Beaten to death but I'm going to ask anyway MAP/RPM

[piperboy84]

I was trained that after take off and once attaining a safe height to reduce the power then the rpm then adjust the mixture (if applicable), basically starting from the left knob and moving right. Then when adding power it's the reverse I. e. right to left. The question I have is on take off that procedure just does not feel right to me, the reason being I can't see the point of revving the living sh&it out the engine at red line 2700rpm when it does perfectly well at 2500rpm, also I read a very high percentage of engine failures on take off occurs at the first power change. It feels far more natural to me and easier on the engine to go everything forward on take off then when about 500 feet agl screw the rpm back from red line to 2500 and leave the throttle wide open till I get to my cruise altitude of say 2000 feet then bring the power back to 23 inches , prop back to 2300 and lean .

Any thoughts ?

[Mark 1]

Engine failures at power change is an Old Wives Tale.

There's nothing wrong with reducing RPM at full throttle. It's a good way of reducing the noise.

Why not 24" and 2200 RPM? 'Under-square' is fine if the POH allows it and gives less noise and fuel burn for the same performance.

[alex90]

Hey Piperboy84,

So I am not sure about which type of plane you are referring to, nor which runway length which may affect procedures.

When I fly the arrow, I would normally go full everything for takeoff, then at 300' or so, gear up, and then at around 500' i would reduce everything for the engine to be happy at 25 : 25 (ish) until cruise height (or TOC). Then go for cruise PAT, which would normally be around 23:24 or 22:23 depending on where I was going / how heavy the plane was.

When I fly the turbo arrow, I would normally initially go full everything, but as soon as the overboost light comes on, I would reduce power to under the overboosting light (normally whilst still on the runway [around 35/2700) and then at around 300' gear up, and 500' cruise climb (which in my plane is around 34" MP : 2500 RPM). To then go into cruise at around 33MP : 2450rpm (and of course lean to suite). This gives me a good 140kts IAS, at around 41litres per hour.

There may not be any need to go full power if for anything other than testing that the engine can sustain it. Say if you have a 2000m runway, you may very well be able to take your time and only push the engine to 25:25, and still get off the ground well before the halfway mark, but a 600m wet and long grass strip, you may very well end up in the trees at the end of the runway (then you'd feel pretty stupid for not applying full power, if you survive that long!).

There may be factors such as noise restrictions which may affect your MP/RPM in particular fields where (if safe to do so) then they kindly ask you to try to reduce power earlier in your climb.

The philosophy instilled in me, from very early in my learning for the PPL was always, why would you take such potential risk? If you have 2000m of runway, use the whole length, we know you will probably be airborne within 300m, but if something did go wrong - wouldn't you prefer to have another 1700m to land the plane in safely, rather than hitting the trees? The less power you give, the slower your acceleration, thus the longer your ground roll, the closer you may be to either the stalling point, or the tree line at the end of the runway.

With regards to the way in which you add manifold pressure, rpm, and then mixture, this has to do with "flying oversquare" which there are a large number of articles about online. Different planes and different engines like different power settings, some prefer being flown oversquare and some dont. In reality, doing the opposite to the manual can often affect the engine lifespan of the aeroplane you are flying. I have heard that incorrect power settings could reduce the lifespan of the engine by up to 40%, but I am yet to bear witness to this. Maybe someone else on here can?

Anyway - I would follow the aeroplane manual, and fly the plane as it was intended to, so as to not incur "unexpected" costs!

[Pilot DAR]

There's nothing wrong with reducing RPM at full throttle.

.... as long as doing so is within the limitations of the engine.

Or, you could wreck an engine. If you reduced RPM at full open throttle on a heavy 185 floatplane just off the water on a hot day, it could end badly for the engine.

There is a margin to detonation, but it is only a margin, and careless engine treatment can close it. Detonation is the ignition of the fuel air charge prior to the spark igniting it. Many factors can be causal. However one factor completely within the pilot's control can greatly prevent detonation. That factor is time. If there is not enough time, detonation is much less likely. If the RPM is high, the time for each combustion cycle is short, and detonation less likely.

During detonation testing I have caused and measured detonation at power settings which a pilot could achieve in flight. Most alarming was that when I removed the conditions I had used to induce detonation, the detonation continued for many seconds, causing me great fear that I might yet damage the engine following my test, rather than during the test.

