912UL 80HP RPM WOT Prop pitch - Take Off / Cruise - for beginner

[Xavier]

Hi all,

 

just to clarify things straight away, my Engine/Mechanical knowledge if very very limited so I apologise in advance if I don't use the correct vocabulary or if the questions asked are silly.

 

I have been flying a Savannah VG with a 912UL 80HP for 6 months now and I am trying to find out if the settings (Engine and Propeller) are correct.

 

The 912UL has 500 hours, the prop is a 3 blade DUC (Diam 68.0 cm, Pitch 13.0 deg).

 

Fuel : ULP95

 

I am normally cruising at 5000 rpm and getting around 75-77 kt IAS

 

at 4800 RPM I get 73kt IAS, not much difference.

 

Idle is around 2200 rpm (feels a bit high to me)

 

at a TOW of around 520kg - 1 PIC, 1PAX, full fuel (MTOW 544kg):

 

- WOT on take off --> RPM = 5200

 

- WOT straight level at 1500ft --> RPM = 5250

 

This doesn't feel right to me.

 

Rotax manual :

 

- Take-off speed --> 5800 rpm (max. 5min)

 

- Max. continuous speed (5500 rpm)

 

- Idle speed --> min.1400 rpm

 

I have been reading the Rotax-Owner forum and it looks like a good balance for rpm settings is to have a rpm of around 5600-5700 on straight level at WOT at the altitude the plane fly most of the time (2000 asl for me).

 

See this thread : LINK

 

So, what do you think ?

 

Is the WOT straight level at 1500ft of 5250 rpm ok ?

 

It would be great if I could get some indications or where to look, prop pitch adjustment, carburetors balancing, other adjustments.

 

Thanks.

 

Xavier

 

 

[pylon500]

Yes, your idle could come down a bit, 80hp should idle down around 15~1600rpm (the 100hp's start to get a bit lumpy down there, they like around 1800)

 

With max WOT level of 5250, looks like someone's been trying to squeeze all the speed they can at top end?

 

The 100hp's start to over-torque the gearbox/crankshaft with a WOT that low, 80hp's not so much a problem, but should still be able to see around 54~5500 straight and level.

 

With a 80hp Sav', you're not really going to get much faster than you've got, but you are probably loosing a bit of your STOL performance with the prop that coarse.

 

General rule of thumb was to set up the prop so that static WOT was between 52~5300, then decide if you had a draggy or clean plane, and go maybe 100rpm either way, ie; if you've got something like an Esqual, you could set to around 5100 static, but with a Savannah, you will probably be closer to 53~5400 WOT static.

 

I'm running a 100hp Foxbat, and can loiter at 70kts with around 4400rpm, and nearly 90kts at 5500.

 

Straight and level WOT, I start to go past max continuos of 5500rpm.

 

It's nearly ALL in the prop, carbi balancing and the like, tend to show up down around idle (rough), jets, needles and balancing are more to do with fuel consumption and are shown through the EGT's.

 

 

[Downunder]

My opinion..... (and I am a fan of Roger) is that the 80hp could rev more than the 100 WOT flat/level. Say, pitched to 5700 min.....You're 20hp less than the 100, so need that extra rpm/power.

 

I think you're loading the engine too much at 5250 WOT.

 

Idle is too high. Drop it back to spec. Just to be clear here, we are talking idle on the ground. Landing will be so much easier......!!

 

Fly 5200 to 5500 cruise. Rotax's love it...... This is what they are designed to do..... If you have EGT monitoring you will see them balance out here too.

 

Keep your oil HOT. 100 to 105 is perfect....

 

 

[rankamateur]

There is a 3 blade DUC prop hanging on the wall over in the Aerokits workshop. It has been there nearly as long as I have been going over there, give Reg a ring and have a talk to him about why it is still hanging there.

 

 

[Xavier]

Thank you for your response, I will have a close look at changing the pitch of the prop and idle.

 

More advice are welcome.

 

 

[Kyle Communications]

I set my prop although its on a 912ULS for 5600rpm max continuous power rating in straight and level full throttle. This gives me around 5300 on climb out at 60 kts. max throttle on the ground ends up at 5250 rpm. I cruise at 85 to 87 kts at 5000 rpm

 

 

[Downunder]

With that 80hp, you might want to consider a cold air intake if you don't already have one...... good for 100 rpm maybe....

 

A bloke I know has a 80hp in a Zenith and it struggles at times, especially in climb. I don't know the "tune" of the engine however.....

 

I just think you really need to get everything you can out of the 80.....

 

 

[rankamateur]

I just think you really need to get everything you can out of the 80.....

Like a Turbo charger!

 

 

[Ada Elle]

I just think you really need to get everything you can out of the 80.....

Lighter slipperier airframe helps. One-up, full fuel, getting 115kias and 1300fpm from the 80. (5500rpm climb, 5250 cruise, not wide open on the cruise.)

 

 

[Xavier]

After some tuning from our local LAME, the Idle RPM has been set to 1600-1700 and if I pull harder on the throttle I can get down to 1400rpm with the engine still running nicely.

 

It makes quite a big difference on the approach, it is easier to get the power settings right. (before the adjustment, even at idle full back, it felt like the plane didn't want to go down)

 

The prop pitch has been changed as well ,down to a couple of degrees and I am getting 5500RPM WOT at 1500ft AG. (5400rpm WOT on take off)

 

The engine feels very nice sitting on a cruising 5000rpm.

 

It feels like I got more horse power on take off and this is what was after, happy days !

 

Thanks for all your feedback

 

Xavier.

 

 

[Downunder]