Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
August 19, 2019, 02:48:35 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 [5]   Go Down
Print
Author Topic: Korda Class C Tractor  (Read 5445 times)
0 Members and 1 Guest are viewing this topic.
calgoddard
Gold Member
*****

Kudos: 23
Offline Offline

United States United States

Posts: 937


Topic starter
AMA, NFFS & FAC Member



Ignore
« Reply #100 on: November 21, 2018, 12:01:00 PM »

The attached picture shows the repairs that I made to the broken lightweight prop of my Korda C Tractor.  Stan Buddenbohm recommended that I splice in some strong stuff across the break. I followed George Bredehoft’s method that he uses to reinforce the hub of a balsa wood prop. I cut two spaced apart radially extending slits across the break with an Xacto knife. The slits go all the way through the blade. I inserted two ¼ x 1 ¼ x 1/64 plywood strips snugly into the slits. They weighed a total of only .14 grams.  I pushed one of the side edges of each strip down flush with the surface of the blade.  I sanded off a slight amount of excess of the other side edges of the plywood strips that were protruding from the surface of the other side of the blade. I then wept thin Volare CA into the slits. It is not visible in the picture but when the blade broke it produced a scarf joint.  So there is no butt joint between the end of the broken blade and the other part of the prop that includes the hub and the other blade.  The plywood strips extend across this scarf joint and past its ends.  I put a few small strips of heavy clear adhesive tape on the backside of the tip of the non-broken blade to re-balance the prop.

Last Saturday I finally got a chance to fly my Korda C Tractor in a contest put on my local flying club.  I did some more trimming in our large flying field on Friday the day before the start of the contest.  Previously in my local park I had tried a low power flight adding 1/16-inch left rudder.  This corrected the previous nearly disastrous problem of the plane spiraling into the ground in a right turn about 15 - 20 seconds after launch at our large flying field.  The airplane now climbs right and glides right in about a 150 foot diameter circle. Apparently when the unusually tall vertical fin is positioned with its flat bottom surface in line with the center line of the fuselage, due to its airfoil shape the fin yields too much effective right rudder. I had been warned about this in a post in this topic above and should have heeded the warning.  Not doing so caused me a broken prop, which took about an hour to repair with the 1/64-inch plywood splines.

With a 16 x 1/8-inch 40-gram rubber motor I gradually increased launch torque at the large flying field in a series of practice flights. The repaired prop held up just fine. The Buddenbhom clutch described in Reply #84 works great. I ended up adding some more down thrust.  Eventually I was very satisfied with practice flight of nearly five minutes.  It was a good thing my Korda C was carrying an RF tracker on that nearly five minute flight.  It has a viscous timer for the DT and I know I set it.  The stab was popped up when I found my Korda C after its long flight.  I need more calibration information on the viscous timer as set up in the DT.  The climb of my Korda C is at about a 45-degree angle and the model gets really, really high.  I found that about 650 - 700 turns and 20 inch-ounces of torque easily produces a max. The 17-inch wide blade balsa wood prop appears to be rotating quite slowly but apparently develops a lot of thrust. It was difficult to judge the duration of the motor run on a flight launched with 600+ turns on the rubber motor because by the time the motor run ends my Korda C is so high that it is hard to discern the transition to freewheeling.  I estimate that the motor run is about 90 seconds long.

In the OTR event at the contest last Saturday my first two official flights were easy maxes.  On my third official flight my Korda C got really high, but unfortunately flew into a downer and was literally sucked down to the ground while continuing to glide forward in a nice attitude.  The time of my third official flight was only 97 seconds.  I lost the OTR event to a friend who flew three maxes with his Gollywock. That was a nice consolation.

I am going to fly my Korda C in the OTR event in another contest this Sunday.  I will first put up a practice flight very early in the morning to see if my Korda C can easily max.  If so, I will put in all three official flights early, in dead air, before any thermals (and downers) can develop.  I learned this strategy from Stan Buddenbohm.  He was the one that told me that the Korda C is a great flier when I was discussing a future build of a small OTR model. Once again, Stan was correct.  He used to launch his Korda C years ago at 40 inch-ounces of torque!  I may work my way up to 30 inch-ounces of launch torque.  Right now it does not seem necessary for me to increase launch torque unless I fly in a contest with 3 minute maxes instead of 2 minute maxes.  Of course, there is always the possibility of getting into a fly-off in a contest that has only 2 minute maxes, meaning that I will need be able to fly 2 ½, 3, 3 1/2 minutes, etc.  

During the contest several fliers commented that my Korda C is ugly.  I don't care how it looks.  I only care how long it flies Smiley
Attached files Thumbnail(s):
Re: Korda Class C Tractor
Re: Korda Class C Tractor
« Last Edit: November 21, 2018, 12:23:40 PM by calgoddard » Logged
OZPAF
Palladium Member
********

Kudos: 180
Offline Offline

Australia Australia

Posts: 5,040



Ignore
« Reply #101 on: November 22, 2018, 12:01:47 AM »

How did they work that out Cal? Smiley Anyway as a friend once said to me - beware the flyer whose model has patches/repairs. He knows his model and it is no doubt competitive Smiley

Anyway - as long as you're having fun - anything else is irrelevant.

Thanks again for your detailed reports - I always find them of interest.

John
Logged
Red Buzzard
Silver Member
****

Kudos: 4
Offline Offline

United States United States

Posts: 120



Ignore
« Reply #102 on: November 25, 2018, 08:09:24 PM »

Yay, Cal,

Way to go! Don't sell yourself short with that motor. There's quite a bit more available. As you work with the trim you can sometimes "trade" down thrust for right thrust as your torque goes up. That can improve your cruise while keeping the climb safe. More torque at launch balances the bit of right thrust at launch. Most of your prop run is in "cruise" and anything you can do to get the nose up even a little in cruise is good.

Best those Gollywocks!

Bill
Logged
calgoddard
Gold Member
*****

Kudos: 23
Offline Offline

United States United States

Posts: 937


Topic starter
AMA, NFFS & FAC Member



Ignore
« Reply #103 on: November 26, 2018, 11:12:32 AM »

I flew my Korda C in my club's combined OTR-NOS Rubber contest yesterday.  Nine fliers competed in the event.

After the fog lifted we started putting in official flights.  There was a two minute max.  The winner would be the highest total of three flights - unless there was a fly-off.

I maxed with my first three flights.  So did another veteran flier with his Gollywock that had a folding prop. Another flier with a Gollywock that had a folding prop just missed his third max.

The CD decided that the fly-off would start with a first flight of 180 seconds.  I decided to go for a new motor for my attempt in the fly-off.  It was identical (16 x 1/8 - 40 grams, TSS May 2015) to the rubber motor I had used for the first three official flights.  With Stan's blessing, I wound a little higher this time - 825 turns and 25 inch-ounces of torque. I easily made my three minute flight with plenty of extra time beyond 180 seconds.  But only 180 seconds counted for me in the first round of the fly-off. The Gollywock had a technical problem and only flew 29 seconds in the fly-off.  

Based on what I have observed, the Korda C is more than a match for the Gollywock, despite its seeming handicap of a fixed prop.  I plan to gradually work up to 30-inch ounces of launch torque.  Red Buzzard - thank you for your comments about adjusting the thrust line as I increase the launch torque.

I am very happy with how my Korda C flies.

« Last Edit: November 26, 2018, 11:58:53 AM by calgoddard » Logged
Pages: 1 2 3 4 [5]   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!