Yes, I like the idea of reducing RPM to reduce noise. Done within the limits of the engine, okay, but the pilot needs to understand these limits. If you can reduce power first, then RPM, you will maintain or increase the detonation margin. Two friends of mine have melted pistons of their O-470, and IO-520 - right through - resulting from pilot induced detonation. It's not worth the risk.

Unless the aircraft operating instructions state otherwise, I always reduce throttle from open first, then RPM, and reverse when advancing the power. It's a sure thing to protect the engine, so why not?

[dirkdj]

The last bit of travel of your throttle control activates the fuel enrichment valve giving extra fuel during full throttle operations. The action of reducing to 25" MAP shortly after takeoff does no good at all and will send the CHTs skywards. Reducing RPM only will be beneficial for noise.

[foxmoth]

Why not 24" and 2200 RPM? 'Under-square' is fine if the POH allows it and gives less noise and fuel burn for the same performance.
I think you mean over square!

[Danny42C]

Trained with the US Army Air Corps in '41.

Was always told to reduce manifold pressure first, then the RPM, and increase RPM before putting up MP.

Reason: danger of detonation (as stated above). Uncle Sam had lost too many engines that way.

D.

[Flyingmac]

Piperboy wrote."


It feels far more natural to me and easier on the engine to go everything forward on take off then when about 500 feet ago screw the rpm back from red line to 2500 and leave the throttle wide open till I get to my cruise altitude of say 2000 feet then bring the power back to 23 inches , prop back to 2300 and lean ."


Pretty much how I fly the PA32.:ok:
It's also more neighbour friendly to pull the prop back.:)

[ShyTorque]

"Rev up, throttle back" was the way the RAF taught power changes during my time (including when I instructed on SEP).

I know there are differences in the precise explanation of terms "across the pond" but the term "detonation" can also be used to describe a situation where the spark initiates the burn normally, but instead of the mixture burning steadily, once ignited, part of it subsequently spontaneously explodes, due to an extremely rapid advancement of the flame front and extreme cylinder pressure.

I was taught that where the mixture spontaneously ignites, it's called pre-ignition or dieselling. Such as when the ignition is turned off but the engine keeps running. MGB cars and Land £overs were notorious for it, cast iron heads and mucky petrol forming carbon deposits which glowed red...

[Silvaire1]

I reduce rpm on my O-320 from 2700 to 2500 as the first reduction of power after takeoff. Any light aircraft engine that is (also) installed with a fixed pitch propeller is designed to allow reduced rpm operation with full throttle, at climb speed. If you fly such an engine with a CS propeller, increasing pitch after takeoff and reducing rpm to some degree, it will therefore be within the engine manufacturer's recommendations as it is for my O-320 and many other smaller non-supercharged engines. They are designed with sufficient detonation margin to allow full throttle climb, on minimum approved fuel grade (often 80/87 octane, as for my engine) at reduced airspeed and rpm with a fixed pitch 'cruise' propeller. The full throttle mixture is slightly richer, which adds additional margin that is not present if you close the throttle to reduce power.

[Johnm]

As others have said the safest way to adjust power is rev up throttle back. On our TB 20 with IO540 we takeoff at full throttle and max revs and once gear and flaps are up reduce MAP to 25 and revs to 25 though max revs is 2575 so that's not a big change. As the climb continues it's necessary to keep opening the throttle to maintain 25 (obviously) and full throttle is achieved at about 5000ft. At which point leaning to maintain egt starts.

Cruise is normally 140 KIAS 23 23 at around 40 to 45 litres depending on altitude.

For descent and approach it's only necessary to throttle back to 20 and keep throttling back to maintain 20 until on final approach when it's necessary to reduce throttle further to get below flap limiting speed.

[Silvaire1]

On our TB 20 with IO540 we takeoff at full throttle and max revs and once gear and flaps are up reduce MAP to 25 and revs to 25 though max revs is 2575 so that's not a big change.

With the TB 20's propeller holding max rpm below the normal 2700 rpm redline for an IO-540, this procedure operates the engine with full throttle and reduced rpm for take off, in line with the original poster's question.

[chevvron]

Flying Rotax 503 powered microlights, I used to retard the throttle gently from fully open at about 500ft until I saw a slight drop in rpm, then advance it a nudge. Did wonders at reducing fuel consumption.
It was surprising how far you had to pull the throttle back before the rpm reduced.

