Aloft Forums
Welcome to Aloft Forums. Register a free account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!
Sparky, Don Srull AMA plan 414 64"
Konrad
Very Strong User
Since I mentioned the wife's tooling stash, she wanted me to close the loop.
These stainless steel pins were purchased at a specialty needlework boutique in Berkeley called Lacis. She uses them for "blocking" knitted lace (stretching it out while wet to open up the stitches). Knitters are very particular about their blocking pins since they stay in contact with the knitting for many hours while it dries, which is plenty of time for the pins to rust and stain the knitting. In an online forum, many knitters have reported that supposedly stainless steel pins odered from Amazon and other online retailers were often not stainless at all, probably just nickel plated, and thinly at that. Counterfeit or mislabeled stuff on Amazon is unfortunately pretty common, so I'd stay away from them and order the pins directly from Lacis.com. They have 2 sizes, the smaller one shown in the photo and a larger size which might be better for forming.
I found her stash of pins a bit odd in that I'd have thought these were precipitation hardened stainless steel. Most precipitation hardened stainless steel will be drawn to a magnet. These not so much. They are slightly magnetic, but the draw is weak. But my ferritic pins do have a strong magnetic pull and do rust like mad when wet!
Be careful not to mix them up with your regular rustable pins - they appear identical to the eye, and you can't use a magnet to sort them out easily since the stainless ones will stick a bit to a magnet.
These stainless steel pins were purchased at a specialty needlework boutique in Berkeley called Lacis. She uses them for "blocking" knitted lace (stretching it out while wet to open up the stitches). Knitters are very particular about their blocking pins since they stay in contact with the knitting for many hours while it dries, which is plenty of time for the pins to rust and stain the knitting. In an online forum, many knitters have reported that supposedly stainless steel pins odered from Amazon and other online retailers were often not stainless at all, probably just nickel plated, and thinly at that. Counterfeit or mislabeled stuff on Amazon is unfortunately pretty common, so I'd stay away from them and order the pins directly from Lacis.com. They have 2 sizes, the smaller one shown in the photo and a larger size which might be better for forming.
I found her stash of pins a bit odd in that I'd have thought these were precipitation hardened stainless steel. Most precipitation hardened stainless steel will be drawn to a magnet. These not so much. They are slightly magnetic, but the draw is weak. But my ferritic pins do have a strong magnetic pull and do rust like mad when wet!
Be careful not to mix them up with your regular rustable pins - they appear identical to the eye, and you can't use a magnet to sort them out easily since the stainless ones will stick a bit to a magnet.
Konrad
Very Strong User
Well, I have to admit it I'm a bit shocked at just how fast the fuselage is eating up the linear footage of 3/16 balsa strips. I still need to find some 3/16 sheet stock for much of the inlay work. But for now I'll let this dry overnight and see what I have in the morning. I hope the thing doesn't come apart like a zipper when I pull the pins.
Konrad
Very Strong User
@Hank GB Z Well, I found the framed kit and a NIB model. I really like that these come with the wood balsa blank for a hand carved prop.
Konrad
Very Strong User
Got both sides more or less framed (no inlay work, yet). I did the classic build the second side on top of the first side. Now since there are stresses being built into the longerons this tend to shift a bit when un-pinned. This is fine as long as the outline stays somewhat the same. I'll come back and make adjustments to get the sides to look closer to being the same.
Last edited:
Konrad
Very Strong User
Some more details on building a built up stick fuselage.
The glue web often left behind against the parting film offers no strength. It does have a bit of mass and can at times be seen distorting the covering. I remove this web with the tip of a number 11 blade. I then come back with some glue to make a full depth glue fillet. One needs to be careful with the fillets to make sure they don't interfere with the bulkheads to be added later.
The glue web often left behind against the parting film offers no strength. It does have a bit of mass and can at times be seen distorting the covering. I remove this web with the tip of a number 11 blade. I then come back with some glue to make a full depth glue fillet. One needs to be careful with the fillets to make sure they don't interfere with the bulkheads to be added later.
Konrad
Very Strong User
Moving into the 3rd dimension, the fuse is no longer looking like a pile of sticks. Looking at the earlier fuse sides you might notice that there was no cabin. This is because historically the little sticks that make up the cabin break off. As the cabin is really just a cube added on top of the ladder fuse I choose to built it at the same time I moved the build into the 3rd dimention. I used the alignment formers as support for the cabin pieces.
Something I found odd with the formers was that there were no cross supports to deal with the upper longeron. I added these to help keep the fuselage from developing an hour glass cross section.
I also added a lot of gussets around these alignment formers. These add little weight and really lock the fuse in place. I really like the anti-racking properties. I've left a corner open as this will be where I place the hard points for the upper anchor for the torsion bar suspension landing gear.
Now this rigid box does make it difficult to address any misalignment one might find after un-pinning. Because of alignment issues I love using the kitchen as my shop space. (The wife has a rather different perspective) Here I'm using steam to soften the glue to re-align the cabin area square. After getting a solid square datum I'll pull the nose and tail together.
Something I found odd with the formers was that there were no cross supports to deal with the upper longeron. I added these to help keep the fuselage from developing an hour glass cross section.
I also added a lot of gussets around these alignment formers. These add little weight and really lock the fuse in place. I really like the anti-racking properties. I've left a corner open as this will be where I place the hard points for the upper anchor for the torsion bar suspension landing gear.
