Author Topic: Pathfinder ARC Electric Conversion Build Log (Read 13519 times)

Crist Rigotti · « **on:** September 26, 2020, 01:59:00 PM »

Guys,
While at the Cleveland contest this PF was for sale. I just missed picking it up. The next day I asked around and found the modeler who bought it and asked if was willing to sell it. He said sure, and we struck a deal. The guy is a real gem that we find in our control line community.

The reason I wanted the PF was for next year, I was planning on going bigger than my usual 575 sq. in airplane. I liked that size because when I flew a larger airplane like 610 to 650 sq/in it was just too much airplane to fly when the wind came up. These were IC powered and weighed between 53 and 57 ounces dry.

I am planning on a 620 sq/in airplane for next year that will be electric powered, of course. Then I saw the PF and thought it would be a cheap way to find out if I can handle a 620 sq/in electric airplane that weighed about 56 ounces. I could get it done in a week or so and find out well before I have to start cutting balsa for next year.

The weight of each of components are:
Fuselage - 168g 5.9oz
Wing - 314g 11.1oz
Flaps - 42p 1.5oz
Stab - 49g 1.7oz
Elevators - 32g 1.1oz
Fin/Rudder - 10g .4oz
Totals - 615g 21.7oz

I'm was going to lengthen the nose from 9" to 11" but I just might make a new fuselage with the longer nose and then I'll be in compliance with BOM rules.

The electric equipment will be:

Either a Cobra 3515/18 or a BadAss 3515-740Kv
Igor's active timer
Spin 44 ESC
6S 2200mah battery
3 blade CF prop TBD

Weight target is 56 ounces.

Frank Imbriaco · « **Reply #1 on:** September 26, 2020, 02:08:54 PM »

Crist :
Please tell us if you find a 6S 2200 lipo . I want to stick with 25 C. Yes, there are 45C out there , but they're heavier. There's a hobby supplier from China who advertises on eBay. Not feeling that I want to deal with them.

TP will not make them unless we give a sizeable order and prove they'll continue to sell. Something about cost to develop and certification.
Frank

Perry Rose · « **Reply #2 on:** September 28, 2020, 04:49:37 AM »

Ad an inch to each end of the stab/elev. It will fly better. Total span 28 inches.

Crist Rigotti · « **Reply #3 on:** October 15, 2020, 07:00:35 PM »

Well, I finally got started on this project. I had to finish another one before this one.

Today I replaced the lead outs and flap pushrod. I kept the same 4" plastic bell crank and added new wrapped lead outs and a ball link for the flap pushrod. I cut away some center sheeting to get to the bell crank mounting bolt. I cut the head off then removed the lower bell crank platform. I used a new 6-32 bolt and spaced the bell crank so it fit between the 2 platforms. I did shim the lower one 1/16 lower so the bolt would fit with the new locking nuts.

Next up I'll cut the hinge slots and do some detail sanding to get it ready for the Monokote.

Crist Rigotti · « **Reply #4 on:** October 17, 2020, 09:04:15 PM »

I cut the hinge slots in both the wing and flaps. I'm using pinned hinges and not he RC type supplied. I also re-glued the entire wing with thin CA and the landing gear blocks with medium CA. I terminated the leadouts and replaced the adjustable LO guide bolt with a longer bolt and the "crimped" the threads so the screw won't come out.

I then detailed sanded everything and vacuumed it all off.

The wing now weighs 319 grams and the flaps weigh 41 grams. A total of 3 grams more, but better glued!

Next up the stab and elevator.

Crist Rigotti · « **Reply #5 on:** October 18, 2020, 10:07:48 PM »

I did the stab today. I re-glued all the joints with thin CA then located and cut the hinge slots in both the stab and elevators. I also bent up the elevator horn.

I decided to taper the stab from 1/2 at the root to 1/4 at the tips. I cut some 1/2 x 1/2 x 1/16 aluminum angle. I basically taper them down 1/8 inch. I then drew the taper lines on the TE and planed the taper close. On the first side I placed the stab in the jig and then used 120 grit to the final taper. On the second side I shimmed up the tip 1/8.

I then rounded the TE, and sharpened the LE and then detailed sanded the whole thing. It is now ready to cover. Weight is now 38 grams.

Next up the elevators.