[dirkdj]

The proper way to handle noise reduction is to reduce prop RPM only, leave the throttle wide open until reaching cruise altitude. I have a JPI engine analyser since about twenty years and you can clearly see the CHTs shoot up if you do the old 'reduce to 25/25 OWT trick'.
As explained before, it is the fuel enrichment valve in action on a fuel injected engine.
Please read the engine management articles by John Deakin if you want to know the how and why.
Search for 'John Deakin's Engine-Related Columns'

[ShyTorque]

I'd say that as is usually the case, read the manufacturer's manual. It's obvious that there will be handling differences between engines (that's why there is a need for formal differences training on some types). That is, if you want to avoid the trap of incorrectly using advice about one engine in another situation.

(After the accident caused by engine failure, in court the pilot said "But I followed advice I found on PPRuNe").

[dirkdj]

ShyTorque,

Some of the sections in the POH are written by the engineers, then rewritten by the salesmen, then re-rewritten by the lawyers. Take your pick.
It is best to understand the why and how of engine operation and apply it. John Deakin's articles are as close as you can get.

[ShyTorque]

Having been in the professional flying game since the 1970s, I'm aware of how POHs are written. I do also know a little about engines.

But advice given on a rumour network, even with the best of intentions, is no substitute. What any individual does with their own engine is up to them, but when you're flying someone else's for a living you had better do as the POH says.

[Pilot DAR]

Some of the sections in the POH are written by the engineers, then rewritten by the salesmen, then re-rewritten by the lawyers. Take your pick.

Though the latter two may have a role in the wording of a Flight Manual It is finally submitted to the certifying authority by the "engineers", and sections 2, 3, 4, & 5 are approved by that authority, (and not lightly, I can tell you from experience!) So you can take your pick to comply with the certifying authority or not....

[Pace]

I can remember as an experiment on a long runway setting the climb power setting for takeoff rather than take off setting! This was in a Senca V

This was a very smooth way of taking off and once airborne no noises for passengers as you set climb power as it was already set

I would not recommend it as your book figures for take off will be out of the window but there were no other negatives

Pace

[Johnm]

The proper way to handle noise reduction is to reduce prop RPM only, leave the throttle wide open until reaching cruise altitude. I have a JPI engine analyser since about twenty years and you can clearly see the CHTs shoot up if you do the old 'reduce to 25/25 OWT trick'.
As explained before, it is the fuel enrichment valve in action on a fuel injected engine.
Please read the engine management articles by John Deakin if you want to know the how and why.
Search for 'John Deakin's Engine-Related Columns'

With TB 20 the converse is true if you don't reduce power as advised in POH the CHTs are higher in the climb

[Big Pistons Forever]

All modern engines will have a manual provided by the engine manufacturer. In it will be model specific diagrams that show the major operating parameters including a chart that provides the minimum RPM for any Manifold Pressure setting. That will be the definitive answer as to allowable RPM vs MP settings. Of note many Lycoming engines can have the RPM set as low as 2400 RPM and still be operated at full throttle.

I highly recommend that every owner buy an engine manual from their engine manufacturer.

Finally don't be in a rush to reduce power after takeoff in SEP's. Altitude= options in the event of an EFATO. Max MP and max RPM will give you the highest climb rate and therefore minimize the time spent in the low altitude, low airspeed danger zone.

[Silvaire1]

Finally don't be in a rush to reduce power after takeoff in SEP's. Altitude= options in the event of an EFATO. Max MP and max RPM will give you the highest climb rate and therefore minimize the time spent in the low altitude, low airspeed danger zone

Along those lines, it's worth nothing that sometimes limitations on continuous max rpm are the result of noise certification issues, only. I have an MT prop that was certified for 2500 rpm max continuous, 2700 rpm redline (like the engine) for takeoff on my airframe. I have written correspondence indicating that this was for German noise certification only. So while I may want to reduce rpm after takeoff when conditions allow, I no longer worry that it's engineering driven.

I agree 100% about getting a copy of the engine operating manual. There's a lot of good info there and for common types I've noticed Google is your friend.

[dirkdj]

Your full-rich fuel flow may be set too low if that happens, or your baffles need attention

[Centaurus]

Lots of good advice so far. But the best advice by far on engine handling can be found in John Deakin's articles under the title The Pelican's Perch.

"Pelican's Perch" Index - AVweb Features Article (http://www.avweb.com/news/pelican/182146-1.html)