News:



  • March 29, 2024, 06:26:05 AM

Login with username, password and session length

Author Topic: New small electric twin build thread  (Read 12852 times)

Online Frank Imbriaco

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 911
  • At the 69 Willow Grove NATS with J.D. FALCON II
Re: New small electric twin question
« Reply #50 on: January 07, 2021, 09:47:10 AM »
 IMO, what Bob is trying to do here really should motivate guys who wish to experience a twin , but desire minimal work and cost.
I built a full fuse twin," TURNING POINT", that Bob designed a few years back.
It's full house ; retracts and all.
 A treat to fly.
 In the hands of someone like Bob, it's a weapon !

Offline Dane Martin

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2804
  • heli pilot BHOR
Re: New small electric twin question
« Reply #51 on: January 07, 2021, 10:43:58 AM »
Dam. I'm jealous of yous guys that paint and make those so beautiful

Offline Paul Walker

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1626
Re: New small electric twin question
« Reply #52 on: January 07, 2021, 12:05:32 PM »
wow Bob. Cool!

Two Park 480's???

I flew the first B-17 with 4 Park 480's at 120 ounces, and power was NOT the issue!
I suspect you will have "ample" power!

Good luck.

Online Dwayne Donnelly

  • 22 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 565
  • Balsa Beavers Toronto Canada
Re: New small electric twin question
« Reply #53 on: January 07, 2021, 12:58:28 PM »
IMO, what Bob is trying to do here really should motivate guys who wish to experience a twin , but desire minimal work and cost.
I built a full fuse twin," TURNING POINT", that Bob designed a few years back.
It's full house ; retracts and all.
 A treat to fly.
 In the hands of someone like Bob, it's a weapon !

Saweet!!  y1 #^ %^@ ;D
My purpose in life is to serve as a warning to others.

Offline john e. holliday

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 22752
Re: New small electric twin question
« Reply #54 on: January 07, 2021, 12:59:53 PM »
Bob, the old DOC gets a lot of info from your construction posts and I've borrowed a lot of them on different planes.  Thanks for all you do here. H^^
John E. "DOC" Holliday
10421 West 56th Terrace
Shawnee, KANSAS  66203
AMA 23530  Have fun as I have and I am still breaking a record.

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin question
« Reply #55 on: January 07, 2021, 01:37:08 PM »
Whew! Glad to hear that Paul! Actually I have two Park 450 motors. I figured that if I was light on power I could go to the 480s. Looks like I won't have to. I'd opt for an even smaller motor if I could find one with 4mm shafts. Actually I was hoping to find a small motor with a 5mm shaft. Guess your experiences with the B-17 and the 480s should assuage my worries.

I'm thinking that a 5S 2400 pack would be more than sufficient to run both motors for 5 minutes and 20 seconds.

Doc: Glad you are getting something out of this thread. I enjoy doing these build threads. Keeps me active...

Dwayne: The photo of Frank's Turning Point twin does not do it justice; it is just gorgeous. And, it is one of the finest flying models I've ever flown. It's right up there with Gordan Delaney's Pathfinder Profile Twin, and anyone who had flown that ship will tell you that is high praise. I'm finally building a Turning Point for myself. When I designed it I was in the midst of another project and didn't want to start yet another stunt model (I already have 7 projects underway...)

 

 

Offline Joseph Patterson

  • 21 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 785
  • AMA member- Supporter
Re: New small electric twin question
« Reply #56 on: January 07, 2021, 02:19:58 PM »
            Bob, that is a great idea that you have made a reality! Yea, and its cool too!
       Doug

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin question
« Reply #57 on: January 13, 2021, 06:06:54 AM »
I left off at the point of opening the sawn slot between the leadout adjustment hole locations in the inboard Lite-Ply tip plate. That slot needs to be wide enough top to bottom to allow that leadout wires to pass through it easily. The tip plates had been glued to the core and then sanded carefully to make the edges of the pates match the core, without altering the airfoil of the wing.

At this point there are two tip options: You can simply leave the tip plates as they are and have a squared-off wing at the tips (as I did with the big test bed twin pictured somewhere above), or you can opt to add carved balsa tips as you would on a normal wing stunt model. On this occasion I chose to go with the carved balsa tips. I decided to make them about an inch wide to allow for a pleasant curve. Photo 1 below shows the two balsa tip blanks. They were cut just a bit oversize to allow them to be sanded flush with the top and bottom of the core at either end of the wing.

The next step is to tack glue the wing tip blanks to the Lite-Ply tip plates. See photo 2. Be sure to align the wing tip blanks so that there is sufficient balsa proud of the tip plates all around to allow them to be sanded flush with the plates.

When the glue has dried, carefully block sand the wing tip blanks flush with the tip plates as shown in photo 3.

Photo 4 shows that a center line has been drawn on the outer edge of wing tip blank, and that two more lines have been drawn that are parallel to the center line. In this case these lines are 3/8-inch above and below the center line.

