Need answers to some questions....

[MarineGrunt]

Looking for the answers to a few more random questions to some gouge:

1) Why are some twins NOT equipped with counter-rotation engines (i.e. advantage of conventional twin)? And I heard the answer is not related to cost.

2) What is normal bleed air temperature?

3) Enroute charts: What does the astrisk mean next to a CTAF frequency? (I thought all astrisks mean "part-time," but that doesn't make sesnse for a CTAF to be part time). I might feel stupid to hear this one...

Thanks!

 

[midlifeflyer]

3. Can you give an example? Asterisks next to a frequency usually do mean "part time" and a CTAF could certainly be set up for less than continuous operation.

More generally, though, an asterisk just means "there's more information about this that we can't fit on the chart, so look elsewhere." "Elsewhere" might in a table on the chart or in the AFD.

 

[LR25]

Bleed air temp is 350F on the 747.

 

[KeroseneSnorter]

Looking for the answers to a few more random questions to some gouge:

1) Why are some twins NOT equipped with counter-rotation engines (i.e. advantage of conventional twin)? And I heard the answer is not related to cost.

2) What is normal bleed air temperature?

3) Enroute charts: What does the astrisk mean next to a CTAF frequency? (I thought all astrisks mean "part-time," but that doesn't make sesnse for a CTAF to be part time). I might feel stupid to hear this one...

Thanks!

What the heck, I'll give it a shot.

1. Most twins are NOT counter rotating. I am sure you know the reasons that some are. Why not all? Well my guess would be the fact that you now have two different engines of sorts hanging on the thing for minimal flying quality improvements. Same engine but turns the opposite direction. In my observations the reverse turning engine seems to have many more failures than the "correct" direction. From personal experience with a Dutchess the right engine has about twice the accessory failures than the left one does. Everything from exhaust brackets to alternators. Officially from Lycoming there is no difference, unofficially factory techs have told us that indeed the counter rotating one has more problems. Interesting enough, in the marine world I have seen more faillures on counter rotating outboard engines than I have from normal ones also. In many years of running fishing boats with twin outboards the right one(the normal one) has on average about half the issues of the left one(counter rotating). Other than that? I would say marketing has a lot to do with the counter rotating on the Duchess and Seminole....marketed to have the appearance of being safer...even if from a pilot point of view there is very little difference. (Much like the "T" tail on both, nothing to do with performance and more to do with sales, in fact on most light airplanes the T tail actually hurts performance or flight qualities.)

2. Normal bleed air temp? Differs from airplane to airplane, I guess they are looking for a # that fits "most". Overtemp protections on most of what I have flown start to kick in somewhere around 200 c to 250 c or so.......maybe that is what they are looking for.

 

[MarineGrunt]

3. Can you give an example? Asterisks next to a frequency usually do mean "part time" and a CTAF could certainly be set up for less than continuous operation.

More generally, though, an asterisk just means "there's more information about this that we can't fit on the chart, so look elsewhere." "Elsewhere" might in a table on the chart or in the AFD.

Examples: Grand Forks, Bismarck and Minot ND. They all have *CTAF ---.-. I'm thinking the CTAF is part-time when tower is not open. (I think that was so obvious, I missed it completely)

As for the bleed air question, I haven't been able to find anything in the KC135 manuals, but I'll look again (they have CFM56's). I think I remember something like 680 degrees on the Beechjet. The only other reference I have is the Turbine Pilot's Flight Manual says around 600-800. I know most are different, just trying to get in the ballpark.

thanks for the answers...

 

[ElCid88]

That is interesting about the counter rotating engine having more engine failures. My first engine failure was back in 1992 on a Seneca with a student, and it was the left engine (LIO-360) that failed. In other words, it was the counter rotating engine. I would like to look into this a little more as far as statistics go. Thanks for the info. By-the-way, the airplane flew fine on one engine.

 

[midlifeflyer]

Examples: Grand Forks, Bismarck and Minot ND. They all have *CTAF ---.-. I'm thinking the CTAF is part-time when tower is not open. (I think that was so obvious, I missed it completely)

Actually, I think it's technically telling you that the =Tower= is part-time and that CTAF is on the same frequency when it's not. You were right in your initial impression that designating a self-announce frequency that may or may not have a human being attached to it at any time of day or night makes no sense (nor did my initial answer ). Same result, though.

BTW, when asking chart questions, it's usually a good idea to specify whether you are talking NACO or Jepp. There are a few differences in charting methodology, so it helps. Your asterisk next to the frequency is an example. I don't think NACO even depicts the frequency.

 

[Gorilla]

On the counter-rotating engine thing:

I think the answer as to why the odd engine fails more has to do with the fact that loads of reconditioned parts are installed periodically on these engines. Let's say you have an alternator that spent 1,200 hours turning in direction "A". Bearings, shafts, mounting stresses, numerous other parts/forces are "set" into the part. It gets surplussed into a box, and later installed in a direction "B" engine. With the forces int he opposite direction, the overall effect is failure.

If nothing but factory new parts are ever used on direction "B" engines, I suspect the incidence of failure wouldn't change. It's the used/reconditioned parts that fail.

Try this: Take your Makita 18V drill and run it full blast in the normal direction. Note the pitch which indicates top RPM. Then, reverse it and do the same. The reverse direction will sound different, and be a lower RPM, than the standard direction, even though all we're doing is swapping the polarity of the battery as applied to the motor. The entire system is perhaps bedded in and set to run normal, and when you reverse, it doesn't like it.

It's my theory and I'm sticking to it!

 

[MarineGrunt]

Actually, I think it's technically telling you that the =Tower= is part-time and that CTAF is on the same frequency when it's not.

Yeah, thats what I was getting at, just saying it backwards...