Three blades or four???

[seb7701]

Hi all.

 

I have a rather nice three blade timber prop pushing along my 503 drifter at present, but am curious as to likely benefits (or the opposite) of this prop as opposed to the more commonly fitted four bladed composite props such as a bolly/brolgas etc.

 

Whilst the timber job is adjustable, I am curious as to the pro's and con's of both, given that I am about to commence tinkering for just a hint more climb performance.

 

As always, any shared wisdom is appreciated!

 

 

 

[M61A1]

The 503's usually had a 3 blade, and the 582's a 4 blade brolga, I spoke to the Bolly people a few weeks ago, as Brolga is no more. They said that the 3 blade 60" , "magnum" was the go for the 582, but was not certified. The were apparently approached about producing the Brolga, so that the certified drifters were looked after, and so they made a "Brolga" by Bolly, but then someone decided that this was inadequate. I think an EO is required to make it all legal, not sure how much that costs, or if a few of got together to share the costs, whether it would be worthwhile.

 

 

[seb7701]

Thanks - glad you mentioned it, as I was of the understanding that they were simply producing a replacement for the brolga which maintained certification. Obviously not the case!

 

Mainly curious in case there was some magical gains to be had from a different breed of prop. At least the three blade is consistent with other 503's...

 

 

[M61A1]

Thanks - glad you mentioned it, as I was of the understanding that they were simply producing a replacement for the brolga which maintained certification. Obviously not the case!Mainly curious in case there was some magical gains to be had from a different breed of prop. At least the three blade is consistent with other 503's...

Well, I'm told that was the plan, in regard to the certification, but after the fact someone moved the goalposts.

As for performance, keep asking, there are some that said the Bolly Brolga was a significant improvement, but others say they couldn't really notice a difference.

 

What revs are you getting at full power in flight? A more efficient prop may make for an all round improvement, but you don't really want to reduce pitch to improve the climb, and then have the engine unloaded in flight, that leads to seizing a 2 stroke. The Rotax manual goes into a bit of detail about correct setup.

 

 

[seb7701]

Thanks for the further insight. Generally speaking, maximum revs never seems to exceed 6000-6100 (I think), as reducing to cruise power (5800) is always only what seems a negligible variation from max.

 

I do think I should get a few more rpm out of it which will help climb a frag, but prop type overall fascinates me as an option.

 

 

[M61A1]

According to the A503 manual, max power should be 6250rpm, cruise at 65% @5100rpm, and climb at 75% @ 5500rpm, avoiding continuous operation between 5800-6400rpm. So it does sound as though it could be a bit over pitched. Remembering that static rpm on the ground will always be a bit lower than in flight.

 

 

[seb7701]

Yep, got those figures re the 65% and 75% figures, but I am also of the understanding that 503's really need plenty of rpm to stay healthy, ie around the 5800 mark? Mine has that rpm warning sticker, but I recall the explanation by Richard Eacott on this forum behind it and I think from memory the reasoning was somewhat redundant.

 

I tend to cruise at 5500 - 5800, but agree - a few hundred revs are missing.