Lycoming O-320 power settings for break in

[az_gila]

Originally Posted by JonJay

While I can not speak for a 9A with an 0320, I know on my IO360 RV6 75% put me right at the start of the yellow arc. I was able to run hard even when it was bumpy, which it was most of the 10 hours I used for my break in period.
More drag is better at this stage of the game. You dont want to have to reduce power for bumps.

This is for a CS prop though, isn't it? Or you live near Sea Level...

The trouble with a FP prop and no wheel pants is the prop will have the wrong pitch for the drag, and be even lower on rpm/power %... add some measurable DA in the mix, and 75% is hard to get...

gil A

[JonJay]

Originally Posted by az_gila

This is for a CS prop though, isn't it? Or you live near Sea Level...

The trouble with a FP prop and no wheel pants is the prop will have the wrong pitch for the drag, and be even lower on rpm/power %... add some measurable DA in the mix, and 75% is hard to get...

gil A

Using "big" words like DA just confused little brains like mine. So, in my pea brain I can understand that the fixed pitch prop would not be matched to the drag? So are you saying it would not be able to reach 75% with more drag, like wheel pants?
(yes, CS and below 3000ft for my machine. My neighbors 6 with an 0320 has no trouble cruising side by side with me once he catch's up, so I assume he could still reach manuevering speed area and not be pushing 75%. If it is bumpy, you would have to pull back).

[gmcjetpilot]

Originally Posted by JonJay

Using "big" words like DA just confused little brains like mine. So, in my pea brain I can understand that the fixed pitch prop would not be matched to the drag? So are you saying it would not be able to reach 75% with more drag, like wheel pants?
(yes, CS and below 3000ft for my machine. My neighbors 6 with an 0320 has no trouble cruising side by side with me once he catch's up, so I assume he could still reach maneuvering speed area and not be pushing 75%. If it is bumpy, you would have to pull back).

The advice to not put fairings on has been around for a long time, but what does it really matter, not withstanding the RPM issue.

Gil keeps me honest, I should not talk for him, but what I think he's saying is your prop will essentially be OVER PITCHED with out the fairings, so your RPM's will be down. Low RPM = less power. If you are flying at higher DA (density altitude) than you may not be able to get 75% power. Some people live at higher altitudes to start with. So if you depart Denver and want some reasonable height between you and the ground, while you fly around breaking the engine in, the OVER PITCHED prop (low RPM) may keep you from making a full 75% power at that high DA?

Lower RPM = less power. You really don't want too much prop pitch (low RPM) during break-in. It's like being in a car going down the freeway, in the right gear and normal operating RPM, all is well. However in that same gear, going up a steep hill, your lugging the engine down (lower RPM). You really don't want to be "going up hill" too much during break-in. On the other hand you don't want to over revving during break-in either. You want to be in the 2,400-2,600 rpm range in the 75% power, while flying at a reasonable safe altitude above the ground. That is what I think Gil is saying. The fairings make a large diff in speed. I'm not a RV/fixed pitch expert; most of my RV time is with c/s props. The fairings may or may not be a factor in making 75% power.


Gear/Wheel fairings - ON or OFF for 1st flights, Myth or Fact?

One reason people say leave the fairings off for 1st flights, is because you're going too fast at 75% power. Yes, you will go faster and have more cooling, which is good for break-in. Going fast is not an issue. Granted you are going fast to nowhere, as you stay close to the airport. In my opinion, this is not the issue. I guess if your engine is running TOO cool, like if you are breaking-in during winter, it might be a small issue. There are ways to get engine temp up besides add airframe drag.

The other argument to support NOT putting fairings on before 1st flights, which I agree with, has more to do with rigging. You want to get the elevators and ailerons adjusted and rigged before adding two big aerodynamic parts (gear and wheel fairings), both of which can change trim of the plane. Still of you are good at installing the fairings straight this is also a small issue. However if you make a mistake and have made your wheel/gear and gear/fuselage intersection fairings, changing them would be a bummer, so leaving those off might be a good idea until you can make sure the fairings are on straight. You can tape the gaps up if you want.

[az_gila]

Originally Posted by gmcjetpilot

.....
Gil keeps me honest, I should not talk for him, but what I think he's saying is your prop will essentially be OVER PITCHED with out the fairings, so your RPM's will be down. Lower RPM = less power. You really don't want too much prop pitch (down on RPM) during break-in. It's like being in a car going down the freeway, in the right gear and nornal operating RPM, all is well. However being in that same gear going up a steep hill, your lugging the engine down (lower RPM). You really don't want to be "going up hill" during break-in. On the other hand you don't want to over revving during break-in either. You want to be in the 2,400-2,600 rpm range in the 75% power. I'm not a fixed prop expert. Most of my RV experience is with C/S props.

Gil can correct me, but it's probably not a big deal either way, fairing or no fairing, during initial break-in, but if you find you can't get enough RPM to get 75% power, with reasonable throttle (MAP) than put the fairings on.

Oops... I thought I had answered the question form JonJay a day or two ago... I guess I pressed the wrong button and it disappeared...

All comments were for a FP installation, and George's description is in line with what I tried to post...

My point was that Density Altitude (DA) does come into play - especially here in the hot SW. At our airport (2940 ft MSL) we are at a DA of 5000 ft when it is 81 F outside - which happens frequently - even 4 days ago!

