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Autocorrelation rocks for Engine RPM

Started by Robert Scott June 10, 2013
On Wed, 12 Jun 2013 09:01:20 +0300, Tauno Voipio
<tauno.voipio@notused.fi.invalid> wrote:

>On 12.6.13 12:48 , glen herrmannsfeldt wrote: > >> Well, one response I remember seeing was that properler RPM was >> more useful than engine RPM. >> >> Could be interesting if the exhaust pipe was close to the >> propeller, as there might be some cross (mixing) terms. >> >> -- glen > > >In a propeller airplane, it is common that the propeller noise >is louder than the exhaust noise. Each blade creates a spiral- >formed wake pressure front. At take-off power, the blade tips >run pretty near the speed of sound. This is a design limitation, >which limits the direct-drive engine RPM to below 3000 rpm.
And that's why many engines aren't direct drive. Reciprocating combustion engines make more power for the same displacement as the rpm increases, so letting the engine's rotating assembly turn much faster than 3000 rpm allows it to make more power for the same size engine without pushing the propeller blade tips too fast. So that with, say, an even number of cylinders and an odd number of blades, or something like that, can make for some oddball expectations in the acoustic behavior.
>In type certification it is required to have an instrument >for propeller RPM. This is a safety requirement to protect >against overspeed.
Yup. http://www.youtube.com/watch?v=yLLG2_ErvJs Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
On 12.6.13 9:21 , Eric Jacobsen wrote:
> On Wed, 12 Jun 2013 09:01:20 +0300, Tauno Voipio > <tauno.voipio@notused.fi.invalid> wrote: > >> On 12.6.13 12:48 , glen herrmannsfeldt wrote: >> >>> Well, one response I remember seeing was that properler RPM was >>> more useful than engine RPM. >>> >>> Could be interesting if the exhaust pipe was close to the >>> propeller, as there might be some cross (mixing) terms. >>> >>> -- glen >> >> >> In a propeller airplane, it is common that the propeller noise >> is louder than the exhaust noise. Each blade creates a spiral- >> formed wake pressure front. At take-off power, the blade tips >> run pretty near the speed of sound. This is a design limitation, >> which limits the direct-drive engine RPM to below 3000 rpm. > > And that's why many engines aren't direct drive. Reciprocating > combustion engines make more power for the same displacement as the > rpm increases, so letting the engine's rotating assembly turn much > faster than 3000 rpm allows it to make more power for the same size > engine without pushing the propeller blade tips too fast. > > So that with, say, an even number of cylinders and an odd number of > blades, or something like that, can make for some oddball expectations > in the acoustic behavior. > >> In type certification it is required to have an instrument >> for propeller RPM. This is a safety requirement to protect >> against overspeed. > > Yup. > > http://www.youtube.com/watch?v=yLLG2_ErvJs > > > Eric Jacobsen > Anchor Hill Communications > http://www.anchorhill.com >
The traditional piston engines are opposing cylinder (boxer), which complicates the sound a little more. I had an opposing- cylinder direct-drive engine (Continental TSIO360) in my previous airplane, with a three-blade propeller. The engine exhaust noise is pretty well muffled, but the propeller is pretty loud at take-off power (36 inch radius, 2750 rpm). In my current airplane, things are different: The engines are modified Mercedes turbo diesels (Austro Diesel AE300) with 1:1.69 gearing and max rpm 2300 at the propeller. The sound is much quieter, despite of two engines. -- -Tauno
On Tue, 11 Jun 2013 12:05:00 -0700 (PDT), Kevin Neilson
<kevin.neilson@xilinx.com> wrote:

>Also, doesn't a 2-cycle engine have a fundamental pitch that is the same as the RPM (or RPS), whereas a 4-cycle, 1-cylinder engine would have a pitch half that of the crankshaft rotation?
Part of the setup of our app is the selection of an engine configuration, which specifies the factor to be used when converting between Hz and RPM. That factor can be whatever the user determines is appropriate. By the way, the app is called Engine RPM, and it is in review right now. If you see version 1.1, that is the old version. The new one with autocorrelation is 2.0. Robert Scott Hopkins, MN
On Wed, 12 Jun 2013 11:15:04 +0300, Tauno Voipio
<tauno.voipio@notused.fi.invalid> wrote:

>On 12.6.13 9:21 , Eric Jacobsen wrote: >> On Wed, 12 Jun 2013 09:01:20 +0300, Tauno Voipio >> <tauno.voipio@notused.fi.invalid> wrote: >> >>> On 12.6.13 12:48 , glen herrmannsfeldt wrote: >>> >>>> Well, one response I remember seeing was that properler RPM was >>>> more useful than engine RPM. >>>> >>>> Could be interesting if the exhaust pipe was close to the >>>> propeller, as there might be some cross (mixing) terms. >>>> >>>> -- glen >>> >>> >>> In a propeller airplane, it is common that the propeller noise >>> is louder than the exhaust noise. Each blade creates a spiral- >>> formed wake pressure front. At take-off power, the blade tips >>> run pretty near the speed of sound. This is a design limitation, >>> which limits the direct-drive engine RPM to below 3000 rpm. >> >> And that's why many engines aren't direct drive. Reciprocating >> combustion engines make more power for the same displacement as the >> rpm increases, so letting the engine's rotating assembly turn much >> faster than 3000 rpm allows it to make more power for the same size >> engine without pushing the propeller blade tips too fast. >> >> So that with, say, an even number of cylinders and an odd number of >> blades, or something like that, can make for some oddball expectations >> in the acoustic behavior. >> >>> In type certification it is required to have an instrument >>> for propeller RPM. This is a safety requirement to protect >>> against overspeed. >> >> Yup. >> >> http://www.youtube.com/watch?v=yLLG2_ErvJs >> >> >> Eric Jacobsen >> Anchor Hill Communications >> http://www.anchorhill.com >> > >The traditional piston engines are opposing cylinder (boxer), >which complicates the sound a little more. I had an opposing- >cylinder direct-drive engine (Continental TSIO360) in my >previous airplane, with a three-blade propeller. The engine >exhaust noise is pretty well muffled, but the propeller is >pretty loud at take-off power (36 inch radius, 2750 rpm). > >In my current airplane, things are different: The engines >are modified Mercedes turbo diesels (Austro Diesel AE300) >with 1:1.69 gearing and max rpm 2300 at the propeller. >The sound is much quieter, despite of two engines. > >-- > >-Tauno >
Nice! Turbos always help keep the exhaust noise quiet, too. Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
On Tue, 11 Jun 2013 04:08:32 GMT, no-one@notreal.invalid (Robert
Scott) wrote:

>>Is it already available in the app store? > >Only the crummy FFT-only version is there now. The autocorrelation >version is only on my development phone so far. I plan to submit the >update to app store in the next few days and then Apple will have to >review it before they let it go live.
The update was just approved today and version 2.0 with the autocorrelation method is now live in the app store ("Engine RPM"). Robert Scott Hopkins, MN
On 6/11/2013 1:11 PM, Kevin Neilson wrote:
> That's interesting. Why does the autocorrelation work so much better? Don't all the harmonics still show up in the autocorrelation graph?
In an autocorrelation the harmonics add into the fundamental while in an FFT all of the frequencies are distinct. -- Rick
On Wed, 12 Jun 2013 11:15:04 +0300, Tauno Voipio
<tauno.voipio@notused.fi.invalid> wrote:

    [Snipped by Lyons]
> >The traditional piston engines are opposing cylinder (boxer), >which complicates the sound a little more. I had an opposing- >cylinder direct-drive engine (Continental TSIO360) in my >previous airplane, with a three-blade propeller. The engine >exhaust noise is pretty well muffled, but the propeller is >pretty loud at take-off power (36 inch radius, 2750 rpm). > >In my current airplane, things are different: The engines >are modified Mercedes turbo diesels (Austro Diesel AE300) >with 1:1.69 gearing and max rpm 2300 at the propeller. >The sound is much quieter, despite of two engines.
Hi Tauno, Did you ever have to parachute out of your airplane, land your plane on the highway, or anything exciting like that? [-Rick-] No. 6: "Where am I?" No. 2: "In the Village." No. 6: "What do you want?" No. 2: "Information." No. 6: "Who are you?" No. 2: "I am the new No. 2." No. 6: "Who is No. 1?" No. 2: "You are No. 6." No. 6: "I am not a number. I am a free man!"
On 16.6.13 1:32 , Rick Lyons wrote:

> Hi Tauno, > Did you ever have to parachute out of your airplane, > land your plane on the highway, or anything exciting like > that? > > [-Rick-]
Nothing so drastic. The heaviest I have met was a pheasant in flight at about 100 ft above the runway on takeoff. I managed to roll the plane so that the bird did not hit the wing, but it crashed with my landing gear. A pheasant is so large that it swayed the small Beech 150 very noticeably. The tower controller said: 'You seem to hit something', and I returned to the airport. My only concern was if the remains of the bird are in my brake, but it was somewhat higher on the landing gear. There was a band of feathers, some of which I stapled to the bird strike report. The airport maintenance found the remains of the bird, so we could verify the diagnosis. I have a civilian stomach, so I do not like to fly upside down with a parachute on my back. With most small airplanes, it is far more safe to make a spot landing than to abandon the plane. -- -Tauno
On 6/12/2013 10:31 AM, Robert Scott wrote:
> On Tue, 11 Jun 2013 12:05:00 -0700 (PDT), Kevin Neilson > <kevin.neilson@xilinx.com> wrote: > >> Also, doesn't a 2-cycle engine have a fundamental pitch that is the >> same as the RPM (or RPS), whereas a 4-cycle, 1-cylinder engine >> would have a pitch half that of the crankshaft rotation? > > Part of the setup of our app is the selection of an engine > configuration, which specifies the factor to be used when converting > between Hz and RPM. That factor can be whatever the user determines > is appropriate.
Well you could learn acoustic signatures and then do classification automatically. That would be really interesting thing to develop. Vladimir Vassilevsky DSP and Mixed Signal Designs www.abvolt.com
Vladimir Vassilevsky wrote:
> On 6/12/2013 10:31 AM, Robert Scott wrote: >> On Tue, 11 Jun 2013 12:05:00 -0700 (PDT), Kevin Neilson >> <kevin.neilson@xilinx.com> wrote: >> >>> Also, doesn't a 2-cycle engine have a fundamental pitch that is the >>> same as the RPM (or RPS), whereas a 4-cycle, 1-cylinder engine >>> would have a pitch half that of the crankshaft rotation? >> >> Part of the setup of our app is the selection of an engine >> configuration, which specifies the factor to be used when converting >> between Hz and RPM. That factor can be whatever the user determines >> is appropriate. > > Well you could learn acoustic signatures and then do classification > automatically. That would be really interesting thing to develop. > > > Vladimir Vassilevsky > DSP and Mixed Signal Designs > www.abvolt.com >
It's also open ended. -- Les Cargill