Happy Holidays,
Just to throw my hat in...As I have too much time on my hands today...
Propeller charts, ram intake effects, cowl mods, prop diameters, etc.
all affect our aircraft's performance data.
I agree with all of you that the Rotax Engine Manual is lacking to non
existent for use in accurate data measurement for cruise. God only
knows what the propeller efficiency is. And since we design off the
engine charts, which in no way reflect actual engine installation
effects, we are best equipped, as experimenters, to follow the age old
technique of recorded pilot data from a specific test aircraft. Namely,
Yours.
When I get a chance to flight test an aircraft for a week or so, I log
as much data as the owner lets me. Unfortunately I don't get to do this
very often as it is quite time consuming and I leave it to the customer
to consider how much he wants me to fly when he has a perfectly safe
airplane. Frankly, most of you want to go fly, and all this data seems
dumb. If you are happy cruising at 5500-6500 ft, 5000 rpm, 26" MP, and
4.5 gph, going as fast as the ground speed says, don't read on. I have
a "simple chart" done up in my flight test book to jog my memory so I
don't do something dumb like just fly around during the customers 40
hour fly off. After all, test flying is supposed to be work.
I've read your posts and you guys are somewhat correct, but talking a
different language. What is needed, in my opinion, is a chart/table,
derived from data that is painfully boring to fill out and takes about 5
test flights. This is the data that then translates to Horsepower vs
Speed charts to be translated into best cruise and climb performance
suited to your aircraft. I've partially tested RV's (4 and 6) and fully
tested a Zenith (Subaru E85) extensively as well as two Europa's, one a
with a warp drive fixed prop the other with an Airmaster using
variations of these data charts, and you can tweak your plane to get the
most performance out of it by proper testing. It will also make the
Rotax engine power curves start to make sense.
Here's the gist:
Cruise data chart for Aircraft make model, engine type, prop type at a
specified gross weight:
Density Altitude, RPM, MP, IAS, TAS, Fuel Flow, additional data (see
note)
Sea Level
2500
5000
7500
10,000
Note: Log for your use items such as; Oil T/P, Cyl. Head, Coolant , EGT
etc. so you can track any future trends.
But wait, there's more. Why climb up to cruise and not record climb
also.
Climb Data for Aircraft make model, engine type, prop type, Gross
Weight:
Climb Speed Start Climb, End Climb Duration, Power Setting RPM, MP
Start Temp, PA, DA Fuel Flow (See Note)
75 knots 100 1000 58sec 5700 38"
15C,100,110 7.5
85Knots 100 1000 65 5700 38.3
15C, 100,110 7.5
etc.
2500 2500 5000 200sec 5500 35
11C 2500, 2750 7.3
Note: Great time to log cyl head and coolant readings.
I try to climb at 75, 85. 95, and 105 Knots just to see the difference
in climb and rates of cooling. Why these numbers? They are easy to see
and chart.
But wait there's even more, so go back to chart one and do the cruise
---From different power settings. Get close to the Rotax/Jabiru numbers
such as 55%, 65%, 75%, and max continuous power settings. The data for
the 912/912S/Jabiru will vary due to intake variations, and be pretty
consistent for the 914.
Don't forget it is all done at a specific gross weight so in-flight
refuel to get the data as accurate as possible or do it over 5 flights.
Record the data as Dykins did in the Europa books (good reading by the
way) and then through some analysis, you will have useable data for
creating charts which can be condensed down to be used in your Pilot
Handbook as an attached performance page.
I copied the idea for the performance info from Dykins, Chris Heinz,
EAA, and anyone else who made a performance data sheet/manual or
checklist and of course my "Airplane Aerodynamics" textbook by Dommasch,
Sherby and Connolly. The data I have acquired so far will be to put
together in the future for proper HP/Speed charts for the Europa and for
my Classic Europa. The data points give me the ability to construct
charts for climb, cruise planning and emergency procedures, such as max
range, divert and glide. Each of our planes is different, so our data
will be slightly different, so don't expect one plane's data to exactly
reflect another's, unless they were built on an assembly line.
