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I should have added that the short & medium short manifolds were tested
using the 2.85 : 1 gear drive and rpm range was 1000 rpm higher than when I used
the 2.176 : 1 drive. Results would probably not be quite as good with the
lower rpm range.
Keep in mind that the long vs short runner issue has very
little to do with performance in cruise, it just doesn't mater that much
there. Especially if you are not at WOT in cruise (most rotaries are
throttled back here) Climb and top speed will be most affected by
intake tuning.
To put some numbers to this, I made 160 HP at 6000 with a virtually untuned
system using carbs. With pretty good tuned EFI I made 180 HP at 6250 (same
prop, so more rpm made part of the increase). These figures on 2.176 : 1
gear drive.
George Graham, one of the early aviation rotary adopters, isn't on the list
so though I'd pass along his latest. After 200+ hours, his second Mazda
manual transmission (2nd gear) PSRU stripped it's gears and he dead sticked
safely on a road about 10 miles from Leesburg Fl yesterday. No damage to
him or plane but he doesn't want to take a chance on the transmission
again. I'll be building him an RD-1A. He glided about 20 miles
from an altitude of only 5000 ft with the prop
freewheeling! I've heard several times that a freewheeling
prop (no engine drag on it) would generate lots of drag. Another
sacred cow shot down : )
Tracy
Tracy
Crook wrote:
Should be an interesting experiment Paul, can't wait to hear
results.
I tried a very short and now a medium-short manifold and find
that it works well IF it is very "clean" (proper diameter runners, no change
in cross sectional area, well matched to ports, etc, etc) The very
short runners gave up some power at climb rpm (FP prop) but did OK at cruise
& top end. The Medium-short version works about as well as my long
(so-so clean) manifold (~17" runners) and real good at top end.
FWIW, my guess about your dripping throttle body is condensation on the
runners & throttle body walls. Gravity does the rest.
Agravating the problem is the "cool side injectors". Someone called
this arrangement the "Holy Grail" of intake design. I'd call it
the "Sacred Cow".
Tracy ( eat sacred cow for lunch).
-----
Original Message -----
Subject:
[FlyRotary] Re: Short intake manifolds
Hi, Tom....I saved a few posts that addressed the problem
you were referring
to. The folks at Mistral also went into a lot of
detail about it. Problem
is, they were talking about the LONG intake
runners, and having the
injectors at the far end, away from the
engine. Power pulses problems,
incorrect fuel mixtures,
etc.
I am not going to try the short manifold,
(since I received one with
the bolt-on fuel/ignition package that I
purchased from Atkins Rotary), and
see how it works. I understand Dave
Atkins has been using his for quite some
time, with a lot of
cross-country trips under his belt.
Also, hearing
Al's comments helps as well. What the heck....I built an
experimental, so I guess it's expected I have the need to experiment a
little. Thanks for the input, Tom. Paul Conner
-----
Original Message -----
From: "Tom" <tomtugan@yahoo.com>
To: "Rotary
motors in aircraft" <flyrotary@lancaironline.net>
Sent:
Tuesday, December 14, 2004 11:36 PM
Subject: [FlyRotary] Re: Short
intake manifolds
> Paul,
> There was a discussion here
a few weeks ago regarding 'back pulses' in the
> intake
manifold. Sorry, that may not be the correct term. IIRC,
seems a
> short manifold may have issues, one being fuel
droplets being expelled
> the
> opposite
direction. Let me suggest the potential for it to pool in
your
> 'outer chamber' and another potential for a backfire to
ignite it.
> Hopefully
> that is blatantly wrong so those who
know will step in and straighten it
> out.
> You can tell by
my terminology that I don't talk motors much. Also, seems
>
I
> read many years ago that the one reason aircraft carburetors are
hung
> below the
> motor is so any fuel remnants would fall
out and evaporate and not pool,
> lessening chances that a backfire
would have something to ignite. This,
> just
> idle
chat.
>
> Tom
>
>
> --- Paul <sqpilot@bellsouth.net>
wrote:
>> My question is....With the
>> short
manifold putting the TWM throttlebody over the top of the exhaust,
>> has
>> Dave had any problems with fuel dripping out
of the throttlebody after
>> engine shutdown? Also, did he
put any kind of heat barrier between the
>> exhaust manifold and
the throttlebody?
>
>
>
>
__________________________________
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>
>>>
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>>>
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>
>> Homepage: http://www.flyrotary.com/
>>
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