700n DFC Helibug build thread

[The Mechanic]

rhode

Yes I agree. As Mr. Shurley pointed out in his threads the Viton line makes a good clunk line. I used the small amount of Viton line that came with the engine for the clunk line. It's still in great shape. I'll need more someday though so Thanks for the links.

[The Mechanic]

It’s been a long time since I did an update. The 700n is still doing great but I’ve only accumulated 5 hours of total flight time. Family activities take priority over my hobbies and I have many of both.






As a teenager it was my (unrealistically expensive) dream to build a radio controlled airplane; preferably a big Cessna 310 like Sky King’s; and fly it off the road that ran by our farm. I envisioned flying out over the neighbor’s field, doing some high speed passes and whatever else was fun and then lowering the retractable gear, putin’ out some flaps and landing back on the road.

Well… after a few years (we don’t need to talk about how many) I have finally lived the dream. It wasn’t the 310 with a ten foot wing span I thought would be so cool; but it was instead my radio control Trex 700n gas; with a five foot rotor, so I wasn’t too far off in size.

It was a year ago last fall, October 2015 when the flight took place. The pictures are compliments of my sister. It was a windy and somewhat gusty day but no way I wasn’t going to fly after getting there with my helicopter all ready to go. It was a lot of fun. Very rewarding.

[rbort]

With all that open space you don't ever need to drive to the field, you live there!!

-=>Raja.

[The Mechanic]

The farm is where I grew up; I now live in a town far away. And I really do miss the space!

[The Mechanic]

I’ve made some improvements this year to the 700 that I really like. I was going to fly today on my day off but the wind is awful so I decided to update this post instead. I’ve done a lot of bench work this year but ironically not a lot of flying because of family activities.

Funny story; I planned on going to my first fun fly at Schiller Park Flying Field (IL) on a Saturday last May. The Wednesday evening before I’m sitting on the sofa doing some programming to my Walkera 12s transmitter when I hear a “tink” from inside the radio. One of the gimbal springs had broken. No way I’m going to get a new spring in 2 days so I bought a Spektrum DX9 from Horizon Hobby and had it by Friday afternoon. Now, normally I would program a new transmitter and fly it on the simulator for a couple of hours to work the kinks out. Then I would program a small heli and fly it with that for at least a few days to get used to it.

But I was not deterred, I finished programming that sucker at 3AM Saturday morning, the day of the fun fly, and was doing my first flight ever with a brand new transmitter at 11AM with no less than my 700N multi kilodollar helicopter. Bless the heli gods it flew fine. And my first fun fly was a blast. One of the most fun things I’ve ever done.

Backing up just a little; when I first built the 700N Gas I had some economy in mind so I used the 5 volt Align tail servo that came with the kit. For all the other servos I bought ProModeler HV brushless servos. So last year (2016) I replaced the Align tail servo with another ProModeler HV brushless servo. I didn’t change anything else and was using a Hobby King RotorStar dual output voltage regulator so the Spektrum receiver, Spirit gyro and RCATS kill switch relay all stayed at 5 volts while all the servos were 7.4 battery voltage. In the following picture you can see the new servo and the metal fuel tank connector with Tygon fuel tubing I’ve mentioned in previous posts.



So now I’ve got the new DX9 Black Edition and I like it. It’s not as “plastic” as it looks in the pictures and, as you would expect, it’s light years ahead of the DX6i I used to use. I like the ladies voice that tells me how much time I have left on the timer. Much better than, “was that one beep or two?” Also, while the deviation firmware I’m using on the Walkera transmitter is awesome I have always had this nagging feeling that using reverse engineered firmware for Spektrum receivers on a really big expensive helicopter might not be the wisest decision I’ve made. I got the Walkera when my biggest heli was a 450. The 700 just got grandfathered in. I’ve never had a problem with the Walkera communicating with any of my many Spektrum receivers or Blade helicopters; but, it only takes one malfunction to be very expensive with a 700.

So I thought, as long as I’m going to use a genuine Spektrum transmitter with my Spektrum receiver I might as well upgrade and use telemetry. I was mainly thinking about receiver battery voltage but as long as I was at it I added RPM and CHT since it didn’t cost very much more. I replaced the AR9020 receiver I’ve been using with an AR9030T receiver with telemetry and installed the Align RPM sensor that came with the 700N kit. I installed a loop temp sensor around the base of the sparkplug for CHT. It would’ve been better to be able to screw a temp sensor directly to the cylinder head but the Zenoah doesn’t really allow for that. A relative temp is all I need anyway. When I originally built the helicopter I had installed the magnets that came with the kit into the clutch bell on the chance I would use them someday. Sometimes things work out.

The new AR9030T:



The RPM sensor was very tricky to install on the inside of the frame. Clearances are close and I wanted to secure the wiring with a couple clamps so I had to split the frame from the engine to have room. I had to fabricate an extension lead with a JST connector as the wire on the sensor came up 2 or 3 inches short. The Align sensor just plugs right into the Spektrum receiver and it works.



This Spektrum temp sensor was new this year I think. Good timing for me. I had to shorten the lead a bit to get the right length.



So now I’m in full-fledged upgrade mode. This year I also replaced my Hobby King HK250-GT helicopter with an Align 250 Pro DFC (and built a 450L because I had some leftovers) and at the same time I bought two Spirit WiFi adapters; one for the 250 and one for the 700. You can see the WiFi adapter in this picture next to the left cyclic servo.