Now this rigid box does make it difficult to address any misalignment one might find after un-pinning. Because of alignment issues I love using the kitchen as my shop space. (The wife has a rather different perspective) Here I'm using steam to soften the glue to re-align the cabin area square. After getting a solid square datum I'll pull the nose and tail together.
Konrad
Very Strong User
I do try to hold the assembly square while building to the datums (plans) with squares and blocks. But when released there are inevitable shifts that result from the built in stresses. ( It is best to try to eliminate these stresses during the build but as the longerons are often curved to get that nice fuselage shape there are stresses)
Here I preload the stresses by hand while steaming. I do try to verify the condition of the fuselage with squares and the plans as I go. The difficult part is that one often needs to over shoot the correction so that when everything cools and you let go of the parts that the fuselage is in fact square and straight. This isn't just for fuselages but also for wings should you find a twist or bow after lifting the wings from the plans.
BTW; This time was dealing with mis-alignments of a little under 2mm more like 1mm, square by most standards.
Konrad
Very Strong User
How many guys does it take to remove a twist. No that not the start of a bad joke!
For many years I thought it was the moisture in the steam that was doing the magic when we steamed the surface straight. But really it is the heat.
I was at Aloft the other day and saw a twist in one of the many prototype project wings. I offered to help straighten it. Key to doing this was being able to heat spar and sheeting on both sides and at the same time. To do this we needed 3 to 4 sets of hands. I had two guys, one on ether side (top and bottom surface) with heat guns. This heat was to soften the glue and wood fibers. Another guy acted as an anchor and the guy with the brains did the actual twisting.
I was a bit surprised at how easy it was to reshape the wing when both sides were heated at the same time. I also learned just how long it took to allow the heated fibers and glue to cool to take the new set.
So to answer the question it takes four guys to straighten a bent wing.
For many years I thought it was the moisture in the steam that was doing the magic when we steamed the surface straight. But really it is the heat.
I was at Aloft the other day and saw a twist in one of the many prototype project wings. I offered to help straighten it. Key to doing this was being able to heat spar and sheeting on both sides and at the same time. To do this we needed 3 to 4 sets of hands. I had two guys, one on ether side (top and bottom surface) with heat guns. This heat was to soften the glue and wood fibers. Another guy acted as an anchor and the guy with the brains did the actual twisting.
I was a bit surprised at how easy it was to reshape the wing when both sides were heated at the same time. I also learned just how long it took to allow the heated fibers and glue to cool to take the new set.
So to answer the question it takes four guys to straighten a bent wing.
Last edited:
Konrad
Very Strong User
When I read plans I try understand what was going on inside the head of the designer. This is because engineering is the science of compromise. I want to understand what opposing factors he was manipulating when he came to the solution laid down on the print. Generally I'm in agreement with the designer's solution. But often times I'll place the emphases some place else. Like performance over ease of manufacturing. This is why I build my models, to have a toy that is different, often superior to what was originally offered for my application.
Don Srull was a designer with a well established reputation for great flying scale free flight and small R/C scale models. So when I see a call out that doesn't make since to me I have to wonder what he saw that I don't. Here Don is calling out for a huge 1/2" doubler for the back of the cabin/wing platform. This looks odd to me. From a manufacturing perspective these small pieces are the only parts called out to be made from 1/2" stock. This adds a lot to the cost of the model, having to purchase a 1/2" sheet of balsa. I also find it odd that this bulk/weight would be added aft of the CG.
While I agree with the need to add a doubler under the rear cabin/wing platform (to address limitations with the grain). I can't see why Don called out the use of 1/2" sheet. I rarely do this but here I'm going to blindly follow what Don has drawn. Basically because he has a proven reputation as a great stick and tissue model designer. (To my eye the use of another piece of 3/16 sheet would be adequate as a doubler).
Don Srull was a designer with a well established reputation for great flying scale free flight and small R/C scale models. So when I see a call out that doesn't make since to me I have to wonder what he saw that I don't. Here Don is calling out for a huge 1/2" doubler for the back of the cabin/wing platform. This looks odd to me. From a manufacturing perspective these small pieces are the only parts called out to be made from 1/2" stock. This adds a lot to the cost of the model, having to purchase a 1/2" sheet of balsa. I also find it odd that this bulk/weight would be added aft of the CG.
While I agree with the need to add a doubler under the rear cabin/wing platform (to address limitations with the grain). I can't see why Don called out the use of 1/2" sheet. I rarely do this but here I'm going to blindly follow what Don has drawn. Basically because he has a proven reputation as a great stick and tissue model designer. (To my eye the use of another piece of 3/16 sheet would be adequate as a doubler).
Last edited:
In 1961 my friend Tim and I put a Sparky together over a few winter months. Spring came and we were ready to launch our pride and joy. We mounted a Cox .020 on the front. First flight it needed a little more wing incidence, so we did that. Next problem was how long of an engine run. With an eyedropper we figured out how long the motor should run. What we didn't figure was holding the airplane and timing the run wasn't correct. When we let go of our Sparky it started a really nice spiral going up and up and up till it went into the clouds. The engine was still running. Man that was a $4.00 engine and plane gone. The next day Tim's brother Jon was driving into town in his Model A convertible and in a very large Oaktree there was our Sparky. We were two happy kids when Jon came home with our Sparky.