More to come... - Bob   

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin question
« Reply #58 on: January 13, 2021, 06:25:24 AM »
I begin shaping the tips by using a number 26 Whittler's blade and a #2 X-Acto knife handle to make a 45 degree angle cut between the upper line and the top of the tip and then from the lower line to the bottom of the tip. See photos 1 and 2 below.

Carving is an acquired skill, and it was my father who taught me how to do it. He almost gave up on me because it took me so long to understand the sequence that is required and the techniques that must be mastered. I did finally "get it." The single most useful tip he gave me was to "take off the high points." To achieve the shape you want, you need to first visualize the finished product and then work slowly and carefully towards making that shape a reality. Every time to shave off a sliver of balsa you will leave two high points; one at the top of the cut, and one at the bottom of the cut. The next swipe with the blade should be to take a smaller sliver off of each of those high points. You will have to repeat this process dozens (if not hundreds...) of times in ever-diminishing amounts until the shape is complete. I hope the above is somewhat clear; it is difficult to explain such a concept in words and still photos. Like the artist said about the statue he was sculpting, "I just take off everything that doesn't look like the thing I'm trying to sculpt." Sound reasonable, but it does take a lot of practice, and a lot of patience! Work slowly and try to bring the shape on the top and bottom down equally until you are happy with the result. The carved tip - ready for sanding - should look a bit like photo #3 below.

When I have carved the tip to almost the shape I want, I use a 1-inch wide sanding stick to blend the shape to a smooth contour. Again, I look for the high points and take off the edges! See photo 4.

Moving on... - Bob
   

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin question
« Reply #59 on: January 13, 2021, 06:40:13 AM »
Photo1 below shows the tip finish sanded and ready to be "popped" off the tip plate for hollowing.

Note: I decided to go with the carved balsa tips after I had already made the adjustable leadout guide in the tip plates. If you know in advance that you are going with carved balsa tips, you can opt to put the adjustable leadout guide in the tip using whatever method you prefer.

In photo 2 the carved tip has been removed from the tip plate. And in photo 3 you can see that I have made a center line on the tip to guide me in making the opening for the leadouts.

Photo 4 Shows a 1/2-inch diameter brass tube with a sharpened end. I twist the tube while pushing down to make a clean hole in the end of the tip.

Bob

   

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin question
« Reply #60 on: January 13, 2021, 07:02:54 AM »
Photo 1 below shows that I have made two 1/2-inch dimeter holes with the sharpened brass tube, and have connected them by carefully cutting with a knife. The edges of the slot have been sanded smooth. Note that If you opted to make the adjustable leadout guide reside in the end of the wing tip, this large clearance hole is not required. I needed a wide slot to prevent the leadouts from hitting the top and bottom of the tip in case the model rolled to any degree in turbulence.

Use a router and a gouge to hollow out the tip to remove excess weight. See photo 2.

Note that with the leadout guide method that I use, the leadouts will pass through two Delrin "bushings." The bushings press fit into the holes that were drilled in the Lite-Ply tip plates. They can be retracted and moved as required to trim the model. See photo 3.

In photo 4 the carved and hollowed balsa wing tip has been permanently glued to the Lite-Ply tip plate. When the glue dries the joint will be sanded smooth with a sanding block.

Bob

 

Offline Crist Rigotti

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3856
  • Electric - The future of Old Time Stunt
Re: New small electric twin question
« Reply #61 on: January 13, 2021, 07:46:11 AM »
Sweeeet!
Crist
AMA 482497
Waxahachie, TX
Electric - The Future of Old Time Stunt

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin question
« Reply #62 on: January 13, 2021, 08:19:11 AM »
Thanks, Crist!

Okay, it's time to think about a control system.

For this model I used a Brett Buck style bellcrank. It was positioned on a 1/8-inch diameter music wire shaft and secured with two 1/8-inch wheel collars. I made shallow flats in the 1/8-inch shaft to be certain that the set screws in the wheel collars were not just hitting on the outside radius of the shaft. After the bellcrank had been positioned and secured, I mixed up some JB Weld and "welded" the wheel collars to the shaft to fully insure that they would not move in the future. See photo 1 below. Also shown in this photo is the ball link and the 3/16-inch diameter carbon fiber pushrod. Note that the aft end of the pushrod does not yet have the rear ball link installed. This will be explained later. Note also that clearance has been cut into the top of the inboard core to allow the pushrod to exit the top of the wing. Another slot to mirror this one will have to be cut in the top of the outboard core.

This model has a built-up fuselage and I wanted the pushrod to exit the wing on the center line of the two cores when they are joined. To achieve this I dry fit two 1/8-inch by 3/8-inch basswood spar pieces in the slots in the top and bottom of the inboard core, and then used a 1/8-inch diameter needle file to make a slot that was 3/4-inch deep into the core just behind the basswood pieces. Photo 2 should clarify this. There will still be room between the bellcrank mount post and the inboard side of the fuselage when the wing is installed. Two plywood plates - one on top and one on the bottom will be fit over the bellcrank mount shaft and the fuselage sides. Those plates will form the actual bellcrank mount.

