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"Tuned" exhausts systems.
Anyone on here have any experience with tuned exhausts on a lycoming, I am reading about a company Power Flow Systems that are going for approval for a muffler for my model of plane
Power Flow Systems, Inc - Tuned Airplane Exhaust Systems - Products http://www.powerflowsystems.com/imag...duct_Sheet.pdf Some of the claimed performance benefits are pretty impressive, any thoughts anyone? Edit: And just how the hell do you " tune" a muffler pipe ? |
I once watched a lycoming powered RV6 undergoing a dynamic propeller balancing.
cowlings were off the engine and it didn't appear to have any muffler, so as it started up I put my fingers in my ears. then I took them out again. the engine had a tuned length exhaust and during the full power run ups it was so quiet you could hear the prop tip noise. by far and away the quietest lycoming I have ever heard. exhaust note was almost silent. I tried to find out what they had done but I am still to see the details. sorry no idea which system it was but it was incredibly silent. just looking at the photos if it wasn't a power flow system it was something similar. the curved pipes are all a tuned length hence the curves to tuck away the length. |
Some of the claimed performance benefits are pretty impressive, any thoughts anyone? I found this out after seeing many hugely exaggerated claims from US Companies, claims I knew from personal experience to be Lies...buyer beware, many US companies take advantage of this legal fraud |
AFAIK tuning an exhaust is about creating standing waves in it, i.e. making it just as long as the wave of sound/pressure that travels through it. That means of course that the effect only works at one given engine speed, as the engine regime will determine the frequency and thus the wavelength of exhaust.
But I also seem to have heard that exhaust tuning is only worth its while on two-stroke engines. |
The Power Flow exhaust is standard fit on the Diamond DA40 for a few years now, so they must have convinced Diamond it's a worthwhile power gain anyone claiming large performance gains by fitting a tuned length exhaust to a Lycoming or continental four stroke is telling porkies As the bloke above mentioned, exhaust tuning is 2 stroke territory. Take a look at a merlin or griffon engine, these engines were optimized for power, they have simple stub exhausts, the only time anything more fancy was fitted was to surpress exhaust flames and these always gave a performance loss |
I can believe that it's possible to improve performance on an aeroplane engine through modifying the exhaust - although whether or not the performance gains claimed are realistic or cost-effective is a different issue!
I'm not claiming that the V8 engine in a Porsche 928 is in any way directly comparable to a flat 4 or 6 cylinder aeroplane engine, but a re-designed exhaust system for the 928 unquestionably increases measured HP on a rolling road (without any change to ECU or fuelling). I have definitive proof that this is the case. For sure, it's small (around 5%), but it's certainly achievable. The improvement is obtained by reducing the exhaust back-pressure, thus helping the engine to "breathe", by replacing the stock manifolds with high-flow headers and / or replacing the exhaust centre section with an X-pipe to increase the speed that exhaust gases are removed from the engine. Both of these are at their most effective at high revs, so may not be applicable to the "lazy" low-ish RPM regime of most Conti-mings. FBW |
A four stroke exhaust can be designed to resonate at a frequency which helps clear the spent charge and allow the fresh charge in, by forming a low pressure region at the port. This is to do with the mass and inertia of the pulsing gas flow. I relate this to a trombone, which can be altered in length to play different notes. As someone has already pointed out, there is no exhaust that will give extra performance right through from idle to maximum rpm, except a more freely flowing one, compared to a quieter but more restrictive one.
A two stroke engine has much more rapid opening of its "valves", which are in fact open ports opened by the rapidly moving piston skirts, rather than cams, which open far less suddenly due to their design. This more rapid opening results in an additional exhaust pulse, a sonic one, which can be further exploited by "tuning" the exhaust design to help "pull" in the next charge of mixture. So two strokes respond better to tuned exhausts than 4 strokes do. However, I would have though that because an aircraft piston engine operates within a fairly narrow rpm band, there would be some scope for exhaust tuning. |
Powerflow Exhaust have become very popular with Grumman AA5 owners in the States. To get some feed back do a search on the Grumman Gang archive site at Grumman-Gang Mail Archive and put a search in for "Powerflow" I think you will find some interesting reading there.
There is a Service Centre/Dealer for the system in the Midlands, PM me for the contact details as I believe advertising is not allowed here. |
Take a look at a merlin or griffon engine, these engines were optimized for power, they have simple stub exhausts |
I don't know if all DA40's have the powerflow exhaust, but the DA40XL does (I thought this was one of the differences between the "normal" and XL versions) and it is certainly quicker. 150 kts TAS at mid levels.
We're going down a different route in our aeroplane, by reducing drag. Aileron and flap gap seals, different fairings to streamline the beacon, modifying the angle of incident of the tail plane (through an STC).....vortex generators. If we get another 10 kts then I'll be very happy :) |
I,m interesting in this exhaust not really for speed reasons but for STOL operations, I notice that they say it increases the rpm on a fixed pitch by between 30 and 130rpm, with my plane which is rated at 180hp at 2700rpm with the fixed prop I don't get more than 2500rpm static, if this thing could deliver another 80 to 100rpm for take off I think that may make a big difference in take off distance as the published take off numbers for my model of plane with a CS prop at 2700rpm versus a FP at 2500rpm static all else being equal are quite significant.
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There maybe some feedback available over in Rotorheads forum, as Power Flow have a system available for R-22 Beta (O-320) they say brings equivalent performance to that of R-22 Beta2 (O-360).
