Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
September 26, 2018, 05:01:26 AM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: [1] 2 3 4   Go Down
Print
Author Topic: Korda Class C Tractor  (Read 3922 times)
0 Members and 1 Guest are viewing this topic.
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« on: July 12, 2018, 04:45:58 PM »

This model has been highly recommended to me by Stan Buddenbohm and Herb Kothe, both legendary free flight modelers.  My five year old Gollywock has been gaining weight from various repairs.  Therefore, I decided I needed to build a new OTR small stick model. The wing span of the Korda C is 38 inches (flat). Its wing area is 143.3-inches (projected).

I could not find a build thread on this model on HPA so I decided I would start one.

I purchased the plan and short kit from Bob Holman Plans some time ago.  They have been sitting on a shelf in my garage. Bob provides excellent quality plans and laser cut parts for a very reasonable price.

The fuselage of the Korda C is built using 3/32 x 3/32 balsa sticks.  I am a little surprised that the relatively large fuselage of this OTR outdoor duration model is not built with 1/8 x 1/8 balsa sticks. But I stuck to the plan.  It said to use heavy balsa for the longerons so I used 12# balsa for those parts. It said to use medium balsa for the uprights so I used 7# balsa for those parts. The weight of the fuselage bones is 10.88 grams. The wing seems relatively small (in both span and chord) compared to the size of the fuselage, but Dick Korda was a legendary OTR builder and flier in the 1930's so I will trust his design.

I purchased a 17-inch balsa wood prop blank from Volare Products. It will need a lot of carving and sanding. I might cap the LE and TE of the prop with strips of bass wood. Alternatively, I may cover this prop with fiberglass and epoxy. I have had good results covering balsa wood props with lightweight fiberglass cloth and epoxy resin from SIG.  It is, however, a very messy and smelly process.  Surprisingly, covering a balsa wood prop in this fashion does not add very much weight. I believe that it adds a lot of strength and durability.

I plan to cover the fuselage of my Korda C with Polyspan "synthetic tissue."  It is much more resistant to punctures than domestic tissue or Esaki tissue. The wing and tail feathers of my Korda C will probably be covered with Esaki tissue. A Korda C with plastic film covering just wouldn't look right as it is vintage model.

A published list from a seasoned old time flier named Gene Wallock gives the preferred rubber motor sizes for many OTR models. I guess it is pretty well accepted. He recommends 16 strands of 1/8 inch rubber and a length of 36 inches for the Korda C.  That sounds like a good starting point to me.  The hook-to-peg distance will be around 26 inches, so I will probably have to braid the rubber motor.

I am going to build the wing in two halves that mate in order that the wing fit in to one of my standard clear plastic Christmas wrapping paper boxes that I use to transport my models.  I did this with my KIWI KOOP F1G and the system worked out very well. I followed Hepcat's advice on how to make a relaible detachable wing connection that was easy to build and use and maintains the required stiffness.

My plan is to make the fin plug into the stab.  The fin is extremely tall, and permanently assembled tail feathers would be cumbersome to transport.  A couple of .030-inch CF rods extending from the root of the fin and a couple of .062-inch Aluminum tube sockets in the stab should do the trick. I might instead use a plug-in tongue on the lower end of the fin.

I can glue one or more balsa wood wedges onto the TE of the fin to adjust the right turn in the power phase, if needed. Stan taught me that trick.  I'll mostly rely on thrust adjustments to achieve the optimum flight pattern in the power phase.  Stab tilt will be used to effectuate a right turn in the glide. With a big free wheeling prop, I don't think much stab tilt will be needed to make the model turn right in the glide.  

My Korda C will have a small balsa box in the fuselage under the wing for carrying one of my RF trackers.  I can just see this model flying OOS.  The Korda C is so large and apparently flies so well that I am willing to accept the 3 gram weight penalty imposed by carrying the RF tracker.

If anyone has built this model and has some advice, please post the same.  Thank you.
Attached files Thumbnail(s):
Korda Class C Tractor
Korda Class C Tractor
« Last Edit: July 12, 2018, 04:57:03 PM by calgoddard » Logged
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #1 on: July 12, 2018, 06:08:46 PM »

Here is the best picture of a Korda Class C tractor that I could find.