Dave Rigotti · « **Reply #6 on:** October 19, 2020, 05:28:39 AM »

What was the weight before you worked on it?

Crist Rigotti · « **Reply #7 on:** October 19, 2020, 08:40:51 AM »

Quote from: Dave Rigotti on October 19, 2020, 05:28:39 AM

What was the weight before you worked on it?

See post #1 for all the weights before I got started on it. 49 grams.

Crist Rigotti · « **Reply #8 on:** October 19, 2020, 02:13:48 PM »

Today I finished the elevators. They were tapered in the same manner as the stab. All ready to cover. Weight for both elevators is 22 grams as compared to 32 grams before I got started.

Next up is the Fin/Rudder.

Crist Rigotti · « **Reply #9 on:** October 19, 2020, 07:53:53 PM »

The Fin/Rudder that came with the ARC was only 1/8 thick. It was nice solid balsa. I determined that it was just too thin for my liking for this model so I made another one.

It was made out of 6# 3/32 balsa and 12# 1/32 balsa lamination's.

The new one came out at 10 grams. The original was also 10 grams.

On to the fuselage.

Crist Rigotti · « **Reply #10 on:** October 25, 2020, 05:18:45 PM »

Just a quick picture. More of an update later.

Brent Williams · « **Reply #11 on:** October 25, 2020, 05:26:58 PM »

Just gotta say that I always enjoy your build tutorials, Crist!
Thanks for going to the extra effort to share your excellent work.

Crist Rigotti · « **Reply #12 on:** October 27, 2020, 12:39:30 PM »

Thank you Brent.

Crist Rigotti · « **Reply #13 on:** October 27, 2020, 01:00:41 PM »

When I started on the fuselage, I was just going to add an extra 2 inches to the nose and make it for electric power. Half way through the conversion, it occurred to me that if I build an entire fuselage, I would qualify for BOM. Also the fuselage that came with the kit was only 1/2 inch wide that was with the plywood doublers. Also the fuselage had a good twist in the aft portion. I missed that before I got started on it!

Time for a new fuselage. This one is a full 3/4 thick and straight. I started out laminating some 1/2 and 1/8 to get the 5/8 core. Then cut some 1/2 wide strips to be used for the top and bottom. I used some 1/8 x 5/8 basswood to build a crutch. After that I filled the aft portion with some pink foam I had laying around. This was then sanded smooth and the each side was epoxied on. The sides were 1/16 balsa with 6# wood used in the aft portion and 9# wood used in the forward section. Each side had the grain running in the opposite way. There are no plywood doublers at all. For the tripler, I used 2 layers of 7# 3/16 sheet with the inner sheet cut out within the motor compartment to accommodate the motor offset of 4 1/2 degrees.

The motor mount is 1/8 5 layer birch ply. The new fuselage weighs 203 grams. The old one was 168 grams. A 35 gram increase.

With all the components done they all weight just 17 grams more than what I started with.

Fuselage 168g v 203g
Wing 314g v 318g
Flaps 42g v 41g
Stab 49g v 38g
Elevators 32g v 22g
Fin/Rudder 10g v 10g
Totals 615g v 632g

Everything is now ready to cover in Monokote.

Ken Culbertson · « **Reply #14 on:** October 27, 2020, 01:32:08 PM »

Quote from: Crist Rigotti on October 27, 2020, 01:00:41 PM

Everything is now ready to cover in Monokote.

NOT YET - Not too late to imbed a target arrow shaft in the fuselage top. You won't regret it. Ship is really looking cool. Hope to see it at the field.

Ken

Crist Rigotti · « **Reply #15 on:** October 27, 2020, 01:38:47 PM »

Ken,
Details?

Ken Culbertson · « **Reply #16 on:** October 27, 2020, 01:51:18 PM »

Quote from: Crist Rigotti on October 27, 2020, 01:38:47 PM

Ken,
Details?

