Red box

[bonal]

Thanks Mike! See now I know more than before MAP is at 21 to 22 depending on the day and running very smooth. Too bad I was just about to hang it up and take up politics.

[aviatoreb]

I know the safe answer is to round down.  However if I were flying a 244hp M20R eagle, and knowing that with an STC I could take the same engine and make it 310hp, then calculating 65% based on 244hp seems extreme.  On the flip side, if I had an ovation 3, and with my 310hp engine, computing 65% of 310hp is 201hp - and knowing that is 82.5% of 244hp of the same engine in the same airframe - it makes me scratch my head.  This is not a trivial issue.

 

In my case, with my airplane, this is entirely a theoretical question because I am forced to lean 40-60deg lop even when at 60% since the TiT is what gets me.  I hate keeping my TiT right at redline of 1650 - so I lean until I see something below 1600.  I loose gobs of power doing that but I get good range and still quite decent speed.  But this prevents me from attaining any of those exciting 75-80-85% power lop settings that some folks boast.

 

Still being a theoretical question, it is a legitimate question since this is not a tiny effect, or a "in the fuzzy margins" answer.  We are taking about the difference between declaring a certain fixed leaning-flow setting as 65% or 82.5%.

[KSMooniac]

Deakin and Braly over on beechtalk have repeatedly stated the TIT limit is a limit for continuous operation, so if your limit is 1650, then cruising at 1649 is perfectly acceptable.  FWIW

[PMcClure]

Are you sure the Ovation 1, 2 and 3 engines are exactly the same? I think at least the O3 550g has a different fin and head design, specifically designed to accommodate the increase in power. 

[aviatoreb]

I'm not sure of anything. :-)

[harrispa]

The engine in the M20SEagle, the Ovation 1,2,and 3are all the same engine! the IO 550G. The data plate on the M20s Eagle even says 280hp at 2500 rpm, same as O1,O2. The factory uses the Midwest stc for the O3 to make it legal for 310hp @2700 rpm. The data plate is then replaced to reflect the change. Using the Midwest stc, you could install the IO550N (cirrus engine), your choice.

Paul

[MooneyBob]

Wow. I thought I am asking very simple question when I started this topic. Now I am afraid to touch anything with a red knob in my plane. Pretty confusing and hot.

[KSMooniac]

These discussion always spin out of control and into all kinds of tangents.

 

If you really want to understand the topic thoroughly, there is really no better way on the planet than to take the Advanced Pilot Seminar.  Yes, it costs money, but I can confidently say you'll save many times the cost in tuition as a result of your new knowledge in terms of operating more efficiently and being able to troubleshoot and diagnose engine maladies yourself, vs. paying a mechanic for many hours of troubleshooting.

[MooneyCFII]

I do seem to have annoyed people and I apologize. If anyone is interested I will be happy to describe what I teach for setting power and mixture for a carbureted engine, a normally-aspirated injected engine, and my 231 (which has no automation in the turbocharger control). These techniques have served me well for 45 years and I have taken several 4 and 6 cylinder Lycoming engines past TBO. I normally operate lean-of-peak where possible. I fly with aircraft with no engine instrumentation to speak of (oil pressure and temperature only) and with aircraft with SOTA engine monitoring. 

[aviatoreb]

Deakin and Braly over on beechtalk have repeatedly stated the TIT limit is a limit for continuous operation, so if your limit is 1650, then cruising at 1649 is perfectly acceptable.  FWIW

 

I know - I know.  I have read Deakins essays on this in detail.  Its just that 1650 gives me the "heeby-geebies".

 

Anyway surely 1650 even if it is allowed for my turbo, it must be awfully hard on the rest of the exhaust system.

 

Is anyone here running at 1649 on their TIT?

 

My engine seems pretty well tuned in all aspects (after lots of work!) and runs well enough LOP.  I have sometimes dreamed of just going for it - and running 85% LOP like the beech rockstars like Deakins and Braly.  Wow its fast already at 75% (ROP) so it sure would be fast at 85%.

[aviatoreb]

Wow. I thought I am asking very simple question when I started this topic. Now I am afraid to touch anything with a red knob in my plane. Pretty confusing and hot.

 

That's what happens on the internet.

[aviatoreb]

I do seem to have annoyed people and I apologize. If anyone is interested I will be happy to describe what I teach for setting power and mixture for a carbureted engine, a normally-aspirated injected engine, and my 231 (which has no automation in the turbocharger control). These techniques have served me well for 45 years and I have taken several 4 and 6 cylinder Lycoming engines past TBO. I normally operate lean-of-peak where possible. I fly with aircraft with no engine instrumentation to speak of (oil pressure and temperature only) and with aircraft with SOTA engine monitoring. 

 

Than you for saying Brian.  I am glad you are not put off and welcome to Mooneyspace. Thank you for bringing your experience.

