Exhaust Design

[rviglierchio]

I fly a canard with an O-320 and 4 separate exhaust pipes. Somewhere in my reading I came to the understanding that this was about the best setup I could have. I'm not sure if this has to do with the pusher setup, the cowl constrictions or what. I just had a conversation with a guy that used to get over 300 mph at sea level in his Formula One racer at Reno and what he said pretty much convinced me the four pipe setup is the worst for HP and the 4 into 1 they used was worth a lot of HP. I know there are some after market setups like this for certified aircraft so that tends to make me think he's got good advice. I don't remember seeing this setup on canards but wondered about the collective knowledge here and your experiences.

[Lynn Erickson]

I fly a canard with an O-320 and 4 separate exhaust pipes. Somewhere in my reading I came to the understanding that this was about the best setup I could have. I'm not sure if this has to do with the pusher setup, the cowl constrictions or what. I just had a conversation with a guy that used to get over 300 mph at sea level in his Formula One racer at Reno and what he said pretty much convinced me the four pipe setup is the worst for HP and the 4 into 1 they used was worth a lot of HP. I know there are some after market setups like this for certified aircraft so that tends to make me think he's got good advice. I don't remember seeing this setup on canards but wondered about the collective knowledge here and your experiences.

Something like these?

[Lynn Erickson]

A few more that I built.

[Waiter]

Lynn;

 

VariNice

 

Waiter

[rviglierchio]

Lynn,

You have probably seen this report: http://cafefoundation.org/v2/pdf_cafe_reports/EPG%20PART%20IV.pdf

 

What sort of improvement did you achieve with your great looking pipes? My friend said they got almost 20% more HP on the O-200!

A couple questions; did you weld up your own pipes, what is the purpose of the internal splitter visible in the collector, did you do anything with the cam to augment the scavaging effect, and what is the pull (?) knob next to your oil cooler?

Thanks for the help!

[Lynn Erickson]

Lynn,

You have probably seen this report: http://cafefoundation.org/v2/pdf_cafe_reports/EPG%20PART%20IV.pdf

 

What sort of improvement did you achieve with your great looking pipes? My friend said they got almost 20% more HP on the O-200!

A couple questions; did you weld up your own pipes, what is the purpose of the internal splitter visible in the collector, did you do anything with the cam to augment the scavaging effect, and what is the pull (?) knob next to your oil cooler?

Thanks for the help!

I have been making the 4 into one exhaust for ez's for ten years. we have seen gains of about 10 to 15%in HP. the biggest gain is in the ability to lean further with the engine still running smooth. the splitter as you call it is the way the end of the pipes come together which is simpler and lighter then the way the car guys do it with all the same gains. the plane shown with the oil cooler is a customers varieze with an O-235 and I believe the knob you are referring to is the primer knob.

[rviglierchio]

How does one become a customer?

[mrlupin]

Nice work on making that exhaust.

 

I am curious.... Wouldn't a solid exhaust such as the one pictured be very highly prone to cracking?

 

I repair airplanes for a living and most of the airplanes I used to work on before moving to the airlines, have some sort of slip joint to avoid cracking. The Piper chieftain comes to mind with the TIO-540J2BD. Even with the slip joints, you would normally get cracking over of some manifolds before TBO was reached.

[hmanvel]

Lynn, do you see a performance boost at just one RPM? Or across a range? I had a 4 into 1 tuned header system built for my front engine (Defiant) and didn't see any improvement. However I recently flew with wide open throttle for about 5 minutes and was surprised to see a very big increase in front engine RPM. I need to test further. But I had no performance gain on takeoff, climbout, or cruise. But at 2700+ rpm it seemed to come alive.

[krwalsh]

In theory, a 4:1 exhaust works on the premise that the length of the primary is tuned such that the low pressure minimum from one cylinder reaches the other valves while one of their exhaust valves is open, helping to expel the exhaust and draw the intake charge into the cylinder during the overlap period. This system of tuned pressure pulses works at a specific frequency based on the length of the individual primaries.

 

Now, theory and reality are only the same in theory. In reality, The primaries are not all the same length, despite your best efforts to make them so. As such there should be a band around which you would gain volumetric efficiency due to the phase of the pressure pulses. I've seen reports that intentionally running two different lengths of primaries will effectively average the peaks that you would get if all four were one length or the other. In this way you get a broader peak, but less magnitude HP increase. For most aircraft installations, this is perfectly acceptable because the operating range is so small. For cruise or max speed you'd be talking about a change in speed of perhaps 100-200 RPM. Choosing primary length to maximize your cruise speed volumetric efficiency would seem to make the best situation, assuming you were not racing the aircraft.

