Exhaust routing

[Edge 513]

Well, I had to redo a foam cut yet a second time and am waiting for the micro to set, so I thought I would bring up a subject that is interesting to me.

Boat tailed exhaust.[bTE]

One single larger center exhaust that contributes to a faster plane and is situated so that a 3 bladed prop doesn't get cooked or blackened Cajun style like the 3 and 9 o'clock plans exhaust does. Lower cowl needs to be changed but adds to the aero equation. Theres some recent posts on Slades forum about Dave timeing his 3 blade and 180'ing it and it will still get blacked, so I remembered this subject- and thought why not bring this up as an alternate? Of course if you have a 2 blade there is no blackening. But the BTE also contributes aero-wise.

Since you posted a couple of years about this innovation you did, and have done for others Lynn, could you elaborate?

Heres a pic from that post[on the old dusty forum]

... and a couple of ideas for mine [short and long].

Lynn, what is the diameter of the outlet tube for the 4 into one? I would think the 3 into one would be much smaller. Also please comment on the performance on the 4 into 1 equipped plane for those who missed the old post...it was great.

Pardon the MSpaint program- it's all I've got.

BTW- this is Chris E's 540 Cozy install that I have crayoned over. I noticed the diameter of his side exhausts that take 3 feeds...is this optimum, or might it be better larger?

These would look awesome in stainless. Drool.

[Lynn Erickson]

Well,

Boat tailed exhaust.[bTE]

One single larger center exhaust that contributes to a faster plane and is situated so that a 3 bladed prop doesn't get cooked or blackened Cajun style like the 3 and 9 o'clock plans exhaust does. Lower cowl needs to be changed but adds to the aero equation. Theres some recent posts on Slades forum about Dave timeing his 3 blade and 180'ing it and it will still get blacked, so I remembered this subject- and thought why not bring this up as an alternate? Of course if you have a 2 blade there is no blackening. But the BTE also contributes aero-wise.

Since you posted a couple of years about this innovation you did, and have done for others Lynn, could you elaborate?

Heres a pic from that post[on the old dusty forum]

... and a couple of ideas for mine [short and long].

Lynn, what is the diameter of the outlet tube for the 4 into one? I would think the 3 into one would be much smaller. Also please comment on the performance on the 4 into 1 equipped plane for those who missed the old post...it was great.

Pardon the MSpaint program- it's all I've got.

BTW- this is Chris E's 540 Cozy install that I have crayoned over. I noticed the diameter of his side exhausts that take 3 feeds...is this optimum, or might it be better larger?

These would look awesome in stainless. Drool.

First of all it if it is a pusher you will get a dirty prop. three blades collect more dirt then 2 blades. exhaust outlet position can help some. you can position a 2 blade in one of three positions. a blade at 10 o clock at TDC is the best for exhaust dirt. a three blade can be only moved 180 degrees relative to the #1 cylinder on a 4 cylinder Lycoming. depending on the exhaust outlet positions there may be a slight difference in one of the two positions due to the fact that some of the standard eze exhaust have one pipe on top of the other and this does change the position relative to the Prop when the cylinder fires. with a 4 into 1 there is no difference in amount of dirt in either one of the two positions. the way the prop is drilled can make a difference, most all 2 blade props are drilled so that there is one hole that lines up with the blade and most 3 blade props have two holes that line up with a blade. this means that there is 30 degree difference in blade position between a 2 blade and a three blade at TDC. the engine model can make a difference some engines have a single lug line up with TDC and some have two lugs at TDC. as for a 6 cylinder well there is no hope for the 2 or three blade prop, there is a best position on both of them but there is little difference between positions.

 

Outlet diameter is probably not as big as you would like to see. most of you guys think the bigger the better when speaking of exhaust systems ( that statement may apply to other subjects as well ) but the 4 into 1 outlet size for a IO 360 is 2.25" on a IO 540 with a 6 into 1 it is 3.25" and a IO540 with two 3 into ones is 1.75"

 

as for stainless steel looking good, well they do until just after first engine start and they turn a dull brown color that just gets nastier with time

[Edge 513]

First of all it if it is a pusher you will get a dirty prop. three blades collect more dirt then 2 blades....

... but the 4 into 1 outlet size for a IO 360 is 2.25" on a IO 540 with a 6 into 1 it is 3.25" and a IO540 with two 3 into ones is 1.75"

 

...as for stainless steel looking good, well they do until just after first engine start and they turn a dull brown color that just gets nastier with time

 

So, on a 3 bladed prop, a 3 and 9 o'clock exit location- 3 into one on each side- is near as dirty as a 6 into one at 6 o'clock?

 

And, a 6 into one would be what diameter?- man that would be a feat mating all 6 together staggered on the front end...why go there? Two stacked would be thinner vertically.

 

And I still think the stainless is a long lived assembly.

What does chrome weigh? Negligible? Lots? Still burn to brown?

 

Thanks in advance.