Go to Wallmart and get a CF Target arrow. It is lighter than the balsa it replaces and will virtually eliminate any fuselage twist at the wing TE. Take a E-Xacto 1/4" hollowing tool and carve out a channel in the top of the fuselage from the wing high point to about 1" behind the stab LE. Epoxy the arrow shaft (take the feathers off first and rough up the finish) into the slot (don't use too much Epoxy). Put a thin 1/32 balsa cap over the mess and sand back to shape. I had pictures of this on my Twister Build some of them I found. The orange lines on the second one are where the shafts are. One is enough with the Fuse you have. The Twister was a slab.

https://stunthanger.com/smf/building-techniques/arrow-shafts/msg566137/#msg566137

Ken

Crist Rigotti · « **Reply #17 on:** October 27, 2020, 02:16:44 PM »

Ken,
Like this one?

https://www.walmart.com/ip/Allen-Company-Kryptos-Carbon-Arrow-31-L-x-0-25-W-x-0-05lbs-Black/590036684

Ken Culbertson · « **Reply #18 on:** October 27, 2020, 02:26:07 PM »

Quote from: Crist Rigotti on October 27, 2020, 02:16:44 PM

Ken,
Like this one?

https://www.walmart.com/ip/Allen-Company-Kryptos-Carbon-Arrow-31-L-x-0-25-W-x-0-05lbs-Black/590036684

Maverick, that's your bogie. I use them everywhere. For a few $ more you can get some that are even lighter from the "top of the line" folks but just like the good old McCoy 40 price ain't everything!

Ken

Brent Williams · « **Reply #19 on:** October 27, 2020, 06:14:13 PM »

I'm curious about your opinion on the 4.5° motor offset. Why build in so much offset?

Crist Rigotti · « **Reply #20 on:** October 27, 2020, 07:41:42 PM »

Quote from: Brent Williams on October 27, 2020, 06:14:13 PM

I'm curious about your opinion on the 4.5° motor offset. Why build in so much offset?

Helps with line tension overhead.

Ken Culbertson · « **Reply #21 on:** October 27, 2020, 08:11:31 PM »

Quote from: Crist Rigotti on October 27, 2020, 07:41:42 PM

Helps with line tension overhead.

I have never had a Pathfinder but I have also never needed that much on anything since the 70's. I think you saw my Sandpiper profile fly, it had 1 degree. The Twister had 1 on the motor and 2 degrees rudder. I later took the rudder out and moved the leadouts back 1/4". Both had exceptional overhead tension. My last PA had zero and zero on the rudder but it did have Keith's CAM rudder that kicked in overhead about 2 degrees.

Bottom line, if it needs it, it needs it but having to reshape that beautiful nose would really suck.

Ken

Crist Rigotti · « **Reply #22 on:** October 28, 2020, 12:13:29 PM »

I added the carbon fiber arrow shaft to the top of the fuselage. It did add some stiffness but it cost me an additional 16 grams. The fuselage now weighs 219 grams.

Now I'm ready for Monokote.

Ken Culbertson · « **Reply #23 on:** October 28, 2020, 01:26:13 PM »

Quote from: Crist Rigotti on October 28, 2020, 12:13:29 PM

I added the carbon fiber arrow shaft to the top of the fuselage. It did add some stiffness but it cost me an additional 16 grams. The fuselage now weighs 219 grams.

Now I'm ready for Monokote.

Interesting. My Twister weighed 2 grams less after adding the shaft.

It was a plank fuselage and rather hard. Maybe that explains the difference. The reduction in flexing at the wing TE will be worth it.

Oh well, with that long nose it will be 16 grams less tail weight to add later!

Good luck! Hope to see it in the spring when I get to start flying again!

Ken

Crist Rigotti · « **Reply #24 on:** October 28, 2020, 04:36:15 PM »

Quote from: Ken Culbertson on October 28, 2020, 01:26:13 PM

.... Oh well, with that long nose it will be 16 grams less tail weight to add later!

Good luck! Hope to see it in the spring when I get to start flying again!

Ken

Ken,
Where do you think the CG should be expressed in % of MAC?

Ken Culbertson · « **Reply #25 on:** October 28, 2020, 11:04:43 PM »

Quote from: Crist Rigotti on October 28, 2020, 04:36:15 PM

Ken,
Where do you think the CG should be expressed in % of MAC?