 

What surprises me is that Lynn is seeing these gains with a secondary that is so short. I'm amazed that the blunt 4:1 collector is enough of a change to reflect the pressure waves back up the primaries instead of simply dissipating them to atmosphere. Pictures of Formula racers that I have seen typically have secondaries that are on the order of the same length as the primaries.

 

As another poster suggested, I'm also surprised this thing doesn't crack. I think if I were to try this I'd use stubs at the cylinders with spring attach, and perhaps slip fits to the 4:1 collector.

[Lynn Erickson]

Maybe a little back ground will help answer some of the questions. first I started with the fact that my plane was going to need an exhaust system for my IO-360C1C6. then the fact that 4 into 1 exhausts do increase HP. the canards have a very draggy cowling caused by the quick turn up of the lower cowling. the cowling needs a boat tail to reduce the drag caused by the detached air flow. I built a boat tail with the correct curves and because the prop is there I cut off the tail end of the boat tail leaving the boat tail open and used it for the exhaust outlet. this eliminates the draggy stock exhaust outlets. the first exhaust I built is a true equal length 4 into one. length is within 1/8". tube volumes where checked and found to be within 1 CC of each other. I tested all the different types of reverse cones and megaphones we could think of and found all of them decreased the HP some. I tested the engine with the 6" long test pipes the same type that Lycoming uses to rate the HP on their engines. and tested the 18" straight pipes that are used on most canards and found them to decrease the HP when compared to the 6" test pipes. the 18" pipes would decrease the static RPM by 100 RPM. as for the short collector, it is not really as short as it seems. the pipes in my design come together a bit different the typical automotive type. the pipes are formed to come closer together in the center which makes for better scavenging with out the use of the fire cone seen in some systems. the fire cones have been known to crack loose and depart the aircraft, and that would not be good for a pusher prop. also you have a big vacuum source just in front of the exhaust outlet. The systems I have built ( in the photos)for the 0235 and 0320 engines are not true equal length as the carb is on the bottom and gets in the way. I have built a couple that are equal length and they do perform a bit better but do cost a lot more to build. some of the best testing was done on a O-320 power varieze which was running the stock exhaust. with the change to a true equal length and the cowling changes to add the boat tail the top speed went from 185 Kts to just over 200 KTs. as for the no springs and slip joints and they might crack, well I am still waiting for one to crack so I can fix it. with the pipes welded together the whole system is very strong and there is no loose end to shake and cause a crack. A vareze that crashed landed and ripped the main gear off had all the weight of the aircraft sitting on the exhaust system and all it did is bent the collector flat on the bottom but no cracks.

[mrlupin]

The exhaust on these normally aspirated engines might not get hot enough to cause the bulging and or cracking I have seen on the turbo charged engines. Then again, it probably takes 10 years for most of the privately owned airplanes to make it up to 2000 hours versus two years for most commercial operations. The failure rate is sure to be more frequent with increased flying.

[Lynn Erickson]

The exhaust on these normally aspirated engines might not get hot enough to cause the bulging and or cracking I have seen on the turbo charged engines. Then again, it probably takes 10 years for most of the privately owned airplanes to make it up to 2000 hours versus two years for most commercial operations. The failure rate is sure to be more frequent with increased flying.

when it comes to heat and stainless its not the number of hours its the number of heat cycles. the same thing is used for jet engines. every time you heat and cool a piece of stainless you work harden it the same as if you bend it back and forth. hot parts should be changed after so many cycles not by hours. turbo exhaust put a lot more stress on the stainless because of the elevated temps and the pressure in the pipe. the fit of the pipe has a lot to do with how long they last. if you put a load on the pipe and then heat and cool it the number of service cycles decreases. this is one reason why the same pipe on two different aircraft will crack on one and others will not. rate of temperature change also has an effect on the number of cycles.

Homebuilts average 100 hours a year so thats 20 years if you use the 2000 TBO for an exhaust system. I don't have a TBO or number of service cycles on my exhaust systems. these systems are experimental as are ALL the other parts on any homebuilt and need to be inspected far more often then any production aircraft. if one of my systems does develop a crack it will need to be fixed or replaced , some day one will crack, thats what happens to all exhaust systems when they exceed a certain number of service cycles. and so the exhaust portion of our flying experiments, continues on.

[Lynn Erickson]

 

 

 

What surprises me is that Lynn is seeing these gains with a secondary that is so short. I'm amazed that the blunt 4:1 collector is enough of a change to reflect the pressure waves back up the primaries instead of simply dissipating them to atmosphere. Pictures of Formula racers that I have seen typically have secondaries that are on the order of the same length as the primaries.

