Using Wide Open Throttle

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JC150

Pre-takeoff checklist
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JC150
I have some confusion about if and when to use wide open throttle, and I would appreciate any input from other pilots here that can help me out with this..

I fly a Normally Aspirated Arrow III, and typically, I will reduce my manifold pressure to whatever 65% power is in the book. At the higher altitudes such as 9,000ft where full throttle is specified, I will still usually pull the throttle back until I see a slight decrease in MP then increase slightly. There's something about being at full throttle that makes me nervous, and it could be because I got so used to flying the C172 where you wouldn't use full throttle at cruise..

Recently, another Arrow III owner told me he uses wide open throttle from takeoff all the way to the approach, and doesn't pull the throttle back at cruise at all, even if he cruises at 3,000ft. The reasoning he said was closing the butterfly valve when reducing the throttle causes turbulence in the induction system. I told him I like to get the lowest fuel burn possible, so I pull the MP back, but he told me just to use RPM instead to manage the fuel burn in cruise.

I was curious what everyone else here thought about this?

1) Is it okay to use WOT at say 3,000ft? I guess you would just reduce RPM until you got to 10gph?

2) Should I be using WOT all the time?

Thanks in advance for your input everyone
 
As long as you don't have any turbo restrictions, I don't see a problem WFO low. If you want to get there, as long as your not over redline, you are good. At altitude, you won't be making rate power so pulling it back in my opinion is only for saving money.
 
I use WOT from T/O to approach. I initially reduce my fuel flow with the mixture and further reduce it with RPM.
 
(disclaimer: I'm new to complex)

my arrow checklist shows a few different power settings, specifically (and typically) 55%, 65 and 75, with 75% being full throttle and 24hunj, although that is stating at 6k'. I don't see why you couldn't run at 75% power settings at 3k' and just lean her out a bit.
 
You really need to truly understand what's going on inside of an engine before you divert from known operating procedures. More engine controls gives you a better chance of ruining the engine.

Personally, I'm WOT from takeoff to approach like the others have said (normally aspirated, constant speed prop). I also almost always cruise above 7,000 feet. 27" and 2,400rpm will probably put you well into the yellow arc.
 
Is it "harder" on the engine to run WOT? I was taught in my training that a lower power setting will make the engine last longer since you're not running it harder.
 
Mooney, WOT, 2700 climb to altitude, WOT 2500 cruise.
 
At any altitude above sea level, WOT is not 100% power in NA engines. At typical cruise altitudes, WOT might only produce 65-75%.
 
JC150 said:
Is it "harder" on the engine to run WOT? I was taught in my training that a lower power setting will make the engine last longer since you're not running it harder.
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There are many ways to be "hard" on your engine, with the prime indicator being high CHT. If your CHTs are 320°-370° (or cooler if LOP is ok, but not ROP. Cooler ROP and you are being almost as 'hard' on your engine as it gets. You need detonation to do more damage.) and the engine is running smoothly, you are not being hard on it.
 
iHenning, are you saying if I run ROP and it's below 320 i'm being hard on the engine? I've been running 50 degrees ROP and get about 280-310 CHTs, during summer time. I would assume the higher the CHT the worse?
 
I always check was percent of operating power I'm using at cruise, and set for 65%. About the only time I'm WOT is above 9K feet. Don't get there that often.
 
JC150 said:
iHenning, are you saying if I run ROP and it's below 320 i'm being hard on the engine? I've been running 50 degrees ROP and get about 280-310 CHTs, during summer time. I would assume the higher the CHT the worse?
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Anything ROP is is coking up your valve stems, faces, and seats. If you are really rich, you'll start washing out your rings. 50 ROP and you'll end up topping the engine or fixing valve problems around mid time.
 
Interesting.. I don't have GAMIs and I heard its not good to do LOP without them. If I do LOP with my IO-360, how many degrees LOP do you recommend? Is it XX degrees from the first cylinder that peaks or the last?

