Ageless Wings wrote:
Mornin', Andy
This is from the VeriEZ scoop. I have the Veri and Long plans on the
Rutan CD in PDF format.
Cheers,
Andy
I have that CD, too! Didn't even think of looking at the VariEze plans! I
guess Burt switched to a prefab part before the Long EZ plans were
available.
Paul...
Now that we have some drawings for reference, I took the dimensions off of
my "prefabbed" cowl. Dimension 'A' on mine is 4.5" (the drawing calls for
4.6 inches), and the long axis of the ellipse on mine is 12.625". The
drawing calls for 12.2".
Also, the radius of the lip on mine varies from 1 inch on the corners, to
1.1 inch measured at the long, straight sections. The plans call for 1.2".
The drawing's chart of dimensions only goes up to 100 horse engines (the
Continental O-200 engine for the VariEze ), whereas the later recommendation
for the Long was the Lyc O-235, which is around 108 hp, depending on flavor.
These dimensions do increase the cross section area of the inlet opening
somewhat, and may have been enlarged to try to make up for the 8 extra HP on
the larger recommended engine.
Harley
Give it 50 square inches roughly. .3 rule of thumb would be a core
about 167 square inches or about 13 by 13. Sounds about right to me
for about 100 HP.
One thing you got going for you in an air-cooled engine is the temp
difference between the fins and the air can be as much as 300 F. Since
the rate of heat transfer is proportional to the temp difference that
is far better than about 110 F you get with a liquid cooled system.
On the other hand the fin surface area of a rad can be far higher
than the fin surface area of an air-cooled engine. Back in WW II
P&W and CW machined the closely spaced thin fins on cylinders using a
gang of cam controlled thin slitting saws. In general the fin surface
area of a rad is proportional to the volume of the rad.
BTW if the temp of the air is 60 degrees higher exiting the rad
than the air entering the rad the back part of the
rad is indeed working less than half as well as the front part of
the rad. This is the reason for the rule of thumb that states the
first half is doing three quarters of the work and why rads are
getting thinner and thinner in cars.
The other factor is a thick rad is limited to the airflow it can pass
at low speeds. Once you jam as much air in there as you can at a given
speed more air will just refuse to flow through the rad regardless of
how large the opening. The air will merely decide to flow around
the opening. At that forward speed and below that forward speed you
will get more air through a larger area thinner rad.
Paul Lamar
I re-did the program for the size of the opening in square inches
for a range of MPH and temps exiting the rad. This assumes of
course all the air volume for that speed and intake hole
size does indeed go through the rad. This is where the .3 rule of thumb
comes into play and a properly shaped 100% efficient inlet duct is assumed.
If for some reason the rad is too thick or the exit is restricted
the air will not go in the hole and merely flow around the outside
of the hole. Making it bigger only works up to a point. It can only
compensate for a duct less than 100% efficient.
Another way of looking at this table is to say this is the
required volume of air flowing through the rad required to cool
the engine. FPM X AREA = VOLUME
Paul Lamar
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/
Copyright 1998-2002 All world wide rights reserved.
Assumptions:
6000 BTU per minute waste heat
Specific heat of air = 0.01988 BTU per cubic foot per deg
20% humidity 100 degree day
_______________________________________________________________
..........10...15...20...25...30...35...40...45...50...55... 60
---------------------------------------------------------------
80 MPH 620 413 310 248 207 177 155 138 124 113 103
85 MPH 583 389 292 233 194 167 146 130 117 106 97
90 MPH 551 367 275 220 184 157 138 122 110 100 92
95 MPH 522 348 261 209 174 149 130 116 104 95 87
100 MPH 496 331 248 198 165 142 124 110 99 90 83
105 MPH 472 315 236 189 157 135 118 105 94 86 79
110 MPH 451 301 225 180 150 129 113 100 90 82 75
115 MPH 431 287 216 172 144 123 108 96 86 78 72
120 MPH 413 275 207 165 138 118 103 92 83 75 69
125 MPH 397 264 198 159 132 113 99 88 79 72 66
130 MPH 381 254 191 153 127 109 95 85 76 69 64
135 MPH 367 245 184 147 122 105 92 82 73 67 61
140 MPH 354 236 177 142 118 101 89 79 71 64 59
145 MPH 342 228 171 137 114 98 85 76 68 62 57
150 MPH 331 220 165 132 110 94 83 73 66 60 55
CLS
'6000 BTU per minute waste heat
'0.01988 BTU per cubic foot per deg
'20% humidity 100 degree day
BTUCon = .01988
OPEN "btu2.dat" FOR OUTPUT AS #1
PRINT #1, "Assumptions:"
PRINT #1, "6000 BTU per minute waste heat"
PRINT #1, "Specific heat of air = 0.01988 BTU per cubic foot per deg "
PRINT #1, "20% humidity 100 degree day"
PRINT #1, "_______________________________________________________________"
PRINT #1, "..........10...15...20...25...30...35...40...45...50...55... 60"
PRINT #1, "---------------------------------------------------------------"
FOR MPH = 80 TO 150 STEP 5
FPM = MPH * 88
PRINT #1, USING "####"; MPH;
PRINT #1, " MPH";
FOR tempF = 10 TO 60 STEP 5
'PRINT #1, tempF;
airflowCFM = (6000 / (.0198 * tempF))
'PRINT #1, USING "############"; airflowCFM;
AreaSF = airflowCFM / FPM
'PRINT #1, USING "###########.##"; AreaSF;
AreaSI = AreaSF * 144
PRINT #1, USING "#####"; AreaSI;
NEXT tempF
PRINT #1,
NEXT
CLOSE #1
SHELL "more < btu2.dat"
SYSTEM