[carusoam]

O3 = IO 550 (n) the cylinders are slightly different. the cooling fins are different. The sheet metal that goes with it is different. The govenor is different, the tach has been modified with the redline at 2700rpm... The prop that comes with it is a TopProp, that's different.

To really enjoy the difference, there are three versions of the TopProp, standard, light weight, and composite. The shiny spinner comes with it too.

According to Rocket Engineering, and my best memory. And RE speaks highly of the engine's initial TCM design spec of 400+ HP, mentioned by someone above...

My goal is to go past TBO with one set of cylinders. Pressing too hard, probably won't fit this goal.

I am still not an expert in Os...

Best regards,

-a-

[harrispa]

Yet to see an O3 from the factory with the IO 550 N engine.  The N engine is an option on the Midwest 310HP STC.   If you go to this website: www.deltaaviationllc.com

 you will find different files and pictures of O3's that show in the logs the IO550G is modified by the factory using the Midwest STC.  Yes, for the 310HP the plane must have the approved prop, but many O1's and O2's already have this.  The Governor is modified to allow 2700rpm, and approved tach showing 2700rpm is required.  Judging from this info, I conclude the O3 does not have an IO550N engine, but has the same IO550G* (modified governor and data plate) as all M20S and M20R.

Paul

[carusoam]

I would expect going forwards...

And the Cirrus uses the (n)...

The (n) may not have been around when the O was in last production?

Keep in mind my source of information.... MidWest Mooney, the purveyor of the STC.

I may have drank the kool aid directly from the company punch bowl.

Pricing from TCM has the (n) slightly lower in cost than the (g). Updated cylinder design and lower cost, hmmm...?

Best regards,

-a-

[MooneyCFII]

Talk about thread drift! This started out with:

Another stupid rookie question :
Can you clarify the term " Stay out of the Red Box" ? Where can I find more about that.
Thanks.

PS. Let me know if I am too annoying.

I tried to answer but got caught up in the "why" rather than just focusing on the "how". I did throw in a fair bit of "how" but I think it got lost in all the other stuff flying around.

 

So, the first answer is, "don't push your engine too hard." The first and easiest way to stay out of the red box with a normally-aspirated engine is to climb to 10,000' or above. If you do that, there is nothing you can do with the throttle, prop, or mixture that will hurt your engine. If you are down lower you just need to set a lower power setting or use a richer (ROP) or leaner (LOP) mixture setting.

 

Here is the logic behind that and it applies to ALL normally-aspirated engines: at 10,000 feet your MAP will be down to about 20"Hg. That is 2/3 of sea-level pressure. That means that no matter what you do with the controls, maximum power available is 2/3 of sea-level or 66%. If you reduce RPM at all you are going to reduce power from 66% to something lower. (At 7500' max available power is about 75% and reducing RPM will select lower power from that.)

 

So for the guy flying behind a carbureted Lycoming engine power management is easy:

1. Take off full-power with a full-rich mixture. 
2. IF you have an EGT of any sort, lean during climb to maintain whatever EGT value you had at take-off. 
3. Climb to 7500' or higher and level off.
4. Reduce RPM (yes, this is the first power reduction) to your desired cruise RPM.
5. Lean the mixture until the engine stumbles. Richen the mixture until the engine runs smoothly again. You are done.
6. Set cruise cowl flaps (if you have cowl flaps).
7. Monitor CHT. If you have normal CHTs all is good. If CHT is high, reduce RPM and/or MAP, relean, and check CHT again.

At 7500'-8500' I would set 2400 RPM. I would use higher RPM values at higher altitudes to get more power but I wouldn't do anything with the MAP. Let altitude set your MAP for you. 

 

If you have an injected Lycoming engine you have a fuel flow indicator that is actually a fuel-pressure gauge. On the face of that gauge you will likely have full-power fuel-flow values for different altitudes. As you climb, lean to the marks for the different altitudes as you climb through those altitudes. In essence, you substitute those indications for step 2 in the above climb procedure. 

 

While it is technically possible to get a carbureted engine to run LoP smoothly it is not likely. I know of two tricks to vary mixture distribution with a carbureted engine: close the throttle from wide-open and turn on carb heat.  By closing the throttle just a tiny bit so that there is only the barest reduction in MAP, the throttle valve now introduces turbulence in the flow and this aids in fuel vaporization which helps mix the fuel and air. If you have a multi-probe EGT you will probable notice a shift in EGT on one or more cylinders. And carb heat raises the induction temperature which helps with fuel vaporization. 

 

I can go on here but I think that addressed the original question. 

 

[N601RX]

So how is the fuel flow indicator actually a fuel pressure gauge? 

[MooneyCFII]

So how is the fuel flow indicator actually a fuel pressure gauge? 