That is a tough one for me to answer. I fly tail heavy compared to most. Ever since I started building my own back in the 60's I have had long tail movements and big stabs. I don't measure mine at MAC. I balance near the center by the fuselage so my %'s are at root chord. The Endgame (my Avatar) balanced at about 30% and was still a bit nose heavy for me but it still had it's clear coats to go. I usually end up just forward of the airfoil high point but every plane is different. I start out nose heavy and keep adding tail weight till I can't control the hunting then back off. I have tried to adapt to the faster pattern with softer corners that most fly today and I am not pleased with the results. When I get back next year I am going to be flying more like Matt or Doug with harder corners. I haven't asked him where his CG is. Maybe he will chime in.

So where to start? Your ship has a pretty long nose so you should have plenty of room to slide the battery around. Electrics, for what ever reason, tend to be more nose heavy and still turn well. Given all of that I would probably start out somewhere around 25% MAC then do the "watch what it does when the motor quits" thing on the test flights. From there it is pretty much how you like it to turn.

Ken

Perry Rose · « **Reply #26 on:** October 29, 2020, 05:49:57 AM »

I've built 3 Pathfinders and still have two. The first from a Brodak kit was .46LA power. The second is scratch built and electric, an Arrowind 2812/07 with HRB 4s 3300 battery. The third has an Evolution .60 in the nose and is the best flier of the bunch. All three have unchanged nose lengths and no more that 2 degrees of engine offset with straight fin/rudders. I did increase the stab span by 2 inches on the third model. Balance points are as shown on the plans. Everyone cringes at my method of setting leadouts so I won't mention it here again.
The plans show the c/g at 2 3/4 inches back from the leading edge or about 23% MAC.

Brent Williams · « **Reply #27 on:** October 29, 2020, 08:38:48 AM »

I can go measure where Gordan Delaney has the CG set on his Pathfinder if you are curious where the designer has it set in 2020.

Gary Mondry · « **Reply #28 on:** October 29, 2020, 05:31:12 PM »

Crist,

Did you get the arrow shafts in the Walmart product description you posted? It said they were 0.25 inch shafts, but those at my Walmart, that looked identical, measured 0.300" O.D.

Crist Rigotti · « **Reply #29 on:** October 29, 2020, 07:01:47 PM »

Quote from: Gary Mondry on October 29, 2020, 05:31:12 PM

Crist,

Did you get the arrow shafts in the Walmart product description you posted? It said they were 0.25 inch shafts, but those at my Walmart, that looked identical, measured 0.300" O.D.

Yeah, it was .3 instead of .25

Joseph Patterson · « **Reply #30 on:** October 29, 2020, 07:18:52 PM »

Quote from: Perry Rose on October 29, 2020, 05:49:57 AM

I've built 3 Pathfinders and still have two. The first from a Brodak kit was .46LA power. The second is scratch built and electric, an Arrowind 2812/07 with HRB 4s 3300 battery. The third has an Evolution .60 in the nose and is the best flier of the bunch. All three have unchanged nose lengths and no more that 2 degrees of engine offset with straight fin/rudders. I did increase the stab span by 2 inches on the third model. Balance points are as shown on the plans. Everyone cringes at my method of setting leadouts so I won't mention it here again.
The plans show the c/g at 2 3/4 inches back from the leading edge or about 23% MAC.
Perry, I sent you a PM
Doug

Perry Rose · « **Reply #31 on:** November 01, 2020, 05:06:04 AM »

Quote from: Brent Williams on October 29, 2020, 08:38:48 AM

I can go measure where Gordan Delaney has the CG set on his Pathfinder if you are curious where the designer has it set in 2020.

Please do, I could use his latest set up. Mr Gordon also suggested some mods a few years ago, ask about those also. He put them on here someplace.

James Mills · « **Reply #32 on:** November 01, 2020, 07:19:52 AM »

Quote from: Gary Mondry on October 29, 2020, 05:31:12 PM

Crist,

Did you get the arrow shafts in the Walmart product description you posted? It said they were 0.25 inch shafts, but those at my Walmart, that looked identical, measured 0.300" O.D.

Crist,

Next time try an archery shop. I bow hunt and most of the time the shafts you can buy there weigh less and are straigher and stiffer. Sometimes they have a "left over" bin that you can pick up for a few bucks each.

James

Crist Rigotti · « **Reply #33 on:** November 04, 2020, 07:00:56 PM »

My ARC is now an ARF, a much better ARF.

Weight gained was 105 grams or 3.7 oz. From bare balsa to finished finish was only 3.7 oz for a 620 sq-in model!

