenke

My Feedback: (24)

You mean in addition to the carbon one? No, that's not necessary. What he's talking about is a Wren pipe that doesn't have *any* bell mouth, just a rolled edge on the front to add some stiffness. I'd still rather have some type of bell mouth, either the aluminum ones or a carbon one, or a bypass...

Bob

CrocEnd

Guy's I am not seeing any pic's here

CrocEnd

OR is it that you are only talking about the first two link pic's

Thanx.

FenderBean

The first thread has two different setups and thats what we have been referring to

rbxbear44

My Feedback: (86)

+1 with Bob. Lot's of folks measure from the outside rim of the bell to the turbine tail cone but it's really where the pipe starts that is your good measuring point for your gap.