Twin .020 Jr Skylark build thread
10-24-2009, 08:13 AM
#326
RE: Twin .020 Jr Skylark build thread
ORIGINAL: JMP_blackfoot
If the model weighs 20 oz and the CG is indeed 1.74'' back from the LE, and assuming the 3.5 oz lead weight is 6'' in front of the CG, then removing 2.75 oz will move the CG back 1'' to 2.74'' from the LE.
This would leave 3/4 oz of lead in the nose.
Removing the lead weight entirely would move the CG back 1.3'' to 3.04'' back from the LE.
If the model weighs 20 oz and the CG is indeed 1.74'' back from the LE, and assuming the 3.5 oz lead weight is 6'' in front of the CG, then removing 2.75 oz will move the CG back 1'' to 2.74'' from the LE.
This would leave 3/4 oz of lead in the nose.
Removing the lead weight entirely would move the CG back 1.3'' to 3.04'' back from the LE.
Please read:
If the model weighs 20 oz and the CG is indeed 1.84" back from the LE (as in drawing shown in post #41, page 2 and above), and assuming the 3.5 oz lead weight is 6" in front of the CG, then removing 2.5 oz will move the CG back 0.9" to 2.74" from the LE.
This would leave only 1 oz of lead in the nose.
Removing the lead weight entirely would move the CG back 1.3" to 3.14" back from the LE.
The plan downloaded from the link in post #20, page 1 shows the CG at 39% , as does another plan of the Jr. Falcon from the same source. This I believe to be the correct place for the CG of these models.
My trusty CG calculator yelds a figure of 40.2%.
10-24-2009, 09:01 AM
#327
RE: Twin .020 Jr Skylark build thread
Never mind, although I wondered it doesn't change much. Static margin would be only 7% now, but that's still enough for this model since it has an elevator and should be a bit aerobatic. And I as well think the C/G position shown in the plan you mentioned is all right giving 15% static margin, though it's not as aerobatic. At least in the simulator the model behaves great with the more aft C/G, partly since it saves even more nose (and over-all) weight. Maybe you'd have to shim the engines for less down thrust.
10-24-2009, 09:49 AM
#329
RE: Twin .020 Jr Skylark build thread
Very good information, thanks Bill! Now that makes sense, that gives the conventional 15% static margin, good even for a rudder-only model.
By the way, does anybody know who this Frank E. Myers was who is mentioned on many Goldberg plans? We were wondering in the "Ed Kazmirski's Taurus" thread in the Classic Pattern forum. The first Taurus plan was drawn by him.
By the way, does anybody know who this Frank E. Myers was who is mentioned on many Goldberg plans? We were wondering in the "Ed Kazmirski's Taurus" thread in the Classic Pattern forum. The first Taurus plan was drawn by him.
10-25-2009, 08:31 AM
#332
RE: Twin .020 Jr Skylark build thread
That's exactly 20% static margin. Obviously, you like it hot, or is there some decalage? 
P.S.: In case I failed to get my ideas across, I mean if the model's planform is maintained, then balancing at 2.25" gives 20% static margin, regardless of the spar position. And if both wing and stab incidence are 2 degrees (no decalage) like on the plan, the model is trimmed for rather high flight speed. That trimmed speed is more than the Pee Wees with 4.5x2 props are able to accomplish, so one has to pull up elevator all time and the model feels weird and having too less prop pitch.
Remedy would be either shimming the wing's trailing edge (1/16") or removing some nose weight (C/G to 2.8"), both giving lower trimmed flight speed. The latter would be better since weight is reduced. I'm curious how the real model will behave after modifications. (I mean I'm wondering if the calculations are right.)
P.S.: In case I failed to get my ideas across, I mean if the model's planform is maintained, then balancing at 2.25" gives 20% static margin, regardless of the spar position. And if both wing and stab incidence are 2 degrees (no decalage) like on the plan, the model is trimmed for rather high flight speed. That trimmed speed is more than the Pee Wees with 4.5x2 props are able to accomplish, so one has to pull up elevator all time and the model feels weird and having too less prop pitch.