[Lynn Erickson]

 

And I still think the stainless is a long lived assembly.

What does chrome weigh? Negligible? Lots? Still burn to brown?

 

Thanks in advance.

Stainless is one of the best choices. the best would be inconel or titanium. the stainless used in most aircraft is Type 321 or 347 an alloy that contains titanium. steel can be used and can be chromed as they do on hot rods. steel pipes will corrode from the inside out from the acid coming out the exhaust. still they could last 20 years. the pipes can be coated with ceramics that will look good for a long time but it is expensive and makes repair to the pipes very difficult. I use the 321 stainless on the pipes I build. the price of stainless has almost doubled in the last year making experimenting with stainless very expensive.

[Edge 513]

If one outlet at the 6 o'clock position, is near the same dirtyness as two at the 3 and 9 positions then it doesnt much matter, but if there is less it might warrant the effort**If so...would the double 3 into one, over and under shotgun style I drew, be able to be kept pretty high up under the engine, so that the boattail was not excessively deep, sim to the photo?

 

**then theres the boatail effect that from what I read in the past is verygood speedwise. I am in the ether about that-as I dont know why, but the #'s I recall on that green plane were very impressive...better than putting retracts on ones Cozy. That is why I was bringing this up originally.

BTW- thanks for your responses.

[Kent Ashton]

One single larger center exhaust that contributes to a faster plane and is situated so that a 3 bladed prop doesn't get cooked or blackened Cajun style like the 3 and 9 o'clock plans exhaust does

I don't think you will see any less deposits on a three-blade with the design you're suggesting. Fewer pipes (as a 2-into-1 or 3-into-1 design) just means twice- or three- times the exhaust pulses from the single pipe, right?

 

I don't think the standard 4-into-4 pipes present any significant problem. The lead/soot that collects is easily removed with a little avgas. I have never seen any signs of overheating on my Performance 3-blade.

-Kent

[Edge 513]

Thanks Kent- I had read about some guys cooking their paint instead of just soot. Certainly soot is a simple wipe down, NBD, but If the 6 o'clock position can near eliminate it- that would be a good thing to me. Thing is- I have nothing against two bladed props except their larger diameter. That is for another thread, but the reason why I am asking about the 3 blade with this BTE location proposal.

[Kent Ashton]

Well, here's my thinking: on a 4-banger Lycoming, a pulse of exhaust comes out every 180 deg. of rotation. If every one of those pulses is directed out at one position as in a 4-into-1 exhaust, and you clock a 3-blade prop so that a pulse comes out in the middle of the gap between two of the blades, then the other 180-out pulse will come out exactly onto the third blade. You can move the prop one bolt (60 degrees) but all you've done is move some other blade directly into a pulse.

 

Anyway, I just have a plain wooden 3-blade prop with a clear polyurethane finish and I've never seen any sign of "cooking" or overheating. I don't know why others have this problem. Maybe mounting exhausts close to the hub is a factor; there is some reverse flow or reduce flow near the hub on a pusher and it might serve to increase temperature near the hub (along with 350-400 degree CHT heat). My exhausts are outside the edges of the cowl opening but still fairly close to the blades.

[ZUCZZ]

OK, here is my Z$ 0.02 (Zimbabwe cents).

 

I managed to cook my prop in less than 2 hours - waste - finished - no longer usable ... because it was not clocked. My 4 in cowl exhausts pulsed right onto each blade. The paint showed overheating, burning the forward face and cooking the fibreglass overlays, worse, the core timber showed the finest cracks in the laminations, exactly where the exhaust outlets hit ... you may see this in my tests results follow the leads from http://mysite.mweb.co.za/residents/cvh/test_flight_06.htm

 

Anyway, when you get a harmonic when you are flying, that was not there just now ... it's the prop telling you something!

 

About the 6 into one ... don't forget some type of safety connection, to prevent it going thru that new prop when it breaks a piece off.

 

Frankly, I'd go 6 separate pipes, in cowl ... but that is me.

 

And you photos look nice!

[Kent Ashton]

I managed to cook my prop in less than 2 hours - My 4 in cowl exhausts pulsed right onto each blade.

That was a two-blade, right Chris? Yeah, that was unfortunate; it could have clocked to avoid the exhaust. Still, it's interesting because it seems to support my thought that an in-cowl exhaust will result in more heating of the prop blades.

[longezdave]

While we are discussing placement of exhausts, I think it is pertinent to point out Mike Mellville's speed increase by moving his exhausts near the hub.

 

Somebody help my memory out here, but I believe he theorized the performance increase was due to less exhaust heat in the part of the prop that does more work. When the exhaust is closer to the tips, the heat causes a lowering of the density of the air in an area that is working hard and the prop then doesn't produce as much thrust. Kinda like when a prop on a boat (extreme example) comes out of the water.

 

Putting the exhaust outside of the prop arc would be the best, but then you have the problems that moving the exhaust out that far would cause.

