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problem 2 or 3 blades

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Old 01-31-2010, 09:14 AM
  #26
da Rock
 
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Default RE: problem 2 or 3 blades

Try a Master Airscrew 3-blade and consider using a Dubro 3-blade ready spinner. They're made for each other. The Dubros fit MAs with no fitting required.

The idea that a 3-blade is less efficient is bad information. It's true, but actually really bad info. A 12-6 two blade isn't as efficient as a 12-7 two blade, so by the same screwed up logic, you shouldn't use 12-6s, probably one of the most used props around.

The only bad thing about 3-blade props is there are so very few of them available. And oh yes, the ignorant advice that you should avoid them.

The recommendations that exist also cause problems. I've used 12x6(3) on my OS61s, 12x8(3) on my OS75s, 14x7(3) on a number of OS91s, and they all matched the engine/airframes really well. The mfg also did not recommend those props for those engines, not even close. Once again, bad info. Engines nowadays are much more powerful than when MA printed that advice.

See the Tiger in the pictures? It and the Skybolt work best with the pictured 3-blades PLUS those props don't cover the planes with grass clippings.
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Old 02-01-2010, 04:13 AM
  #27
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Default RE: problem 2 or 3 blades

My Seagull Extra 260 with it's O.S. .91FX-Ringed Just loves the Master Airscrew 14x7(3). It flies very scale like and has that nice prop wash sound on those fast, low fly-by's.




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Old 02-01-2010, 09:33 AM
  #28
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Default RE: problem 2 or 3 blades

BTW, you can see from the last couple of posts just how far off the usual advice is concerning 3-blade props. In the last couple of posts, the Master Airscrew that works so well on OS91s is a 14x7(3) right? Actual users show those 14x7(3)s on actual models that love 'em.

I've got 4 OS91s that love the 14x7(3) MA props. One is a IMAC style that gives better vertical and everything else with that prop. Sorry to have left that picture out, but I figured 5 pictures were more than enough.

Yet Master Airscrew recommends 11x7(3) to 12x8(3)s for .90 displacement engines. Amazing..... I've got 12" 3-blades on my OS61s and they love 'em.

And Master Airscrew recommends the 14x7(3) for 1.5-1.8 engines. How far off could they be...........

No wonder people don't know how great those 3 blades work. Even the mfg is giving lousy advice.
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Old 02-20-2010, 12:12 PM
  #29
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Default RE: problem 2 or 3 blades

Dear Redfox,

First I would like to send my correction...it is not 14x8 but 14x9 3-blade MA.

My 14x9 3-blade spinner read 8200 on the ground at full throttle
Is this alright? How can i know the approximate equivalent MPH?

OS FS110-a RPM range is from 2000-11000.... but this figures are for 2-blade...mine is 3-blade

Hopefully that will be my last query.  Thanks in advance for feedback.
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Old 02-20-2010, 03:08 PM
  #30
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Default RE: problem 2 or 3 blades

[link=http://www.rbbi.com/folders/prop/propcalc.htm]speed calc[/link] here is rough speed calc.

the only way to really gauge speed is buy either a 2 points and a stopwatch, fly from one point to another point 100 feet away and time it or a radar gun
unless of course you know multi variable calculus and even then its an approximation. There are just to many variables to calculate trueairspeed,
weight of plane, drag coefficient on the plane and the prop, combo of prop diameter, side area of rudder, length of plane and rpm all effect right turning tendency, even on model this has an effect. Temp density alt and humidity also play a roll.
8200 rpm is perfect, just don't go over 9K. your 8200 will probably go up a few rpm as the motor wears in more
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Old 02-20-2010, 10:10 PM
  #31
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Default RE: problem 2 or 3 blades

Dear Redfox,

Thanks for the reply. My WM P51 Model A155 weigh 4 kgs without fuel.  A local friend of mine advise me not to play or close the needle valve
to much to lean the 4-stroke.  He said, it is not really good to lean out or close the needle valve just to get the right RPM of the engine or propeller I am testing.

At the moment, my needle valve seeting if just at 2 turns (from fully close).  I believed my OS fs110-a started from 3 to 4 opening of needle valve from fully close.

Will it damage the engine if I set the needle valve to 1.5 from fully close?

Also, another question, I also have WM P51 size 46 engine is OS 55AX and I installed a 3-blade propeller 11x8 with tru-turn spinner.
Can I get your feedback about this combination?  I flew it twice......so fast with Apc 13X6 propeller.  Now, I tried to enabled flaperon and hoping it will slow it down plus the help coming from 3-blade.  WM P51 size 46 doesn't have FLAPS.  I hope have seen this model.