I am attaching two excel files, one of my old blank performance data
checklists and the other, my personal Europa checklist (they are old
versions from a memory stick found at home, but good enough to show the
performance page I made in my checklist). It is this type data analysis
that prevents pilots from over-boosting their 912/914/Airmaster
combination and dumping gas out of the tailpipe because they blindly set
a power setting and never plotted the A/S vs Power curves to get max
range computations... Guys always want more gas. Slowing down a few
knots can get you 100 miles farther per leg or even more if you slow
down to around 90-95 KIAS. You can even plot accurate charts for
headwind / tailwind effects. Another way is to just figure your miles
per gallon to get your best cruising power settings for max range. I
see many folks getting 20 mpg instead of 28 mpg. It's just data, and
you have the power to analyze it to get your desired information.
The attached checklists were made for my use and are not a replacement
for factory manuals or formal flight test manuals. Their use is for
late in the test flight phase when all the bugs have been worked out.
Data accumulation requires extensive preflight ground run throughs
a.k.a. chair flying, and thorough preflight planning so as not to get
your head down, when you should be flying. Data doesn't kill you, it's
the ground and other airplanes. My checklists are from my personal
random thoughts and experiences (scary). Use the company pilot handbook
as it is the best policy, then add the performance data you acquired to
it just as you did for your weight and balance.
So... If you are looking for something to do, go out and get some
formalized data. After landing, analyze the data, plan how to get more
data when flying to the next fly-in breakfast and then over time, adjust
your normal climb/cruise operations based on the data to suit your
flying needs. If you feel like sharing, put it on the web. If you
don't know what to do with the data, send it to me and I will try break
it down for you.
Enjoy the holidays,
PS, I still haven't shut down a perfectly good engine to get glide
data...Too many dependents or I'm getting too old for the adventure. Go
figure.
Bud
Custom Flight Creations
----- Original Message -----
From: Remi Guerner<mailto:air.guerner@orange.fr>
To: Europa-List Digest Server<mailto:europa-list@matronics.com>
Sent: Friday, December 26, 2008 3:52 PM
Subject: Europa-List: power settings
Ira,
I disagree with your assertion that altitude is not needed in your
table. A given setting, i.e. 5000 rpm and 22" will give you more power
at 8000 ft than at 1000 ft. because the temperature being colder at 8000
ft, the density of the air at a given manifold pressure is higher.
As an exemple the following power settings are extracted from the
Cirrus SR20 Flight Manual:
2000 ft, 2500 rpm, 23.8"
4000 ft, 2500 rpm, 22.3"
6000 ft, 2500 rpm, 21.8"
8000 ft, 2500 rpm, 21.2"
All these settings produce the same 65% power on the Continental
engine.
So your table as it is today is valid at low altitude only. To be
exhaustive, it would be necessary to compute one table for each density
altitude. If you are prepared to do that work, I am interrested in
getting the results.
Best regards
Remi
>>>>>>>>>>>>The table is engine performance with a constant speed
(AirMaster) prop.
All certificated manufacturers provide a table like mine which shows
the relationship between throttle, selected RPM, and power output.
Rotax does not. The graph is useful to select which combination
works best under specific circumstance, particularly when fuel flow
and TAS are added to the table. My data collection is unfinished for
the
bigger version of the table. In this version of just engine, not
airframe
performance, density altitude is unneeded. No matter what density
altitude, throttle sets manifold pressure, and obviously without a
turbocharger/supercharger, the maximum MP declines with altitude.
The desired rpm is set on your prop control. Green is the usual
operating range, the other colors are not important here.
Example: 75% power is obtained at 27.5" and 4800 rpm or
26" and 5000 or 24" and 5500 rpm. The "standard" cruise setting
on Continental or Lycomings of 25 squared (or 2500 rpm @ prop at
25" MP) doesn't work out for Rotax because 2500 rpm would be over
6000 engine rpm, but by extrapolation would be over 80% power.
Or, if you set your prop to 5000 rpm for cruise, then you get 75% at
26" (only possible up 4000' DA), and 65% at 23" MAP.
While there are small inaccuracies due my simple model of the Otto
cycle, so far as I know, this table I created is the only published
attempt to provide guidance for 912s drivers with a constant speed
prop<<<<<<<<<<<<
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on>
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avigator?Europa-List>
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