Attached files Thumbnail(s):
Re: Korda Class C Tractor
Logged
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #2 on: July 13, 2018, 09:45:27 AM »

The plan for the Korda C does not indicate any wash-out in the wing tips.

The 38-inch span wing has a horizontal center section and two outer wing sections with 3 1/2-inches of dihedral.  See the photo of the Korda C model in Reply #1 to get a feel for the overall configuration of the wing. The wing has under camber which I understand provides increased lift at lower speeds but increased drag at higher speeds, compared to a wing with a flat bottom.

I normally build washout into the wing tips of my outdoor rubber powered models.  I have heard many explanations for the advantages of wash-out in the wing tips. The explanation the makes the most sense to me is that it improves lateral stability by lessening the chance that the model will spiral into the ground during the glide portion of the flight.

When I built my "New Gollywock" the plan also did not show any wash-out. I asked John Hutchison (FAC Hall of Fame member) whether I should build wash-out into the wing tips of my New Gollywock. He said it was not necessary. So I followed his advice and that model flies great.  The only time it spiraled into the ground was when I launched it without noticing that one of the tiplets on the stab had previously broken away. When it transitioned into the glide, it gradually began circling tighter and tighter until it spiraled into the ground.  Apparently the drag of the lone tiplet on the stab caused this.  When I replaced the missing tiplet, I got the same great flights as always.

For those not familiar with the New Gollywock (1941), it is basically the same as the original Gollywock (1939) except that the former has no sub-fin and instead has tiplets on the ends of the horizontal stabilizer. But I have digressed.

Dick Korda was reportedly a very accomplished flier.  It would seem that however he built his Korda C would be the way to go.  But perhaps the advantages of wash-out in the wing tips had not yet been discovered in the 1930's.

So you experts out there, should I build wash-out into the wing tips of my Korda C?
« Last Edit: July 13, 2018, 10:29:50 AM by calgoddard » Logged
Bigbandito
Silver Member
****

Kudos: 5
Offline Offline

United States United States

Posts: 153




Ignore
« Reply #3 on: July 13, 2018, 11:26:10 AM »

Thanks for posting Cal. I'll be following to learn new tricks and cheer you on.
Logged

"If you love something, set it free...  Just make sure you've got a DT on it."  - Richard Bach (paraphrased)
strat-o
Gold Member
*****

Kudos: 5
Offline Offline

United States United States

Posts: 315



Ignore
« Reply #4 on: July 13, 2018, 02:09:23 PM »

Can this model compete in OTR with a folding prop?

Marlin
Logged
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #5 on: July 13, 2018, 04:03:02 PM »

strat-o -

You asked an interesting question.

The Korda Class C Tractor was designed to fly with a fixed 17-inch prop.  

I am not familiar with the AMA rules or the SAM rules that would apply to Old Time Rubber ("OTR") models.  It appears that the Korda Class C Tractor would be considered a "small rubber stick" under the SAM rules. AMA does not have an "OTR" event per se. It looks like the Korda Class C Tractor could be flown in the Moffett event.

I don't know if you can change the prop from that shown on the plan under the SAM rules.

The rules of the Flying Aces Club ("FAC") prohibit folding props on all models.

The model I am building is the Korda Class C Tractor.  Don't get it mixed up with the Korda Class C World Record which is a different model.  Plans for the latter model are available at www.outerzone.co.uk
Logged
Bargle
Gold Member
*****

Kudos: 22
Offline Offline

United States United States

Posts: 675




Ignore
« Reply #6 on: July 14, 2018, 12:22:08 PM »

Here is the best picture of a Korda Class C tractor that I could find.