Since a FP prop is usually pitched to reach 2700 rpm at full throttle at 7000 or 8000 ft (again, use Density Altitude) which is around the 75% power range from the Lycoming charts - this sets the highest DA that 75% can be reached. Leave off the wheel pants and fairings, and the prop pitch will be incorrect as George describes above - with less rpms giving less % power - setting an even lower maximum altitude for 75% power.

JonJays plane with an adjustable pitch prop is a whole different set of circumstances... as is the RV guys living back east at near sea level...

When I broke in my Tiger cylinders after a TOH, I flew for an hour in circles at 1500 ft above our airport. In June, even before 7:00 am this gave a DA of about 7000 ft... and 2650 rpm is about 74% power. If I had higher drag, this level of power would not have been obtained.

DA does make a big difference, and needs to be allowed for in the hot SW...

If you are breaking in a new RV engine, use a high altitude field, and it's the hot time of year... perhaps having the fairings on might be the best approach?

gil A

[rv9av8tr]

I recall from the lycoming tables that WOT at 7500' (which results in approx 22" MP) at redline (2700 +/-) will result in very close to 75% pwr.

You definitely want to use WOT when using a carb, otherwise you won't get even fuel flow to all the cylinders!

[vlittle]

Originally Posted by rv9av8tr

I recall from the lycoming tables that WOT at 7500' (which results in approx 22" MP) at redline (2700 +/-) will result in very close to 75% pwr.

You definitely want to use WOT when using a carb, otherwise you won't get even fuel flow to all the cylinders!

You may find that this does not hold true in an RV. Due to the efficient ram-air system design, I got an extra inch of manifold pressure. I had to go to about 9,500 feet in order to run WOT and get 75%. This is a good reason to have a MAP gauge on a FP installation.

For break-in, though, you want to run a bit harder so 7500 feet is not a problem if you can keep the prop rpm within limits.

Here's an excerpt from my post the percent horsepower thread:

=================================================
Lycoming O-320 B and D series Horsepower Formula (Rich Mixture)

h=(H-((R-r)*(5.58-0.125*(M-m))/100 + 7.35*(M-m)) + 2.0*pa/1000)*sqrt((519-3.58*pa/1000)/(460+ta))

h% = h/H*100

where

Constants:

H= maximum sea level horsepower at maximum manifold pressure (from manufacturer’s data)
R= maximum sea level RPM at maximum manifold pressure (from manufacturer’s data)
M= maximum sea level manifold pressure at rated RPM (from manufacturer’s data)

For Lycoming O-320 -B and -D series:

H= 160
R= 2600 (Sensenich prop limit)
M= 28.6

Variables (inputs)

r= actual RPM
m= actual manifold pressure
pa= actual pressure altitude (altimeter set to 29.92 inHg)
ta = actual air inlet temperature at pressure altitude

Outputs

h = calculated horsepower
h%= calculated percent horsepower

============================

V

[az_gila]

Thanks Vern... that is good to know on the altitudes.

Did you fly without pants/fairings (wheel pants, that is......) and see the reduced HP due to increased drag?

gil A

I will have MP and even % HP on my Dynon...

Originally Posted by vlittle

You may find that this does not hold true in an RV. Due to the efficient ram-air system design, I got an extra inch of manifold pressure. I had to go to about 9,500 feet in order to run WOT and get 75%. This is a good reason to have a MAP gauge on a FP installation.

For break-in, though, you want to run a bit harder so 7500 feet is not a problem if you can keep the prop rpm within limits.

Here's an excerpt from my post the percent horsepower thread:

=================================================
Lycoming O-320 B and D series Horsepower Formula (Rich Mixture)

h=(H-((R-r)*(5.58-0.125*(M-m))/100 + 7.35*(M-m)) + 2.0*pa/1000)*sqrt((519-3.58*pa/1000)/(460+ta))

h% = h/H*100

where

Constants:

H= maximum sea level horsepower at maximum manifold pressure (from manufacturer?s data)
R= maximum sea level RPM at maximum manifold pressure (from manufacturer?s data)
M= maximum sea level manifold pressure at rated RPM (from manufacturer?s data)

For Lycoming O-320 -B and -D series:

H= 160
R= 2600 (Sensenich prop limit)
M= 28.6

Variables (inputs)

r= actual RPM
m= actual manifold pressure
pa= actual pressure altitude (altimeter set to 29.92 inHg)
ta = actual air inlet temperature at pressure altitude

Outputs

h = calculated horsepower
h%= calculated percent horsepower

============================

V

[vlittle]

Originally Posted by az_gila

Thanks Vern... that is good to know on the altitudes.

Did you fly without pants/fairings (wheel pants, that is......) and see the reduced HP due to increased drag?

gil A

I will have MP and even % HP on my Dynon...

For my first few flights I did not have pants or fairings. That was more to make sure that the brakes and tires worked ok.

Now, Van's REQUIRES that the nose wheel pants be installed at all times (part of their SB).

[n5lp]

Originally Posted by gmcjetpilot

...See the two pwr charts below. The first chart formate is more for fixed prop. The the second chart is more for c/s pitch prop...

The second chart may have some uses for a constant speed prop setup but it is more for a fixed pitch prop. I am pretty sure of that because I am the one who made it, except I didn't black out my N number. I tailored it exactly for my needs with an O-360 and fixed pitch Sensenich 83" prop. The chart has two sides and together they lean much more toward the higher RPMs more likely to be run by fixed pitch folks.

[Bevan]

[QUOTE
Now, Van's REQUIRES that the nose wheel pants be installed at all times (part of their SB).[/quote]

Why?

bevan