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Author Topic: LA 40 speeds up down wind, normal?  (Read 1449 times)

Offline Allen Eshleman

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LA 40 speeds up down wind, normal?
« on: May 14, 2016, 02:50:43 PM »
I am adjusting an LA 40 on a Banshee.  It has a 4 oz. Hayes Tank, no pressure.  It runs gorgeously when I get the needle set right.  Today,  I was flying in very windy weather.  I don't know the wind speek.  I didn't try any maneuvers.  However, I noticed a phenomenon that I've never experienced.  It ran slower (the engine I mean) into the wind and with the wind behind the plane, the motor leaned out.  I changed props from a 10 1/2 x 4 1/2 APC  to an old wooden 11/3.  That change did not improve anything.  I ran out of time.  Thinking of an 11/4 or 11/5.  I just never had this happen. Maybe, because I'm used to a 4-2-4 on a B-40 or Fox 35.  Any thoughts?  I got a 7 plus minute run on the 4 ounces.  Plane seemed to be flying slow.  First time - too rich.  
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Offline Mark Scarborough

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Re: LA 40 speeds up down wind, normal?
« Reply #1 on: May 14, 2016, 03:03:55 PM »
what rpm are you turning with teh 3 inch pitch prop,,
in order to get much meaningfull advice we need to have th ewhole package
rpm, ruel , brand of porp, rpm, it all matters,,
If you are using the same rpm with a 3 inch pitch prop as you are with a 4 inch prop, it will be much slower,,
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Offline Allen Eshleman

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Re: LA 40 speeds up down wind, normal?
« Reply #2 on: May 14, 2016, 03:54:54 PM »
I don't have a tach.  Started flying a tad rich, 4 cycle.   The prop is an old Power Prop  R C.  Fuel    5%  11 1/2 x 11 1/2.
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Online Dan McEntee

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Re: LA 40 speeds up down wind, normal?
« Reply #3 on: May 14, 2016, 04:28:54 PM »
   If flying in a stiff wind your engine can speed up and slow down in relation to the wind. Into the wind, extra air down the venturi draws extra fuel, thus richer, and going down wing it will speed up for the opposite reason. Extra pressure in the fuel tank vents affects it also. Some have used "caps" for the vent that restricts the vent a bit to help with this issue. Some times an intake filter of some type on the venturi will help also, but may not eliminate it altogether.  Another good reason to run pressure if you are looking for one but it will still speed up and slow down some, you just may not notice it as much. An APC 11-4 or their 11.5-4 has always worked well for me.
   Type at you later,
   Dan McEntee
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Offline Tim Wescott

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Re: LA 40 speeds up down wind, normal?
« Reply #4 on: May 14, 2016, 04:41:56 PM »
Next time it happens try a bit of fuel tubing from the tank vent no someplace where there's no airflow, like inside the crankcase backplate.

Or see if it'll work well with muffler pressure.

If we keep throwing suggestions at you, something will stick!
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Offline Steve Helmick

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Re: LA 40 speeds up down wind, normal?
« Reply #5 on: May 15, 2016, 12:51:37 AM »
Muffler pressure will fix that nicely...but you want to make really certain that you don't have a leak develop...like the muffler go loose & wonky. Running a hose into the backplate cavity is a safe fix that works reasonably well. Both help keep tiny bugs and seeds out of the fuel tank, a big plus.

What Dan was referring to will happen. It's all about wind increased line tension "powering" the airplane in the maneuvers. Props can help some, but stepping downwind and reducing line tension will help more. One of those subtle tricks, not often mentioned, sometimes hard to remember to do!   D>K Steve
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Offline Tim Wescott

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Re: LA 40 speeds up down wind, normal?
« Reply #6 on: May 15, 2016, 10:34:54 AM »
Quote from: Steve Helmick on May 15, 2016, 12:51:37 AM
Muffler pressure will fix that nicely...but you want to make really certain that you don't have a leak develop...like the muffler go loose & wonky.

Or fall apart entirely because someone's bounced it off the tarmac in a previous flight.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Steve Helmick

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Re: LA 40 speeds up down wind, normal?
« Reply #7 on: May 15, 2016, 07:08:24 PM »
Yes, but if the pressure hose keeps the muffler shards attached to the airplane so that the muffler remains can continue whacking the snot out of a nose-heavy and poorly trimmed aeroplane, the results are well worth it! WELL WORTH IT!  LL~ Steve
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"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline Mark Scarborough

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Re: LA 40 speeds up down wind, normal?
« Reply #8 on: May 15, 2016, 09:21:57 PM »
now boys,, while this was mildly traumatic to watch unfold, after the first couple laps, and finding a tree to hide behind for when that chunk of tongue finalle left the airframe on its parobolic arc, I must confess, I have not laughed so hard at a contest in awhile,, and no real serious harm was had by objects or flying devices save for the aforementioned failed tongue muffler
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For years the rat race had me going around in circles, Now I do it for fun!
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