Noise abatement departure VP prop

[overandout]

Operating from a small and very noise sensitive private strip I always reduce power in my fixed pitch prop at about 150ft lower the nose and slow low cruise for a minute or so till clear of the area before re-applying climb power.
However in changing to a VP Prop..Assuming the prop noise is the worst and all the chat about operating "square".
Can I immediatley reduce RPM to reduce noise to 2200rpm and maintain full throttle. Or even reduce RPM itraightaway and then reduce manifold pressure.
ie how important is it for the engine to reduce manifold pressure before rpm in a scenario as described?
I really have to do all I can to minimise take-off noise.
Thanks guys.

Overandout

[gcolyer]

When I fly the PA32 or 337, it is usualy out of a noise sensetive area and I have the same issues.

As soon as I am out of ground effect and the aircraft is climbing (about 100 feet ish) I reduce RPM and manifold pressure, obviously lower the nose to maintain airspeed. I usualy begin an immediate bank to clear any sensetive areas(depending on the airfield). Also because of the low climb rate initially I dodge hills/high ground, so at times it is fun/interesting especially when I have a full load of PAX's + bags.

[IO540]

Can I immediatley reduce RPM to reduce noise to 2200rpm and maintain full throttle

You need to see the operating area graph in your engine manual to answer that.

Some engines, e.g. mine, have a minimum rpm for full throttle at sea level. Mine is 2350rpm IIRC. This is to do with crankshaft stresses; at a given fuel flow rate, the lower the RPM the higher the torque.

One general rule with VP props is to drop the prop rpm just a little, e.g. from 2600 to 2500, as soon as safely airborne. This makes a lot of difference to noise.

[FlyingForFun]

I agree with IO540, have a look in your POH and you'll find a graph which will give you the answer.

But.... I wonder if, especially with the (I presume) increased climb performance of your new aircraft, you might achieve better noise abatement by climbing at max rate, or max angle, to get vertically clear of the noise sensitive area as quickly as possible? Maybe a ground observer could observe two departures (at a time of day least likely to cause noise concerns!) and let you know which profile is quieter from the ground?

FFF
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[Zulu Alpha]

If you've got lots of get up and go or a long runway, you don't need to use fully fine on takeoff. Try setting the position that gives 2500 or 2400 rpm and see what that does to takeoff. In my aircraft it hardly affects the takeoff roll but greatly affects the noise footprint.
DJ

[Nathan Parker]

Assuming the prop noise is the worst and all the chat about operating "square".

The "oversquare" thing is a myth. However, different engines do have different combinations of MP and RPM that are permitted. The Operating Manuals generally do not include these charts, at least in the US. You're probably safe to reduce RPM at least by 100 RPM during the climb out, leaving the MP the same. (But it will rise when you pull the rpm back.)

[javelin]

Reduce the prop before you take off. We operated a Cessna 207 G-PARA for some time at Sturgate years ago and always took off at gross weight with the prop back to 2500 - makes a huge difference to the noise and little to the takeoff roll.

Also, don't forget, you don't need full fime on aproach for all the same reasons - 2400 is good enough unless you are really overweight !

What aeroplane, how long a strip ?

PM for more info:ok:

[moonym20]

do remember that a RoT for VP props:

its considdered bad practice to have a high MP (i,e, full MP) and a low(er) RPM set up... it can put a lot more pressure on the cylinders and encourage an oil seal to blow,

your best using normal t.o power, once in a positive climb at a good speed and safe height reduce MP slightly then adjust RPM to suit :ok:

[Chilli Monster]

its considdered bad practice to have a high MP (i,e, full MP) and a low(er) RPM set up... it can put a lot more pressure on the cylinders and encourage an oil seal to blow,

So why do some POH's (Arrow IV for example) quote an MP higher than the RPM figure? 75% power, 2400 RPM is 25.5" at seal level reducing to 24.4" at 4000ft.

And don't forget Turbo's where 2200 RPM / 28" (on one of the aircraft I fly) is the norm for the cruise.