Remedy would be either shimming the wing's trailing edge (1/16") or removing some nose weight (C/G to 2.8"), both giving lower trimmed flight speed. The latter would be better since weight is reduced. I'm curious how the real model will behave after modifications. (I mean I'm wondering if the calculations are right.)
10-25-2009, 09:37 AM
#333
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RE: Twin .020 Jr Skylark build thread
Bob Harris, Correct me If I am wrong, but didn't you take some dihedral out and change the spar arrangement on the Early RC design? Cheers! Bill
10-26-2009, 07:12 AM
#334
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RE: Twin .020 Jr Skylark build thread
Bill, My prototype, (Red One) pictured here flew with single channel Mattel pulser. I lessened the dihedral by 3/4 inch and she had over 50+ flights without any problems. The second picture is from a friend's 2 channel version with full dihedral. It also flew great with the standard incudence and balance.
The only modification I did to the Early RC kit from the original was the spars were made from hardwood instead of balsa. Their location should be exact in comparison to the original. All incendences are as per the original but I show on the plans how to lessen it back to zero to reduce the climbing tendency which was common for single channel but unwanted for multi channel.
Bob Harris
The only modification I did to the Early RC kit from the original was the spars were made from hardwood instead of balsa. Their location should be exact in comparison to the original. All incendences are as per the original but I show on the plans how to lessen it back to zero to reduce the climbing tendency which was common for single channel but unwanted for multi channel.
Bob Harris
10-26-2009, 04:28 PM
#335
RE: Twin .020 Jr Skylark build thread
One other thing to consider is this: Have you de-shellaced the Pee Wee Cylinders with fine #0000 steel wool? If they get shellaced/varnished, which happens during break-in and in areas of high humidity, the engines will not produce full power and sag when they get hot.
About the TD .010 comment: A hot TD .010 will run circles around a Pee Wee. We took the Pee Wee off my Ace Guppy and replaced it with a TD .010, that made it fly much better.
About the TD .010 comment: A hot TD .010 will run circles around a Pee Wee. We took the Pee Wee off my Ace Guppy and replaced it with a TD .010, that made it fly much better.
02-21-2010, 10:59 PM
#336
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RE: Twin .020 Jr Skylark build thread
WEDJ,
Any progress on your skylark? I just finished restoring the big brother recently. I thought it was going to be heavy but it comes in right at 5lb w/out recvr and battery. With the 2 OS .20FP's it should go pretty good. I got one question though. Does yours have a fixed nose wheel or did I miss something when reading? I didn't see where you installed any linkage for the nose wheel.
When the weather gets nice I will be doing my maiden of this fine bird.
Shane
Any progress on your skylark? I just finished restoring the big brother recently. I thought it was going to be heavy but it comes in right at 5lb w/out recvr and battery. With the 2 OS .20FP's it should go pretty good. I got one question though. Does yours have a fixed nose wheel or did I miss something when reading? I didn't see where you installed any linkage for the nose wheel.
When the weather gets nice I will be doing my maiden of this fine bird.
Shane
02-21-2010, 11:37 PM
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RE: Twin .020 Jr Skylark build thread
He's got the little Skylark with no throttle .020s, so a steerable nose wheel would be pointless.
My Skylark 56 twin, which is like yours has a steerable nose gear because I wanted one. You'll love this airplane. Just make sure you have a clear idea what to do with an engine out (my advice is free for the asking!) Russ Farris
My Skylark 56 twin, which is like yours has a steerable nose gear because I wanted one. You'll love this airplane. Just make sure you have a clear idea what to do with an engine out (my advice is free for the asking!) Russ Farris
02-22-2010, 12:12 AM
#338
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RE: Twin .020 Jr Skylark build thread
Hello Russ, I chatted with you on another thread I was trying to get some info on. I am really looking forward to flying this plane, my first twin but I feel pretty confident even if I do have an flame out on one engine. I remember asking this but can't remember what you said, but what was the CG on your 56 skylark? We have so much snow now it feels like Spring will never make it. If anything comes to mind I will definitely ask.