Dave Rigotti · « **Reply #34 on:** November 04, 2020, 07:16:10 PM »

Looks GREAT! The transparent Monokote probably saved 3/4oz over "solid" color Monokote.

Total weight of airframe less landing gear and power stuff looks like 26oz? Should make 56oz target easy no?

Crist Rigotti · « **Reply #35 on:** November 04, 2020, 07:34:21 PM »

Quote from: Dave Rigotti on November 04, 2020, 07:16:10 PM

Looks GREAT! The transparent Monokote probably saved 3/4oz over "solid" color Monokote.

Total weight of airframe less landing gear and power stuff looks like 26oz? Should make 56oz target easy no?

The airframe less landing gear and power stuff is about 28.3 oz. Not going to make 56 oz. Might hit 57 oz but no more than 58 oz.

Crist Rigotti · « **Reply #36 on:** November 10, 2020, 12:38:02 PM »

It's finished. Came out at 55 1/2 oz and a 15% MAC CG. Right where I wanted it. As a recap it has a Cobra 3515/18 motor, Spin 44 ESC, and Igor's Active timer. CNHL 6S2200mah battery, APC-E 13 x 5.5 cut down to 11 1/2 prop, 2 inch Great Planes spinner. All Monokote finished with some Nelson paint here and there. CF push rods, and adjustable elevator horn. A "fixed" adjustable rudder.

Ken Culbertson · « **Reply #37 on:** November 10, 2020, 01:38:31 PM »

Quote from: Crist Rigotti on November 10, 2020, 12:38:02 PM

It's finished. Came out at 55 1/2 oz and a 15% MAC CG. Right where I wanted it. As a recap it has a Cobra 3515/18 motor, Spin 44 ESC, and Igor's Active timer. CNHL 6S2200mah battery, APC-E 13 x 5.5 cut down to 11 1/2 prop, 2 inch Great Planes spinner. All Monokote finished with some Nelson paint here and there. CF push rods, and adjustable elevator horn. A "fixed" adjustable rudder.

Looks great. Hope I get to see it soon. Curiosity point...the 15% MAC, is that because of the straight LE. I tend to end up around 25-30% MAC except on my Twister which was about 15%. Also, I was needing a 2800mah for my 3520/12. Since I haven't ordered a new one yet what advantage would the 3515 have?

Ken

Crist Rigotti · « **Reply #38 on:** November 10, 2020, 01:44:42 PM »

Quote from: Ken Culbertson on November 10, 2020, 01:38:31 PM

Looks great. Hope I get to see it soon. Curiosity point...the 15% MAC, is that because of the straight LE. I tend to end up around 25-30% MAC except on my Twister which was about 15%. Also, I was needing a 2800mah for my 3520/12. Since I haven't ordered a new one yet what advantage would the 3515 have?

Ken

Thanks Ken.

15% MAC is where I wanted the CG. Electrics fly with a more forward CG. Nothing to do with the L.E.

I don't know, I don't have a 3520 to compare it to.

Ken Culbertson · « **Reply #39 on:** November 10, 2020, 01:51:02 PM »

Quote from: Crist Rigotti on November 10, 2020, 01:44:42 PM

Thanks Ken.

15% MAC is where I wanted the CG. Electrics fly with a more forward CG. Nothing to do with the L.E.

I don't know, I don't have a 3520 to compare it to.

I still have not figured out the forward CG just because it is electric but they do still turn better with a forward CG than an IC would. That in itself does not make me want to move it forward. Probably just me. I used to marvel at how far aft Gieseke's CG's were back in the Fox 35 days. Trying to keep up with his corners got me used to it being back there. Maybe I should join the crowd!

Ken

Dennis Adamisin · « **Reply #40 on:** November 10, 2020, 06:09:20 PM »

ANOTHER fantastic build thread Crist! Looks GREAT

Crist Rigotti · « **Reply #41 on:** November 10, 2020, 08:42:22 PM »

Thanks Dennis. Tomorrow I fly it. I'll report on how it goes.

Sina Goudarzi · « **Reply #42 on:** November 11, 2020, 04:10:57 AM »

Another great product from Rigotti Aircraft Co.
thanx for sharing Crist.