Plane looks good, but how does that guy see with that big white thing over his face? Wink
Logged
tgwhitley
Bronze Member
***

Kudos: 1
Offline Offline

United States United States

Posts: 32



Ignore
« Reply #7 on: July 14, 2018, 11:19:57 PM »

FFQ issue # 52 has article with useful information about Korda C Stick. Tips from several great fliers Karl Gies, Carl Redlin, Herb Kothe, Ed Hardin, and Stan Buddenbolm.  Search for ways to buy back issues in PDF format at Free Flight Quarterly.
Tim
Logged
Hepcat
Platinum Member
******

Kudos: 271
Offline Offline

United Kingdom United Kingdom

Posts: 1,774



Ignore
« Reply #8 on: July 15, 2018, 09:38:38 AM »

Cal,
I am probably about to lose all my friends so I will try to be brief so that I can run away before they get me.
Scale models may occasionaly need a little wash out on the tips if a bad subject has been selected to model.  Duration FF models should not need any.  Worries about tip stalling and dropping into a spin are usually nonsense.  FF models don't have a man inside pulling back on a stick to make the aeroplane fly slower and slower for a landing.  If a FF model is approaching a stall it is better to get it over early and settle in a few undulations. If the stall is delayed, perhaps by excess thrust or rank bad trimming then the stall may continue on and on and on until it reaches the ground. It is important to remember that a FF model almost invariably flies in circles.  If it stalls you hope it will drop the wing that is on the inside of the turn and do a turn or two, which is the quickest way out of a stall.

I think you will find that most expert follow this principle by having more incidence on the inside wing.  They will almost certainly vary on which panel has what incidence and that, of course, is a major reason of why polyhedral wings are so popular.
John.
   
Logged
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #9 on: July 15, 2018, 09:43:05 AM »

tgwhitley -

Thanks for the tip on FFQ issue #52.  I will get a copy of the same.

Hepcat - thanks for you explanation.  Per your advice, I will not build wash-out into the wing tips of my Korda C. That makes the building process easier as well.
Logged
danberry
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 943



Ignore
« Reply #10 on: July 15, 2018, 11:56:33 PM »

Put some washout in it. You won't regret it.
Logged
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #11 on: July 16, 2018, 03:13:40 PM »

I built the nose block for my Korda C Tractor.

There is nothing novel in my approach but I will summarize the same for those readers of this thread who may be new to building OTR models. Also, some of you experts may tell me how to improve my technique.

When I got started in this hobby John Hutchsion emphasized that a tight fitting nose block is extremely important. It is necessary in order to maintain the thrust lines that you arrive at during the trimming process that are critical to the model flying correctly during the power phase. Of course, he was right about this.

I laminated four rectangles of medium density 1/8-inch sheet balsa wood, cross-grain, with Titebond carpenter’s glue. The sheet rectangles were slightly larger than the width and height of the front end of the fuselage. I drew an outline of the nose of the fuselage onto one side of the cured laminated block. I used that outline as a guide when I sawed the four sides with a balsa saw so that the block was close in dimensions to the outer dimensions of the front end of the fuselage.  I glued a backing sheet of 1/64-inch plywood to the rear side of the laminated block using Titebond carpenter’s glue.

I then built a snug fitting rectangular frame of ¼-inch x 1/16-inch hard balsa wood strips inside the nose, tacking the corners of the frame together lightly with medium viscosity CA so they would not be glued to the nose. I then glued the rear side of the nose block (the plywood side) to the rectangular frame with the same CA, being careful to align the nose block with the exterior of the fuselage.  After a few minutes, I pulled the nose block out of the fuselage and liberally applied CA to the long joints between the rectangular frame and the plywood backing sheet.  After some drying time, careful sanding of the outer sides of the rectangular frame was needed so that I could fully insert the nose block into the fuselage.

The front of the nose block was sanded into a rounded shape using a Dremel tool and a sanding block.

I drilled a 3/16-inch hole through the center of the nose block to receive an Aluminum thrust bearing that I purchased from either Volare Products or Retro RC. It is designed to receive a .062-inch music wire prop shaft.  The relatively large 17-inch prop of the Korda C will be driven with a lot of torque so I am not comfortable with using anything smaller than a .062-inch prop shaft.  I suppose you could get away with a .055-inch prop shaft, but then you might have difficulty finding a suitable thrust bearing. I used 30-minute epoxy to glue the Aluminum thrust bearing into the nose block.