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From the Experimental Aircraft Association piperboy84. A bit of reading to wade through. If you have access to the actual 1996 magazines you will find photos and graphs of test results. In summary for those who don't
Substantial negative pressure waves can be generated in tuned aircraft exhaust systems and the timing of their suction can be arranged so as to improve engine power. Such improvement should produce more power, better efficiency and a cleaner combustion chamber. The 4 into 1 collector exhaust systems appear to offer the best combination of low opening pressure, some pumping gain and good scavenging, though the crossover and Tri-Y systems can also obtain good scavenging during the overlap stroke. The addition of a suitable megaphone to the collector of a 4 into 1 exhaust system usually produces an increase in the negative pressure achieved at the exhaust valve, but at a substantial penalty in noise. The use of swiveling ball joints on the collector of a 4 into 1 exhaust system has a neglible effect on the EPG and provides an important vibration-isolation benefit to the system. The optimization of pipe geometry for the crossover, Tri-Y and 4 into 1 exhaust systems can be found by study of the EPG. Fast Fourier transforms, derived from the EPG, could facilitate the development of an electronic, active noise-cancelling muffler. Aircraft exhaust systems, by their limited RPM range, are particularly well-suited to such a muffler. The Coanda nozzle did not produce a noticeable increase in power. Fabrication and durability problems make this nozzle of limited attractiveness. Exhaust jet thrust was measured and calculated for several exit sizes, RPM's and fuel flows. It can produce significant thrust at high power settings, especially at cruising altitudes. The stock camshaft used in an aircraft engine is typically optimized for reliability and tractability and is not optimized for the tuned exhaust systems tested here. To fully realize the potential benefits of tuned exhaust systems for the aircraft engine, the camshaft timing must be suitably altered by making exhaust valve closure occur later and the overlap period of longer duration and higher lift.9 Many of the scavenging systems here do not exhibit as much effect upon the intake manifold pressure during the overlap as might occur if the camshaft had greater valve overlap. The effect of cylinder head temperature, mixture (EGT), and outside air temperature on the EPG were studied and found to produce minimal changes. Further study should include the correlation of climb and cruise airspeeds with EPG's taken in flights controlled for power setting and aircraft weight. These should be per- formed using exhaust jet nozzles, megaphones, altered ignition timing and other variations. EAA Members Only Flight Reports - EPG and Aircraft Exhaust Systems 3 Flight Reports - EPG and Aircraft Exhaust Systems 4 |
Excellent post from Mr. Abraham :ok:
Anyone doubting the effects on 4-strokes, need look no further than Formula 1 racing cars. Both inlet and exhaust tracts can be tuned, but without corresponding alterations in cam-profile and ignition-timing, the results are limited. Experimental research engines have been built,where it's possible to alter valve-timing and completely stop it . Thus, a fully tuned engine, running at the speed where the induction/exhaust tracts are at resonance, can continue to run with the valves permanently open! Direct-drive Aircraft piston-engines are ideally suited to tuning ,because they are operated mainly in a tightly-defined rev-band. As a generalisation, noise= energy = wasted power. the conundrum to the designer, is how much low power do you throw away,in order to generate higher-power........look at the enormous waste energy from a dragster! Tuning is a balancing act between economy, efficiency, absolute output and longevity. Your average car ,nowadays, is electronically controlled, "chipping" (reprogramming) the engine can make enormous differences. invariably, there are some risks. With Aviation, reliability is paramount. that's why the Lycosauruses survive. they are fairly well optimised to their intended usage-profile, but there is room for improvement A quieter exhaust does not mean you have to suffocate the engine, contrarily, it can mean you do, inded , make usable power instead of noise. The Merlin exhaust story is worth looking at....again, the stubs were more than just to stop the paintwork getting burnt. They had a big effectfor such a seemingly insignificant item. |
one reason why you don't see tuned aircraft exhausts is weight.
the pipe work on a tuned system will be almost twice the weight of a standard can exhaust. |
Following on from what Dubble Yew Eight said, the effect of the extra weight of an exhaust on the attachment of the manifold to the cylinder heads must be considered. The additional inertia may strip the nuts or pull the studs out of the head. This is particularly likely at idle RPM when torque reversal maximizes cylinder head movement. A flexible coupling is one option, however the location of this must be carefully thought out, as failure of the coupling may expose vulnerable parts of the airframe to hot exhaust gas, or the cockpit to carbon monoxide. The Puss Moths and the SE5a both had long exhausts, so the technology to do so has been around a while though.
If I remember correctly, Janspeed made their name with an exhaust which replaced the Ford Consul's restrictive stock cast iron manifold with a 4 into 2 into 1 tubular manifold which gave an immediate 10hp increase. |
the PF system works, I installed one on my 172 a few years back and the results were instant, with the aircraft held on the brakes the engine produced 100rpm more than for identical conditions prior to installation, I have no idea what the climb improvement was but at max weight we get at least 200fpm more than the book figure and about a gallon an hour reduced fuel burn in the cruise to boot.
Yes it weighs more but only a few kilos more than the stock exhaust, but this is the only downside as far as I can see. and no I don't work for them. |
The 4 into 1 clearly does have some performance benefits as the quickest Reno Formula 1 aircraft are all running 4 into 1 systems.
Given the amount of time and money spent reducing every single ounce of weight possible in the first place they must be seeing some decent gains Vs short stacks. Regards UA |
the PF system works, I installed one on my 172 a few years back and the results were instant, with the aircraft held on the brakes the engine produced 100rpm more than for identical conditions prior to installation, I have no idea what the climb improvement was but at max weight we get at least 200fpm more than the book figure and about a gallon an hour reduced fuel burn in the cruise to boot. Yes it weighs more but only a few kilos more than the stock exhaust, but this is the only downside as far as I can see. and no I don't work for them. Rubbish |
You are welcome to your opinion LR, I am enjoying paying less per hour for my fuel despite flying the same distance (108 nm cross country leg) while cruising at the same speed that I was prior to the conversion.
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