Raptor 90 (converted 60) needs more power - Please Help

[creightoncarr]

I've got a Raptor 60 which I've converted to a 90. I'm using the OS 91SZ-H non-pumped. The engine seems to be running well and seems to have plenty of power for mild pitch pumping maneuvers and FFF. It also seems to have decent, but not great, power though rainbow type tictocs. During stationary tictocs and other maneuvers requiring greater cyclic inputs (flips, rolls, piro flips, etc) the head REALLY bogs. During a backwards loop this afternoon the rotor rpm just seemed to die. The unfortunate result was a crash at the bottom of the loop as it was leveling out. If I'd of had another three feet I think I would have been in the clear. :( Part of the problem may be that I've gotten too used to the near almost instant power of the electrics, but this 90 is just not performing as I feel it should.

Setup:

Pitch: +/- ~11.5*
Cyclic: 7.5*
V-Blades 690's
95mm V-Paddles
S1 and S2: 100% throttle curves limited to 1850 and 1950prm respectively with rev max.
Gear ration: 7.75 (93T main with 12T pinion)

With a gear ration of 7.75, at 1950rpm on the head the engine is running at about 15,100prm, right in the power band according the specs I've seen. Would I be better off running a gear ratio of 8.27 (91T main and 11T pinion) and running the head at 1850? Would I be better able to maintain HS at this ratio through more demanding maneuvers? I want to like this heli, but so far I've been a little underwhelmed. What can I do differently so that I can fly it more aggressively?

[capebob]

A couple of ideas. First unless you're really good at collective management 11.5 degrees is probably a bit too much especially if your cyclic pitch is ~7 degrees. Second your RevMax only limits the top end RPM. If your idle up throttle curve is too low in the center the RevMax won't do a thing about it where a standard governor would correct this deficiency.

Bob

[creightoncarr]

Thanks Bob. My throttle curve in idle ups is flat 100%'s so that shouldn't be the problem. Without trying to toot my own horn, I readily admit my collective management has room for improvement, but IMO it is pretty good nonetheless.

With my low gear ratio (7.75:1), at 1950 rpm on the head the engine is at 15,100rpm, right at the peak of the power band. I wonder if when I load the head I'm dropping the engine out of the power/torque band and that's why I'm bogging so badly? I haven't tach'd the head under load yet. I'd planned on doing it Sunday, but unfortunately it was tough to do when the heli was in pieces on the ground. :D

In my previous post I asked about an 8.27:1 ratio. I'm also wondering about 8.45:1. At 8.27 and 1900rpm, or at 8.45 and 1850 rpm, I'd be running a little higher in the power band unloaded. Maybe when I load the head the engine will still end up in the lower end of the power zone and bog less?

[flyinfool]

I agree wit Bob that 11.5 pitch is to much. especially at 1950.
By having more pitch than the engine can handle, when you do get into a tight spot where the instinct is to add power it will only get worse if the engine can not do it.
As you lower the head speed that you are geared for you can run more pitch because the higher gear ratio will have the extra power needed.
As you can see this will be a compromise between pitch and headspeed, you have to tune this to match your flying style.

Since peak HP is at 15,000 you want to gear for about 5% more engine rpm or 15,750.
The reason for this is that as you load the engine and start to bog you will bog into the peak power. If you are setup to run at peak and you bog the head the power drops and there is no chance of recovery till the load is removed.

[creightoncarr]

Thanks flyinfool. I had reduced pitch to +/- 10* but was still noticing a lot a bogging. I very rarely get near the extreme pitches in either direction, and if I do, only for a fraction of second to arrest movement. I was beginning to think the biggest part of the problem was that I was bogging the engine out of the power band. Peak power is at ~ 15,000 and I was running at 15,100 unloaded.

I think I'm going to try 1900rpm on the head at 8.27 which should have the engine running at just over 15,700rpms with +/- 10* on pitch. Think I'll see a noticeable improvement over my last setup?

[Lota Fun R]

This is exactly what I'm dealing with at the moment. From what I've read, 8 to 1 is ideal for the 90 with the C spec. I wanted to use a 90t main an 11t pinion to achieve this but can't find a 90t main so I'm going to use a 95 main and 12t pinion which puts it at 7.92 to 1 which might even be better?

My understanding is that a head speed of 19XX is where I want to be, and with the gearing I'm going to use I'll be able to get a max head speed of 2021 at just below 16000 rpms

At 1950 I'm at 15437rpms, bog the blades a little and it puts the engine in the sweet spot.

Run it up to 1975 and it may work even better. 2000 may be perfect? (15833 rpms)

I'm set up with 11 deg + & - pitch with a rev max throttle jockey. Now my understanding is that I"ll have to set my throttle curve in idle up to be above the 50% it's currently at. 100-50-100....it should be something like 100-75-100 ?

I think the only difference between mine and yours is I'm running 710 Radix main blades. Oh, and I'm using the 91 C spec w/pump. 3.1hp,,,,,,maybe a bit more with the Muscle pipe?