I coated the entire front surface of the rounded nose block with medium viscosity CA. An easy way to do this is to put a polyethylene sandwich bag over one hand and use it to spread around CA liberally applied to the nose block. The glue won’t stick to the sandwich bag.  The cured CA gives the nose block a hard outer shell to resist any possible deformation under load. The shell of CA also resists motor lube.

The upper outer edge of the rectangular frame on the rear side of the nose block was sanded round.  This allows the nose block to pivot out of the front end of the fuselage should a blade of the propeller strike the ground on landing. This lessens the chance of having a broken balsa wood prop.  The rounded edge has been colored with a red Sharpie pen to remind me that the nose block is inserted with this edge UP.

Using CA I glued two segments of wooden toothpick into corresponding 3/32-inch holes drilled into the upper and lower sides of the nose block. They hold the rubber band that secures the nose block to the front end of the fuselage. You cannot rely on the snug fit to avoid losing the nose block and prop in flight or upon landing.  The rubber band that holds on the nose block will stretch to allow the nose block to pivot if a prop blade strikes the ground upon landing.

The plan for the Korda C Tractor indicates 2 degrees of down thrust and 1 degree of right thrust. I sanded the front end of the fuselage with a sanding block and got something close to this.  I may have sanded in more like 2 degrees of right thrust. However, I will sand in further adjustments to the thrust line, as necessary, during the trimming process.  Once any final sanding of the front end of the fuselage has taken place I may coat it with CA or glue on some 1/64-inch plywood strips to make it more durable and to lock in the optimum thrust line. The finished nose block of my Korda C came is much heavier than I would like at 5.01 grams but it is extremely strong.  Besides, as several experts have told me “nose weight is your friend.”

Over the years I have learned that building a larger outdoor model strong is very important, if you want it to last.  Light is good, to a point, but not to the point where the model is prone to warping or breaking during normal handling.

Stan Buddenbohm told me he launched his Korda C at 40 inch-ounces of torque.  Wow! If I want to get near that launch torque, I better have a strong model.

Any input about my build would be appreciated. Thank you for reading this post.
Attached files Thumbnail(s):
Re: Korda Class C Tractor
Re: Korda Class C Tractor
« Last Edit: July 16, 2018, 03:31:06 PM by calgoddard » Logged
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #12 on: July 17, 2018, 09:00:04 PM »

I carved the 17-inch balsa prop from a Superior Props blank that I purchased from Volare Products.  This prop blank is shown in a photo that is attached to the first post in this thread.

I used a sharp knife and followed the usual technique.  The carving took a little over an hour.  There is a nice video on YouTube that shows the technique.

As I recall the P/D of this prop should turn out to be 1.3, which I think will be good for this model.  The plan does not indicate the P/D of the prop. It just shows how to cut the prop blank for carving.

As you can see in the photos, after some sanding, the weight is currently a little over 10 grams.  The prop blank was marked to indicate 7.5# per cubic foot density.  I still need to do some more sanding, and in particular, sanding of the rear sides of the blades to yield some under camber.

I am leaning toward covering the prop with light weight fiber glass cloth and epoxy resin from SIG.  I have done this in the past and such covering adds considerable strength and durability with surprisingly little weight gain.
Attached files Thumbnail(s):
Re: Korda Class C Tractor
Re: Korda Class C Tractor
« Last Edit: July 17, 2018, 09:12:44 PM by calgoddard » Logged
Craig G
Bronze Member
***

Kudos: 2
Offline Offline

United States United States

Posts: 39



Ignore
« Reply #13 on: July 18, 2018, 12:25:24 PM »

Looking great Cal. I have a new-to-me Tractor that I finished setting up the DT last night, hoping to get it going in time for some official flights at the NATS next week.
Logged
Red Buzzard
Bronze Member
***

Kudos: 3
Offline Offline

United States United States

Posts: 93



Ignore
« Reply #14 on: July 18, 2018, 01:33:09 PM »

Hi Cal,

I am sure that George at Volare took the original prop profile into consideration. It's worth remembering freewheeling props require somewhat higher pitches to reduce drag during the glide. It will also give you a longer prop run and enhance the LONG motor this model can accommodate. Take advantage of it. If you want to make a tweak use a higher p/d ratio. The only other worthwhile(?) note I can offer is to add a bit of LEFT rudder for initial testing. The lifting rudder can give a fair amount of RIGHT turn in early testing at low torque. Both of my Lanzo Duplexes took an alarming right swoop on low turns that left me breathless. In the end I trimmed them both with 1/32" LEFT skew of the entire tail group. I could have just as easily used a tab. I flew them both right/right with the original props.