[Say again s l o w l y]

Really mooney. How do you work that one out?

Low RPM and high manifold pressure will blow the engine apart....... Aye right. We aren't talking about a massive radial, but a simple Conti or Lycoming.

How about this. With a normally aspirated engine. When the RPM is zero (ie engine off) the MP is at it's highest value. Do you see the seals popping? A bit facetious I know, but you get the point?

As has already been said. Look at the RPM/MP diagrams in your POH, pulling the prop back a bit after T/O is highly unlikely to do any damage or stuff your climb out too much.

Any guff about "oversquaring" an engine is just that. If we measure MP in something other than inches, this would not be an issue.

A lot of these engine myths built up around the extremely complex operation of huge radials. They simply don't apply to little engines of low specific output.

[moonym20]

whoa dont go shooting me down

everone with aeronautical sense knows to look at the POH and follow that, those are the facts and figures for that particular aircraft.

I had said as a rule of thumb (should i have added General?) every instructor would it be private for diferences traning or a commerical insturctor all concur with the saying about its not best pratice about placing a low RPM against a high MP - particularly the order to setting up the power profile for your particular stage of flight.

I don't recall saying anything about any engines blowing up, all i simply said was it places extra stress on the cylinders and can (in some cases) encourage an oil seal to leak/blow

just my 10cents :bored:

[Fright Level]

I've been following this and other threads discussing the "over square" issue. Like many, I was always taught this was not the right way to operate an engine with comparisons of booting your car with it in too high a gear being bandied about. It was easy to fall for the myth.

The TB21 (turbonormalised) POH has many of the power settings "over square" with examples of 65% @ 1,000' = 26/2100 and 75% @ 9,000' = 26.5/2300 which caused me to look further into this. There is a link to this Lycoming information (http://www.prime-mover.org/Engines/Lycoming/Flyer/Operation.html) in other posts here. Makes interesting reading to debunk the OS Theory with "modern" flat 4's & 6's.

To answer the original question, I wouldn't be confident to operate the engine at any power setting not mentioned in the manual, but for noise abatement, a low rpm and MP to suit 75% or whatever max cruise power is quoted may work for the initial departure.

Interestingly when we depart LHR late at night (jet), we use full power as opposed to reduced thrust to lower the noise footprint (higher/quicker) rather than low power settings for a longer duration over residential areas. Could that together with a short field technique help more in your situation?

[overandout]

Very helpful and interesting replies everyone.
I have a 500m strip very close to sensitive village and am upgrading from an Old C-172 (0-300-D) to a C-182

[BIRK]

I fly the R172K (Conti IO-360K) out of noise-sensetive area, and i use full throttle, reduce the rpm to 2400-ish on t/o roll (about two twists on the prop leveller) and don't reduce MP until 500ft AGL to around 25" (and keeping the RPM constant)

Haven't had a complain from the Nimby's nor the engine......yet :}

[dirkdj]

It is best to leave the MP wide open, the last bit of travel of the throttle opens the fuel enrichment valve that makes the mixture extra rich during take-off and initial climb.
Having an extra rich mixture slows down the flame front and helps keep the temps down since it amounts to a slower burning mixture peaking later in the downgoing cycle of the piston.
If you reduce RPM it will have the effect of advancing (relatively speaking) the peak pressure point and increasing the CHT temps. The piston will not have traveled so far downwards when the peak pressure pulse is reached..
Reducing RPM and at the same time retarding throttle (cutting off the fuel enrichment valve) is a NO-NO, you are combining two unfavourable effects. For noise reasons you can reduce the RPM by 100 RPM or so while keeping the MP full open.

[Flyin'Dutch']

It is OK to retard the revs on/after take-off.

The IO-540 in a Lance has the redline @ 2700rpm the Maule has the O-540 (essentially the same engine) and the redline @ 2400rpm.

MP at FT is exactly the same in both.

As Dirkdj says; don't pull back the throttle during the take-off as you do need the extra fuel going in.