% hps

[FBCK]

I read a little while back something about calculating the % hp when lean of peak, it was a formula involving fuel flow, engine compression (Mine is a TCM 360lb, in a intercooler 231), I dont know what the compression ratio actual is if some is so good to provide that as well.  Could some provide details on this.

[danb35]

For a turbocharged engine, 13.7 x fuel flow in gph should be close enough--it varies slightly with the compression ratio (which you can find on the type certificate data sheet, or probably in your POH), but if 13.7 isn't the exact multiplier, it's close.

[johnggreen]

Dan's 13.7 multiplier produces a horsepower figure that correlates perfectly with the Lycoming Owners Manual for my Bravo.  The engine manufacturer's manual is probably the most over-looked reference in general aviation.  I think one thing that makes it daunting is that it usually covers all engines of that type.  For instance, mine covers all Lycoming TIO model engines and there are a bunch of them.  First thing you should do is go through the manual and throw out all of the charts and spec pages that don't relate to your engine.  Then, you will be amazed at just how much info is put in there for you.

The original post brings up the issue of LOP for turbos.  Does the engine manufacturer approve of LOP for the 231?  They certainly don't for the Bravo.

JG

[jetdriven]

A 231 can run LOP.  A Bravo, for some reason, it simply won't do it.  Lycoming does not approve LOP operations for any of its engines, although some Continentals such as the Cirrus SR22, ONLY allow LOP for high speed cruise. 

Lycoming needs to admit that the sun comes up in the east, and LOP done right will not simply "burn up" your enigne.

[johnggreen]

Well, I too am of the old school, I suppose.  Until Lycoming says it's OK, I'm certainly not doing it.  I'm not one to get too focused on fuel burn anyway.  It is, after all, a rather small percentage of total operating costs.

I have operated my Bravo long enough to find a sweet spot that wll deliver some fairly impressive mpg numbers.  My main purpose here is not the cost, but range.  I do a lot of flying, in fact, most of it, on trips that are at the limit of my cruising range, especially if I'm headed west.  If I can get to 12 to 17 thousand without too much headwind, I can set in a low power setting that yields 173-183 true (depending on the exact altitude) and burn only 13 gallons.  That gives me over five and one half hours with reserve.

JG