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Hi Mark,
I know you are saying that you are not
overly concerned with BSFC, but what you’ve described is exactly that.
If the IO-540 and the rotary both have similar
BSFC, then equal fuel consumption will net equal power.
That is to say, if you are burning 10.5
GPH @ 20” MP, you are making about 123 HP figuring .51 lbs per hp/hr.
BSFC
If the IO-540 is making only 123 HP and its
BSFC is also .51, then it too will burn only 10.5 GPH
If your BSFC is as good as .49 lbs per
hp/hr then 10.5 GPH would yield a little over 128 HP.
128 HP with the IO-540 with a BSFC of only
.51 would net 10.88 GPH.
The difference between mogas and 100LL is
where the real savings might be.
Pat
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
On Behalf Of Mark Steitle
Sent: Tuesday, March 03, 2009 5:24
AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Questions
on buying a rotary plane
I'll throw my 2 cents worth in here. Regardinging fuel burn, I'm
not overly concerned with bsfc, although its not that bad if you're running
EFI. What we're really interested in is cost per mile. I have
burned nothing but mogas in my 3-rotor Lancair. The last time I purchased
fuel, it was $1.65/gallon. My N/A 3-rotor burns between 10 and
11 gph at around 20" MAP. So, it will cost me somewhere around
$16.50 - $18.15/hr to fly. Other Lancair ES's are running IO-540's,
or some derivative of the "540". From what I hear, they burn
between 12 - 15 gph. With the cost of 100LL running around $4/gallon,
that would cost between $48 - $60/hr in fuel. So, figuring
cost per mile, I don't see how a Lycoming could come close to matching a
rotary. The fuel savings alone will more than cover the cost of an
overhaul.
And hope the Lycoming doesn't burn a valve, or any number of other
common ailments which can take a serious bite out of your
checkbook. Most of the things that break on a piston engine aren't
even present on the rotary. If it ain't there, it can't break.
So, would I use a rotary if I were to do it over, yes, absolutely!
On Mon, Mar 2, 2009 at 11:31 PM, William Wilson <fluffysheap@gmail.com> wrote:
I have not found an
accomodating A&P but I attribute that to the fact that I have not looked
yet. Given that I live in Seattle
I am pretty sure I can find one. Seattle
is crawling (fluttering?) with homebuilt planes. If anyone has
suggestions, I am listening, but I had not started searching yet.
Plan is not to take apart a perfectly good flying plane to change the engine,
but ideally to get one with a rotary in it already, or replace only at overhaul
time. In each case I save as much on the cheaper engine as I would lose
on resale value... and if the plane has the rotary in it to start with, I get
to pay the lower price up front too, which makes price difference just plain
better.
For efficiency what I said was that homebuilt planes are more efficient than
factory built, not that rotary are more efficient than Lycoming, though in that
case it should be quite close. Bad fuel economy of rotary engine is
overstated, economy is comparatively bad at low power & RPM but at high
power it is not bad at all. As long as you are not turbocharged, you can
run much leaner than a piston engine, making up for less efficient combustion
chamber shape. Rotary BSFC in the lab has gone as low as .375 (for
renesis), and .44-.46 measured in real world racing applications even with
traditional type engine. So I think I would not see a significant
difference in fuel economy between rotary and piston. Weight & drag
of the plane it is in will matter more.
In any case all advice is welcome, even dissenting opinions ;)
I highly recommend you check around to make sure you
can find an A&P who will do a condition inspection with the rotary engine
installed BEFORE you commit. Many A&Ps I've talked to dont want anything to
do with Experimentals let alone an engine that looks nothing like what they are
used to. There's simply too much potential liability (real or perceived) to go
out on a limb like that. The A&P who used to do the condition inspection on
the RV-6A I used to own (Lycoming powered) was willing to do it because the RV
structure is similar to typical spam cans. He wont have anything to do with wet
layup homebuilts (EZs, Cozys, etc...). He doesnt even like doing annuals on
Diamond aircraft with the Rotax 912/914 and they are certified.