Dry fit the bellcrank assembly into the inboard core. At this point you will need to verify that the bellcrank can swing through the opening in the Lite-Ply spars with no rubbing anywhere. Note that the 1/8-inch bellcrank mount shaft has been shortened so that only about 3/16-inch of the shaft extends above and below the core. Shortening the shaft requires a cutoff disk and a hand tool. The cutting generates a lot of heat. Too much heat will melt foam... Get the picture? Shorten the shaft before installing the bellcrank!

Photo 3 shows the bellcrank assembly glued into the slot in the inboard core half. I use 30 minute epoxy and micro balloons to do this. Here's a tip: Use a round toothpick to position the epoxy accurately in the slot. Put the bellcrank assembly into the slot, check the alignment one more time, and then put some more epoxy onto the bellcrank mount post. If you look closely in Photo 3 below you will be able to see the epoxy.   

Photo 4 shows the bellcrank swung aft. Check its swing in both directions before moving on.

Bob



 



 

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin question
« Reply #63 on: January 13, 2021, 10:04:32 AM »
Big piece this time! We are going to prepare to join the cores into a wing!  #^

The lower cradles (the pieces from which the cores were cut) need to have about i-inch of material removed at the root from their length. The reason for this is that we are going to lay the cores in their respective cradles and use the cradles as fixtures in which the wing halves will be joined. If the cradles were left full span, the glue might seep down from the joint and glue the cores to the cradles.  We will line up the tip end of the cores with the tip end of the cradles to insure that everything is in proper orientation. See photo 1.

On this wing the flaps are integral in the cores and will be separated from the wing after the carbon mat has been applied. You can see in the photos below that I have marked the foam portion of the flap leading edge, and the rear of the foam on the core. The separation between these two lines indicates where balsa framing will be glued on later. This piece of foam will be removed later. The flaps will have a 3/8-inch wide leading edge piece installed that will have a bevel for proper movement, and accept the hinges. The rear of the wing portion will have a 3/16-inch wide trailing edge cap installed to accept the hinges. The lines I drew may not be visible trough the carbon later on, so I have made saw cuts at the leading edge of the foam portion of the flaps and the trailing edge of the foam on the wing side at the tip on both top and bottom. I've also cut away the foam at the root to allow me to know where to later position the straight edge to enable me to cut the flaps loose and remove the foam piece between the flap leading edge and the wing trailing edge. Hopefully this is clear; if not, it will become clear later on... See photos 2 and 3 below.

Next, position the cores into their respective lower cradle pieces and line up the tip of the core with the end of the cradle. Tape the core to the cradle in several places along its length to insure that it will not shift. See photo 4.

Bob

   

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin question
« Reply #64 on: January 13, 2021, 10:31:35 AM »
Quick note here: I forgot to mention that I carved and hollowed the outboard wing tip and then installed a tip weight box into the tip. Everyone has their own favorite method of making a tip weight box, so I won't go into detail on that.

Photo 1 below shows what you will need for the next step - joining the cores into a wing! Note that the cores are taped in place in their respective lower cradles, and that a piece of 48-inch long, 1/8-inch by 3/8-inch basswood has been selected to be the top spar piece. Yes, the wing is longer than 48 inches when joined, so you will have to center the basswood spar in its slot and then add short filler pieces at the ends of the slot later on. The stresses are so low at that point on the wing that it really doesn't matter...

You can use either Titebond II Aliphatic Resin glue or 30 minute epoxy to join the cores. On this wing I used the Titebond.

Time to join the cores! Note that I glue and insert round toothpicks into the holes that held the cutting templates onto the foam blank when the cores were cut. These holes are right on the center line and they help a bit in sliding the wing together accurately. Not a must, just something I do... Apply glue to the mating face of one of the cores (see photo 2) and then carefully slide the cores together on a FLAT bench. Your wing will only be as accurate as the bench on which you join it together!. Pull the cores together using strips of masking tape.

Next, run a generous bead of glue along the bottom of the spar slot and then push the basswood spar into the channel. Some glue may ooze out from around the edges of the spar. Just use a paper towel wetted with water to clean those areas. Next, place a number of weights onto the basswood spar to hold it down firmly in the spar channel. The weights need to be supported just by the basswood spar and not be pressing down on the adjacent foam. See photo 3 Let this assembly dry throughly and then invert the wing and realign it in the cradle pieces and glue in the bottom basswood spar in the same manner as you did the top spar piece. Again, let everything dry throughly! Photos 3 and 4 should clarify the above steps for you.

Bob


Online badbill

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 385
Re: New small electric twin build thread
« Reply #65 on: January 14, 2021, 12:59:52 PM »
Awesome build, everything is so easy to understand. Question- Why not have the slot for the vertical bellcrank support in the middle of the spar slot, then just have a hole drilled in the spar that fits over it?? That way it's supported by the spar? Or is this something I'll understand in the next step  y1
Bill Davenport
AMA 28141
If some is good, and more is better, then too much is just right!

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #66 on: January 14, 2021, 02:40:52 PM »
Hi Bill:

Glad you find this easy to understand; that was my goal...