Lycoming normally provides/specifies an analog gauge for fuel flow. If you follow the plumbing you will find that it connects to the flow divider that sits on top of the engine and feeds fuel to each of the injectors. The gauge is just a pressure gauge. When you have an orifice, i.e. the injectors, fluid (fuel) flow through the orifice is going to be proportional to the pressure. So if you know what the fluid is (its viscosity is the key here) and the size of the orifice, you can calibrate the gauge to read flow as a function of pressure. More pressure, more fuel flow. Less pressure, less fuel flow. It is that simple.

 

Is this accurate? For the most part it is pretty accurate. OTOH if the orifice(s) are dirty or partially blocked, the gauge will no longer be accurate. A partially-blocked injector will require higher pressure to flow the same amount of fuel. A partially-blocked injector will result in low fuel flow and a leaner mixture for that cylinder. If you have a multi-port EGT and/or CHT you can see that the EGT and/or CHT values no longer read the same as they did for the desired fuel flow. (Knowing what your EGTs and CHTs normally read for a give power setting and altitude is quite useful for keeping track of how the engine is working.) If you have added a vane-type fuel-flow gauge (shadin, JPI, whatever) then the two gauges will no longer agree. That is a hint you need to do maintenance on the injectors. 

[N601RX]

That is not the way Mooney sets the fuel pressure gauge up.  They connect it to the inlet of the servo so that it only shows the mechanical or electrical fuel pump pressure.

 

On the E's and F's that I've saw the gauge port  on the spider was plugged from the factory.

[orionflt]

That is not the way Mooney sets the fuel pressure gauge up.  They connect it to the inlet of the servo so that it only shows the mechanical or electrical fuel pump pressure.

 

On the E's and F's that I've saw the gauge port  on the spider was plugged from the factory.

and most after market fuel flow gauges use a flow meter not pressure to read fuel flow and that does not translate to pressure.  

[rbridges]

can I add another dumb question?  I like to run my prop at 2400 rpm, even if I'm doing 24+MP.  they say lower rpm=increased cylinder pressure.  Is that true?  Because the formula for %HP is based on MP and RPM.  It seems that using a lower rpm would give you more red box clearance, but not if it's increasing cylinder pressure.  Am I missing something?

[MooneyCFII]

Every aircraft manufacturer does different things. And people add things to their airplanes. Mooney does have a fuel pressure gauge that is different than the fuel flow gauge I was alluding to. The gauge I was talking about is typically a 3.25" analog "steam" gauge with a pointer that rotates and is calibrated in GPH. Every *injected* Lycoming engine I have flown behind has had this analog fuel-flow gauge on the panel somewhere. It does indeed sense fuel pressure in the flow divider and translate than into a fuel flow indication. And it is possible that Mooney never put this gauge on some models with injected engines, instead deciding to put in a vane-type fuel-flow indicator, e.g. Shadin. After all, manufacturers get to make changes and the certify the aircraft that way.

 

BTW, this does not apply to Continental engines with fuel injection. The Continental fuel injection system is VERY different from the Bendix RSA fuel injection system used on the Lycoming engines. (I am a fan of the Bendix RSA system myself.) I like the Bendix RSA system because it is a true fuel servo system that controls fuel flow by mass airflow. 

[orionflt]

Every aircraft manufacturer does different things. And people add things to their airplanes. Mooney does have a fuel pressure gauge that is different than the fuel flow gauge I was alluding to. The gauge I was talking about is typically a 3.25" analog "steam" gauge with a pointer that rotates and is calibrated in GPH. Every *injected* Lycoming engine I have flown behind has had this analog fuel-flow gauge on the panel somewhere. It does indeed sense fuel pressure in the flow divider and translate than into a fuel flow indication. And it is possible that Mooney never put this gauge on some models with injected engines, instead deciding to put in a vane-type fuel-flow indicator, e.g. Shadin. After all, manufacturers get to make changes and the certify the aircraft that way.

 

BTW, this does not apply to Continental engines with fuel injection. The Continental fuel injection system is VERY different from the Bendix RSA fuel injection system used on the Lycoming engines. (I am a fan of the Bendix RSA system myself.) I like the Bendix RSA system because it is a true fuel servo system that controls fuel flow by mass airflow. 

I have flown behind a number of Lycoming fuel injected engines and a fuel flow was not standard equipment on many of them.

[KSMooniac]

I too have never seen the pressure-driven fuel flow gauge in any Mooney.  I think some Pipers had them.  I know my '77 J did not come with any fuel flow system at all.  It was added my later with the EDM-700.  All I've ever seen in older Mooneys are fuel pressure gauges.  I'm sure 90s+ models came loaded with everything, though.

[harrispa]

Some planes come with no fuel flow or pressure gauge at all, others come with just a fuel pressure gauge, others a pressure gauge calibrated in fuel flow, and still others come with the fuel flow gauge driven by a flow transducer in the fuel line.   We could go on forever naming the different planes and the particular gauge they have.