Wouldn't you get higher CHTs at WOT?

@Steingar, thats what I've been doing too, minus the WOT part. But it sounds like I should be doing WOT all the time? I'm just concerned that will run it too hard, but from what others have said above, Its just fine?
 
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JC150 said:
I have some confusion about if and when to use wide open throttle, and I would appreciate any input from other pilots here that can help me out with this..

I fly a Normally Aspirated Arrow III, and typically, I will reduce my manifold pressure to whatever 65% power is in the book. At the higher altitudes such as 9,000ft where full throttle is specified, I will still usually pull the throttle back until I see a slight decrease in MP then increase slightly. There's something about being at full throttle that makes me nervous, and it could be because I got so used to flying the C172 where you wouldn't use full throttle at cruise..

There should be nothing to make you nervous. The manifold pressure is what it is, regardless of the throttle position. Piston engines run most efficiently unthrottled (WOT).

Recently, another Arrow III owner told me he uses wide open throttle from takeoff all the way to the approach, and doesn't pull the throttle back at cruise at all, even if he cruises at 3,000ft. The reasoning he said was closing the butterfly valve when reducing the throttle causes turbulence in the induction system. I told him I like to get the lowest fuel burn possible, so I pull the MP back, but he told me just to use RPM instead to manage the fuel burn in cruise.

You should be using the mixture to regulate fuel flow, not throttle or RPM.

I was curious what everyone else here thought about this?

1) Is it okay to use WOT at say 3,000ft? I guess you would just reduce RPM until you got to 10gph?

In cruise? "Yes" provided you are running LOP and controlling the power via fuel flow to a level below 75%. Power is controlled by limiting whatever is not in excess, e.g. oxygen if running ROP (throttle) or fuel if running LOP (mixture.) But you need to know what these quantities are, as your POH does not tabulate them. There are formulas to calculate LOP power from fuel flow.

2) Should I be using WOT all the time?

You will be WOT anyway, normally, above 5,000 feet. On climbout, and a lower cruise, again, you need to have a good knowledge of your engine's LOP performance on climbout and lower cruise levels.

Thanks in advance for your input everyone
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Anyway, that's my take.
 
JC150 said:
Interesting.. I don't have GAMIs and I heard its not good to do LOP without them. If I do LOP with my IO-360, how many degrees LOP do you recommend? Is it XX degrees from the first cylinder that peaks or the last?

Wouldn't you get higher CHTs at WOT?

@Steingar, thats what I've been doing too, minus the WOT part. But it sounds like I should be doing WOT all the time? I'm just concerned that will run it too hard, but from what others have said above, Its just fine?
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If your engine runs smoothly LOP, it's fine. Otherwise, it's not. My Arrow does not have Gami's and I have no issues running 50 degrees LOP.

You will get lower CHT's at WOT, as it's air that is cooling the engine running LOP, not fuel.
 
And, for a 360 Lyco, all of this is darned close to the old method of lean until rough, richen just to smooth.
 
JC150 said:
Interesting.. I don't have GAMIs and I heard its not good to do LOP without them. If I do LOP with my IO-360, how many degrees LOP do you recommend? Is it XX degrees from the first cylinder that peaks or the last?

Wouldn't you get higher CHTs at WOT?
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My first pull takes me to 5°LOP, that barely loses any power, and then I pull back until the power drops off, then re-enrichen until the power surges up and gains a throat, the engine should also be smooth at that point. Where you end up LOP for that will vary, but that is the kindest and most efficient mixture. As long as your EGT spread is within limits, GAMIs are not required for LOP, even GAMI tells you to test and if you don't need them, don't buy them.

The big mistake people make in thinking they are being kind to their engines is reducing RPM. These engines already run at the bottom of their productive range for gasoline because of the RPM restrictions that the prop puts on them. The lower the RPM for a HP rating, the more pressure you have to make in combustion chamber. Even with big 5" pistons, these engines would much prefer to turn 3400 due to the fuel burn speed. That's why these engines only make 1/2hp per cubic inch. Once you start making more at these RPMs, you are starting to get into 'the red box' of detonation risk with the combustion chamber pressures required at 2600rpm.