I didn't want to compromise the integrity of the basswood spar in any way; it is the heart of the Lost-Sheeting method. The way I showed to mount the crank is exactly how I do it in my fully sheeted foam wings and in my built-up wings. The two aforementioned plywood bellcrank mounts that will reside between the fuselage sides and brace up against the fuselage doublers has proven to be very effective. In this model those plywood plates will also be glued to the outside of the basswood spars for even more strength.

Also, the basswood spar is centered over the Lite-Ply vertical spar and there just isn't room fo anything else at that location.

Later - Bob

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #67 on: January 14, 2021, 05:42:28 PM »
I cut the cores so that the trailing edge of the flap section is 3/32-inch thick. That allows me to glue a strip of 1/4-inch by 3/32-inch basswood onto the back of the flap area to give that area some stiffness and to prevent it from getting dinged from use. See photo 1 below. I attach this strip with Titebond II glue and use several strips of masking tape to hold it in position accurately.

When the glue on basswood strip has dried, I lay the trailing edge down against a flat bench to support it and very carefully taper it to conform to the wing's airfoil shape. It is very important here to not allow the sanding block to mar the core's surface. See photo 2.

I next cut a piece of .2 carbon mat that is an inch to two inches larger all around than needed to do one half of one wing panel. I lightly sand the root edge of that piece of carbon to feather its edge. This prevents the carbon from forming a stress riser at one point along the wing's chord line. See photo 3.

Position the wing in the lower cradle pieces. I like to place a piece of waxed paper under the wing to prevent the glue from getting onto the cradle during the next step. Note that outboard panel is the first one that will be covered, and that I've laid the root end of the carbon over the center joint and out onto the the inboard panel a bit. Later I will overlap the inboard piece of carbon out onto the outboard panel a bit to yield a double overlap of carbon on the area where the fuselage will reside. See photo 4.

Bob


« Last Edit: January 14, 2021, 06:04:15 PM by Bob Hunt »

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #68 on: January 14, 2021, 06:00:07 PM »
The carbon is attached to the wing using a mixture of Titebond II Aliphatic Resin glue and water. The exact mixture is about 5 parts glue to 1 1/2 parts water. You will understand better how much of each to use when you actually start trying this method. The important thing is to use just enough water to allow the glue to be brushed easily through the carbon and onto the foam below. It's a "feel" thing... I use either an acid brush or a 1-inch wide chip brush to apply the glue/water mixture. See photo 1 below. You need to work fairly quickly, and insure that the carbon is laying down perfectly against the foam's surface. You can brush out any wrinkles. Be very careful trying to smooth the wrinkles out with your hand as that may actually move the fibers in the carbon enough to separate them and leave a bare spot - not good... (Don't ask me how I know...)

When you are finished brushing the glue through the carbon and the entire wing is covered, hold the wing up to a light and "candle" the surface to insure that the carbon is laying down perfectly. See photo 2. I like to wrap the carbon just a bit more than half way around the leading edge of the wing and then trim it with a sharp #11 blade knife. before the glue starts to dry. There is no photo showing this. 

After the glue has dried, you can use a sanding stick to "trim" the carbon against the trailing edge. See Photo 3.

Repeat this process to cover the other three panels on the wing. See photo 4. When the entire wing has been covered and the glue is throughly dry, very lightly sand the surface of the wing to make it smooth. Don't sand too much!

Bob


Offline Crist Rigotti

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3856
  • Electric - The future of Old Time Stunt
Re: New small electric twin build thread
« Reply #69 on: January 14, 2021, 11:03:55 PM »
Nice!
Crist
AMA 482497
Waxahachie, TX
Electric - The Future of Old Time Stunt

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #70 on: January 15, 2021, 07:36:54 AM »
Thanks, Crist!

Just a note about the carbon covered foam, its strength and rationale for making wings in this manner. I covered (no pun intended...) some of this earlier, but it needs repeating and perhaps clarifying.

The genesis (you just knew I'd get that word in here somewhere...) of this idea goes back to the days when I was the Contest Director of the Brodak Fly-In. We were adding Slow Combat to the contest menu and I needed an event director. I called my very good and long-time friend, Phil Cartier and asked him if he would serve in that capacity. He agreed, but with one big stipulation; I had to enter and fly in the slow Combat event! I told him that I didn't have any combat planes and hadn't flown in Combat since the 1960s (well, except for one flight at a meet somewhere in the 1970s). Actually I started my competition career in Combat and even flew in the Junior division at the 1961 Nats in Willow Grove.

Phil said not to worry; he'd lend me a plane, engine and arrange for a pit crew. He told me all I had to do was go as far as I could in the contest until I was eliminated and he'd be happy. Okay, that sounded fair to me. Little did I know that he planned (now, he will deny all this, but you be the judge...) to set up the "stunt kid" to be knocked around by some of the very best Combat fliers in the area, starting with our now departed good friend Gil Reedy, and followed by Bub Reece and the man himself, Phil Cartier. Hey, it was all in good fun. At least it was for me; at the end of the contest I gave Phil back his plane and engine, thanked him for the loan, and then collected my first place trophy in Slow Combat! I had won every match!