Thanks again for your support and constructive comment and feedback.
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Old 02-21-2010, 11:41 AM
  #32
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Default RE: problem 2 or 3 blades

that should be put in the engine forum but

no you don't set the needle to obtain a certain desired RPM. you get your desired rpm range from the right prop. you set the needle for proper operation and proper cooling. you set the needle by finding peak rpm then richening it listening or using a tach to set the right rpm drop.

needle valve setting are all about generalization, there is no right answer. it's about experiance, a trained ear, trial and error. but for 4-strokes

after intial break in, running sloppy rich on the ground for first tanks never exceeding 4k rpm. tanks 2 and 3 still on the ground run sloppy rich but leaning out to peak rpm for a few seconds every minute.
After that run the prop your going to use for the plane. lean out to peak rpm then back off (richen the needle for an 800 rpm drop) that is approximate, if its 750-850 your fine, the rpm dynamics is going to change as the motor wears in. at about tank 5-6 you can fine tune the lower end needle for a tick over idle. the low end can be tough to get right since the low and high end needles effect each other, this also is dependant on the fuel tank being set up right, no holes in the line, tank outlet nipple even with the center of the carb on the engine. after about 2 gallons of fuel you can set the high end needle for a 500 rpm drop, but then again your in a very hot place so you might want to stick to an 800 rpm drop.

for the low end needle.
set your high end, peak rpm then richen for an 800 rpm drop
reduce throttle to idle
now pintch the fuel line to the carb and listen to it closley becuase its very suttle
if the engine just dies the low end is lean
if the engine speeds up and dies the low end is rich
if the engine runs for a couple seconds and quits its fine

now advance to full throttle and reset high end.

if you andvance and the engine quits your low end is lean, if it sputters and slowy advances your low end is rich it should advance fairly quickly with no hesitation. turn the low end in 1/4 turn incruments
once you have the low end were you want it richen the low end 1/4 turn, this with prevent flame out on final landing on a low fuel tank.

take it slow and be patient, it will take a good 15-20 min to get the high and low end close, once set leave the low end alone.


as far as the 55ax, one of my favorite engine apart from 4-strokes. the 55ax will do fine but it might be kinda of heavy for it so don't get to slow with it for the first few flights. usually with 2-strokes try to stay with a 2 blade prop. 2 strokes make their power with high rpm and little torque but the 3-blade prop will work. As far a flaperons on the wp p-51. I recommend you test the flaperon affect on the model a couple mistakes high. with that big motor and flap placement you might get into a spin, it can be fun but unwelcome when unexpected.
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Old 02-21-2010, 12:24 PM
  #33
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Default RE: problem 2 or 3 blades

Thanks AGAIN for then lesson.

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Old 02-21-2010, 01:41 PM
  #34
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Default RE: problem 2 or 3 blades

whoops that was the boat prop calc disregard here are a few calc to play with

http://brantuas.com/ezcalc/dma1.asp

http://www.csd.net/~cgadd/eflight/calcs_motortest.htm

http://www.flyingmodels.org/main_right_e.htm
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Old 05-07-2010, 02:18 AM
  #35
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Default RE: problem 2 or 3 blades

I am a little bit concern with my two World Model P51.Size 60 and 46. Last night I tried to check the CG using the GreatPlane CG Balancer i bought and found that i need to stickgrams of lead on the tail before they balanced.

WMP51 (model A155)size 60 /4-StrokeOS 110FS-a
BEFORE: 15x8 2-blade propeller Master Airscrew / 4" Plastic Spinner with aluminum backplate
NOW: 14x7 3-blade propeller Graupner / 4" Tru-Turn Spinner
REMARK: need to add 120 grams of lead on the tail
CURRENT Weight (with added lead / tank empty)= approx 4.2 KG.
as per MANUAL Stated FLYING WEIGHT = 3.6 KG

WMP51 (model A055)size 46 /2-StrokeOS 55 AX /
BEFORE: 13x6 2-blade propeller Master Airscrew / Plastic Spinner with aluminum backplate
NOW: 11x7 3-blade propeller Graupner / 3" Tru-Turn Spinner
REMARK: need to add 70 grams of lead on the tail
CURRENT Weight (with added lead / tank empty)= approx 3 KG.
as per MANUAL stated FLYING WEIGHT = 2.7 KG

Can I have your comment? since I was not able to maiden the size 60 due to unexpected call of duty and weather condition.
But I already flew size 46 before...when it is still 2-blade and it is levelled. I am concern for both weight. Am I still in their range...weight load?
I think the 3-blade propeller + tru-turn spinner made them more nose heavy.
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Old 05-07-2010, 08:10 AM
  #36
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Default RE: problem 2 or 3 blades

ece your slight overweight from stated manual figures do not seem to be particularly out of line and quite often weight figures listed in manufacturs specs are flights of fancy anyway.

The larger three blade prop you listed as 'before' for the 55 engined airplane seems quite excessive and the 11x7 you listed right in the ballpark for that engine however.


As always all modelers who actually fly should start from the beginning accumulating a
'propwall'. In otherwords a selection that you can experiment with what works best for you.

John
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Old 05-07-2010, 08:13 AM
  #37
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Default RE: problem 2 or 3 blades

Quote:
also be very patient because balancing 3 bladed props can be frustrating
Shouldn't be frustrating. Just balance the two lightest blades (so that the heaviest blade hangs straight down), then lighten the heaviest blade so that all three are equal. This is easier than balancing a two-blade prop, and you don't have to mes with the hub.
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Old 05-07-2010, 05:17 PM
  #38
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Default RE: problem 2 or 3 blades

da Rock

Your 2 War birds made me drooling Lovely pics and 3 bladed props look awesome on those.


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Old 05-09-2010, 04:17 PM
  #39
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Default RE: problem 2 or 3 blades

I have used 3 blades Master Airscrews on several occasions and found them to give very good performance. When I found the optimum prop it was slightly slower than the best two blade but take off thrust was better and approaches were more controlled due to aero-braking of the 3 blade prop.
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