Props, Props and more Props

by Roger Lee in General Tech Discussion 12 years ago

Hi All,

I just got through research and testing 5 Sensenich props of different lengths both 3 blade(68" and 65") and 2 blade (68" and 70") models. They were tested against a Warp Drive 66", a 3 blade (65") and a two blade Neuform.

The bottom line no matter what the length or blade count so long as each blade was set at the same WOT rpm (5550 rpm flat and level)(same aircraft) then they all performed the same. Same climb and same WOT speed. No one had any better performance one way or the other. There were a few different static rpm differences and even some difference in climb rpm, but the performance didn't change.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Props, Props and more Props

by key dismukes » 12 years ago

key dismukes

15 11 6

Roger

Very interesting and useful. Thank you. But one question: if you set the pitch for 5500 wot in level flight, isn't that heavily toward cruise? What sort of rpm did you get during initial climb and at what speed?

Key

Thank you said by: George Tanguay

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Re: Props, Props and more Props

by Roger Lee » 12 years ago

Roger Lee

125 5.12k 4.52k

Hi Key,

You climb stats will be different as all aircraft profiles are different. You should set your prop to at least 5500-5600 WOT flat and level at your normal cruise altitude. Setting it lower loads the engine and if you get too low in rpm's then it can cause damage. Most of us have ground adjustable props. We need to balance climb, cruise and fuel economy. Setting the prop over 5600 WOT flat and level gives you a better climb prop, but looses top end. Setting it at 5400 gives you a better cruise prop, but you suffer in climb and fuel economy. The difference between 5100 and 5550 rpm for fuel is around 1.5 gph and up to 2 gph. As you load a prop up with too much pitch fuel starts to take a big hit.If you go below 5400 you loose climb, cruise and fuel economy. You don't have the torque and HP to turn it efficiently. 5500-5600 rpm WOT set for "your normal cruise altitude" is a pretty good place to be. You get a balance of climb, cruise and fuel economy. The rpms on each prop for static, and climb rpm was different, but most of the over all performance stats were the same. Don't worry about any numbers for any other plane. Set "your individual plane" up to get 5500-5600 rpm and that will give you the best overall performance for your individual aircraft. Over the years I have re-set tons of prop pitch on planes that were under 5400 rpm. Not a single person has ever wanted to go back the other way.
If you fly some sort of special circumstance like real heavy with floats or heavy at a high field elevations as a norm then you may want to have a little higher rpm, but never lower.

Your engine was built with specific run spec and rpms in mind. Cruising less than 5000 rpm, running over 5800 rpm or with a WOT setup less than 5500 wasn't in the plan.

p.s.

You should try 5500-5600 RPM WOT pitch setting. If you don't like it you can always go back to where you are, but I personally don't know a single person that ever went back.
You can set a prop in 30 minutes so it doesn't take long. If you want to know an easy way just give me a call and I'll explain it. Sometime in the future I'll try to make a short video on the "How to" set your prop.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Props, Props and more Props

by Tony Garrett » 12 years ago

Tony Garrett

20 37 11

Good morning Roger
Lockwood Aviation (The Rotax Service Center) says I should set my prop to give at least 5200 RPM at the beginning of the takeoff roll. This yields ~6100 RPM with WOT flat and level in cruise.

Setting my prop for 5600 RPM WOT in flat and level cruise causes the initial takeoff roll RPM to be ~4800.

Thoughts?

Thanks, Tony

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Re: Props, Props and more Props

by Roger Lee » 12 years ago

Roger Lee

125 5.12k 4.52k

Hi Tony,

Finding harmony can be a quest.

This is a good question. You can find in the Rotax books the reference to 5200 rpm at take off and like you found it you will then be at over speed for cruise WOT and maybe an over speed accident. You would have a good climb prop, but a terrible cruise prop and fuel would suffer too.
The 5200 rpm is better taken in context with a constant speed or in flight adjustable prop. Then you can dial in the best of both worlds. The problem here is Rotax did not directly address the ground adjustable prop. There really should have been two separate subjects on this, for for in flight adjustable props and one for ground adjustable props. They were lumped in together and they are two different animals.
The main problem here is that most of aren't allowed an in flight adjustable prop so setting a ground adjustable prop to see 5200 rpm at take of is self defeating and a poor balance between the climb, cruise and fuel economy.
I just tested 5 props for Sensenich which drove this home very well.
You need to strike a balance between climb and cruise, fuel economy will follow. It is even taught in Rotax schools that 5500-5600 rpm is a good balance with the ground adjustable prop. This rpm should be set for your average cruise altitude. The static and climb rpms on the props I just tested varied as much as 250 rpm at static and climb, but each was set to achieve 5550-5600 rpm WOT flat and level. I ran these against the same planes side by side (make, model and year) and each had a different prop (.e. Warp Drive, Neuform 2 blade, Nueform 3 blade and the 5 Sensenich props) and so long as they were all set to the same WOT rpm they all flew side by side at WOT and climbed the same.
Bottom line, if a prop MFG may says he is the best thing since sliced bread take it with a grain of salt and so long as every thing else is equal so are they.

If you are getting the 5600 rpm WOT flat and level then don't worry about where all the other rpms are, since we have a ground adjustable prop you are now in a pretty balanced state between climb, cruise and fuel economy.

Now go enjoy your plane.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Props, Props and more Props

by Tony Garrett » 12 years ago

Tony Garrett

20 37 11

Roger
Thanks for the great input.
I currently have a 3-blade 74" Kiev prop. Maybe the extra length is making my prop pitch settings and RPMs a difficult compromise. I am thinking of buying a 3-blade Warp-Drive replacement prop. What length do you suggest. My plane is a Savannah VG (like a Zenith 750) with a 100 hp 912 ULS engine. I am more interested in short field and climb performance than cruise speed.
Tony

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