Well, naturally Phil, Bub and Gil had some well-deserved egg on their faces, but we all got a good laugh out of it. The problem was, Phil had lit an old fire and now I wanted to fly Slow Combat and Stunt competitively!  I started calling Phil almost every day with questions about how to get started with the best equipment. He suggested building one of his Gotcha series Slow Combat models. Being a foam cutter myself, I opted to work from plans and make my own fleet of planes. Phil schooled me about the construction techniques required to make a foam wing model without any sheeting. The basswood spars with shear web technique all came from Phil. He advised me to also use his plastic film covering material over the wing (I forgot the name of that material...). I fully understood the practicality of using that material, but to be truthful, I really didn't like the look of it. Yeah, my aesthetic sensibilities from years of building Stunt models kicked in.

At that point the Stunt world had discovered the .2 oz/Sq. Yd. carbon mat material, and we were attaching it to the balsa airframes using Nitrate dope. I liked the way the Stunt models looked covered with the carbon before the painting process started. I reasoned that the carbon could be attached to the raw foam wing cores using water thinned Titebond, and quickly did a test panel using that method. It worked so well, added so little weight, and imparted so much strength that I went ahead and used it on my first Slow Combat model, which, by the way I named "Slip Knot," after the Grateful Dead song of the same name. Hey, I'm a huge Jerry Garcia fan...

There was a Slow Combat event scheduled for the next weekend at Middlesex, NJ, and Phil, Gil, and Bub said that they would stop by (my house was on the way to the contest) and pick me up. I kind of felt like the "rookie" member of their Combat team at that point. They arrived at my house early in the morning and walked into my shop. I had my new carbon covered model all ready to go. I had built it like a small Stunt model; everything was carefully fitted, sanded and finished, and I even had made up a "Slip Knot" logo to go on the wing! It looked like a competition profile stunt model! I'll never forget what Phil said when he first saw that model; "You are going to fly that in Combat? It's too good looking!" 

That model flew very well; albeit for a very short time. I got mid-aired during my first match with the Slip Knot. But, I did get to have a few practice flights with it before the destruction began. Suddenly my bubble had burst; I wasn't going to repeat my performance at the Brodak meet... I probably should have quit while I was ahead.  :P

I did finish a second Slip Knot and took it out to a practice session with Phil, Bub and Gil at their field near Hershey, PA. Phil took a flight on that model and told me that it was about the best flying Slow Combat model he'd ever flown. That just amazed me.

Well, as you probably guessed, my Slow Combat career never really got off the ground (so to speak...). But, a few years later the lessons learned from building those models would pay some dividends. My good buddy, Mark Weiss called and asked me if I would like to come down to South Carolina and help out with the CL portion of the Joe Nall Fly-In. Mark and his crew had been teaching people to fly control line using the Ringrat models that are manufactured by Stevens Aero. They did the job of basic flight training perfectly, and proved to be so rugged that they have survived that duty for many years now.

Mark had the idea to have a more advanced model available at the "Nall" for those who had graduated from the Ringrat and were ready for some aerobatic training. I volunteered (was volunteered...?) to design and build five simple profile models for that year's upcoming Fly-In. Trouble was, it was only a couple of weeks away! That's when Dean Pappas and I brainstormed the Joe Nall Cadet. It was designed to look a bit like the Yak full-scale aerobatic design that had a big radial engine. Hey, that look was the vogue at that time.

I enlisted an all-star team to help make parts for the Joe Nall Cadet, including Ken Armish, Tom Hampshire. Frank Imbriaco, Mark Weiss and Buddy Wieder. I took on the chore of making the foam wings and the foam core/balsa sheeted fuselages for that model and it hit me that the carbon mat method used on the Slip Knot would be the perfect way to expedite these models. I have no idea how we did it, but on the day Ken Armish and I were scheduled to leave for the Fly-In, there were five ready to fly Cadets to put in Ken's trailer. I must at this point give some credit to my good friend, Warren Walker, who used his amazing metal working skills to produce the custom dural landing gear legs for those models in record time. Some things are just meant to be.

I reasoned when getting ready to cover the wings for the Joe Nall Cadets that only the leading edge and trailing edge areas really needed to be covered. The strength in those wing came from the basswood spars and the shear webs between them. And, those models flew very well They were full pattern capable and impressed a lot of people with their performance at the Fly-In.

Around that same time Buddy Wieder and I had built the big test bed twin that was pictured earlier in this thread. Again we covered the leading edge and the trailing edge areas - and the flaps - with the carbon mat. The test bed twin flew very well, but Dean Pappas suggested that it might fly even better with the entire wing covered with the carbon mat. And so we did that, and he was right; it flew a bit better! We then retrocovered (new word?) some of the surviving Joe Nall Cadets in that manner and they too flew better.

 I did one more model using the carbon mat/Titebond glue method recently. It is the E-Bug Lite, a profile electric version of Bob Baron's Humbug with some updated aesthetics to make it look more jet-like. See photos below.

So, when it was decided to design a simple to build, inexpensive electric twin, the carbon mat/Titebond glue method just made sense. Of course, if someone wanted to build this model with a balsa covered foam wing, it would work just as well, and I will supply that type of wing for this design in the future, as well as the Lost-Sheeting cores. Let's get it finished and test flown first...

