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Maintaining Even RPM... HOW???

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Old 09-26-2008, 11:40 PM
  #26
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Default RE: Maintaining Even RPM... HOW???

sledge_78: To paraphrase an old Hair Club ad: I have not only READ the horror stories, but experienced them personally. Keep both fans blowin'!!

spotter: I don't understand the question.

mt

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Old 09-26-2008, 11:44 PM
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Default RE: Maintaining Even RPM... HOW???

Thank You, Sir!

May I have another?!
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Old 09-26-2008, 11:47 PM
  #28
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Default RE: Maintaining Even RPM... HOW???

spotter:

Oh! Post # 9.

Maybe it's Aussie for "low speed needle?"
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Old 09-27-2008, 12:05 AM
  #29
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Default RE: Maintaining Even RPM... HOW???

Explanations for the morbidly curious:

Picture #1: My first VQ-38....8th flight. Cause of Death: Pure Pilot Stupidity. Flying at a twin meet. I went up first of three 38's for a planned "Squadron Flight." Waited a while for others to get in air, then had so much fun I lost track of time. About 2,000 ft away on Turn 2 of my last oval when one engine ran out of gas. Never had a chance.

Picture #2: My beloved Yellow-38 with 3W-24's....flew her for almost four years till one October during an otherwise beautiful flight, I lost my right engine. I was more experienced and it was closer to me, so I ALMOST got 'er slowed down and leveled off before impact. It took me months to figure out why my engine stopped. Cause of Death: cracked solder joint at the switch caused intermittent loss of ignition power. Didn't figure that out till I flew that engine on a single-prop plane several times!

Just goes to show you how many teensy little things can go wrong and perhaps is an argument for Twin Sync no matter how careful you are with your engines.

mt
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Old 09-27-2008, 06:16 AM
  #30
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Default RE: Maintaining Even RPM... HOW???

Hi!
First of all...Your OS .60 engines are way, way to large and powerful (No! Throttle management is no option) for the relatively small B-25.
If you insist it will fly like a pattern plane and not like a B-25...at scale speed.

Second your OS .60 two strokes are one of the best for not saying the best engines available when it comes to reliability and throtteling.

Using the correct fuel (5-10% nitro) and right glow plug (OS 8 or Enya 3) and using 11x8, 12x6, 13x5,14x4W,14x5N APC or RAM props,depending on model is vital. Also using the correct tank and tank placement is vital. Tettra "Bubbless" tanks are superior to everything else but next best is using 2 clunks (Uni-flow system) in an ordinary Sullivan or Kavan tank .
It's no problem having the engines run nearly exactly the same if you follow these recommendations.
A good article of how to Setting up a a twin was written in the August 2007 issue of Model Aviation.
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Old 09-27-2008, 09:34 AM
  #31
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Default RE: Maintaining Even RPM... HOW???

Not sure how my credibility's fairing after my last coupla posts, but I have to disagree that O.S. .61's are too much power. Tune them to 3-blade props and use good throttle control and take advantage of all the excellent qualities of the engine you mentioned.

Were you talking about too much power for the 70" B-25 or the 94" P-38?

For the B-25, maybe a little too much.

For a 94" P-38, I would be tempted to upgrade to O.S. 91 2-strokes.

Here's a link to one of my 83" P-38's flying on O.S. .61's

www.youtube.com/watch?v=V5ndsHN7hE8

Clearly NOT too much power.

mt

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Old 09-28-2008, 08:20 PM
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Default RE: Maintaining Even RPM... HOW???

Gents,
Thanks again for the tips, absolutely priceless stuff! My engines run perfectly via the tests and they were set that way individually. The only reason I use the knob is to set RPM. The issue now is spool up differential. Due to the lag in spool up on the left it’s pulling hard to the left on the ground roll. What cha think about them apples?...
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Old 10-15-2008, 09:25 PM
  #33
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Default RE: Maintaining Even RPM... HOW???

Although I agree with nearly all of the suggestions in this fourm, trust me, after flying big iron for a number of years, engine sync IS important. The big planes WILL tail wag (yaw)with engines out of sync. The models will do the same to a lesser degree.
Currently I operate a Twinstar with O.S. .25's (first twin trainer), Seagull Dual Ace with EVO .52'S (installed with shoehorn), and Nitro D.H. Mosquito with O.S. .040 cases and .046 head, liner, and pistons. All planes have the engines Y-harnessed on the throttle channel. Radio equip. JR 6102, 6 channel Tx.
Idle is set to within 200-250 RPM, full throttle is set (by hi-speed needle) to sync the strongest engine to the weaker engine. The way I have found best to find the strong engine is to run a tank of fuel through each engine, set at peak, and check run time.
However, in my opinion, the best way to get relibile performance is to do GOOD break-in runs on the TEST STAND.
Channel mixing may work well, or the sync units may do the job, but good engine and fuel system set up is of first priority.

KEEP THE BLUE SIDE UP

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Old 10-16-2008, 11:10 AM
  #34
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Default RE: Maintaining Even RPM... HOW???

Quote:
The issue now is spool up differential. Due to the lag in spool up on the left it’s pulling hard to the left on the ground roll. What cha think about them apples?...
The slow engine is too rich on the low speed needle. The low speed needle controls the mixture over the entire lower half of the throttle range and it generally has to be as lean as it can be without killing the engine on accelleration.

The only other thing it could be is the glow plug. Both should be the same type and age.

Jim
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