Perry Rose · « **Reply #43 on:** November 11, 2020, 05:39:21 AM »

With the battery on the outboard side it could go further than the plane.

Dennis Nunes · « **Reply #44 on:** November 11, 2020, 07:33:26 AM »

Quote from: Crist Rigotti on November 10, 2020, 12:38:02 PM

It's finished. Came out at 55 1/2 oz and a 15% MAC CG. Right where I wanted it. As a recap it has a Cobra 3515/18 motor, Spin 44 ESC, and Igor's Active timer. CNHL 6S2200mah battery, APC-E 13 x 5.5 cut down to 11 1/2 prop, 2 inch Great Planes spinner. All Monokote finished with some Nelson paint here and there. CF push rods, and adjustable elevator horn. A "fixed" adjustable rudder.

A very nice looking Pathfinder Crist! With the Cobra 3515/18 motor you should have plenty of power. My Circulas 46 IIe is about the same size as a Pathfinder, uses the exact same motor and it weights a hefty 65 oz. Plenty of power to pull it through the pattern.

Dennis

Crist Rigotti · « **Reply #45 on:** November 11, 2020, 02:18:40 PM »

Thanks guys.
Went flying today. 60 degrees, wind 2mph gusting to 5 and CAVU.

Flew 2 1 minute flights, then a 3 minute flight. Then 2 2:45 flights, then 4 full flights. The first 2 1 minute flights were checking wings level, lap speed, LO position. Then the 3 minute flight spent more time inverted for wings level and some overhead stuff. By now the plane was close to basic trimmed. The 2 2:45 flights were spent with varying lap speeds and getting equal turn rates. The 4 full flights were mostly full patterns with some minor adjustments.

It flies very good. It has a good corner and it is well behaved out on the lines.

This is with the pusher prop combo.

This afternoon, I'll convert it to a tractor prop combo. I'll remove the 2 degrees of up thrust, and realign the control surfaces back to zero. Then tomorrow I'll start all over. This is to see the differences between the 2 are.

Stay tuned.

Steve Dwyer · « **Reply #46 on:** November 13, 2020, 07:30:21 AM »

After following this thread I have become motivated to take my Brodak Pathfinder kit down from the shelf and build it electric vs the LA 46 I had in mind.
Because I "bounce around" to different park fields with less than desirable smoothness I'm considering converting it to conventional landing gear vs gear in the wings. Any concerns, too big a span?

Steve

Brent Williams · « **Reply #47 on:** November 13, 2020, 08:03:31 AM »

Quote from: Steve Dwyer on November 13, 2020, 07:30:21 AM

After following this thread I have become motivated to take my Brodak Pathfinder kit down from the shelf and build it electric vs the LA 46 I had in mind.
Because I "bounce around" to different park fields with less than desirable smoothness I'm considering converting it to conventional landing gear vs gear in the wings. Any concerns, too big a span?

Steve

https://hobbyking.com/en_us/carbon-fiber-landing-gear-for-profile-model-40-60-class.html

Dennis Adamisin went with a traditional front landing gear on his P.F.

SteveMoon · « **Reply #48 on:** November 14, 2020, 01:37:05 PM »

I was at the flying session with Crist on Thursday and I can attest that
his new Pathfinder is a beauty and it flies great.

Steve

Steve Dwyer · « **Reply #49 on:** November 19, 2020, 05:54:17 AM »

Perry,

Can you explain how you decided to increase stab span by 2" and not increase fuse length as well as was done with the Fancherized Twister? See your note below. Isn't there a rule of thump on stab area to wing area? Do you think the added nose weight and power with the EVO 60 in conjunction with the added stab area forces contributed to a better combination? I want to go with electric with out changing the nose length. Trying to make a decision on the best changes.

Steve

I've built 3 Pathfinders and still have two. The first from a Brodak kit was .46LA power. The second is scratch built and electric, an Arrowind 2812/07 with HRB 4s 3300 battery. The third has an Evolution .60 in the nose and is the best flier of the bunch. All three have unchanged nose lengths and no more that 2 degrees of engine offset with straight fin/rudders. I did increase the stab span by 2 inches on the third model. Balance points are as shown on the plans. Everyone cringes at my method of setting leadouts so I won't mention it here again.
The plans show the c/g at 2 3/4 inches back from the leading edge or about 23% MAC.