Okay, that is a bit of backstory on this technique, and some history of the models on which it was used (thank you Sheldon...).

Later - Bob
 
« Last Edit: January 15, 2021, 11:49:22 AM by Bob Hunt »

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #71 on: January 18, 2021, 06:56:53 AM »
Hope everyone had a great weekend. And I hope Mahomes is going to be okay to go against the Bills on Sunday... Hey, I'm a life-long Giants fan, but it is hard to not root for an amazing talent like Mahomes. Come to think of it, Allen isn't to shabby either!

Okay, back to work...

In photo one below I've cut strips of .2 ounce/Sq. Yd. carbon with which to double cover just the flaps.

In photo 2 you can see that one strip of carbon has been positioned on the flap. Actually I cover forward into the area that will be removed to allow for a 3/16-inch thick balsa trailing edge cap on the wing and a 3/8-inch balsa cap on the front of the flaps. This insures that all of the flap will be covered with the second layer of carbon, but that none of the wing portion will get a second layer.

Photo 3 shows the carbon wetted with the Titebond II glue and water mixture. It will be allowed to dry thoroughly before the flaps are separated from the wing.

In photo 4 you can see that I'm using a straightedge and a sharp #11 blade to cut through the carbon and the foam along the flap separation line. Note that the knife is tilted. Repeat this on the bottom of the wing along the flap separation line and the result will be a "tent peak" of foam that can be block sanded to yield a flat surface onto which the flap leading edge cap can be glued.       

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #72 on: January 18, 2021, 07:06:15 AM »
Repeat the process of tilting the knife to cut along the back of the wing where the trailing edge cap will reside, only this time tilt the knife as shown to leave the "tent peak" of foam rearward. See photo 1.

Photo 2 shows the separated parts and the piece of foam between the wing and the flap that will be discarded.

Sand the trailing edge of the wing flat and then sand the leading edge of the flaps flat. See photo 3.

I threw photo 4 in just because it is a neat perspective of the wing. Looks long doesn't it? Looks can be deceiving...

Bob
 

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #73 on: January 18, 2021, 07:18:25 AM »
Cut two strips of 3/16-inch thick balsa that are just a bit wider than the trailing edge of the wing, and then glue them to the wing and use strips of masking tape to hold them in place. See photo 1 below. Don't use too much glue as the tape will cause it to ooze out of the joint and make it much more difficult to trim and sand in the next step .

Lay pieces of 3M Blue Painter's tape along the edge between the wing's surface and the trailing edge strips See photo 2.

I then use a Solingen Razor Plane to carefully trim the trailing edge cap down close to the tape's surface. See photo 3 below.

The next step is to sand the trailing edge caps down flush with the tape's surface as shown in photo 4.

Next, remove the tape and very carefully sand the trailing edge cap flush with the wing's surface (no photo). 

 

Offline Crist Rigotti

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3856
  • Electric - The future of Old Time Stunt
Re: New small electric twin build thread
« Reply #74 on: January 18, 2021, 08:27:32 AM »
Bob's build logs are the best!  He is very detailed and his pics are perfect.
Crist
AMA 482497
Waxahachie, TX
Electric - The Future of Old Time Stunt

Offline Randy Powell

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 10484
  • TreeTop Flyer
Re: New small electric twin build thread
« Reply #75 on: January 19, 2021, 09:08:41 AM »
That is so cool. I like the process.
Member in good standing of P.I.S.T
(Politically Incorrect Stunt Team)
AMA 67711
 Randy Powell

Offline ericrule

  • 2014 Supporters
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 330
Re: New small electric twin build thread
« Reply #76 on: January 26, 2021, 11:40:58 AM »
Hi Bob;

Saw in a pervious reply that someone said the KR does not have a retract feature. That is incorrect. KR has a retract version. It works as follows: 15 seconds after the motor starts the retract come up (this time can be adjusted) when the motor "blips" (10 seconds before the flight ends) the retracts come down.

When Dave Sabon built his electric twin I sent him one of the KR's which he used with good success. Dave also used two motors with ESC's plus a single battery.

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #77 on: February 01, 2021, 09:32:54 AM »
Good information , Eric. I have never used the KR system, so I couldn't comment on its features. I do know that the active timer I am currently using, and intend to use in my competition twins, has a retract feature that insures that the gear will come down whenever the motor (s) stop running - for any reason... That is comforting. y1

The Hubin retract function is by timer, and I used that in my Second Wind twin with no problems; I just like the added safety of the motor off/gear down feature no matter where it happens in the flight. The Fiorotti system I am using now has that feature. I'm pretty sure the Igor timer system has that feature as well, but I'm not certain of that. Someone enlighten me...

This thread has come to a brief (hopefully) stop while I'm waiting for some more .2 carbon mat. I did a stupid thing (latest in a long line of them...) and broke one of the flaps. I cut a new one, but I ran out of carbon. It should be here this week and I'll get going again.