 

 

Surprised me too but the more we cut off the better the performance. the one in the pictures is for a O-235 and with the low RPM engine it is very hard to get much gain from the collector. the O-235 uses 1.75" outlets and they are to big for the engine so in this case most of the gain is from having a system that exits the exhaust in the most aerodynamic way possible. dissipating the exhaust into the low press near the prop hub is also far better then exiting into the high press bow wave of the prop blades at mid blade span.

the systems on the IO-360s work a bit different and have a different collector. they are tuned better to the engine and seem to give the best performance up in the higher RPM range 2900 to 3000 RPM and the engine comes to life. most of us do not fly much in that range so the collector is tuned a bit different and it is a trade off of getting more HP and making the engine run smooth with leaner fuel settings.

If a Lycoming would run up to 18,000 RPM then the exhaust system would look very much like an F1 system. that would be cool. at least mine sounds a lot more like a F1 car then the standard straight pipes which sound a lot like a John Deere

most of the resent work I have done is to keep the HP and get better mileage. have you seen the price of fuel?

[krwalsh]

Sorry, my bad. By Formula racer I meant Reno Formula One Class racer (e.g. Nemesis) not out of this world expensive auto chassis made in England and raced everywhere but the US... I saw the Toyota F1 car at Laguna Seca one year. At 18k it makes the most pleasing sound. Like a sewing machine on steroids.

 

I think the reason you are getting away with such a short collector is that the very blunt exit acts to reflect the wave, so you do not need the inertial effect that a secondary would give you. Also, the relatively large exhaust pipe diameter and low operating RPM mean the gas velocities there are relatively low, so the gains from a secondary are outweighed by the wall friction losses of having one.

 

The craftsmanship on your pipes looks superb, which is likely why you've not found cracking to be an issue. I still think I'd use stubs and springs to hold them to the cylinders, but my theoretical pipe design obviously means nothing to your real-world experience.

 

Have you done any before-after testing of the 4:4 with standard cowl and a 4:1 with boat tail to quantify the changes? Obviously you would need a test program to discern the differences between aerodynamic improvements and power production or efficiency improvements.

[rnbraud]

Hey Lynn, and others.

 

How about a 6 into 1???

 

Would this still give the same benefits?

 

Due to the number of pipes, could you stack them 2-2-2 vertically so that they adhere to the boat-tail shape?

 

Thanks.

[gullikson]

I have always understood that the scavenging effect from a header system relies on the collector used. I'm certainly in no position to speak on the four-into-one setups for the EZ's but.... the collector is certainly a short one and it almost looks like it would have a negligible effect compared to an automotive system with a much longer collector.

[Lynn Erickson]

Sorry, my bad. By Formula racer I meant Reno Formula One Class racer (e.g. Nemesis) not out of this world expensive auto chassis made in England and raced everywhere but the US... I saw the Toyota F1 car at Laguna Seca one year. At 18k it makes the most pleasing sound. Like a sewing machine on steroids.

 

I think the reason you are getting away with such a short collector is that the very blunt exit acts to reflect the wave, so you do not need the inertial effect that a secondary would give you. Also, the relatively large exhaust pipe diameter and low operating RPM mean the gas velocities there are relatively low, so the gains from a secondary are outweighed by the wall friction losses of having one.

 

The craftsmanship on your pipes looks superb, which is likely why you've not found cracking to be an issue. I still think I'd use stubs and springs to hold them to the cylinders, but my theoretical pipe design obviously means nothing to your real-world experience.

 

Have you done any before-after testing of the 4:4 with standard cowl and a 4:1 with boat tail to quantify the changes? Obviously you would need a test program to discern the differences between aerodynamic improvements and power production or efficiency improvements.

not having a dyno, I have done some ground testing using max static RPM to compare the different exhaust systems with a club prop to get to 2700 RPM on the ground. we have installed a few on aircraft that had flown with the 4:4 but to do this you need the boat tail to run the new exhaust. the results in all testing did show an improvement in performance. my best guess at this time is that 50% of the gains are from the exhaust. when I first built my system it had the springs, and slip joints on the primary tube flanges and a ball joint between the collector and the megaphone. during the testing phase the only problems I had with keeping the exhaust system working was the springs, slip joints and the ball joint so I eliminated the problem areas by welding every thing solid and no more problems for 300 hours. I have also made a few 4:4 systems without the springs and they have not cracked either. I believe that the builders that have gone to the springs is because they were having problems with the flange to tube joint cracking. on my systems I use two doubler plates on the flange joint to spread the load on the joint to a larger area of the pipe. This is the same way it is done on many Cessna and production aircraft and the don't use springs either.