Let the engine spin, limit fuel to reduce power first, and if you want to slow down for more efficiency when you get the mixture all the way down to the tip of the nose of the mixture graph as described before, then you start pulling back RPM to reduce power some more.

The best way to gauge percent power when LOP is by TAS. Use the TAS at altitude in the performance charts and work it backwards to the % power. On your way back through, check the fuel flow comparison. An engine designer/engineer told me regarding engine longevity and multiple duty cycle ratings: "The engine is good for "x" amount of fuel to go through it. How long it takes and how far you get going through that fuel is your choice in how to manage."
 
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I have a couple of stickies in the Maintenance Bay forum that you should read. They might help address some of your questions.

Look at the POH approved power settings and use those. Manifold pressure is manifold pressure, there is no benefit to your procedure of having the throttle slightly pulled back with the same manifold pressure. The engine in your plane can run 2,000 hours (or more) at full power just fine.

Steingar has a fixed pitch prop, so his technique is not applicable to your constant speed prop.
 
I can't tell you how much I just learned from this post. Seriously, this is the kind of stuff that makes being PoA so awesome!

Thank you a hundred times! Awesome.
 
JC150 said:
Interesting.. I don't have GAMIs and I heard its not good to do LOP without them. If I do LOP with my IO-360, how many degrees LOP do you recommend? Is it XX degrees from the first cylinder that peaks or the last?

Wouldn't you get higher CHTs at WOT?

@Steingar, thats what I've been doing too, minus the WOT part. But it sounds like I should be doing WOT all the time? I'm just concerned that will run it too hard, but from what others have said above, Its just fine?
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You CANT have both a carburetor and GAMI fuel injectors, it's either/or. Do you have an O-360? Or an IO-360?

I run mine WOT/2700 from departure to altitude, whether that's 1500 msl or 10,500 msl. Above 6 or 7 thousand, I lean a little in the climb (research Target EGT). Once I level off and accelerate, I pull the throttle back just enough to make the manifold pressure needle move, because I want the throttle body cocked enough to create turbulence in the carb. Why? Because turbulence will atomize the fuel better (smaller droplet size is desirable), and I'm hoping it will make for a more uniform mixture of fuel and air before sending it out to the four cylinders.

Then I set RPMs, with reference to the Performance Tables. At lower altitudes, I will actually reduce throttle more to stay in the 65-70% power range. Then lean to peak. Sometimes I can get sort of smooth operation slightly LOP, if I'm high enough; usually I can't, some enrichen to where I want it.

Last weekend I flew back from WV at 10,000 msl running 20"/2500 and about 25° ROP. Managed 460 nm in a little under 4 hours, plus ~40 mins of sightseeing before heading out, on 39 gallons. I was indicating 145 mph.

It boils down to knowing your plane and your engine. I keep a laminated copy of the Performance Tables on my kneeboard; they are provided every 2500' from sea level to 12,500 with every approved RPM setting (1900-2700, skipping 2000-2300) and a variety of MP settings for each. It makes setting power pretty easy.
 
Henning said:
I use WOT from T/O to approach. I initially reduce my fuel flow with the mixture and further reduce it with RPM.
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For those that say WOT from T/O to approach, I'm curious: what are you doing to manage airspeed on the descent from cruise? Are you really letting the MP build back up to takeoff power and then pulling the power back all at once on final???

I'm a WOT from T/O to somewhere in the descent. During the descent I will start easing the throttles back to maintain whatever my cruise MP setting was. So, basically, if I'm cruising at 8k WOT around 22", I'll end up on the initial approach segment with 22". I find that in the Baron this gives me a consistent speed and I'm right where I need to be when it comes time to add flaps/gear.
 
