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Author Topic: Mercury Mallard.  (Read 421 times)
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Fergy
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« on: July 09, 2020, 03:39:57 AM »

My first Mercury Mallard contest power model was built in 1958 from a kit Santa brought me. It was powered by an E.D. Hornet 1.46cc diesel motor bought second hand for £1.50p. After many enjoyable flights, several of which ended in trees, I lost it out of sight.

Now, a few years later I have an electric powered, R/C version with motor, rudder, and elevator controls. So hopefully it won’t be lost O.O.S. this time.

The motor is a DYS A-2830/8 1300kv., rated at 275 watts driving an APC 10 x 5” propeller, and the Mallard goes up as if powered by an E.D. Racer.
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Mercury Mallard.
Mercury Mallard.
Mercury Mallard.
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rgjones
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« Reply #1 on: November 22, 2020, 06:33:52 PM »

Hello,

I am building a mercury mallard electric with 3 channel control like yours.  I am having trouble balancing the plane and adding too much weight because of the heavy tail.  Could you give me any pointers on how you built your plane?

Thank you,
rgjones
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TimWescott
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« Reply #2 on: November 22, 2020, 07:57:11 PM »

...  I am having trouble balancing the plane and adding too much weight because of the heavy tail.  ...

Where are you trying to put the balance point?  With that ginormous tail, I'm penciling out a balance point about 80% of the wing chord back from the leading edge (note that this is eyeballing the stab area at 1/2 the wing area -- if it's less, the starting CG needs to go forward!).  If you're trying to put it 25% back, or "on the spar", it's not back nearly far enough.

Having said that -- usually free flight competition planes put the balance point way further back than would be sane for RC (I suspect that thing had it right on the trailing edge).  So if there's a balance point on the plans that's intended for free-flight, you definitely want to go farther forward than that, and that definitely requires shoving all the gear as far forward as you can, and then maybe extending the nose.  For the actual balance point I'd go with my guess above (or I'd build a chuck glider, see below), and I'd be ready to adjust the balance point forward or back.

Here's my source: http://www.zenithair.com/kit-data/ht-90-4.html  Note that I only ever use this as a starting point, and always fine-tune the CG after test flying.  Moreover, if I don't trust my numbers I grab some foam or scrap balsa and make a chuck glider to verify the balance point.  Usually I find out that I should have trusted my numbers.
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rgjones
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« Reply #3 on: November 23, 2020, 09:52:01 AM »

Thank you so much for responding to my message.  I am trying to balance at 30%.   I have been studying your pictures and see a lot of my problem is that I added control surfaces to the horizonal and vertical stabilizers instead of building them into the existing structures.  That added a lot of rear weight.  I did get the plane to fly with a temporary nose with 20 0z of weight but it flew very badly and crashed the landing gear when it landed due to the extra weight.  I  will reluctantly start to dismantle my stabilizers and rebuild the structures like you have built.  Does your plane balance at 25%?  What servos did you use in that tiny fuselage?  What size battery are you using and where did you locate it in the fuselage?
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rgjones
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« Reply #4 on: November 23, 2020, 10:05:45 AM »

 More questions.  What are the dimensions of your elevator and what sheeting thickness did you use on the fuselage?
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