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cmouton · 07-23-2014, 11:25 AM

Good day,

I have been running my T-Rex 700 Nitro Pro with the original 8:2:1 gearing at 1900 headspeed which give you 15500 engine rpm with my gearing.

The practical rpm of the OS91HZ Max engine are between 2000-16000 rpm, with the most power at 15000rpm. With 15500rpm, you should have enough room if your rpm should drop.

Lately, I have heard from a few people that this engine perform best at 1950 rpm. For me to achieve this, my engine will run at 16000rpm with my gearing. Will I not kill the engine when running at 16000rpm?

I now this topic were discussed a lot in the past, BUT with mixed answers.

For those that are running at 16000 engine rpm, have it shortened the life of the engine and do it run at it's best at that rpm?

Thank you in advance.

banditpowdercoat · 07-23-2014, 01:12 PM

No you will Not hurt your engine. The Practical RPM is up to 16000. That isnt the redline RPM either. And Max power at 15000. You actually want to be just over your max power so when you load up the head and the RPM drops it will come closer to its power peak and makes more power, when you need it.

cmouton · 07-23-2014, 04:00 PM

Thanks! I also did some more research and the trend are that most people fly their 700n 's at 1950 headspeed. Very few flew at 1850/1900 for example.

cmouton · 07-30-2014, 10:10 AM

Getting a OS105HZ with matching Hatori 3D muffler!

Were do you guys run this engine? 16000-16500 engine rpm?

Can't wait!

Frequency · 08-28-2014, 02:27 AM

Quote:

Originally Posted by cmouton

Getting a OS105HZ with matching Hatori 3D muffler!

Were do you guys run this engine? 16000-16500 engine rpm?

Can't wait!

Nice cant wait to hear how you like it I would like a comparison between the 91hzr 3d and the 105 hzr

ticedoff8 · 08-28-2014, 12:45 PM

The practical maximum head speed for the 690mm - 710mm blades is 1950 RPM.
Above this head speed, there is a big drop off in efficiency (high drag) and a lot more noise.
The best efficiency is lower head speed - and you get longer flights.

In electrics (750W = 1HP. Many 700mm electrics use 10,000W systems), there is so much excess power available that other than a shorter flight time, there is not big drawback to running up to 2100 or 2200 RPM head speed.

In IC helicopters, you are lucky to get 3.5HP to 4HP (3,000W).
That is why most Nitro guys use 1950 RPM for the head speed - we need to respect the efficiency of the rotor system because we cannot waste the power available to us.

Replacing the OS 91HZ with a 105HZ will not change your head speed. You should keep it at 1950.
But, the 105HZ will have higher torque and that will get you more collective / cyclic range.

The best bet is to look for replacement main gears / pinion gears that allow you to tune the engine's RPM to match the desired head speed (1950).
There are after market gears that you can use.
Or, just stick to the stock gear ratio and run the head at 1950.

Rob43 · 08-28-2014, 07:59 PM

I have 8:1 gearing. Running a YS 91sr. It's been a terrific engine so far. I set up my Vbar governor for a target speed of 2000 rpm to put the engine at 16000 peak. It bogs a bit when I am heavy in the pitch when running at this speed. So, I backed off the throttle curve which reduces the requested speed proportionately. I think I am presently at 98.5% throttle, which means more like 1970 rpm on the rotor. I am now fine tuning pitch to get a nice balance of performance without excessively laboring the engine. I think it's part of the fun to tweak all the parameters to achieve the best all around performance. I have been astonished at how cool the YS 91sr runs when flying it hard. Tank of fuel doesn't last long, as the YS seems to be happier a touch on the rich side.

Drivelayer · 09-23-2014, 02:31 PM

how do you know what RPM your engine is running at?

marc8090 · 09-23-2014, 08:41 PM

Engine speed is head speed multiplied by the gear ratio.

Rob43 · 09-23-2014, 09:46 PM

Running Vbar governor here, and it takes a desired target headspeed as the input value. It does the calculation of engine speed to seek based on the gearing ratio you also input on the menu. For example, when I set up my governor menu, I entered my 8:1 gearing, and set maximum speed at 2000. So, this will make it so that the governor will try to deliver 2000 rpm at the rotor when throttle is set at 100%. I am now running at 99% throttle in IU2, and it seems to tach very accurately. 2000 is just too much for my engine. Just a hair under that now.