Fearless Tower said:
For those that say WOT from T/O to approach, I'm curious: what are you doing to manage airspeed on the descent from cruise? Are you really letting the MP build back up to takeoff power and then pulling the power back all at once on final???
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Mooney has a very high redline, so I leave cruise power in for a while and let it come downhill at 180-185kts. At 5000msl or so, I start pulling off 1/2" or so every 500 feet of decent. That way by the time I'm down to 3000msl, I'm at ~23".
 
Fearless Tower said:
For those that say WOT from T/O to approach, I'm curious: what are you doing to manage airspeed on the descent from cruise? Are you really letting the MP build back up to takeoff power and then pulling the power back all at once on final???

I'm a WOT from T/O to somewhere in the descent. During the descent I will start easing the throttles back to maintain whatever my cruise MP setting was. So, basically, if I'm cruising at 8k WOT around 22", I'll end up on the initial approach segment with 22". I find that in the Baron this gives me a consistent speed and I'm right where I need to be when it comes time to add flaps/gear.
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Props back first for descent then I'll lean to near ICO if I need to reduce speed more; MP is irrelevant to power when LOP. The higher your MP LOP, the more cooling you are getting. When I come near the bottom of my descent and start setting up for maneuving in the airport traffic area VFR, or am approaching the IAF IFR, is where I consider 'approach' to begin, and I revert to low response time to full power engine operations and set up with partial throttle and mixture in an appropriate ROP range and I typically keep the props back around 2300-2400 as long as I'm making power to keep my noise level down. If I need more power I can always advance them. Once I'm on final and my throttles are below the governor I'll put the prop handles forward.
 
Just for educational purposes, why is MP irrelevant to power when LOP? Also why is cooling greater with a higher MP at LOP? Is it because you have more airflow? I'm trying to educate myself so I can get smarter with this...
 
JC150 said:
Just for educational purposes, why is MP irrelevant to power when LOP? Also why is cooling greater with a higher MP at LOP? Is it because you have more airflow? I'm trying to educate myself so I can get smarter with this...
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Once you are LOP, power is limited by fuel flow, not airflow, ROP it is limited by airflow, and for that MP is the accurate indicator.
 
Just to recap to make sure I get this right... so when I level off at cruise, I'll just leave my throttle WOT, pull the prop back to 2400, and then use mixture to get 50 degrees LOP? And that would be 50 degrees from the first cylinder that peaks?
 
JC150 said:
Just to recap to make sure I get this right... so when I level off at cruise, I'll just leave my throttle WOT, pull the prop back to 2400, and then use mixture to get 50 degrees LOP? And that would be 50 degrees from the first cylinder that peaks?
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Almost. When you get to wherever you want to lean (I do it around 200') leave the prop forward and lean to get the hottest EGT 5° LOP. This is your first big test on whether you need to do GAMIs to run LOP; will the engine run smoothly at 5° LOP on the hottest. What is your EGT spread across hottest to coldest? Typically with a bar graphing EGT display, if you can keep it to a 2 dot spread between hottest and coldest, you'll be okay for smooth in most LOP ranges you'll typically see. Getting lean enough to get a shake will probably have you slower than you want to be.

From that point of 5°LOP, stay full prop, and keep leaning to the point it either starts shaking, or the power falls off. At this point richen up until it stops shaking, or if it isn't shaking, to the point where you feel a surge of power and all of a sudden the engine exhaust note resonance has a large gain. if you are 50° LOP at that point, you are golden. Note your fuel flow at both of those settings, that is what you use from now on to rough set your mixtures, and 95% of the time it's what you'll stay with.

When it comes time to descend, or if you want to slow down for range, only then do you pull back the prop. Otherwise prop stays full continuous RPM.
 
Seriously, this may be one of the best engine management threads I've ever read. Y'all are awesome!
 
