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Author Topic: Big Dog for Slow Gas  (Read 754 times)
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BigR
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« on: April 14, 2017, 12:38:52 AM »

Hi All,

I’m thinking of building a Big Dog for slow gas at the Lost Hills contest next week. The kit has been sitting around the garage for awhile and needs to be built before I lose any parts. Already the instructions have done a walkabout, but it doesn’t look too complicated, the plans are there.

I’m going to use a Veco 19 on a Taibi tank mount, salvaged from the late Tom Hammond’s Perris Special. The distance from the back of the tank mount to the prop hub (rear of the propeller) is three and three eighths inches. The plans show the firewall to be 4 inches in front of the base of the pylon. I think the nose will be too long. What would be a logical distance from the prop to the pylon?

BTW, any idea what the starting CG should be?

Thanks,

John in Kalifornia
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John in Prescott
flydean1
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« Reply #1 on: April 14, 2017, 10:57:17 PM »

Figure out a way to make the pylon moveable.  Don't glue it down until the model is finished, covered, painted etc., with engine, timer and all other hardware attached.  Shift the pylon with the wing forward or backward until the CG is where the plans show.  Then epoxy it in place.
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BigR
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« Reply #2 on: April 15, 2017, 03:36:17 AM »

That's a good idea. I will build the tail and wing then check the CG with motor, tank and timer on the plane. I'm going to estimate the approximate location of the prop and adjust the length of the fuselage to match that. Based on the TVC the CG should be 55 percent.

John in Kalifornia
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John in Prescott
danberry
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« Reply #3 on: April 15, 2017, 11:35:07 AM »

I would guess that the plane needs to balance around 75% of the wing chord. A FF Gas plane balancing at 55% is unheard of unless it has asphalt-i.e. auto surfaces.
I'm not familiar with the design unless you actually mean 'Big Dawg'. If that that's the case, Scott Lapraik can help you out.
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BigR
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« Reply #4 on: April 15, 2017, 12:29:27 PM »

Of course, it is the Big Dawg, the electric plane. I looked at the NFFS site and found some references to a conversion. One reference was to a "Shocer" fuselage. I'll look into that.

The CG was calculated by using the tail volume coefficient, which has been useful in the past. I think I'll just email the folks at Top Knotch and see what they recommend. (Lost the instructions, no CG on plans).


John in Kalifornia
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John in Prescott
danberry
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« Reply #5 on: April 15, 2017, 08:38:51 PM »

Scott and Jim Jennings are who you need to hear from.
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BigR
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« Reply #6 on: April 21, 2017, 10:11:24 PM »

Here's dem Dawg Bones. 9 ounces bare with no fittings. All doped and sanded ready to cover. The wing is very stiff; I built in the warps and think they will stay.

I opted to shorten the nose by three inches. You can see where I faired in the round firewall to the square fuselage. Yes, the timer is on the RIGHT side; I am left handed.

John in Kalifornia
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John in Prescott
Craig G
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« Reply #7 on: June 29, 2017, 09:44:22 AM »

I couldn't find the CG on the plans or in the instructions. Scott says to start at 80%. My just finished Electric A/B version balances at 77% with a few grams in the tail.
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jswain
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« Reply #8 on: June 29, 2017, 12:06:19 PM »

Hi Craig.

I'm very interested to hear your flying experiences with this model when it happens!

A flying friend and i each have one of these kits but unbuilt so could appreciate your thoughts
and plane specifics (weight, covering, motor/esc/lipo specs, etc) .

My experience with the e36 Mutt has been great and this looks just like a super-sized version so
expect the same ease of trim and even more duration.

best wishes on first flights, john s. in so. cal.

I couldn't find the CG on the plans or in the instructions. Scott says to start at 80%. My just finished Electric A/B version balances at 77% with a few grams in the tail.
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