Power Settings - New Engine - Fixed Pitch Prop

[Heliplane]

Hi Everyone - I'd be grateful for a bit of advice:

Our 1992 AA5 has just had a factory remanufactured engine fitted and, weather permitting, I will be conducting the first flight test tomorrow (following a ridiculously thorough preflight...) The engine is a 180hp O-360-A4K and we have a fixed pitch cruise prop.

Lycoming advises the 1st flight to be conducted at 75% power for the 1st hour and at settings between 75% and 65% for the second hour (and generally for the 1st 50 hours to be flown at 75%).

As those familiar with Grummans will know, the Tiger POH does not publish power settings by RPM (we're supposed to get these from Lycoming directly). The Lycoming engine manuals, however, rather unhelpfully assume that you know the manifold pressure setting (our aircraft, similar to most other fixed pitch a/c, does not have a manifold pressure gauge). Therefore, the Lycoming power setting charts are completely useless in this case.

From past experience and other aircraft, I think 75% power is about 2,550 RPM and that 65% is somewhere in the region of 2,400 RPM (at reasonably low altitudes and roughly standard temperatures).

Does anyone else have any experience with this or know the exact figures?

Alternatively, does anyone have access to a better chart from which I can ascertain what RPM I should set to achieve a given percentage power setting at a specific altitude/temperature?

Thanks!

[RatherBeFlying]

I don't have my Tiger POH handy; so this is conjecture:

Fuel consumption can be used as an indicator of horsepower. Remember that POH fuel consumption figures usually are based on correct leaning.

If the Lycoming manual gives fuel consumption for specific horsepowers; then you can match the fuel consumption for 75% & 65% against the POH fuel consumption for a specific airspeed and pressure altitude.

[Heliplane]

Yes, that would work but there'd be a lot of trial and error with that approach (given we don't have any type of fuel flow gauge).
Would be a very good way of ascertaining the correct RPM settings with a fuel flow gauge though.

[Lister Noble]

Heli,you may get a better response if you post it in the tech section>
Lister:)

[Big Pistons Forever]

Heliplane

I think you are over analysing this. The critical thing in a break in is to run a high power setting to ensure high cylinder pressures so the rings properly seat. Prolonged running of the engine at low power settings will result in a glazing of the cylinders and permanent excessive oil consumption. Any reasonably high power setting like 2550 RPM will do. The critical thing is to avoid prolonged running on the ground. When I replaced all the cylinders on my 0235 Lycoming we did about a 1 min initial power run shut down did a complete check over of the engine and then I timed my start up so I could start, do a very quick runup and immediately takeoff. I then did a hour of circles over the airport reduced power slightly did another hour of local flying and returned. Compressions have been in the high 70's and oil consumption of 1 lt per 12 hrs ever since. Oil Temp is a good indicator of how the break in is going. It will be initally very high and then slowly drop during the first 30 min.
After the first hour it should be near normal for the conditions.

As an aside this is one example where knowing what "normal" engine indications for most conditions is a big help. This is a personal pet peeve as it seems to be most pilots seem to believe as long as the needle is in the green as is well. When I instruct I periodically cover the engine guages and ask the student where the needles were as a way to build good engine management habits.

[gordon field]

Follow the advice from Big Pistons for Ever. Don't baby the engine get airborne and fly hard. An oil change at 20-25 hours would be a good investment.

[RatherBeFlying]

My POH is for the 150 Hp Cheetah.

The Cruise Performance Chart shows:

rpm, % power, TAS and gph

for various altitudes and temperatures.

Your POH should have the same information.

Mind you a different prop will change those numbers, but in a perfect world you would have an amended cruise performance chart for that case:O

And yes, don't baby the engine.

[tacpot]

This advice may be hard to stomach, having just had the expense of an new engine, but have you considered fitting a fuel flow meter before you start the engine break-in?

A fuel flow meter pays for itself very quickly, even without considering what it might save you by avoiding glazing the cylinders.

The well known avionics retailer in Edinburgh is selling the excellent JPI FS 450 for £425 incl VAT.


