Simviation Forums

Just a quick question Chums......

Technical query: (Flight Sim 2004).

On my Engine Tachometer(s) for my Lycoming and Continental piston engines, there is a red line after the green cruise area at 2,400 RPM, and before the max revs limit 2,500/2,700 RPM.

Does it indicate a particular critical engine speed which suffers/may suffer from dangerous vibration, and the Pilot must avoid dwelling in it for extended periods?

Note the max revs can be maintained safely for take-off climb, and fast cruise, (at the expense of fuel consumption).

F---G-BPLF... 8-)...!

I would imagine that you're asking this in terms of the real world ? (not sim edition sepcific)..

From my experience flying 4 Cyl

Well, I don't know about props, but some jet engines are designed to shear off if they come under too much pressure.

In the event of excessive loads on the Boeing 747 engines or engine pylons, the fuse pins holding the engine nacelle to the wing are designed to fracture cleanly, allowing the engine to fall away from the aircraft without damaging the wing or wing fuel tank.

The "red line" is also an indicator that at those rpms, you're pushing your luck in terms of general wear and tear-  run at redline long enough and watch the oil temp go up and the pressure down, especially in an old rental.  ;)

The bearings, etc are only designed to run happily up to a given rpm, after all.


But as Brett points out, your typical bug-smasher would have to be flown very, um, creatively to exceed redline for very long.  The most likely scenario would definitely be a  long descent with too much power.

A pretty foolish decision, all around- power is not really going to make you come down any faster, at least not in something with the hp-to-weight ratio of a 172.

Could this be what you're talking about?



If so, then you are correct. Some engine/propeller or engine/airframe combinations have an issue with resonance in certain RPM ranges below redline. The type of tach pictured above is a bit confusing, most of the aircraft I've seen use a yellow arc for that region.

I found a good picture of a Grumman Tiger panel, which has the more typical yellow-arc on the tach:

http://www.n28819.com/full/panel.jpg

I found a good picture of a Grumman Tiger panel, which has the more typical yellow-arc on the tach:

http://www.n28819.com/full/panel.jpg

That's the sort of thing I was referring to...



I have an idea that the peak revs on the R-R Continental O-240 Engine fitted to the Cessna 150 fixed prop Aerobat, is around 2,750 RPM, which can be achieved in racing conditions, (and certain tail-wind conditions), developing maximum Horse Power.

The red line on this instrument is at located 2,400 RPM which made me wonder if that was the; ""Do not linger in this area", engine revs......!

Very often "Throttle/Pedal to the Metal" is used to obtain maximum Revs/HP, and I have a feeling that that often exceeds the red line on the Tacho.

Most of the time the maximum revs at full throttle, (and therefore Horse-Power), are limited by the effort required to pull the aircraft through the air, but once that effort is reduced, (in the cruise), the engine revs increase automatically at a set Throttle.....
...and in the case I mentioned, easily exceed the "red warning line" on the Tacho.

...but there again, I could be wrong, although the Lycoming and Continental motors can be run flat-out, maybe its not recommended for extended periods, and under normal conditions one should not exceed the red line on the Tacho for that particular aircraft!

F...G-BPLF... 8-)...!

P.S Listening to the engines on the Aircraft competing in our local Air Races, I'm sure they are exceeding the "Thin Red Line" most of the time!... ... ... ...!

I think this answers your question Paul. It confirms your vibration theory & also what Splinter said. http://www.easa.europa.eu/ws_prod/c/doc/Safety_Info_Reports/SIB%202008-38%20Propeller%20RPM%20Resctrictions%20&%20Placards.pdf

[quote]Propeller manufacturers determine a propeller

[quote]I think this answers your question Paul. It confirms your vibration theory & also what Splinter said. http://www.easa.europa.eu/ws_prod/c/doc/Safety_Info_Reports/SIB%202008-38%20Propeller%20RPM%20Resctrictions%20&%20Placards.pdf

[quote]Propeller manufacturers determine a propeller

I don't know if it's related but I know of a couple of recent incidents of propeller failure. This was with wooden fixed-pitch props which can delaminate or split under certain conditions..

The Fairey Reed metal fixed-pitch prop fitted to some light aircraft is also susceptible to failure in flight. I suspect this incident was caused by cracks in the hub. He was lucky to get away with it. http://www.leamingtoncourier.co.uk/news/Plane-lands-without-propeller.1039362.jp

I thougth that might be the case.. especially with bigger, more exotic engines, propellers... But rest assured.. the red-line on you little Cessna tachometer is a 'Do Not Exceed' line. I've never hear of a resonant or harmonic problem at below-maximum RPM on any of the common, GA light singles.

If one ever did rear its head..  you can be sure that the crank-shaft and/or propeller would be modified/balanced to eliminate it.

I don't know if it's related but I know of a couple of recent incidents of propeller failure. This was with wooden fixed-pitch props which can delaminate or split under certain conditions..

The Fairey Reed metal fixed-pitch prop fitted to some light aircraft is also susceptible to failure in flight. I suspect this incident was caused by cracks in the hub. He was lucky to get away with it. http://www.leamingtoncourier.co.uk/news/Plane-lands-without-propeller.1039362.jp

Something like this happened to the president of the club I fly out of, in Ohio. He (25,000+ hour mentor) was on final, at night, in our club's Liberty XL2 and lost the prop about 5 miles from the runway..

http://www.simviation.com/cgi-bin/yabb2 ... 314111/2#2

I don't know if it's related but I know of a couple of recent incidents of propeller failure. This was with wooden fixed-pitch props which can delaminate or split under certain conditions..

The Fairey Reed metal fixed-pitch prop fitted to some light aircraft is also susceptible to failure in flight. I suspect this incident was caused by cracks in the hub. He was lucky to get away with it. http://www.leamingtoncourier.co.uk/news/Plane-lands-without-propeller.1039362.jp

Something like this happened to the president of the club I fly out of, in Ohio. He (25,000+ hour mentor) was on final, at night, in our club's Liberty XL2 and lost the prop about 5 miles from the runway..

http://www.simviation.com/cgi-bin/yabb2 ... 314111/2#2

I remember seeing that when you posted it. Also the previous prop-strike. One has to wonder if the two incidents are related. The Liberty XL2 is basically the US version of the Europa XS which is very popular among private owners in this country. According to the manufacturer's website the XL2 is fitted with an MT two-blade fixed-pitch prop which is of composite construction with no RPM restrictions. http://www.mt-propeller.com/en/entw/fixed.htm

The Europa XS is powered by a Rotax engine & usually fitted with a composite 3-bladed prop.

It was a neat little airplane..  my only gripe about it was the finger brakes...

The Liberty XL2 has a more convential aviation power-plant .. very similar in size/displacement/HP to what's put in C152s and Piper Tomahawks. I don't have the exact specs handy, but 115HP sounds right.

The neat thing about it, was that it was so light and 'clean'..  That 115HP would push it along at 130KIAS at less than 6GPH  :)

...as opposed to a 160HP C712 ... 110KIAS 9GPH ..

I remember your objection to the finger brakes. I suppose it depends what you're used to. I've noticed several different types of modern aircraft fitted with this feature. Of course, the Europa Classic is a monowheel which doesn't use brakes for ground handling. It's also a homebuilt with a lighter construction. (The standard Tri-gear kit features toe operated brakes. Finger brakes cost an extra