Thanks,
Shane
Thanks,
Shane
02-22-2010, 07:37 AM
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RE: Twin .020 Jr Skylark build thread
ORIGINAL: maxpower1954
Just make sure you have a clear idea what to do with an engine out (my advice is free for the asking!) Russ Farris
Just make sure you have a clear idea what to do with an engine out (my advice is free for the asking!) Russ Farris
02-22-2010, 08:56 AM
#340
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RE: Twin .020 Jr Skylark build thread
One idea for a twin is to have counter rotating engines and out thrust on both engines. Enya makes engine pairs for twins where one engine runs the one way and the other, the other way. http://www.enya-engine.com/store/ind...1&keyword=twin
02-22-2010, 10:04 AM
#342
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RE: Twin .020 Jr Skylark build thread
For an update, I intend to use the 35% fuel and bush and trim the 4x4 props to get 16k rpms. If that is not sufficient, I plan on getting two PeeWee 049s.
09-05-2010, 10:27 AM
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RE: Twin .020 Jr Skylark build thread
Well, after staring at this plane all winter and most of the summer, I have decided to sell it.
The PeeWee 202's just won't do it, and I have too much emotion into the plane to rip it up for electric (which I think would be the best idea.) You would have to rip into the wing for wiring, or run the wires underneath the wing exposed, I suppose.
I will be bringing it to the Octoberfest, I would like $100 firm for the airframe, and $25 each for the 020's.
Any takers? You can also send me a PM.
The PeeWee 202's just won't do it, and I have too much emotion into the plane to rip it up for electric (which I think would be the best idea.) You would have to rip into the wing for wiring, or run the wires underneath the wing exposed, I suppose.
I will be bringing it to the Octoberfest, I would like $100 firm for the airframe, and $25 each for the 020's.
Any takers? You can also send me a PM.
09-06-2010, 08:08 PM
#346
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RE: Twin .020 Jr Skylark build thread
SOLD
I hope Brian enjoys it as an electric, I can't wait to see it actually perform.
So, I still have a pair of 020's to sell.....................
I hope Brian enjoys it as an electric, I can't wait to see it actually perform.
So, I still have a pair of 020's to sell.....................
09-07-2010, 01:37 AM
#347
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RE: Twin .020 Jr Skylark build thread
ORIGINAL: WEDJ
SOLD
I hope Brian enjoys it as an electric, I can't wait to see it actually perform.
SOLD
I hope Brian enjoys it as an electric, I can't wait to see it actually perform.
Beautiful plane. I'll have my buddy size the motors and battery. If we can get the motors a little more forward and switch to pull-pull on the tail it might still weigh 20 oz with the lipo battery.
09-08-2010, 10:16 AM
#348
RE: Twin .020 Jr Skylark build thread
So sad, that plane being hacked up as an electric, what a sorry fate for a classic. All it needs is a pair of TD .020 engines and it will be a fine flyer, to make electric is travesty , especially when it's all silk and dope.
09-08-2010, 06:10 PM
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RE: Twin .020 Jr Skylark build thread
ORIGINAL: jaymen
So sad, that plane being hacked up as an electric, what a sorry fate for a classic. All it needs is a pair of TD .020 engines and it will be a fine flyer, to make electric is travesty , especially when it's all silk and dope.
So sad, that plane being hacked up as an electric, what a sorry fate for a classic. All it needs is a pair of TD .020 engines and it will be a fine flyer, to make electric is travesty , especially when it's all silk and dope.
Neu sells some really nice inrunners that would give me the 24,000 rpm of the tee dees but they are $50.00 a piece plus mounts, speed controllers, prop adapters, props and battery. Using the outrunner package Damon recommended the electric conversion complete will cost less than $55.00 shipped. Counter rotating three blade props, throttles and pop bottle cowls on the nacelles should all add up to a nice looking and flying plane. The parts should be in next week.