I guess I could get started on the crutch construction as the fuselage sides are ready. Again, I have a manual that shows how I build my fuselages. I call my technique Tru-Fit Fuselage Construction. That manual (and a few others) is available for free. Just send me an email at robinhunt@rcn.com and I'll forward it (them) immediately.

Hope to be posting photos and text again soon.

Later - Bob Hunt   





 

Offline Igor Burger

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 2165
Re: New small electric twin build thread
« Reply #78 on: February 01, 2021, 02:54:22 PM »
I'm pretty sure the Igor timer system has that feature as well, but I'm not certain of that. Someone enlighten me...

I see I again missed great thread here, sorry Bob I did not see it before. I like that building, I see I must show it to our kids, I am sure they will make milion of different models this way :- ))))

But to your question -

Yes and no  ;D. My timer does not do anything only controlls motor. I always concentrate to make the function fully implemented tested and well working and not to give other side fancy functions. So no, my standard timer does not have any buttons, landing gears lights and similar things. However my timers are modular, so in case that model needs another function there is no problem to add any other specialized gadget. In this case I have specialized timer for landing gears synchronized with main timer. Of course it is programmable by Jetibox and beside its normal function it has also input for RPM sensor with adjustable rpm. It can be any standard R/C device, so it will work with sensor for standard motor, or also magnet sensor for IC engines etc. That means it can be used also without my timer with accelerometer. Optionally it can be also connected to speed sensor or centrifugal sensor, but that is not good solution because it needs very good ajusting (so that does not extend when model slows in fugures, but act safely when it is really needed, does not react to whipping etc.) and I think it is not good idea to test landing gears with risk of landing to belly. Setting RPM is much simpler, exact and repeatable even on ground. Timer has many settings, beside RPM for emergency gear down with adjustable servo angle, it has slow motion retracting to look better (but emergency gear down function is quick). Unfortunately speed setting has no effect with electronic LGs. And of course it has "go home" button/jumper.

It also works with normal servos and standard hardware with lock arm, also servos without lock arm (so that it make hardware much simpler) and it is also tested with servo-less electronic landing gears which has little bit tricky controlls. Chris can tell stories about it :- ))

Here is picture how to connect it with my normal timer.




Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #79 on: February 02, 2021, 12:53:21 PM »
Hi Igor:

Thanks for that clarification!  H^^

Later - Bob

Offline Maksim Dubovitsky

  • Trade Count: (0)
  • New Pilot
  • *
  • Posts: 14
Re: New small electric twin build thread
« Reply #80 on: February 07, 2021, 02:59:19 AM »
Hi Bob, very, very interesting project! What are the dimensions of the model - wing span, wing area? What is the expected takeoff weight ?

Online Dwayne Donnelly

  • 22 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 565
  • Balsa Beavers Toronto Canada
Re: New small electric twin build thread
« Reply #81 on: February 07, 2021, 11:25:02 AM »
Hi Bob, very, very interesting project! What are the dimensions of the model - wing span, wing area? What is the expected takeoff weight ?

Welcome aboard Maksim.  y1 #^
My purpose in life is to serve as a warning to others.

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #82 on: February 08, 2021, 09:35:02 AM »
Hi Bob, very, very interesting project! What are the dimensions of the model - wing span, wing area? What is the expected takeoff weight ?

Hi Maxsim:

Thanks for the interest in my little build blog.

The wing span of the Double Take (working title) twin is 54 1/2 inches, with a wing area of 538 square inches (including flaps). The hinge line to hinge line measurement is 16 inches. Te all up projected weight with battery is in the 45 to 47 ounce range. That may seem high for the area, but we have found that twins supply a lot more span of artificial air blast over the surfaces and hence a lot more lift, so the projected weight is actually very light for a twin.

It is my hope to be able to continue this thread very soon; still waiting for the carbon mat to make the new flap to replace the one I broke.

Later - Bob

Online Dwayne Donnelly

  • 22 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 565
  • Balsa Beavers Toronto Canada
Re: New small electric twin build thread
« Reply #83 on: February 08, 2021, 11:29:04 AM »
Hey Bob, I'm seriously considering this at around 600 sq in. range.
My purpose in life is to serve as a warning to others.

Offline Randy Powell

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 10484
  • TreeTop Flyer
Re: New small electric twin build thread
« Reply #84 on: February 08, 2021, 11:34:53 AM »
Hey Bob, where are you getting you're carbon veil?
Member in good standing of P.I.S.T
(Politically Incorrect Stunt Team)
AMA 67711
 Randy Powell

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #85 on: February 08, 2021, 01:23:55 PM »
Hey Bob, I'm seriously considering this at around 600 sq in. range.

You are a better (and braver...) man than me Gunga Din...

Bob

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #86 on: February 08, 2021, 01:24:44 PM »
Hey Bob, where are you getting you're carbon veil?

I get mine from Aerospace Composite Products, but Fiberglast and CST also carry it.

