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hgmckay
Joined: 23 May 2006
Posts: 397
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 Posted: Wed Jul 30, 2008 12:34 pm Post subject: Take-off Distance for Allegro 2000 |
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Gentlemen:
I have a rather convoluted question concerning Density Altitude and take off
run for the Allegro 2000. I am well aware of the influence of high altitude
and hot humid days on takeoff run length (i.e. high elevation + hot temp. +
high humidity = long take off runs. However, with the specific information
given below, I cannot complete calculating the rate of climb and the
approximate take-off distance required for the Allegro 2000 to clear a 50
foot obstacle for the specific set of circumstances given below.
(Field conditions)
Elevation - 1025 msl
Runway - Grass
Length = 2000 feet
Temp. - 95 degrees F, (35 degrees C)
Relative Humidity - 70%
Dew Pt. - 77 Degrees F
Barometer - 29.89 " Hg
Condition of Aircraft (Allegro 2000)
MTOW - 1232 lbs. (560 Kg.)
Empty Wt - 727.5 lbs. (includes BRS System)
Max. Fuel Load - 153 lbs. (main and wing tanks full)
Pilot - 155 lbs.
Passenger - 180 lbs.
Luggage - 16.5 lbs.
Actual TOW = 1232 lbs
C.G. = 12.6" behind the leading edge of wing
Standard Temperature, Pressure Altitude, and Density Altitude
For the above conditions I calculate the following values:
Std. Temp. = 12.95 degrees C
Pressure Altitude = 1055 Ft. msl
Density Altitude = 3260 Ft. msl
Standard Temperature Sea Level Take-off Distance for the Allegro 2000 at
MTOW
With all this information I could use the Kotch Chart for Altitude and
Temperature Effects on take-off distance, and Effect on rate of climb. What
I don't have is the standard temperature sea level take-off distance to
climb to 50 feet for the Allegro 2000 at MTOW 560 Kg (1320 lbs.), and the
normal sea level rate of climb for the Allegro 2000 at this MTOW. Pages 28
and 29 of my Allegro 2000 Flight and Operating Manual gives some performance
numbers, but they are for test flights made at the Pisek air field El. 1351
Ft and at an air temperature of 27 degrees C. The standard temperature sea
level take-off distance given on page 29 of the manual is for a MTOW of 520
Kg, not 560 Kg. This is either a typo or it is indeed for 520 Kg.
I need to know the Standard Temperature Sea level Take-off Distance for the
Allegro 2000 to clear a 50 foot obstacle at MTOW of 560 Kg., and c.g. at
12.6" behind the leading edge of the wing. I also need to know the normal
sea level rate of climb for the Allegro 2000 at MTOW of 560 Kg., and c.g. at
12.6" behind the leading edge of the wing. I have contacted the US
Distributor to get this information but have not heard from him yet. Can any
of you who own an Allegro 2000 provide these two bits of information?
With kind regards,
Hugh McKay
Allegro 2000
Rotax 912 UL
N661WW
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Thu Jul 31, 2008 3:05 am Post subject: Take-off Distance for Allegro 2000 |
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Hugh,
There are other variables that you did not mention that can have a
dramatic effect on rate of climb and take-off distances. The most
obvious is the pitch of the prop. Others, perhaps a little less
obvious, include the condition of the engine and the technique and
skill of the pilot. Also, which fuel are you burning? If it is E-10 it
will be producing roughly 3 1/2% less power than if using auto fuel
that is not laced with alcohol or 100LL. Also, the take-off distance
varies greatly with type and condition of surface. I know a pilot in
Hawaii who lives at ~4,000 msl with a short grass strip. He keeps one
have the width mowed short for take-off and the other half mowed long
for landing.
That said, you can make an educated guess at rate of climb (ROC) at a
given density altitude (DA) because it degrades at a nearly linear
rate up to the service ceiling. Of course this requires knowledge of
the service ceiling, which I would estimate to be around 15000' DA
with the 80hp engine with the prop set for best cruise at low DA. I
know I've had our Allegro up to 12500' msl and still getting about 400
fpm ROC. This was solo so at MTOW it would have been a good bit less
ROC. I don't recall what the DA was at that altitude on that day but
it was in cool weather.
I think you are over analyzing this. The safest thing to do is do some
take-off and climb testing at different weights and atmospheric
conditions on a long runway with a helper to pace off the take-off
roll. Since you live in North Carolina, you can fly to one of the
highest elevation airports east of the Mississippi River in reasonable
time and do the tests there too. There is nothing like empirical
testing to get the information you want because that will be done with
you at the flight controls and you controlling the loading etc. Get
enough data points under enough varying conditions and you can
extrapolate to get reasonably accurate figures under other conditions.
This will likely be more useful than some theoretical numbers that do
not take into account the variables not included in your original
question.
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_________________
Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
- Anonymous |
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Thu Jul 31, 2008 4:34 am Post subject: Take-off Distance for Allegro 2000 |
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Thom:
Your points are well taken, but here is my situation. I have just filled my
wing tanks for the first time and belly tank, and am at my home grass field
N92 (i.e. max fuel load). The numbers you saw in my post are real. I have
taken off from this field many times with a full belly tank and the same
conditions as stated with a 200 lbs. passenger, 15 degrees on the prop, but
no fuel in the wing tanks. Under those conditions I use about half of the
2000 foot grass runway. All conditions being the same, except for 65 more
pounds of fuel in the wing, would my increase in take-off roll be linear or
something else?
Hugh
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Fri Aug 01, 2008 3:49 am Post subject: Re: Take-off Distance for Allegro 2000 |
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Hugh,
Attached is a scanned image of a graph from my old Cherokee 140 operator's manual. It shows the relationship among varying density altitudes and take-off weights. I can not tell you with any certainty that the relationship will be similar or not on your Allegro, but it is worth reviewing nonetheless.
That said, I have operated out of 2,000' long grass airports at DA of 2,000' at take-off weight of 1130 lbs with no worries in our similarly equipped Allegro with prop pitch set for best cruise.
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| Description: |
| Cherokee 140 POH take-off performance graph |
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take-off-perf.PDF |
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20.93 KB |
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607 Time(s) |
_________________
Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
- Anonymous |
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Fri Aug 01, 2008 4:43 am Post subject: Take-off Distance for Allegro 2000 |
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T
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Fri Aug 01, 2008 4:49 am Post subject: Take-off Distance for Allegro 2000 |
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Thom:
Many thanks for your input. I just needed some independent feedback on the whole matter relative to the Allegro 2000. I will check the TO roll with the MTOW to see what I get.
With regards,
Hugh
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