Henning said:
Almost. When you get to wherever you want to lean (I do it around 200') leave the prop forward and lean to get the hottest EGT 5° LOP. This is your first big test on whether you need to do GAMIs to run LOP; will the engine run smoothly at 5° LOP on the hottest. What is your EGT spread across hottest to coldest? Typically with a bar graphing EGT display, if you can keep it to a 2 dot spread between hottest and coldest, you'll be okay for smooth in most LOP ranges you'll typically see. Getting lean enough to get a shake will probably have you slower than you want to be.

From that point of 5°LOP, stay full prop, and keep leaning to the point it either starts shaking, or the power falls off. At this point richen up until it stops shaking, or if it isn't shaking, to the point where you feel a surge of power and all of a sudden the engine exhaust note resonance has a large gain. if you are 50° LOP at that point, you are golden. Note your fuel flow at both of those settings, that is what you use from now on to rough set your mixtures, and 95% of the time it's what you'll stay with.

When it comes time to descend, or if you want to slow down for range, only then do you pull back the prop. Otherwise prop stays full continuous RPM.
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Henning, I'm always interested in your commentary and insight. Glad you're back.

Not to hijack this thread, but since my engine is a pretty common engine, I think there is a lot to learn on this for others, and it's on topic.

I've never heard of managing performance based on RPM rather than using MP. This is a very new concept for me (other than in a fixed pitch prop). I always run mine at peak (since it is POH sanctioned!) So, with my big bore IO-540, here is my procedure. Please tell me what you would do differently:

Takeoff: WOT/FULL PROP (2700 RPM/REDLINE)
Traffic Pattern Altitude: Pull back prop to 2500, Pull back mixture to around 20GPH
Level off/Cruise: Pull back prop to 2400, Throttle back to 75% indicated on EDM-800, Mixture to rough, then back in... right around peak.
Descent: Pull back throttle to descent (19"-21"), adjust mixture a little heavier than cruise.
Final: Throttle 16" or so, Full prop, Mixture close to full.

So, are you saying you're WOT the whole time and you're managing RPM only? So, would you drop the RPM down to, say, 2000 or 2200 on a descent?
 
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ahkahn said:
Henning, I'm always interested in your commentary and insight. Glad you're back.

Not to hijack this thread, but since my engine is a pretty common engine, I think there is a lot to learn on this for others, and it's on topic.

I've never heard of managing performance based on RPM rather than using MP. This is a very new concept for me (other than in a fixed pitch prop). I always run mine at peak (since it is POH sanctioned!) So, with my big bore IO-540, here is my procedure. Please tell me what you would do differently:

Takeoff: WOT/FULL PROP (2700 RPM/REDLINE)
Traffic Pattern Altitude: Pull back prop to 2500, Pull back mixture to around 20GPH
Level off/Cruise: Pull back prop to 2400, Throttle back to 75% indicated on EDM-800, Mixture to rough, then back in... right around peak.
Descent: Pull back throttle to descent (19"-21"), adjust mixture a little heavier than cruise.
Final: Throttle 16" or so, Full prop, Mixture close to full.

So, are you saying you're WOT the whole time and you're managing RPM only? So, would you drop the RPM down to, say, 2000 or 2200 on a descent?
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I don't pull the throttle at all in the descent unless I have to do it. I pull the prop back first to the lowest permissible setting or until roughness occurs. I keep the EGT at the point at which I start my descent. I'm always watching the temps and pressures.

As I approach 5,000msl, I keep the MAP under 25" and back it off an inch thousand feet or so. I land with the prop at 2300-2400rpm and the mixture leaned out (perfectly leaned for taxi).

My go around would be: mixture, prop, and then throttle. The ops vary between every person. Learn all you can and experiment safely. No two engines like the same thing.
 
Cpt_Kirk said:
My go around would be: mixture, prop, and then throttle.
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That's a lot of crap to be messing with if you had to really go-around, especially considering you still have flaps, gear and trim to be dealing with.
 
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