2 blade V 3 Blade vexed question

[Stu_D]

Over the last week or so i have been mulling over the following question .
(Bear in mind this relates to IMAC flying of 35 - 40% planes .)

Can we get the same or better advantages from a higher pitch 2 Blade
than from using a smaller diam/same pitch three blade prop ?

I have posed this question to three people who are much smarter than me
and was given three different answears . To paraphrase the answers they
were the following .

1 :- No
2 :- Sometimes
3 :- Depends what you like ,not what it does.

I suppose all put togethet these were the answers I wanted because it shows that
there is no clear view .

When the question crossed my mind I was thinking how almost all of the glow
pattern flyers have been using 12 - 14 pitch for years and seem to be pretty happy
with the results . When I pointed this out to one of my friends he said the pattern
guys have much lower drag and better power to weight than we have , good point.

Surley the losses in efficiency of a three blade could be made up by a two blader
and the noise problem would be removed by a higher pitch . While I know many
brands of air frames are just too low to consider large diam props and a 3 Blade
IS the only option but what about it when size is not an issue .

What do you guys think and who has done testing in this direction .

Stu

[Buzz Lightyear]

	Quote: Originally Posted by Stu_D
	Over the last week or so i have been mulling over the following question . (Bear in mind this relates to IMAC flying of 35 - 40% planes .) Can we get the same or better advantages from a higher pitch 2 Blade than from using a smaller diam/same pitch three blade prop ? I have posed this question to three people who are much smarter than me and was given three different answears . To paraphrase the answers they were the following . 1 :- No 2 :- Sometimes 3 :- Depends what you like ,not what it does. I suppose all put togethet these were the answers I wanted because it shows that there is no clear view . When the question crossed my mind I was thinking how almost all of the glow pattern flyers have been using 12 - 14 pitch for years and seem to be pretty happy with the results . When I pointed this out to one of my friends he said the pattern guys have much lower drag and better power to weight than we have , good point. Surley the losses in efficiency of a three blade could be made up by a two blader and the noise problem would be removed by a higher pitch . While I know many brands of air frames are just too low to consider large diam props and a 3 Blade IS the only option but what about it when size is not an issue . What do you guys think and who has done testing in this direction . Stu

Good question Stu

IMO, it all boils down to the airframe/prop combo.

I agree totally that the Yak needs a 2 blade prop. When you consider different weather conditions and field altitudes where we are holding comps, you need a good around prop.

Obviously the C-ARF MX2 and 260 are going to go well on pretty much any prop you throw on it. Yeh, slight speed change and noise change, but the model will do anything you need it to. This is out of experience and trying several prop on the MX2 and 260. Both have Mejzlik 28x12 3 blades on them now.....but they are not draggy Yaks!

I used a Engel 31.5 x 14 2 blade on the C-ARF 3.0 Exta 330. Loved it! I think Chrisby used it on the Yak and liked it too. Strangely it is noisier than a Mejzlik 32x10, but pulled like a train....sounded like a Mooo Cow

On the Extra the Engel 31.5x14 was hard to land due to pitch...remembering the 16x14 on the OS140RX days. I would think the Yak would be OK.

Lucky for us IMAC is only a in flight noise score, so if you are good on the throttle, you can get away with a 2 blade. This is the direction I am going to head anyway.

Dave Macca has always said we should be running more pitch to replace diameter.

I am going to avoid using 3 blade props if I can.

With due respect to the novice pilot, I think they are better off with a 3 blade prop as it is smoother and if their not good with throttle management, the noise police will have them very quickly. Rip that prop a couple of times at a comp and your comp is over. IMO A 3 blade will benefit them.

Sounds like we are on the same wave length.

Talk more at Albury

Cheers

Anthony

[jack strickland]

	Quote: Originally Posted by Stu_D
	Over the last week or so i have been mulling over the following question . (Bear in mind this relates to IMAC flying of 35 - 40% planes .) Can we get the same or better advantages from a higher pitch 2 Blade than from using a smaller diam/same pitch three blade prop ? I have posed this question to three people who are much smarter than me and was given three different answears . To paraphrase the answers they were the following . 1 :- No 2 :- Sometimes 3 :- Depends what you like ,not what it does. I suppose all put togethet these were the answers I wanted because it shows that there is no clear view . When the question crossed my mind I was thinking how almost all of the glow pattern flyers have been using 12 - 14 pitch for years and seem to be pretty happy with the results . When I pointed this out to one of my friends he said the pattern guys have much lower drag and better power to weight than we have , good point. Surley the losses in efficiency of a three blade could be made up by a two blader and the noise problem would be removed by a higher pitch . While I know many brands of air frames are just too low to consider large diam props and a 3 Blade IS the only option but what about it when size is not an issue . What do you guys think and who has done testing in this direction . Stu

Hi Stu, I'm confused about the statement that pattern planes have better power to weight ratio than our big birds. Was not aware that pattern engines/props would develop three times the thrust that the plane weighs. Please enlighten me regarding this. Thanks
Regards
Jack