Props, Props and more Props

by Roger Lee in General Tech Discussion 12 years ago

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Re: Props, Props and more Props

by Roger Lee » 7 years ago

Roger Lee

125 5.11k 4.52k

Yes there were differences.
3 blades tend to be smoother than 2's. 2 blades just produce a different frequency pulse in vibration. I can usually hear it in the cockpit and can feel it in the aircraft hull. The 3 blades tend to have a higher pitch frequency noise and the 2 blade a lower frequency noise. Longer blades also produce different frequencies in vibration and sound over short blades props.
In my research project I tested 14 different props and flew them all side by side with 4 identical aircraft to reduce some variables. Many people who like a prop over another is like taking a placebo as a medication. If you believe one is the best thing since sliced bread then you won't think others are comparable or possibly better. What the stats should was for most props rpm was the deciding factor and not the prop Mfg as many would like you to believe. Every Mfg will all tell you theirs is the best thing since sliced bread. After my research that just wasn't true.

I prefer a longer light 3 blade composite blade.

Now some of this will be like Chevy's and Ford's. You may not like both and prefer only one of them, but they both get you to where you are going.

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

Thank you said by: Paul Dressendorfer, Chris Beebe

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Re: Props, Props and more Props

by James Ott » 7 years ago

James Ott

22 321 357

Roger, curious about what you mean that rpm was the deciding factor? Do you mean how the blade pitch was adjusted for cruise rpm, climb, etc.?

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Re: Props, Props and more Props

by Roger Lee » 7 years ago

Roger Lee

125 5.11k 4.52k

Everyone will tell you how great their prop is. Just ask them. In all my testing it all boiled down to the final rpm setup at WOT at your average altitude.

As an example:
If you have two 2006 Flight Design CTSW's and each has the same prop or even a different prop the one that can turn 5600-5650 in level flight at lets say 5K' MSL vs the one that can only get 5400 rpm will be faster, climb better, get better fuel economy and cruise faster at a lower rpm.
The 5600-5650 one will be the over all better balanced setup.

For the normal guy you are striving for a balanced flight performance envelope with a ground adjustable prop. If you have a special need for more rpm in climb like flying with floats or always at high altitude airports you may want even a tad flatter pitch prop. Each pilot needs to ascertain what they want for the mission of each plane.

There are ZERO redeeming qualities with an over pitched 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 Dr. Robert N. Reinhardt » 6 years ago

Dr. Robert N. Reinhardt

0 2 0

Roger:
I found reading this thread most informative, but I'm left with one (maybe two) question(s). You always refer to WOT at the set point. I have a Searey with a 914 and Warp Drive Nickle Edge. WOT for me is full boost on the turbo and not recommended for more than 4-5 minutes. I normally only use it for take off climb out. Below 5800 RPMs (my true WOT) I can adjust to any RPMs. Can you explain how I should be going about testing what kind of pitch set-up I have, given that I'm going to be able to achieve different RPMs in full boost and without it? Second do you have any data on pitch angle vs hp vs weight?
Thanks

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Re: Props, Props and more Props

by Roger Lee » 6 years ago

Roger Lee

125 5.11k 4.52k

Most of these discussions are for ground adjustable props. If you have a variable speed or constant speed then these may not apply.
Just a note: The 912 gets to use any rpm over 5500 up to 5800 for 5 minutes just like you and your boost. Having the prop pitch set on the 912 or actually any plane affects it characteristics through all throttle positions and flight positions and not just one area of flight. (i.e. take off, climb & cruise)

I do know through a research project I did years ago you could get much better climb performance with something different than a Warp Drive. That proved out many times back then. When we have only a ground adjustable prop we have to pick a so called sweet spot to set the pitch since we have no adjustment in flight. So we want to pick a sweet spot that gives us a BALANCED flight package for climb, cruise, fuel economy, engine temps and even engine stress. Anything under 5500 rpm at WOT at your average altitude in level flight is counter productive and you lose out on all items listed above. Over pitched. If you picked 5800 WOT at your average altitude then you'd have a good climb prop, but lose out on cruise and fuel economy. This though may be a better setting if you do fly off of floats or need better climb for short runway back country air strips or fly real heavy from high DA fields. If you're the average everyday flier then we would like a good balance for all these. During my research I found this to be 5600-5650 rpm WOT at your average altitude. We all know there are times we may fly lower and some times we fly higher. So we pick an average altitude and a balanced prop pitch that will give us the best balance between all of these factors. You don't want to set a prop pitch for 2K AGL and then always fly 8K AGL all the time. We know that with the 912 series engine it looses performance the higher we go so it needs to be able to spin the prop efficiently when we fly at higher altitudes.

Now you are in a different boat so to say. You have a 914 turbo. So altitude and high DA fields aren't as big a deal vs the 912 guys. You get to keep your HP & torque. Since you are taking off from water and are a little heavier then you may want a little better climb prop. Personal choice.
Some of your decision may include what rpm you cruise at. With your setup you may cruise at 5500 rpm all the time. If you chose to cruise all the time let's say at 5200 rpm you still do not want that to be at WOT throttle setting. You'd still want the engine to get a much higher WOT if you advanced the throttle, but you just chose to fly at a reduced throttle.
If you have a ground adjustable prop on a 914 you lose all it's benefits that a turbo can offer.

I have no data for pitch vs hp and weight. For me it's all about the numbers and aircraft performance for my places of flight which can be slightly different for each user, aircraft and personal choice, but there are some parameters to stay within and prop pitch vs rpm that shouldn't be use. People have cracked engine cases from over pitching and over stressing their engine.

Being a tad too flat a pitch isn't bad, but remember there are NO redeeming qualities if you are over pitched. It is all negative performance.

p.s.
I wrote this right after I got up this morning so if it doesn't make sense let me know and I'll try to explain it better. :) LOL

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

Thank you said by: Garrett Wysocki

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