Bill
Logged
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #15 on: July 18, 2018, 08:19:47 PM »

Craig G - thanks for the complement.

Red Buzzard - Thanks for the trimming advice. I don't want this model to crash in a low torque trim flight. I measured my carved and sanded balsa wood prop and by my calculations its P/D is approximately 1.3.

After sanding the top surfaces of the blades a bit more, and after sanding in some under camber, the weight of the 17-inch balsa wood prop is now 9.66 grams.  I am definitely going to cover both sides of the prop blades with light weight fiber glass cloth and epoxy resin.

The late Karl Gies lined the LE and TE of the blades of the prop of his Korda C Tractor with 25 pound test monofliament fishing line before covering them with fiberglass.  I am not sure this is necessary.  

I toyed with the idea of inserting a thin plywood spar into the hub of the propeller as suggested by George Bredehoft but decided against this.  I think the fiberglass covering should make the light weight balsa wood prop sufficiently strong.

The prop will be painted some bright color so I have better chance of finding it should it somehow come free from the model during a flight.  I could tell you a sad story about a dumb mistake I made that has driven me to paint this prop.

Logged
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #16 on: July 19, 2018, 06:30:15 PM »

I glued 1/64 x 1/16 Bass wood strips to LE and TE of the prop blades.

I used Titebond glue because it makes a very strong wood-to-wood joint. It sands reasonably well, unlike CA. I will sand the edges of these strips flush with the front and year surfaces of the blades

This reinforcement should lessen the likelihood of nicks being taken out of the LE and TE.  I only covered about 2/3's of the length of the perimeter of each blade.  That's what single strip would cover and I figure the innermost portions of the LE and TE nearer the hub have less need for such protection.

These Bass wood strips were sold in a bag indicating that they are HO model train lumber. The strips easily curved around the ends of each blade. No pre-soaking of the strips was necessary.

I am still planning on covering the relatively large balsa wood prop with fiberglass and epoxy.  Maybe the addition of the Bass wood strips was not necessary, but they added very little weight.  
Attached files Thumbnail(s):
Re: Korda Class C Tractor
Logged
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #17 on: July 20, 2018, 05:41:38 PM »

As l previously indicated, I am building the wing of my Korda C so that it can be taken apart in two sections. This makes transport easier.  Several years ago, I decided to transport all of my models to our flying field safely and efficiently in IRIS brand clear Christmas wrapping paper boxes.  They have removable lids and nest nicely in stacks of three or four boxes. These boxes measure 33.9-inches long x 12.1 inches wide x 6.3 inches tall.  Why spend a ton of time building a nice model and trimming the same, only to have it damaged in transport?

I still have my first FAC Rubber Scale model - a 30-inch wing span Fairchild 24. It takes a monstrous carboard box to be safely transported as the wing and tail feathers are not removable.

When I go to a contest, space in the back of my car is at a premium. I can fit three P-30 models in one IRIS box, three Coupe models in another IRIS box, several OTR models in another IRIS box, and so forth. Because these boxes are transparent, I can identify their contents just by looking at them.  Where I fly we quit at noon because the wind comes up by then.  Depending on the time of year, I often need to lug all my models into a hotel room.  It can easily reach 120 to 130 degrees F. inside my parked car and my models would warp in such conditions.  Therefore, I often I load all my airplane boxes onto a luggage dolly and roll them into my air-conditioned hotel room. I take a lot of kidding from other fliers when they see me doing this.
 
The fuselage of the Korda C will fit diagonally in one of the IRIS boxes.  However, a fully built Korda C wing will not as the wing has a span of 38-inches (flat).

