Used Avionics

John Harper wrote:
: I love my turbo. It is of course a waste of time/money/etc at lowish
: altitudes, say below 8000'. But the freedom to climb at keep on climbing,
: not to mention high-performance take-off without having to worry
: about density altitude (well, not so much anyway) is enormous.
: I can climb to FL200 at a steady 500 fpm - the plane would probably
: go quite a lot higher although it is not certificated to do so and I haven't
: tried it. On long journeys going up high is a real bonus, especially over
: unfriendly terrain.

A non-turbo Comanche-260 will pretty much hold 500 fpm up to
higher than you can fly without oxygen. Unless you go full-tilt into high
altitude with O2, etc, a Comanche-260 seems to outperform a turbo Arrow in
just about every respect. It also doesn't have the drawback of the
extremely abused TIO-360 Continental in the mid 70's Turbo Arrow. My
mechanic just bought one of those, and all I can say is that he's
comfortable with the twitchiness of that engine. Something to be said for
simplicity... either normally-aspirated, big-bore, or at most a
turbo-normalized engine.

YMMV...

-Cory


--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

wrote in
:

A non-turbo Comanche-260 will pretty much hold 500 fpm up to
higher than you can fly without oxygen. Unless you go full-tilt into
high altitude with O2, etc, a Comanche-260 seems to outperform a turbo
Arrow in just about every respect. It also doesn't have the drawback
of the extremely abused TIO-360 Continental in the mid 70's Turbo
Arrow. My mechanic just bought one of those, and all I can say is
that he's comfortable with the twitchiness of that engine. Something
to be said for simplicity... either normally-aspirated, big-bore, or
at most a turbo-normalized engine.

A friend of mine used to have a partnership in a Comanche 260. And
yes... I fly a turbo-Arrow III. One a number of trips we would wind up
chasing each other (both coming back from the same meeting, but couldn't
plane-pool up there; or I would take him up to pick up his plane when
another partner had left it somewhere due to weather or repairs). It
was always a fascinating exercise in flight planning to see which plane
would chase which.

The Comanche clearly was faster at low altitude. Down around 8K or less
the turbo Arrow flies pretty much like a straight Arrow - figure 145
knots or so. And initially the Comanche has more "get up and go" climb
performance from sea level.

OTOH, at high altitudes (low flight levels) my Arrow will true out
around 175 knots (it has the Merlyn wastegate) and burn a LOT less fuel
(GAMIjectors). Also, at those high altitudes, my ability to get more
direct routing is a lot better. [BTW, both the GAMI and the Merlyn
greatly reduce both the "abuse" and the "twichiness" of the turbo
Arrow.]

Objectively, it was about half and half who one. Long trips,
particularly with a tailwind, and I would virtually always win. Short
hops of 150 nm or so and the Comanche would always win. Fun...

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

James M. Knox wrote:
: The Comanche clearly was faster at low altitude. Down around 8K or less
: the turbo Arrow flies pretty much like a straight Arrow - figure 145
: knots or so. And initially the Comanche has more "get up and go" climb
: performance from sea level.

: OTOH, at high altitudes (low flight levels) my Arrow will true out
: around 175 knots (it has the Merlyn wastegate) and burn a LOT less fuel
: (GAMIjectors). Also, at those high altitudes, my ability to get more
: direct routing is a lot better. [BTW, both the GAMI and the Merlyn
: greatly reduce both the "abuse" and the "twichiness" of the turbo
: Arrow.]

: Objectively, it was about half and half who one. Long trips,
: particularly with a tailwind, and I would virtually always win. Short
: hops of 150 nm or so and the Comanche would always win. Fun...
:

Yeah, that's about the way I figure it. Having never flown a
turbo'd plane, I haven't gotten used to the notion of much above 12kft.
Flying east is great, but my plane's slow enough that the speed gain from
altitude doesn't come close to making up for the headwind hit. Flying
west I'll usually cruise 2000' AGL and argue with the bumps and slightly
faster groundspeed.

Question though... my mechanic recently did the the wastegate
upgrade, but it seems like it didn't do a whole lot for it. Stock setup
was atrocious (make boost all the time and regulate MP with throttle
only). It was almost rotation speed before he was able to look up from
the MP and tach on takeoff, because it wanted to overboost so much. Even
with the new one, it seems flakey and prone to overboost. True? Any way
to add an intercooler to the setup too?

-Cory

--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

wrote in
:

Flying east is great, but my plane's slow enough that the
speed gain from altitude doesn't come close to making up for the
headwind hit. Flying west I'll usually cruise 2000' AGL and argue
with the bumps and slightly faster groundspeed.

The higher you go, the more likely the winds are out of the west - as
you say. In the summer they may "drift around" a bit, but in the winter
you can almost count on it. On shorter flights, or against the
headwinds, I will usually try to stay fairly low - probably below 10K
(although sometimes in the summer I *have* decided that 1+30 in cool
smooth air was better than 1+00 in thermals and with the OAT reading
over 100 F.

Longer flights will *usually* make it worth it to climb into higher
altitudes. I'll usually break even, even with a headwind, and get
better conditions, less traffic, and better routing if IFR.

WITH the wind... well, coming back from El Paso one winter day after
dropping off an Angel Flight patient, I was throttled back to 55% in the
low flight levels, sipping about 8.5 gph, and watching the groundspeed
vary between 250 and 275 knots!!!! [Of course, a *significant* part of
that was tailwind! G]

Question though... my mechanic recently did the the wastegate
upgrade, but it seems like it didn't do a whole lot for it. Stock
setup was atrocious (make boost all the time and regulate MP with
throttle only). It was almost rotation speed before he was able to
look up from the MP and tach on takeoff, because it wanted to
overboost so much. Even with the new one, it seems flakey and prone
to overboost. True? Any way to add an intercooler to the setup too?

The stock wastegate setup used by Piper (and by Mooney) on many models
is 14 karat CHEAP! It's a bolt screwed into a hole in a pipe, period.
No matter how you set it up, at sea level you are providing boost (and
heat) when you least need it. And at higher altitudes you are dumping
half your boost overboard. About the ONLY thing that could be said good
for it is that it's cheap, and well, it can hardly break.

The other downside, as you noticed, is that it makes bootstrapping a
significant issue in setting the throttle. Add throttle and the MP will
continue to rise (substantially) after you stop moving the throttle.
Reduce the throttle, and you will often find yourself having to add some
back in.

With practice it is not as bad as it sounds. You get used to it... and
throttle movement becomes somewhat automatic -- just the "automatic"
part is in your head rather than in the controls. G Still, it is NOT
really a good thing for a plane on the leaseback or flight training line
- precisely where many of them are used. This is been a major reason
that many turbo Arrows have gotten a bad reputation for short engine
life.

Something like the Merlyn automatic helps a lot. At sea level and
cruise power the wastegate is fully open - you are running essentially
unboosted. Temperatures stay low. Climbing high the wastegate
completely closes and adds almost 6K feet to your critical altitude -
that REALLY helps with the climb. Bootstrapping is still there - but
it's much better. Not nearly as sensitive until you get up into the
flight levels (where, with the wastegate fully closed, you are back to
being the same as before in terms of bootstrapping sensitivity).

There is an aftermarket intercooler mod. I know another pilot here in
Austin that has one on his turbo Arrow and he likes it. I don't have
one on mine, and haven't really ever had significant temperature
problems. There is a "cooling kit" that basically adds some more vents
to the cowling - most have had this added, and it is very recommended.

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------