[ZUCZZ]

Yes my prop is 2 blade.

 

Don't think there is that much more heat, if any.

Just maybe because the actual distance from the end of the pipe to the blade is closer that the standard Cozy plans set-up.

 

When I switch off, and get out swiftly to feel the prop, then it is less than luke warm to the touch, tepit if that describes it.

 

cvh

[Edge 513]

OK, here is my Z$ 0.02 (Zimbabwe cents).

 

 

About the 6 into one ... don't forget some type of safety connection, to prevent it going thru that new prop when it breaks a piece off.

 

Frankly, I'd go 6 separate pipes, in cowl ... but that is me.

 

And you photos look nice!

 

Jannie, [referencing the pic I posted of the 4 to one above] how would a tube that 'breaks off' get out of the cowl to go through the prop. I know you are thinking of your incident here, but it would have to melt through the cowl to get out and airborne. Now thats a useful observation though, stress in the assembly of two 3 into ones or the 6 to one. Th 540 being a bit smoother engine- I would think the stress cracking at the flanges would be less prone to occur. But you did lose an exhaust, what happened exactly- I dont remember?

[Hennie Engelbrecht]

Jannie, [referencing the pic I posted of the 4 to one above] how would a tube that 'breaks off' get out of the cowl to go through the prop. I know you are thinking of your incident here, but it would have to melt through the cowl to get out and airborne. Now thats a useful observation though, stress in the assembly of two 3 into ones or the 6 to one. Th 540 being a bit smoother engine- I would think the stress cracking at the flanges would be less prone to occur. But you did lose an exhaust, what happened exactly- I dont remember?

ZUCZZ is not Jannie

 

Hennie

[Edge 513]

please pardon then.

[ZUCZZ]

No pardon required

 

We're both short & live in Jhb ... easy to confuse

 

Jannie Versfeld (ZU-DAR) had a 3 into one on each side. the RH side decided to let go at the last connection & spat the pipe out, which then took a chunk out the prop as it left the plane. Curt Smith from the USA was with him on that flight. Jannie now has 3 individual pipes on each sides (Ex USA - real nicely made)

 

Chris Van Hoof (ZU-CZZ) has 4 individual in cowl pipes. Had on one occasion not hooked the #4 pipe springs onto the hooks at the flange (My mother raised a slow child, OK) it all held together during the climb untill I levelled out. At his point the pipe left the flange & dropped into the cowling, sliding forward towards the firewall. Noise & fire hazard, but OK to take me home - in this case not very far

 

Good luck w your installation!

[ZUCZZ]

I really like the manner that you faired in the trailing edge of the wing into the cowling!

(ref : your very first picture)

[Edge 513]

That was a Cozy than Lynn worked on. Very nice work in the aft end all around.

[Jack Morrison]

My E-Racer has a fairing similar only more radical, mine looks more like the nose of the SR71. The oil smears stay attached all the way to the end of the cowling, top and bottom. I'll post some photos when I get them developed. On the exhaust, I have tried about all locations. 540 3into 1, directed each tail pipe up about 35o toward the spinner, lots of dirt and heat on the inside of the prop hub and spinner. Saw Dave R. Berkut at OSH last year and looked at his exhaust, looked excellent. Turned my exhaust facing outward like Dave's and it lasted about 15 minuets, completely broke the last foot of the right exhaust off and fortunately fell inside the cowling, burnt the heck out of the cowl. Noticed the change in sound and headed back to the airport immediately. I now have the exhaust going straight out the bottom cowl and so far they work fine, have about 20 hrs and no problems or change in airspeed.

 

Jack

E Racer 113

[Edge 513]

Very good Jack..when you can, photo's would be great.

Sounds like thorough R&D, as with all your assemblies. Though it is specific to YOUR cowl, any input is good input for/to me.

[Jack Morrison]

What I have is a compromise because of room in the cowl. Lynn's system on his AC in my opinion is about as good as it gets.

 

Jack

[Neverquit]

I now have the exhaust going straight out the bottom cowl and so far they work fine, have about 20 hrs and no problems or change in airspeed.

 

Are you saying its down then straight back like 4 and 8 o'clock?

[Jack Morrison]

Greg

 

Looking from the top down, they taper toward the spinner from the chylinder heads. From the side view, they run about straight back and turn bown at the end, like and auto exhaust tip that deflects the exhaust to the ground. They exit the lower cowl at about 5 and 7 oclock. Photos will follow in a couple of days.

 

 

Jaqck

E Racer 113

[Neverquit]

Jack,

 

Aha! Exactly what I've been asking about for months with no answers! Years and years of canards and design mods and I could never find an answer to this one. Great! So, how about the soot? Any problems?

[Jack Morrison]

They still hit all three blades equally but are by far the best location I have had as far as soot is concerned. The AC inside is also is a little quieter with the exhaust outside the cowl.

 

Jack

E Racer113