Later - Bob

Offline Randy Powell

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 10484
  • TreeTop Flyer
Re: New small electric twin build thread
« Reply #87 on: February 08, 2021, 04:04:15 PM »
Thanks, Bob.
Member in good standing of P.I.S.T
(Politically Incorrect Stunt Team)
AMA 67711
 Randy Powell

Offline Maksim Dubovitsky

  • Trade Count: (0)
  • New Pilot
  • *
  • Posts: 14
Re: New small electric twin build thread
« Reply #88 on: February 09, 2021, 09:13:46 AM »
projected weight with battery is in the 45 to 47 ounce range.

Wow, It seems that this will not be easy to do, given that the moto setup will weigh about 20 ounces, an empty plane should weigh no more than 26 Oz. What density foam are you using? And how much does a wing weigh without flaps now? And another question: will the model be painted?

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #89 on: February 09, 2021, 11:47:36 AM »
Hi Maksim:

The wing without flaps weighs 8.8 ounces. The flaps each weigh .80 ounces for a total of just over 11 ounces. The leadouts are not yet served, so there is some extra weight to be lost there, and there is no Flap horn installed yet, so there will be a few grams added there, but I think it is safe to say that the entire wing with flaps and controls will weight not over 12 ounces, and that is with the finish on! That gives me 14 ounces to hit the 26 ounce dry weight mark. That is easily doable.

See the photos below.

Later - Bob

 

Offline Maksim Dubovitsky

  • Trade Count: (0)
  • New Pilot
  • *
  • Posts: 14
Re: New small electric twin build thread
« Reply #90 on: February 10, 2021, 08:41:08 AM »
Great job, Bob!

Online Dwayne Donnelly

  • 22 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 565
  • Balsa Beavers Toronto Canada
Re: New small electric twin build thread
« Reply #91 on: May 23, 2021, 01:20:13 PM »
How's it going Bob, are you still working on this build?
Thanks
My purpose in life is to serve as a warning to others.

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #92 on: May 23, 2021, 01:57:30 PM »
Hi Dwayne:

It will be finished after the NAts. I've been working on my "real" twin in hopes of having it ready for the Nats.

Later - Bob

Offline Tom Luciano

  • 24 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 888
Re: New small electric twin build thread
« Reply #93 on: May 23, 2021, 06:08:49 PM »
Wow! Thats BA!
AMA 13001

Offline Crist Rigotti

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3856
  • Electric - The future of Old Time Stunt
Re: New small electric twin build thread
« Reply #94 on: May 23, 2021, 07:53:42 PM »
Crist
AMA 482497
Waxahachie, TX
Electric - The Future of Old Time Stunt

Online Dwayne Donnelly

  • 22 supporter
  • Trade Count: (0)
  • Captain
  • *
  • Posts: 565
  • Balsa Beavers Toronto Canada
Re: New small electric twin build thread
« Reply #95 on: May 24, 2021, 03:07:10 PM »
Hi Dwayne:

It will be finished after the NAts. I've been working on my "real" twin in hopes of having it ready for the Nats.

Later - Bob

Thanks for the reply Bob, looking forward to it, plane looks very nice good luck at the Nats  y1
My purpose in life is to serve as a warning to others.

Online Matt Colan

  • N-756355
  • AMA Member
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3440
Re: New small electric twin build thread
« Reply #96 on: May 24, 2021, 06:37:53 PM »
Looks awesome Bob!! Can’t wait to see it!!
Matt Colan

Offline Page Peterson

  • 24 supporter
  • Trade Count: (0)
  • New Pilot
  • *
  • Posts: 13
Re: New small electric twin build thread
« Reply #97 on: September 15, 2021, 10:19:48 AM »
Bob, thanks for the directions and help.

Here is how my lost sheeting attempt came out. I am going to build one more of an Oosa-Amma. I wanted the two to look similar in the air and be able to reuse some of the templates. It will go a lot faster the second time. I will also keep in mind that this is not a long term model and be a little less concerned about some things being just right. Other than paint, I am not sure this one would have taken me any longer to do as a standard plane with sheeted wings and molded fuse shells. The wing can definitely be done quickly and it turns out light.

The foam fuse shells were a bit of a pain. On the second attempt, I made a template similar to a mold buck. I stuck the foam block in with double sided tape and then sanded to template shape. That turned out well. I used a hot wire to cut out the hollow in block and then used slices of the cut out for formers. Covered the fuse foam the same way I did the wings with veil and Titebond.

Double coats of veil work pretty well for numbers and the cockpit.

Page

Offline Brent Williams

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1260
    • Fancher Handles - Presented by Brent Williams
Re: New small electric twin build thread
« Reply #98 on: September 15, 2021, 11:54:40 AM »
Looks really great Page!  I'm looking forward to seeing this in person soon.
Laser-cut, "Ted Fancher Precision-Pro" Hard Point Handle Kits are available again.  PM for info.
https://stunthanger.com/smf/brent-williams'-fancher-handles-and-cl-parts/ted-fancher's-precision-pro-handle-kit-by-brent-williams-information/

Online Bob Hunt

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2691
Re: New small electric twin build thread
« Reply #99 on: September 23, 2021, 06:00:48 AM »
Yikes, Page, that looks great! Very nice job! Please keep us informed of your progress with this model as you get some flying time on it.

Bob Hunt


Advertise Here
Tags:
 


Advertise Here