View Full Version : YS91 ST4 - Power output ?
Aviation addict
10-08-2006, 05:09 PM
Guys,
I have a YS91 ST4 and out of interest I'd like to know the rpm at which the engine produces the most power, i.e. with the 91SZ, 3.3 PS/15,000rpm. It's not stated in the YS manual. It just says Practical rpm 2,000 - 17,000rpm.
I understand the actual power output will be affected by the Nitro content, engine tuning and exhaust - but I'd be interested in any information you have.
My set-up includes a Viperhead/ 20% Magnum and the Hattori SB16FH. Are we looking at 3.0 at 15,600 rpm ish as the YS is said to be less powerful than the OS but higher revving?
DavidH
10-09-2006, 09:05 AM
YS has never put HP ratings in the specs of their engines that I remember. I used YS engines for 10 years.
The OS engines have a more power in my opinion. They seem to have more torque.
Curtis Youngblood could probably answer your questions about power output. He has a dyno table that was designed by his dad and him. They use it to test engines. He has tested a YS 91 I believe. He uses OS engines.
David
Aviation addict
10-09-2006, 02:50 PM
Thanks david. I'll try asking Curtis and get back with the answer if I get one.
DavidH
10-09-2006, 05:14 PM
http://www.curtisyoungblood.com/faqs/search.php?category=Engines::YS%2091
That should answer some of your questions.
David
WayneBrown
10-09-2006, 07:43 PM
if I read all that right, I'm running the wrong ratio.. I have 8:45 on my YS powered Stratus. Makes you wonder what the difference will be if I change to 8:18?
marked23
10-10-2006, 03:03 AM
The 8.18 was recently discussed briefly here:
http://www.helifreak.com/viewtopic.php?t=18622
-Mark
Aviation addict
10-11-2006, 04:55 PM
I have the 8:18 YS combo and am being advised that 8:45 is the right gearing. Its a minefield. Does anyone have the definitive answer?
Whats the ideal rpm to run the YS for 3D? 14,700 as suggested in the above link?
marked23
10-11-2006, 05:11 PM
As I understand it, the 8.45 gearing was created for the YS80. Understandably, a little less power (than a 90) would require slightly different gearing. Then the YS91 came out and people stuck to the 8.45 gearing for that.
Here is my take on this [opinion]:
If you like to run high head speeds (1900+), go with the 8.18 gearing. I have found that the 8.18 is not great for my less-than-perfect tic-toc technique. Nothing else (mild 3d, including funnels and piro flips) has been a problem. I run 1900~1950 head speed.
If you like regular head speeds (1750 ~ 1900), use the 8.45. I have not tried this gearing, but I'm sure it would be more forgiving for my tic-tocs. So in that respect, I would say 8.45 is the place to be for aggressive-collective.
If you read the other thread, you already know that DavidH has used 7.91 with success. I imagine he was not doing aggressive-collective 3D, but maybe he will join in and tell us what sort of "personality" that ratio gives.
-Mark
Knud Pedersen DENMARK
10-12-2006, 06:27 AM
Hi
Wouldnīt the gearing also de depending on what type of muffler your using (muffler power band) :?: :?:
Iīm now using YS91/MP2/8.18, running 14750/1803. power is fine - but it might be better with a faster RPM - i will try 15600/1900 and higher next toime I go flying.... :D :D
I have seen Nigel Browm flying 16126/1950/8.27/Hatori 18 in is Synergy - looks like it has the same power as an OS......
EDIT
PS:
I have flown the YS91/Hatori Sb16FH/8.4(canīt remenber what RPM)
for about +500 flight, power was OK - but as I remeber (in between I have flown 100 flight with my OS91PS/8.18) it was not as good as with the 8.18 - or maybe my pitch managements is know better.....
ChopperKnud
capebob
10-12-2006, 08:43 AM
I am very fortunate in that I have two Strati (Stratuses :? ) one 8.18 the other 8.45 both with MP2s. Gentlemen it's a tossup. If someone held a gun to my head and asked me to tell the difference I would say that the 8.18 gets slightly better mileage and the 8.45 has a very slight edge on power. I prefer the 8.18 because it seems smoother on the pipe and has enough power for me.
Bob
TooLy
10-12-2006, 11:07 AM
Are the two Strati back together already?
capebob
10-12-2006, 04:12 PM
Yep, but the transmitter is in for repair. I've got one of them set up on my 8103 along with a R50 so I'm flying.
Bob
Aviation addict
10-13-2006, 04:35 AM
Now my engine is run if fully I've tried her out on 8:18 (YS91 Hatorri SB16) at 1850rpm and have no complaints at all. No bogging at all. Might just stick with 8:18. If the YS powerband is 14,700 to 15,100 rpm then I guess being in the top of this band is the place to be when loading the motor during maneuvers.