07-23-2014, 11:25 AM	#1 (permalink)
cmouton Registered Users Join Date: Mar 2011	OS91HZ @ 16000RPM? Good day, I have been running my T-Rex 700 Nitro Pro with the original 8:2:1 gearing at 1900 headspeed which give you 15500 engine rpm with my gearing. The practical rpm of the OS91HZ Max engine are between 2000-16000 rpm, with the most power at 15000rpm. With 15500rpm, you should have enough room if your rpm should drop. Lately, I have heard from a few people that this engine perform best at 1950 rpm. For me to achieve this, my engine will run at 16000rpm with my gearing. Will I not kill the engine when running at 16000rpm? I now this topic were discussed a lot in the past, BUT with mixed answers. For those that are running at 16000 engine rpm, have it shortened the life of the engine and do it run at it's best at that rpm? Thank you in advance. __________________ Align T-Rex 600&700 Nitro Pro DFC SAB Goblin 630 Competition SAB Trioblin 500 Futaba 8FG Super

07-23-2014, 01:12 PM	#2 (permalink)
banditpowdercoat Registered Users My HF Map location Join Date: Sep 2010	No you will Not hurt your engine. The Practical RPM is up to 16000. That isnt the redline RPM either. And Max power at 15000. You actually want to be just over your max power so when you load up the head and the RPM drops it will come closer to its power peak and makes more power, when you need it. __________________ Dan Pesonen FBL, Don't think about it, DO IT. mCX2, nCPX, mCP X, Blade 400, MSH PRÔTOS, T-700N "Tri-Flow" I put that S*** on everything!"

07-23-2014, 04:00 PM	#3 (permalink)
cmouton Registered Users Thread Starter Join Date: Mar 2011	Thanks! I also did some more research and the trend are that most people fly their 700n 's at 1950 headspeed. Very few flew at 1850/1900 for example. __________________ Align T-Rex 600&700 Nitro Pro DFC SAB Goblin 630 Competition SAB Trioblin 500 Futaba 8FG Super Last edited by cmouton; 07-23-2014 at 04:01 PM.. Reason: correction

07-30-2014, 10:10 AM	#4 (permalink)
cmouton Registered Users Thread Starter Join Date: Mar 2011	Getting a OS105HZ with matching Hatori 3D muffler! Were do you guys run this engine? 16000-16500 engine rpm? Can't wait! __________________ Align T-Rex 600&700 Nitro Pro DFC SAB Goblin 630 Competition SAB Trioblin 500 Futaba 8FG Super

08-28-2014, 07:59 PM	#7 (permalink)
Rob43 Registered Users Join Date: Oct 2008 Location: Midland, Michigan	YS 91 by comparison... I have 8:1 gearing. Running a YS 91sr. It's been a terrific engine so far. I set up my Vbar governor for a target speed of 2000 rpm to put the engine at 16000 peak. It bogs a bit when I am heavy in the pitch when running at this speed. So, I backed off the throttle curve which reduces the requested speed proportionately. I think I am presently at 98.5% throttle, which means more like 1970 rpm on the rotor. I am now fine tuning pitch to get a nice balance of performance without excessively laboring the engine. I think it's part of the fun to tweak all the parameters to achieve the best all around performance. I have been astonished at how cool the YS 91sr runs when flying it hard. Tank of fuel doesn't last long, as the YS seems to be happier a touch on the rich side. __________________ = Rb43 =

08-28-2014, 12:45 PM	#6 (permalink)
ticedoff8 Registered Users Join Date: Jan 2010	The practical maximum head speed for the 690mm - 710mm blades is 1950 RPM. Above this head speed, there is a big drop off in efficiency (high drag) and a lot more noise. The best efficiency is lower head speed - and you get longer flights. In electrics (750W = 1HP. Many 700mm electrics use 10,000W systems), there is so much excess power available that other than a shorter flight time, there is not big drawback to running up to 2100 or 2200 RPM head speed. In IC helicopters, you are lucky to get 3.5HP to 4HP (3,000W). That is why most Nitro guys use 1950 RPM for the head speed - we need to respect the efficiency of the rotor system because we cannot waste the power available to us. Replacing the OS 91HZ with a 105HZ will not change your head speed. You should keep it at 1950. But, the 105HZ will have higher torque and that will get you more collective / cyclic range. The best bet is to look for replacement main gears / pinion gears that allow you to tune the engine's RPM to match the desired head speed (1950). There are after market gears that you can use. Or, just stick to the stock gear ratio and run the head at 1950.

09-23-2014, 02:31 PM	#8 (permalink)
Drivelayer Registered Users Join Date: Jan 2012	how do you know what RPM your engine is running at?

09-23-2014, 08:41 PM	#9 (permalink)
marc8090 Registered Users Join Date: Sep 2006	Engine speed is head speed multiplied by the gear ratio.

09-23-2014, 09:46 PM	#10 (permalink)
Rob43 Registered Users Join Date: Oct 2008 Location: Midland, Michigan	Running Vbar governor here, and it takes a desired target headspeed as the input value. It does the calculation of engine speed to seek based on the gearing ratio you also input on the menu. For example, when I set up my governor menu, I entered my 8:1 gearing, and set maximum speed at 2000. So, this will make it so that the governor will try to deliver 2000 rpm at the rotor when throttle is set at 100%. I am now running at 99% throttle in IU2, and it seems to tach very accurately. 2000 is just too much for my engine. Just a hair under that now. __________________ = Rb43 =

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