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Author Topic: Goldberg 1/2A Blazer  (Read 1145 times)
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Balsa-Buster
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« on: April 20, 2011, 12:33:56 AM »

Built a 1/2 Goldberg Blazer as my first try at 1/2A power. Is set up with about 2 degrees down thrust and 2 degrees right thrust with stab tilt for right glide. Is powered by a Cox .049 sure start with Tatone tick-off engine timer. Engine has more than enough power for this plane. Plane does a nice long stable glide with right turn when test glided. Plane does fine in power climb but as engine quits does a significant dive straight down. Last flight broke the single strut landing gear and broke prop. What adjustment(s) can I make to get rid of the stall so plane glides out of the power phase? I'm currently doing test flights with 5 second engine run and plane climbs straight ahead. Would increasing the run to 10 seconds possibly cause the plane to turn right and eliminate the power stall?
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applehoney
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« Reply #1 on: April 20, 2011, 01:37:00 AM »

At five seconds you need to be seeing a little turn to the right, from which you should get a better transition. Try an inch of 3/32 sq at right side of fin TE, fly on 3 seconds, full rpm's, and watch if a turn is coming in. If it gets too tight, reduce length of strip -- and add for more turn.
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FF Bruce
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« Reply #2 on: April 20, 2011, 08:51:35 PM »

A Blazer was my first model back in 1964 and I had a Baby Bee Cox on it. The wheel was the first thing to come of. It also needed a bunch of weight in the nose to get the CG right. It did fly well as I remember. You say you have right thrust in it, you might try 2 to 3 deg. left thrust that way you can put in some right rudder tab in and that should help with the recovery. But as applehoney said go slow and don't get in to much of a hurry.
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glidermaster
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« Reply #3 on: April 21, 2011, 12:20:05 PM »

This is a pretty short plane with fin on the tail - I think I would add rudder quite cautiously - perhaps start with half of what Applehoney/Jim said.

I had this kit, and I don't recall the plan calling for right thrust (but I might be wrong, it's been a while since I sold it). I agree with Bruce though, I think removing the right thrust is safer, it's easy with short models like this to induce a spin.

You seem to be saying that the radius of recovery is too large. It stalls when the engine cuts and hasn't bottomed out of the stall before the ground intervenes, in which case you could shim the trailing edge of the tail, and make it get the nose up a bit sooner. A little nose weight can restore the glide. This in turn will make it pitch more nose up when the engine is running, but that little bit of right rudder can take care of that.

My 2 cents - but maybe a penny is all it's worth.
John
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danberry
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« Reply #4 on: April 21, 2011, 08:00:40 PM »

I'm reading that you have negative incidence in that stab.
>First question-----is it balanced correctly?

It can glide if out of balance. It cannot fly under power and glide if the CG is out of whack. Many newbies do not understand the cg and it's importance. I've seen countless (OK,3 or 4) guys with a first FF that would glide because they jacked the stab until it would glide, then ran it under power and watched it crash. CG is VERY important for an established design.

Right thrust isn't a good idea. Left thrust for a pylon plane is usually a better idea, although this plane is under-powered with a SureStart and it won't be such a problem.

The plane needs to turn right while rolling left in order to get the transition. Where do you live? Help at the field is a big deal for FF.
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FF Bruce
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« Reply #5 on: April 21, 2011, 09:25:35 PM »

Yes I agree with Danberry may be we should get a little more info. as to how much you know as to set up your model for success. Little things like warps and where they are,the balance point, engine thrust & incidence all should be in a general range and if they are your model should fly. I do hope I haven't scared you,these things are very well known ideas that gas fliers have learned over many years.
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Balsa-Buster
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« Reply #6 on: May 14, 2011, 02:30:02 PM »

Pictures of my 1/2A Blazer are attached. As noted in previous post, power is a Cox .049 sure-start with down and right thrust fed by an old Perfect 1/8 oz. tank mounted inside fuselage and fed through a Tatone tick-off fuel cutoff. Down thrust is per plan and one washer of right thrust was added per suggestion of folks in my free flight club. They advised right thrust for the lower engine mounted Blazer, but advised left thrust would work better for a high engine mounting such as on a Goldberg 1/2A High Thrust Viking. Dethermalizer is a Badge unit set up for tilt up stab. Model balances per plans at three inches from back of wing trailing edge. Some weight at tail was needed to obtain correct balance. Models does a nice long stable glide with some right turn produced by tilted stab. Will add an inch 3/32" square on the right side of fin (viewed from rear of plane?) as applehoney suggests and try more testing. Thanks to all for the comments & help.               
Attached files Thumbnail(s):
Re: Goldberg 1/2A Blazer
Re: Goldberg 1/2A Blazer
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applehoney
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« Reply #7 on: May 14, 2011, 04:13:58 PM »

Nice looking model but .... be very wary of that right thrust no matter what your club members may have said.  I'd take that washer out before you fly, and maybe place it on the other side.

The majority of pylon models use a little left thrust to keep things happy in a first second or so before speed builds up to allow intentional warps/rudder to take effect.   Don't add that piece of 3/32 sq unless flight trimming suggests it's needed
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FF Bruce
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« Reply #8 on: May 14, 2011, 05:50:45 PM »

Well your club members have it backwards.It's left thrust,right rudder for a pylon model.May be they where thinking right power pattern and thought thrust was the way to do it.You do want it to fly to the right under power,left or right in the glide(I like right glide).As Applehoney has said thrust controls the first part of the flight and as you speed up the rudder becomes more effective.By the way your model looks great,nice job. 
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johnffav8r
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« Reply #9 on: May 15, 2011, 07:54:42 AM »

A close look at your pictures shows that you have a left hand rotation pusher model type prop installed.  If that is the case, all normal power trim adjustments for a pylon type gas model are null and void. The reed valve Cox will certainly run in either direction.  Are my eyes decieving me?

John
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Balsa-Buster
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« Reply #10 on: May 17, 2011, 02:16:07 AM »

Thanks to johnffav8r.

You're right about the prop on the Blazer. Compared it to the props on my free flight rubber power planes and it appears to have opposite (pusher) configuration.

So, changed the prop to the correct tractor (puller) configuration.

Given Cox motors affinity to want to run backwards on some starts, it explains why every time I fired it up with the pusher prop it appeared to be running OK (prop wash to rear of plane), but the engine was probably running backwards.

With the prop change, am ready to attempt some more test flights.

Thanks again to all for the comments and input.       
Attached files Thumbnail(s):
Re: Goldberg 1/2A Blazer
Re: Goldberg 1/2A Blazer
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Zeiss Ikon
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« Reply #11 on: May 17, 2011, 07:15:04 AM »

Given Cox motors affinity to want to run backwards on some starts, it explains why every time I fired it up with the pusher prop it appeared to be running OK (prop wash to rear of plane), but the engine was probably running backwards.

I would say rather that the Cox reed valve engines run about equally well in either direction, so lack of a starting method that ensures a good pull-through on the second compression stroke means they sometimes start in the direction you didn't want...  Wink  When I was a kid, I learned it was often easier to get a "good" start by flipping the propeller "backward".

FWIW, if you have the engine running in left hand rotation, you should in theory be able to simply swap right for left in all setup and trim instructions (so a pylon model like that one will fly left instead of right -- might be a practical approach for a southpaw).
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