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Old Jul 21, 2013, 04:35 PM
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Albuquerque, NM USA
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Build Log
Manzano Builder Kits - Mckellar GeeBee Z - 42"

Ok, so here is a teaser of, hopefully, some things to come.

Some time back I had discussed with Rob McKellar the idea of enlarging his littel 28" Gee Bee Z. He thought it would be a good idea so here is the idea.

Some of our kits are set up to cut on 4"x24" balsa and 24" long ply sheets. Our laser can cut 6"x36" sheets and 36" long ply. So, if I enlarge the cut files to 150% then the files will fit perfectly on the larger sheet. The other part is that a 50% enlargement is pretty close on wood sizes. 1/16 becomes 3/32, 1/8 becomes 3/16 and so forth. In some cases there is not a simple size up, eg, I made 3/32 into 1/8. Due to other issues some sizes would be done by laminating sheets. 1/4 becomes a sheet of 1/4 and a sheet of 1/8. Ply has the same issue. 1/8 liteply becomes a sheet of liteply and a sheet of 1/16 birch ply. So, before the build the parts are laminated to make up the necessary bits.

So, if you are expecting a build thread you will be disappointed. I will explain. Putting together one of these is not like a regular kit. There is some careful fitting of parts. Some parts need additional reinforcement. Motor mounts need to be fabricated, etc, etc.

Here are some pics of the almost finished product ready to maiden.

Specs
42" span
34 oz
2217/8 motor
3s or 2s (not decided yet)

PS sorry, I do not do detailing until after the maiden. I have Callie's graphics for this plane, also scaled up, that will be applied after it flies.
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Old Jul 21, 2013, 04:54 PM
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Albuquerque, NM USA
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More details.

First off the build went extremely smoothly. Rob's design is a great example of a "tab and slot" build and his instructions are extremely good. I did not even print a full size copy of the plans as they are not really needed for the build.

This type of build does require some engineered changes. That is why, if it works, will be sold ONLY as a "builders kit", ie, it will not fly as supplied, it will need modifications.

Why you might ask? If you think about it, the answer becomes clear. When something is enlarged the width may only increase by 1.5 times, 28" to 44". But, the volume increases by the cube, ie, 1.5 times 1.5 times 1.5 or 3.375. Weight increases with the volume. The original weighed 8.5 oz and this one weighs 34 oz (yes, I tend to build heavy ). From 10oz/sqft to 17oz/sqft, no longer a lightweight park flier.

So, knowing the weight would increase I modified the LG design. I still used the wheel pant material, but, the wire attachment to the wing and the structure in the wing are modified to handle the extra weight and speed.

I also added some reinforcing in some key places.

None of this will be part of our offering, if it comes to be. It will be up to the builder to determine where to make any changes. Modifications may also be done to make it lighter so guidelines will not be made in this regard.

Once the maiden is done I will report back on this one and see if we will try to do any more of these.

Before everyone starts writing and wanting one of our kits at 110% or 125% or even 150% keep in mind that our excursion here will be limited for several reasons.

1) We do not own the designs on our web site. The original designer will be consulted to see if they agree with such a change in their design and how we will approach the change.

2) Some designs are not suitable for such an enlargement. We will be reviewing our current offerings to see which ones might actually work.

3) Some designs have wood sizes and parts that just will not scale correctly.

4) We will not offer a kit until I or the designer have at least framed it up at the larger size, and in some cases actually flown the plane. We will not do prototypes for people so don't ask.

Basically, we will not just do enlargements for people. If we do offer enlargements they will be at 150% increase ONLY. Not 110% or 170%. So please do not ask as we will just say no.

So, standby and keep your fingers crossed

charlie
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Old Jul 21, 2013, 05:01 PM
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PS Peter Rake's designs will not be included in this review. If you want a Rake design at a different size, tell Pete. If he agrees he will design it. Be careful what you ask for. If you ask, then you are signing up for a prototype build which carries with it certain responsibilities.
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Old Jul 21, 2013, 07:11 PM
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Sonoma County CA!
Joined Jul 2007
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That looks really nice, Charlie. I've often looked at Rob's small version as benchmark for efficient design.

Looking forward to the flight report but I'm pretty sure that it will fly well at that weight.

Good luck!

