Caution Range on Tachometer

RyanB

RyanB

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Ive seen some Tachometers that have either a red or yellow range on them, usually from around 1800 to 2200 rpm or something close to. Then it has a label stating "avoid continuous operation between..." Etc. why do some rpm gauges have this warning and color range? And why are you not supposed to operate under those power settings?
 
i never knew what this was for, thank you!
 
Wow, I just learned something new as well!

Great post!
 
My Tiger had a yellow caution range that was eliminated if and when a different prop was installed. Since my out-of-limits McCauly is hanging on my living room wall, I think it was a change to Sensenich that got rid of the caution range. But I may be "misremembering".
 
Correct answer given. It's an engine/prop issue. Changing props can fix it, but to me that's not a good reason to change a prop as the RPM range is typically in an area that you don't use anyway.

Now one friend of mine has a BE95 Travel Air with restrictions in a range that goes all the way up to 2350 RPM.

Although not placarded on tachometers, many Continental engines have a SB on them that recommends not operating below 2300 RPM in cruise.
 
My Rotax 912ULS tach has a yellow arc from 5500-5800rpm. That range can be used for a maximum of five minutes, and is not for continuous operation due to engine stress, not harmonics. 5500rpm is max continuous power.

So the effect is the same (don't cruise there), but for a slightly different reason.
 
bullwinkle said:
My Rotax 912ULS tach has a yellow arc from 5500-5800rpm. That range can be used for a maximum of five minutes, and is not for continuous operation due to engine stress, not harmonics. 5500rpm is max continuous power.

So the effect is the same (don't cruise there), but for a slightly different reason.
Click to expand...

Yes, the IO-520-Es in the 310 I fly are the same. 2700-2850 is for 5 minutes.
 
bullwinkle said:
My Rotax 912ULS tach has a yellow arc from 5500-5800rpm. That range can be used for a maximum of five minutes, and is not for continuous operation due to engine stress, not harmonics. 5500rpm is max continuous power.

So the effect is the same (don't cruise there), but for a slightly different reason.
Click to expand...


But the specific range he mentioned is one on many PA-28's, especially the IO-360-C1C -- which is prop harmonic caused. ((spelled out boldly in the AFM))
 
The Pponk conversion for the O470-50 has a yellow band at the top of the arc for maximum 5-minute power.

As others have said, mid arc yellows are due to harmonic/vibration issues.
 
Prop, engine, airframe vibration. Standard on a lot of C-177s.
Was checking out a new pilot in a C-177B and told the pilot, put your feet on the floor, feel the vibration? What are you going to do about it? Got a blank look, hint, look at your tach.

DOH!
 
Jeff Oslick said:
The Pponk conversion for the O470-50 has a yellow band at the top of the arc for maximum 5-minute power.

As others have said, mid arc yellows are due to harmonic/vibration issues.
Click to expand...

T-41B has that too. 2800 RPM for max power, but roll the RPM back when safe to do so, normally about 500ft AGL works. Still full throttle.
 
Ryanb said:
Ive seen some Tachometers that have either a red or yellow range on them, usually from around 1800 to 2200 rpm or something close to. Then it has a label stating "avoid continuous operation between..." Etc. why do some rpm gauges have this warning and color range? And why are you not supposed to operate under those power settings?
Click to expand...

Our Scout has something similar but says "Avoid operation between 1800-2200 during descent" * I assume that means it is OK to operate there in level flight. Which is necessary when formation flying with a J-3.

Brian

*just guessing at the actual RPM range
 
Yep, metal prop stinsons have a harmonic range shown as a yellow arc right below low cruise too. Same deal with some PA24s, and tons of other planes too.

Never seen one with a partial RED arc though
 
Stewartb said:
??? Mine doesn't.
Click to expand...

May be different for the install in a 180 vs. a 182. Ours is yellow arc from either 2500 or 2550 (don't recall) to 2700.

It is horribly loud above 2600, mostly turning fuel into noise, so we pull it back immediately after takeoff unless we really need that little extra bit of performance.
 
I've heard lots of guys say that. A couple have even said that 2600 pulls harder. Once while having my prop balanced the mechanic asked if I knew the prop was spinning up near 2900. Clearly I didn't. When I adjusted it back down (and bought a new tach) the performance was reduced. Not much, but the idea that slower is better is not true in my plane. That was summer but our summers are around 70*. Ask a 185 guy if they'd give up 2850 for 2700 when they have a short strip and tall trees. They'll say hell no. Hmmm.
 
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Stewartb said:
I've heard lots of guys say that. A couple have even said that 2600 pulls harder. Once while having my prop balanced the mechanic asked if I knew the prop was spinning up near 2900. Clearly I didn't. When I adjusted it back down (and bought a new tach) the performance was reduced. Not much, but the idea that slower is better is not true in my plane. That was summer but our summers are around 70*. Ask a 185 guy if they'd give up 2850 for 2700 when they have a short strip and tall trees. They'll say hell no. Hmmm.
Click to expand...

Indeed

I've also heard of some folks putting a clothes pin on the prop control for non super STOL conditions, limiting the revs for alleged increased engine life.
 
FastEddieB said:
My Tiger had a yellow caution range that was eliminated if and when a different prop was installed. Since my out-of-limits McCauly is hanging on my living room wall, I think it was a change to Sensenich that got rid of the caution range. But I may be "misremembering".
Click to expand...
With the Lyc O-360 AVCON conversion on 170/172's there's a yellow (avoid continuous operation) arc that applies to Hartzel constant speed props and another one that applies with Sensenich fixed pitch props. With the McCaully fixed pitch prop the yellow arc is eliminated.
 
I remember that some 3 blade mods on Piper Arrow have a red vibration rpm band to avoid. Always hated how the engine/prop would vibrate pulling the power back in the flare.
 
peerlesscowboy said:
With the Lyc O-360 AVCON conversion on 170/172's there's a yellow (avoid continuous operation) arc that applies to Hartzel constant speed props and another one that applies with Sensenich fixed pitch props. With the McCaully fixed pitch prop the yellow arc is eliminated.
Click to expand...
Curious. I have a 172N with the Air Plains O-360 and a Sensenich prop. No yellow arc.
 
FastEddieB said:
My Tiger had a yellow caution range that was eliminated if and when a different prop was installed. Since my out-of-limits McCauly is hanging on my living room wall, I think it was a change to Sensenich that got rid of the caution range. But I may be "misremembering".
Click to expand...
Nope -- you got it right.
 
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