|
|
I prowled around the test page a bit, & the numbers are really not good at all (pitiful, really) if you compare numbers to Lyc powered RVs. The 'best' numbers from the latest chart he supplied (copied below) show 151 kts (173mph) tas at 9.3 gph (56 lbs per hr). That speed is roughly what Van claims for a 160hp -6A at 55% power (7.3 gph) at 8000 ft. That's a 26% penalty even if you ignore the 3,000 ft altitude (lower drag) efficiency advantage. At 11,000 ft & that fuel burn, he would be going around 200 mph with a Lyc.
Since there are 2 big variables (plus airframe/cooling drag) in this equation, you can't tell how much blame to assign to the engine or the prop.
Don't be seduced by the *potential* advantage of a controllable prop. It's already obvious that the cruise/top speed numbers are much worse. I'm a bit too lazy to dig this deep, but you should also compare his climb rate/fuel flow numbers to Van's fixed pitch numbers. Do you really need a climb rate in excess of what the a/c can supply with a fixed pitch prop? If not, the only remaining reason is a drag brake for landing. That's the one area where fixed pitch RV's suffer. High sink rate low speed descents into emergency landing zones are a lot more difficult to achieve, but the -9's already lower landing speed than a -6 should help you there.
Charlie
Altitude Prop OAT TAS RPM MAP Knob FF EGT1 EGT2 EGT3 EGT4
10,500 7 -2 129 4000 22 -5 43 1205 1302 1205 1186
10,500 7 -2 129 4000 22 -8 41 1233 1327 1225 1214
10,500 7 -2 129 4000 22 -10 40 1253 1346 1242 1225
10,500 9 -2 141 4250 25 -5 53 1289 1347 1258 1240
10,500 9 -2 141 4250 25 -8 51 1310 1370 1276 1258
10,500 9 -2 141 4250 25 -10 49 1318 1381 1292 1269
10,500 6 -2 127 4250 20 -10 40 1281 1363 1275 1248
10,500 6 -2 124 4000 20 -10 38 1252 1338 1237 1207
11,000 10 -2 151 4375 27 0 62 1268 1299 1209 1206
11,000 10 -2 151 4375 27 -5 58 1317 1345 1257 1246
11,000 10 -2 151 4375 27 -8 56 1350 1379 1293 1275
Tracy Crook wrote:
Just reading the TAS number (181 Kts) it doesn't look bad. The trouble is in the other numbers. Let's take a closer look. 17,000 ft . You always get more airspeed per pound of thrust at higher altitude. Only reason most people don't quote TAS at this altitude is that the engine looses power (lower thrust) at altitude. This was not the case in this test since the engine was turbocharged and boosted to ABOVE ambient at sea lever (34"). The airplane SHOULD have been hauling ass under this condition. No fuel burn number was given but that would have been interesting.
This isn't a perfect example but for rough comparison purposes, my RV-4 averaged (from a dead stop) 189 Kts at sea level with just a bit over 30" manifold pressure. If you corrected that for altitude at 17,000 feet, that would be well over 220 Kts. (don't have my E6B handy to do the actual calculation).
The only way to do a real comparison is to put a different prop on the same plane and fly it under the same conditions.
Tracy Crook
On Wed, Nov 12, 2008 at 1:48 PM, Kelly Troyer <keltro@att.net <mailto:keltro@att.net>> wrote:
Doug,
Did Ross state his "IVO" diameter and if 2 or 3 blades
!!............... --
Kelly Troyer
"Dyke Delta"_13B ROTARY Engine
"RWS"_RD1C/EC2/EM2
"Mistral"_Backplate/Oil Manifold
-------------- Original message from DLOMHEIM@aol.com
<mailto:DLOMHEIM@aol.com>: --------------
Ross Farnham, who posts in the Van's Airforce "alternative
engine" forum (and who if he wasn't a Subie guy would most
likely be a regular on this list); has done quite a bit of
testing with the IVO Magnum "high pitch" version on his RV-6A,
turbo Subie. The best "top speed" (for what that's worth in
this day and age) I could find in his data was at a DA of
17,000 ft. and " 34 inches 5000 rpm, mixture -10%, 181 knots
TAS". That really isn't too bad for the price you pay for an
IVO in my opinion. See this link for his IVO testing
information: http://www.sdsefi.com/rv13.htm
His web pages also fully document the many cooling
modifications he went through with his installation until it
finally was "right", much like those who have gone before on
this list have had to do. This also is well documented and
makes for interesting reading if you haven't checked out his
site before. http://www.sdsefi.com/rv12.htm
I plan on using an IVO on my RV-9A installation since it
appears from Ross's data that it should provide more than
adequate climb performance and will also cruise well in the
150-160 mph range (where I plan on spending most of my time). An MT would be nice, but the cost is prohibitive on my
budget. Here is a summary of Ross's IVO conclusions from his
web page:
07/21/04
At the 90 hour engine/prop time mark we have some more
observations on the IVO Magnum:
1. We have had no issues with bolts or blades coming loose.
2. The in-flight adjustment works well. We use a 0-20 amp
ammeter to judge blade position.
3. After the first set of brushes laid down carbon on the slip
rings, brush life now exceeds 30 hours between changes
4. Despite having /too low a reduction ratio for our
airframe/, the Magnum offers good takeoff and climb
performance. */Medium speed cruise performance is comparable
to other certified aircraft propellers/*. High speed
performance also seems comparable although we'd like to have a
lower reduction ratio to turn the prop faster and absorb more hp.
5. Given the speed vs. fuel flow considerations on our
turbocharged RV6A, this prop is matched well and is a viable
alternative to expensive constant speed, certified propellers.
A fixed pitch prop on the turbocharged engine would degrade
performance considerably, especially in the takeoff, climb and
high altitude cruise regimes.
6. A slight vibration is set up if the propeller is coarsed
out too much for the flight speed, likely due to the blade
being partially stalled.
7. Ambient temperature and altitude (density altitude) affect
pitch angles required for a given hp and rpm.
For takeoff using 38 inches MAP, 4800 engine rpm/ 2182 prop
rpm we set pitch at 3 amps fine of neutral pitch. This is at a
hp of around 170, prop torque is 409 ft./lbs. Density altitude
3500-4500 MSL.
For climb at 35 inches MAP, 4500-4800 engine rpm/ 2045-2182
prop rpm we set pitch at 2 amps fine to neutral. This is at an
IAS of 80-95 knots. Hp is 150-155, torque at prop is about 374
ft./lbs. Density altitude around 6000 MSL.
For cruise at 30 inches MAP, 4200 engine rpm/ 1909 prop rpm we
set pitch at 13 amps coarse. This is at an IAS of 130 knots.
HP is around 114, torque at prop about 314 ft./lbs. Density
altitude 11,000 MSL.
We don't run the pitch past 15 amps coarse and figure that
this results in a pitch of 95 to 100 inches.
(note: italics are mine...)
Doug Lomheim
RV-9A; 13B/ FWF
------------------------------------------------------------------------
Get the Moviefone Toolbar
<http://pr.atwola.com/promoclk/100000075x1212774565x1200812037/aol?redir=http://toolbar.aol.com/moviefone/download.html?ncid=emlcntusdown00000001>.
Showtimes, theaters, movie news & more!
------------------------------------------------------------------------
No virus found in this incoming message.
Checked by AVG - http://www.avg.com Version: 8.0.175 / Virus Database: 270.9.2/1783 - Release Date: 11/12/2008 10:01 AM
|
|