The horizontal center section of the Korda C wing is 12 inches long so I built it in two 6-inch sections that plug together. I faced the two mating center ribs with 1/64-inch plywood and added some gussets to the inner bays. One 6-inch section has a pair of .057-inch carbon fiber (CF) composite tubes that plug into segments of 3/32-inch Aluminum tubing in the other 6-inch section. These components are supported on medium density balsa wood spars that extend between adjacent ribs.  Thread was wrapped around these parts and some CA applied for added strength. The CF composite tubes are very rigid and very strong.
 
I am building the outboard dihedral wing sections separately and will join them to the 6-inch center sections later on.

The center section of the Korda C wing will be covered on top with 1/32-inch sheet balsa wood where the hold down rubber bands do their squeezing.  Unsupported tissue covering in this area would take too much of a beating. These rubber bands will also prevent the wing halves from creeping apart, although that is unlikely. There should not be any forces acting to pull the wing halves outwardly.  I used a similar set up in my first Coupe and it has served me very well.  I have not had any problems with this wing connection scheme.

Onward with my Korda C build.  

Attached files Thumbnail(s):
Re: Korda Class C Tractor
Re: Korda Class C Tractor
Re: Korda Class C Tractor
Re: Korda Class C Tractor
« Last Edit: July 20, 2018, 07:05:12 PM by calgoddard » Logged
OZPAF
Palladium Member
********

Kudos: 159
Offline Offline

Australia Australia

Posts: 4,345



Ignore
« Reply #18 on: July 20, 2018, 08:30:28 PM »

Quote
There should not be any forces acting to pull the wing halves outwardly.  I used a similar set up in my first Coupe and it has served me very well.  I have not had any problems with this wing connection scheme.

That is supported by my experience with early RC gliders. The dihedral of the wings provides sufficient inwards holding force together with small amount of friction, to hold the wings on. As the wings became heavier, with less dihedral and ailerons - it was then necessary to have more holding power and this was actually tape on F3B class models of around 2.5kg weight.

John
Logged
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #19 on: July 21, 2018, 03:17:06 PM »

I took a break from building in order to make up a rubber motor for my Korda C.

It is 16 x 1/8-inch, 38 grams.  I braided the rubber motor so that its length is about equal to the estimated hook-to-peg distance of 26 inches.  It will stretch some after winding and I don't want motor bunching and CG shifting. I would rather not have to install a spring tension mechanism in the nose block.  

I used a Crocket hook of course.  Some prefer T-hooks.  There is a wobbly motor peg at the rear end of the rubber motor that will fit loosely over the 3/16-inch Aluminum motor peg.  I not sure it will provide any benefit in terms of even unwinding of the braided rubber motor.  It will still make it easier to install the rubber motor in the fuselage.

I used May 2015 TSS rubber because a friend gave me several pounds of it.  I have never tested this batch of rubber.  However, I have heard that any TSS rubber batch from 2009 on is pretty good, with June 2016 being exceptional as I recall.

By my rough calculation the estimated breaking turns for this 38 gram rubber motor will be around 950.  I will do some test winding on the bench to see when the torque leaps up.  Once I get the fuselage covered with Polyspan it will have enough torsional strength to allow me to do some test motor runs on my stooge.   I am hoping I can get a motor run of longer than 60 seconds.  Of course the motor run will be slightly different for the same number of turns when the model is flying on the power portion of its fight pattern.
Attached files Thumbnail(s):
Re: Korda Class C Tractor
Logged
Red Buzzard
Bronze Member
***

Kudos: 3
Offline Offline

United States United States

Posts: 93



Ignore
« Reply #20 on: July 21, 2018, 09:52:09 PM »

Cal,

Nice braid! I think your basic set-up will work fine with a Garami free-wheeler. Wobbly peg works great. It's a good idea to make the wobbly peg a little wider than your blast tube so you can unload the blast tube with a broken motor in it instead of trying to fiddle with it in the fuselage. There is a chance your broken motor can kink the wobbly peg and jam it against your tube that goes through the fuselage, but stuff happens. With a wide wobbly peg you at least have a chance.