I'm just reached 8 hours on my rebuilt engine (O-320), although on my aircraft the extra fuel flow of operating at 75%+ power doesn't seem to produce much extra speed, just extra RPM! (I have a JPI FS 450 and would not be without it!)

Good luck with the break-in.

tp

[Final 3 Greens]

If you are going to use your tacho, do you know the error?

I used to fly an Archer which underead by 125rpm.

Big Pistons approach sounds pretty good to me.

[IO540]

A fuel flow meter pays for itself very quicklyCouldn't agree more, plus a multicylinder monitor like an EDM700.

The manufacturer's break-in instructions should be followed, and it is the first few hours that are seriously critical as to glazing.

Otherwise what one needs to do is run at high power until the oil consumption stabilises, which can take anywhere from 10 to 50 or even more hours. In fact I would run at high power (75%) until all spark plugs cease to be dripping with oil when you take them out.

Most Lyco engines are rated at 100% power (which needs fully rich mixture to reach) continuously and most are rated to run at 75% power at peak EGT.

I had my IO540 rebuild (SB569A) last winter and found it was burning 1qt of oil per hour initially, reducing to 1qt per 6hrs after about 20hrs, and now after about 120hrs it is burning 1qt every 15hrs which is about right, and it is only quite recently that the last of the oily plugs ceased to be oily.

An oil change at 25hrs is necessary, then at 25hrs, then every 50 as normal. And do oil analysis - I use this (http://www.avlab.com) very good company. Most people don't do oil analysis, and looking at the AAIB report from one recent totally avoidable multiple-fatal accident there are some whose "maintenance company" doesn't even cut open the oil filter.

For checking the RPM, there is a little program around which you run on a laptop or PDA and it analyses the sound and reads out the exact RPM.

[justinmg]

You can not work it out without either an MP or Fuel flow meter.
To get close you could ask the prop manufacturer if they can tell you from the blade pitch. We have a Sensenich with a 78in pitch. Ed Zercher at Sensenich gave us an idea of the performance. RPM is useless unless you can factor in other stuff. Most RPM guages are 100-200 out, either way.

Probably the only way for you to get any where close to accurate is just to go to 8500ft on an ISA day, and fly with the throttle wide open (but being in London, that may be tricky!)

[Heliplane]

Thanks all - very successful 2+hr first flight today and everything is running well.

[A and C]

The 25 hour oil change is not just a good idea it is a requirment of the Lycoming SB that covers the break-in.

The oil filter should also be cut open for inspection at this point

[IO540]

The oil filter should be cut open at every oil change :)

[jxk]

This advice may be hard to stomach, having just had the expense of an new engine, but have you considered fitting a fuel flow meter before you start the engine break-in?Fitting the fuel flow meter would require a minor mod and that may take a little time.

[MikeBradbury]

The oil filter should be cut open at every oil change

Wholeheartedly agree. A recent 100 hr check on our aircraft found all sorts of interesting bits & pieces in our oil filter that shouldn't have been there.

Glad it was discovered before the big fan at the front stopped :)

[NutLoose]

Make sure you avoid low power settings, we avoid any circuit work for at the least 25 hours, but normally up to the first 50Hr, all our engines have made it to TBO plus extension, treat it well now and it will repay you later on in its life.

This is well worth a read

http://www.lycoming.com/support/tips-advice/key-reprints/pdfs/Key%20Operations.pdf

The TDC is here BTW

http://www.grumman.net/cgrcc/a16ea.pdf

[Big Pistons Forever]

After an overhaul I would do the first oil change and oil filter internal examination at 10 hrs for two reasons.

1) The purpose of the break in is to rub all the pieces together so they mate properly. This will inevitably result in crud in the oil, therefore an oil change will remove the debris rather than have it continue to be circulated in the engine.

2) An early examination of the filter will reveal any gross contamination caused by failing parts (usually due to improper assembly).

In general private aircraft should have the oil changed every 25 hrs or 6 months as it is lack of use which is hardest on a aircraft piston engine. Regular oil changes gets rid of the acids and other nasty combustion
byproducts before they start to rot the engine from the inside out.