Erich_F

Granting that this test was done at 5000 feet MSL in Colorado, my Extra tested at 89dB with a Brison 6.4, J&A smoke mufflers, and Mezjlik (sp) 26X10. They retested me two times because they couldn't believe the test was right. My RPM was 6600 also.

I have not had a chance to sound test here at sea level now that I'm in Tampa.

Erich

Baron Johnson

Chris,

If you want 3D capability with a 3-blade, you'd better go for a smaller diameter. For pure IMAC (which is what I used it for), it was perfect... kept very consistent speed throughout the sequence (still had unlimited vertical) and provided excellent downline braking. I've always switched to 2 blade props for 3D myself, though I've seen people fly the AM 25x12 3 blade for 3D. Not sure how that size would sound test though.

Hope this helps,
Baron

Pinhead159

My Feedback: (33)

ok thanks for all your help.
chris

Silvanskii

My Feedback: (17)

Don't get a 24x12 3 blade, at least an NX one. I had one on my 3w-100 and it ripped BADLY. I think it was prop tip flutter actually, but bad nonethless (but man it sounds cool!).

Anyone tried one of the new Enge 4 bladers?

rcob

I can tell you that the 3 blade prop will have a little more fly away on the top's and more brake on the down line.

DMichael

My Feedback: (5)

I'll back up some of the comments made already. I have been flying IMAC for the past few years and, regardless of whether or not the rules are strictly enforced, it has been evident to me that our planes are clearly getting quieter. Just the fact that you must get your plane sound checked has the effect of coercing pilots to do the right thing-- it's a badge of shame to have a truly noisy plane now at an IMAC meet.

I don't fly in that many IMAA events anymore, however, I did attend the Joe Nall this year. I have a 40% composite-arf extra with a 160 on JMB in fuse mufflers and had a Bambula 30-12. It was so quiet I couldn't hear it unless I was coming across the deck in front of me. It can be done.

Having said that, I can't say that I competely disagree with the spirit of the first post. When I go to an IMAA meet, it is now shocking to me how noisy some of the planes are- Many of the planes are still using what are essentially exhaust diverters and loud props on high revving engines- and it's not just the IMAA fellows- as was pointed out earlier, I have seen a number of "top aerobatic pilots"- guys who are well known names in the hobby- seemingly continue on without any apparent effort to quiet their planes. And I can't buy any argument that would say that they can't afford it- not by looking at the type, quantity and quality of their equipment.

I personally feel a lot of pride to be associated with a group who has taken some effective steps to quiet our planes and now believe that other special interest groups should follow IMAC's lead.


Dave Michael

rmh

The 3 blade props are quieter -across the board - no question about that -
We have seen horrible rippers changed to *****cats just by changing to a 3 blade from a two blade - no other changes - on 150 cc engines (both DA and 3W).
Personally, we are trying a slightly different tack on a new project model.
We are opting for a larger engine with small, light in cowl mufflers and higher pitched props . In two blade setups -
actually a ZDZ160 in a plane designed for 100's .
The idea is to use props that simply do not unload .
for example 28"x12 or 14" pitches and the engine not running full tilt -

Luke 3D

rather than just having a rule, they should have a score bonus for in flight quiteness.
This would also encourage more throttle control which would reduce the number of times when the prop howls surely- i have seen a lot of pilots with these 40 %ers going along in level flight at full power!Why?
The good thing about big engines is that their pitch is a lot lower so they sound a lot quieter and easy on the ear- until they howl!

rcob

I would drive across full throttle so that I would have the smash I needed for the next maneuver. Speed = more control authority.

Baron Johnson

Luke 3D,
IMAC does have an in-flight score for noise.

Luke 3D

what manuver would you have full power in level flight for?
Desides Youre flying IMAC not 3D!
Why don't you just increase the control throws for more authority?
If there is an in noise bonus (as youve said) then why are there still really noisy planes?
Luke

rmh

I thing some of these guys have not competed in IMAC.
My newest model is another attempt at a quiet, overpowered setup - a 160 in a 27 lb model.
The PLAN is running the engine way back on the power -to lower cyl pressures and swing a high pitched smaller (28") prop.
It should work - but what the heck - I can change it if it doesn't.
The 11 lb 40 setup worked great - as does the 60 in the 18 lb setup - so here goes ---

Baron Johnson

Most people flying IMAC have very quiet planes now. You may see people flying scale aerobatic planes that are still loud, but they probably are not flying IMAC with the same setup, if at all. If you get a "Too Loud" score you get warned by the CD and take the penalty on your score. If it happens the next round, you're disqualified.

You can read all about the sound issue and regulations that IMAC has in place on the Sound Task Force page of the IMAC website: http://www.mini-iac.com/pages/SoundTaskForce/stf.asp