You can make a test rig to test motors outside your fuselage with a simple 2x4 and some plates to support your rear peg and your nose block. Make it the same length as your motor base - or adjustable for other models - then you just hook it up to a bench vice, wind up your motor, and watch stuff fly around your garage when the motor breaks. It's good practice, just make sure you have some room!

Bill
Logged
LASTWOODSMAN
Gold Member
*****

Kudos: 19
Offline Offline

Canada Canada

Posts: 536


REAL PLANES HAD ROUND ENGINES AND TWO WINGS



Ignore
« Reply #21 on: July 21, 2018, 11:25:24 PM »

     Hi calgoddard - does that sleeve that is held by the rear rubber motor's final  loop, does that sleeve slide over the rear motor peg?   Also, could you please show how the blast tube fits onto the rear motor peg?   How do you make your blast tubes ?    How do you load a blast tube into the fuselage?   With the rubber all knotted and twisted up inside the blast tube - how does that blast tube slide off of the wound motor - don't they rub against each other?
     That is a very symmetrical braided motor.    Shocked  Cool   One more dumb question    Undecided - is the motor 16 strands of 1/8"  rubber, each braided strand is appx  26" long, correct?  
     I am following your "Old Time Rubber"  OTR  38"  KORDA  CLASS "C" TRACTOR   Outdoor Duration   build with great interest ...    Smiley
     Thanks

LASTWOODSMAN
Richard
« Last Edit: July 22, 2018, 12:00:27 AM by LASTWOODSMAN » Logged

OH, I HAVE SLIPPED THE SURLY BONDS OF EARTH ... UP, UP THE LONG DELIRIOUS BURNING BLUE ... SUNWARD I'VE CLIMBED AND JOINED THE TUMBLING MIRTH OF SUN-SPLIT CLOUDS ...
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #22 on: July 22, 2018, 10:33:25 AM »

Red Buzzard -  All good points.  Thanks.  Does a wobbly motor peg do any good with a braided rubber motor or is it only beneficial for a non-braided rubber motor?

LASTWOODSMAN - I am probably only possess an intermediate level of skill as an outdoor builder and flier.   I only got started in this hobby about 5-6 years ago.  Hopefully the real experts on HPA will weigh in to correct me and/or supplement my explanations.

A wobbly motor peg is essentially a segment of Aluminum tubing (or a bobbin) that has an ID that is larger than the OD of the motor peg.  Preferably the difference between the ID and the OD are such that the wobbly motor peg can wobble on the actual motor peg. The wobbly motor peg should be short enough so that its ends do not rub up against the sides of the fuselage. A good example of a wobbly motor peg is a segment of 1/4-inch Aluminum tubing that slides over a motor peg made of 3/16-inch Aluminum tubing.   See the attached picture.  Note that the flared ends of the wobbly motor peg help retain the rear end of the rubber motor on the wobbly motor peg. You can flare the ends of the 1/4-inch Aluminum tubing by inserting large Phillips screw drivers in opposite ends and then pushing and twisting.

Here is some theory about wobbly motor pegs from an article I wrote a few years ago that was published in our local flying club's newsletter.

George White summed up the problem pretty well in his article entitled Taming the Rear Motor Peg in which he stated:  “As the motor unwinds it wants to squirm about and flex up and down at the rear peg. The use of a solid peg interferes with that and the motor has a gathering at the tail.” A wobbly motor peg is essentially an outer motor peg that rotates around a fixed inner motor peg.  Tom Arnold explained how the wobbly motor peg works in his article entitled An Article About Very Long Rubber Motors in which he stated:  “The explanation of how it works . . . is that by allowing the motor to shift, roll, and twist at the peg as it unwinds it prevents that big knot from forming around the peg. For some reason it works itself out of a jam and lets the full winds come out. Now you still have a long sloppy motor to slide back and forth but you have gotten every turn out of it you could before then.”    

While not required, preferably a blast tube has a bayonet lock that permits it to lock onto the motor peg with a twisting motion.  See the attached photos. Without this feature, the blast tube will creep forward during winding unless you have a bystander hold it in place.