Paul
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Old Jul 21, 2013, 09:00 PM
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Moab, Utah, USA
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Quote:
Originally Posted by portablevcb View Post
Why you might ask? If you think about it, the answer becomes clear. When something is enlarged the width may only increase by 1.5 times, 28" to 44". But, the volume increases by the cube, ie, 1.5 times 1.5 times 1.5 or 3.375. Weight increases with the volume. The original weighed 8.5 oz and this one weighs 34 oz (yes, I tend to build heavy ). From 10oz/sqft to 17oz/sqft, no longer a lightweight park flier.
Your numbers are good, Charlie. But when it comes to flyability, the simple wing loading going from 10 oz/ft^2 to 17 oz/ft^2 isn't the whole story. Larger aircraft can tolerate a larger wing loading. Using your figures to calculate wing cubic loading (wcl), the wcl goes from 11 to 12. That is a barely noticble difference in flyability and the two airplanes should handle very much the same. The stall speed should go from approximately 12 mph for the 8.5 ounce model to 15 mph for the 34 ounce model.

Larry
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Old Jul 21, 2013, 09:33 PM
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Thanks Larry.

I agree with you. I use wing loading to compare airplanes of similar size and weight. Like you said, it does not relate well across a wide range of sizes.

And, yes, it will be a bit faster than what I normally fly. For example, the 40" P47 only weighs 24oz. Just have to keep the speed up a bit
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Old Jul 21, 2013, 11:10 PM
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Phoenix, AZ
Joined Oct 2004
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Hi Charlie, the Gee Bee looks great! Best of luck on the maiden.

D-Rock
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Old Jul 22, 2013, 07:24 AM
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Kars, Ontario, Canada
Joined Apr 2004
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She looks great Charlie!

Best of luck on the maiden!!!

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Old Jul 22, 2013, 08:29 AM
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Norfolk, England
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Another fat little beggar, mate?
Mind you, I'm deeply upset that my designs are excluded from whatever. Downright slighted, in fact. You make me sound like a real slave driver. Oh, that's right though, I am. Silly of me to forget that.

Gee Bee looks promising. I wonder what an 18" one would fly like? Too darn fast for me, that's for certain.

Pete
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Old Jul 22, 2013, 09:24 AM
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USA, FL, Tampa
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Quote:
Originally Posted by PETERRAKE View Post
Another fat little beggar, mate?
Mind you, I'm deeply upset that my designs are excluded from whatever. Downright slighted, in fact. You make me sound like a real slave driver. Oh, that's right though, I am. Silly of me to forget that.

Gee Bee looks promising. I wonder what an 18" one would fly like? Too darn fast for me, that's for certain.

Pete
LOL!

The little E-flite GeeBee flies very well with the as3x gyro stabilization. it is a bit on the fast side but is surprisingly stable. I know, foam.. But I couldn't help myself when they were clearing them out for 60 bucks. I liked the model so much I went back and bought another one to keep as a spare! I even bought the USB dongle so I could monkey around with the gyro gain settings.

Charlie, maybe you try one of the orange gyro units in your GB?

Glenn
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Old Jul 22, 2013, 10:33 AM
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Glenn, the only gyros I use are for ground handling issues. The SPAD and my 60" Camel have them. Don't like them for flying (I say this before I have a chance to crash it ).

Pete, yes you are a slave driver, but, rightfully so!! I'd just hate to have twenty more prototypes of yours in never-never land You are also good enough to have many of your designs in different sizes already.

18" yes, probably a bit fast. But, try an 18" E type. Bit more wing area for the size of the fuse. Or a D type. No big cowl to create drag. That might make a really nice little addition to your "brick" fleet

And, yes, big round engines do appeal to me, even in these barrel bodied fuselages.

I put a watt meter on the motor last night. An 11x7 prop on 3s was around 300W!!! But the same prop on 2s was just over 100W. I will try a 10x7 on 3s and a 12x8 on 2s to see how things work out.
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Old Jul 22, 2013, 04:27 PM
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United States, MI, Roseville
Joined Dec 2000
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17 ounce w.l. is not bad, I would love one of my birds to be there
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Old Jul 22, 2013, 10:57 PM
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Mark, to you this will be a slow flier

Got a 12x8 prop on 2s and it gives 150W. I put a 10x7 on it with 3s and got just over 200W so will start with that one. Static thrust is really good too.

Looks like maiden will be Thu if winds permit.
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Old Jul 23, 2013, 04:59 PM
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United States, MI, Canton
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Hey Charlie,

Best of luck with your maiden. It really looks great. I have had a lot of fun flying my Charlie Pipes "Y" this year. I look forward to your flight report. I guess I would like to have a model of Lowell's little Yellow Bee as he did his final flights at the Wayne County Airport (now Detroit Metropolitian DTW). Which is about 20 miles from where I live. My Dad and Uncle witnessed his last flight....

Denny
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Old Jul 25, 2013, 10:45 PM
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Well, not yet. Got to the field but found that 1) the hatch was blowing off and 2) the two elevators did not line up (don't know how I missed that one ).

So, will try again on Sat or Sun.
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