If you buy a flying homebuilt that is Lyc or
Continental powered, before you convert it to rotary power seriously think
about what you are doing to the resale value - if you could ever sell it that
is. My guess is that you'll give up at least $10,000 in resale value, maybe
much more. No big deal if you plan on keeping it for life.
I dont know where you got the idea that rotaries are
more fuel efficient. Lycosaurs/Continentals typically have BSFCs in the low
.40s. The commonly accepted number for a rotary is about .50. Some here seem to
do better, others worse. With a grand total of 2 hours on my rotary I cant say
what my experience will be but hope its close to the Lyc I used to fly.
Finally dont underestimate the effort required to make
the change. I started building my RV-4 in late 1995. The airframe was
essentially done in 2000. My first flight was last month. Granted I took longer
than many and much of the trouble came from my desire to eliminate the cowl
cheeks on an already cramped engine compartment. But thats eight years of
tinkering to get the engine installed and running to the point where I had
enough confidence in it to fly it.
Not trying to discourage you, but go into this with
eyes wide open.
----- Original Message -----
Sent: Sunday, March 01,
2009 7:46 PM
Subject: [Norton AntiSpam]
[FlyRotary] Re: Questions on buying a rotary plane
This is great news.
Thanks Charlie and Bob :)
On Sun, Mar 1, 2009 at 7:34 PM, Charlie England <ceengland@bellsouth.net>
wrote:
William Wilson wrote:
I am in the market for a plane and would prefer a rotary-powered, as I
have lots of experience working with rotary engines. As a bonus,
homebuilt planes all seem to get about twice as much fuel economy as factory
built planes. So that is nice too. I know there are a few rotary
powered planes available for sale, but not too many.
I have neither the time nor desire to build my own plane, so my question is
more about maintenance and inspections. I'm not an official A&P and I
don't know if I will be able to find an A&P to work on a home built plane
with a car engine in it! I am happy to do engine maintenance, but am not
entirely clear on the legality of it, since I would not be the original
builder.
Similarly when it is eventually time for an engine rebuild, would I be able to
remove the engine, take it down to Atkins (who are not far from me) and have
them rebuild it, or rebuild it myself, and then reinstall it, and find an
A&P to just sign off on the work?
Plan B is to buy whatever plane even if it has a Lycosaurus, but when time for
overhaul comes, get rid of the Lycoming and replace it with a rotary.
Thought in this case is to get the rotary tuned, a little broken in and
running on a stand in the hangar in advance, so that when the time comes to do
the swap it can be done with a minimum of downtime. (I know it cannot
really be tuned for altitude in this way but it is better than nothing!).
But again, the fact that I would not be the original builder makes me
worry about legalities. I have heard that this has been done so question
is more about the how.
I do not really understand all the law involved and hopefully somebody here can
help. Thanks!
I can't speak with authority, but I can speak from experience.
Experimental homebuilts can be maintained or modified by anyone. No FAA
blessings required. Annual condition inspections must be performed by either
the holder of the 'repairman's certificate' (only available to the builder of
record) or by the holder of an A&P ticket (no IA required).
Once the airworthiness certificate is awarded, *anyone* can do any maintenance,
repairs, modifications etc desired. The post-modification requirements vary
somewhat from plane to plane depending on when the a/w was issued, but in
general terms, you notify the FAA in writing that major mods were made, ask for
a defined test area, make a log entry detailing the return to 'phase one'
testing, fly test flights for (typically) 5 hours, then make another log entry
saying that the plane has been tested with the mods & is being returned to
'phase two' (normal operational) status.
'Major modification' isn't clearly defined, but if you have to ask, it's major.
:-)
The availability of an A&P to sign off condition inspections is all over
the map (literally). It's never been a problem for me, but in some parts of the
country people can't find an A&P who will sign off *any* homebuilt,
no matter what engine. If you have that problem, get to know the guys who
sign off the crop dusters in your area.
Hope that helps....
Charlie
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