You will need a tool called an extractor in order to use a blast tube.  This is a long piece of music wire with a handle at one end and a hook at the other end.  The extractor must be long enough so that it can fit all the way through the blast tube with the hook protruding out the rear end of the blast tube. Once the rubber motor has been installed in your model and your model is mounted on a stooge, do the following: 1) insert the extractor all the way through the blast tube; 2) connect the hook on the extractor to the Crocket hook or T-hook at the front end of the rubber motor; 3) slide the blast tube off the extractor into the fuselage of the model as far as you can; 4) lock the rear end of the blast tube onto the motor peg; 5) disconnect the extractor hook from the Crocket hook; and 6) connect your winder to the Crocket hook. Reverse the process when you are done winding and connect the prop shaft hook of your prop assembly to the Crocket hook.

You can make a blast tube out of PVC pipe.  Preferably a blast tube is made out of lightweight Aluminum tubing or clear plastic tubing from an aquarium store.

The ID of the blast tube must be large enough so that the knotted rubber motor does not bind against the inside surface of the blast tube. The OD of the blast tube must be small enough so that it can be inserted through the nose of the model.

Braiding rubber motors is much easier to do than to describe.  There is a nice YouTube video showing the technique.

The rubber motor I made for my Korda C is 16 strands of 1/18 inch rubber.  I made one very large loop of rubber (approximately 38 grams) and folded it in half three times to get 8 loops (16 strands). I then wound about thirty turns (counter-clockwise) into one group of 4 loops.  Holding that group aside, I did the same to the other group of 4 loops. I then put the two groups together on my winder and they wound themselves into the braided configuration shown in the photo that is attached to Reply #19. The braided motor is about 26 inches long. The 26 inches includes the length of the Crocket hook. Before braiding the rubber motor is a little longer.  The amount that braiding shortens a rubber motor depends on the number of strands, the width of the strands, and the amount you wind each group.  Expert F1G (Wakefield) fliers often make their rubber motors with 1/16-inch rubber for reasons that I will not get into here. When braiding, I wind each group just enough so that the groups are almost ready to start forming knots.  

Note - most experts will tell you to that when braiding a rubber motor, you should wind each group of rubber loops clockwise.   I don't like this approach, because the braiding seems to largely disappear when you wind the rubber motor for flying.  

I hope I adequately answered your questions LASTWOODSMAN. Thanks for following my Korda C build thread.  I am a slow, methodical builder, but I enjoy the process.
Attached files Thumbnail(s):
Re: Korda Class C Tractor
Re: Korda Class C Tractor
« Last Edit: July 22, 2018, 11:30:34 AM by calgoddard » Logged
Red Buzzard
Bronze Member
***

Kudos: 3
Offline Offline

United States United States

Posts: 93



Ignore
« Reply #23 on: July 22, 2018, 12:46:12 PM »

Hi Cal,

As I stated earlier, I braid everything. Simply put, in addition to the advantage of avoiding most bunching, braiding just makes the whole motor easier to handle and deal with in general use. The wobbly peg concept, I believe, promotes even distribution of knots and consistent unwinding. It just seems to make things more-predictable. I cannot quantify any of this. BUT I do know that without the wobbly peg concept, particularly a peg that spans the blast tube's diameter, a broken motor is a real pain. The locking slots that you illustrate at the end of the blast tube are essential to keep the blast tube from flying out the front of the fuselage and spearing the winder in some broken motor events.

Do you know how long your skeins were before you put in your braiding turns? That would be the number I would use to calculate maximum turns.

Very nice explanations to Woodsman.

Bill
Logged
calgoddard
Gold Member
*****

Kudos: 17
Offline Offline

United States United States

Posts: 876


Topic starter
FAC Member



Ignore
« Reply #24 on: July 22, 2018, 12:57:36 PM »

Red Buzzard -

Thanks for the follow-up on the benefits of using a wobbly motor peg.

Thanks also for the complement regarding my explanations.

I didn't measure the length of the skein of 1/8-inch rubber that I used to make up the rubber motor for my Korda C.  It was super long.

I need to correct a typo in Reply #22, in the third paragraph from the end.  I meant "1/8 inch" rubber. NOT - - 1/18 - - .  The modify icon is gone for that reply.
Logged
Pages: [1] 2 3 4   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!