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18x6 prop for a 26cc Zenoah, wood or plastic?


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Excuse what i guess for some of you is a pretty basic question, i have not flown petrol or glow for years but am putting a Zenoah 26 mag engine in an 82" plane and need a prop for it. Can anyone recommend a make, what would be the best choice, wood or plastic for this, something that isn`t too noisy either, i gather the prop can make a big difference. I had a look at the Falcon 18/6 beech prop, would that be a good choice? Many thanks for your thoughts on this............

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Posted (edited)

Here goes and will probably start a debate fiercer than party gate 🥴 as opinions vary so much, 100 flyers = 100 different answers  😀  Xoar props ( beech wood) seem very good and reasonably priced and are my first choice for petrol engines. All the ones I have been excellent quality wood with good finish and seem fairly well balanced but I alway try to get an exact balance if possible. They also seem to pull air efficiently . Some props just don't perform as expected. You might want to experiment with di and pitch to get the best from your zenoah.

I try not to use composite props on petrol engines as they are very unforgiving in a light ground strike. They will/ can twist or bend a petrol crank. I believe your zenoah will have a passed together crank that can be twisted comparatively easy and a wooden prop will splinter and break easier than a composite .

Ps. Look around at swap meets . You can often pick up large props in new condition for a fraction of their value.

Edited by Engine Doctor
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Posted (edited)

For a racing type model you might want more than 6 inch of pitch. I would use 6 inch for a tiger moth or similar with 8-10 inch for WWII fighters. As your model is somewhere in the middle of tiger moth and WWII fighter 8 inch would probably be about right. 

 

As for prop choice, like ED i have no problem recommending wooden props with menz, fiala, xoar and falcon all being good choices. Menz tend to be fairly heavy as a load and fiala run fast from what customers have told me. Falcon seem to be in the middle. Xoar also offer scale props that are painted/a nice shape and although their efficiency might suffer (i have no data on this) there is an advantage in looks. 

 

If my memory is accurate the z26 offers similar performance to a laser 155 so 16x8-10, 17x6-8, 18x6 etc would be in the ballpark as a range of props. I would proably start with a 17x8 and see how the revs are. if you are in the 7800-8200 range then all good, if you find its faster then perhaps add an inch and go for 18x8 at around maybe 7200-7500? 

 

Prop selection can make or break the performance of a model and it will take some experimentation. Each prop brand offers different performance and an 18x8 from one brand will not match the performance of that from another. As an example, based upon customer reports i think the fiala props run a good 500-800rpm faster than the menz for the same DxP on the same engine. 

 

Edited by Jon - Laser Engines
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ISTR that it's good practise to fit a wooden prop to an engine with a pressed-together crankshaft and web such as the Zenoah. the thinking is that if you nose over and catch the prop, then a wooden prop will break before the crank moves.

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