The Spirit WiFi adapter, in theory, is a great convenience tool. It’s wireless after all and you can just pull your phone out of your pocket to check the gyro log or make adjustments. In theory. But it didn’t work. I fussed and fussed with that thing. Made some people mad at me on the Spirit help forum (I didn’t think I was that critical). It would sorta but not always work after I got familiar with the whole thing and how it’s supposed to be set up. Then; through logical troubleshooting I finally figured out the RotorStar voltage regulator and the WiFi adapter hated each other. The RotorStar was acting flaky with false low voltage alarms and when I bypassed it the WiFi link finally worked the way it should.

It was then I wondered, why did I ever use a voltage regulator anyway? If I had bought all HV servos to begin with I could have just run the whole electrical system at 7.4V in the first place. Except for the RCATS kill switch. It has to be 5V. Truth is I was a little scared of running 7.4V to the gyro and the receiver. Five volts just seemed safer for the high-end electronics. I don’t know. But now I was committed to an idea so the RotorStar had to go. It was going to be 7.4 volts all the way or bust. Except for the kill switch relay.

Turns out Futaba makes a cute little 5V servo voltage regulator that is just the ticket for what I need. Servo City sells a servo power board kit that allows connecting up to 16 devices to the battery with Futaba servo plugs. Also just what I need. I bought a small, lightweight 10 amp switch and some real nice 14 gauge wire from Amazon. I hated to give up the pin switch on the RotorStar that was real convenient but it too was becoming somewhat flaky as of late so it was time for a change.

The powerboard had just light electric traces in it and not all 16 positive and negative pins were connected in parallel. Not sure why. So I took the center conductor out of RG6 cable and after I soldered all 48 pins in the board I strapped all the positive pins together by soldering the heavy copper wire to the back of the board. Repeat with the negative pins. Sorry I didn’t take a picture of that.

The pins on the board are arranged into 2 groups of 8 sets with the same number signal pins in each group tied together. So signal pin 1 of the first group is tied only to signal pin 1 of the second group and so on. I made use of that with only one connection for the throttle servo which is connected to the receiver. That allows both the receiver and the throttle servo to get battery power from the servo power board. Both the receiver and the gyro have double power connections. One of the very few redundancies on the aircraft.

Instead of trying to fabricate an enclosure for the board I used 2 layers of 1/16th inch phenolic sheet on the bottom of the board with the center of the top board cut out to provide clearance for the RG6 wires. Then I just added a couple of small phenolic boards at the ends on top of the PCB where the mounting screws go and the traces are exposed. A simple 90 degree angle of aluminum sheet provides the mount.

The connector lugs on the switch are made for push on spade connectors but I drilled out the small holes in the lugs for 2mm screws with nuts. I had some aircraft quality AMP ring terminals for the 14 gauge wire and covered the connections with shrink tubing. This picture is a little closer look at how it turned out. The switch peaks out from under the canopy when it’s installed. The Futaba voltage regulator is just below the wires to the switch.



Everything is working rock solid now and I feel a lot more confidence in the robustness of the whole system. I was always a little skittish about using a Hobby King voltage regulator but at the time it looked like the perfect solution. Now that I look back I can see it was kinda silly to bother with a voltage regulator in the first place now that so many devices are high voltage compatible. That’s how we learn I guess.

And all of this started because a little spring in my transmitter broke.

[The Mechanic]

From the last post forgot to mention, while changing wiring during the tail servo upgrade last year I switched from 4 PWM wire connections between the RX and the gyro to just one SRXL wire connection. There's still a lot of wires but 3 less is a little better! I guess it's the same protocol used between Spektrum satellite receivers and whatever they're plugged into so it should be reliable.

One other thing I forgot to mention. At the fun fly a gentleman asked me what my head speed is. He got a kick out of it when I told him in a funny voice, "I dunno".

So with my new telemetry I can now report 2000 RPM in a hover and 1700 balls to the wall FFF. I'm using the 17 tooth pinion. 6.58:1

[cr@sh]

hey there, when i was about 10 years old, i dreamed of flying an rc heli, now i have a shed full of them haha ...now, about 30 something years on, i am at the pinnacle of what i would have imagined as a 10 year old..and hey, its great! haha. i guess what im tring to say, is, that i know how you feel :-)

[The Mechanic]

Yes; living the dream! nz, New Zealand right? Happy Summer! It's minus 3 at my house right now.

[The Mechanic]

I wrote this update back in November 2017. The engine work was accomplished in October. I'm just now getting it posted.

The tail on the 700N has always been a little unsettled and not rock-solid steady like my electric helicopters. This year it seemed to be getting worse. At first I suspected the tail servo wasn’t good enough but upon paying closer attention I realized the “slight” miss in the engine at mid power was causing the unsettled tail. I’ve mentioned in previous posts I thought this was as good as this engine was going to do but after watching some youtube videos of other Zenoah engines I decided my engine should be running better.

When the 700 was hovering, you could hear the pitch of the engine had a waver in the tone. I had the carburetor high idle screw at 1-1/4 turns and the low idle screw at 1 turn. I should have had the high idle screw less than that but I tried it once and it didn’t seem to make a difference; maybe a little less power so I put it back to 1-1/4 turns and left it there. The engine was definitely running rich and I should have left it leaner even if I thought it made slightly less power. A view of the spark plug would have told me that but I didn’t mess with it. I was also concerned about the engine internals getting too hot and just being lazy.

I decided to take the engine out and change the crankcase gasket, cylinder gasket, flywheel end crankshaft seal, carburetor insulator, carburetor insulator gasket and the carburetor gasket. I put a thin film of Permatex #2 sealant on all the gaskets during install. I’ve never liked that the original gaskets were installed dry at the factory and I’ve always wanted to re-install the fasteners with Loctite and a torque wrench anyway just to be sure; so this was a good time to do all that. I used a torque wrench on every engine fastener and the spark plug.

Picture before cleanup:







After cleanup:




New carburetor:




Sealed with Permatex #2:







I also found out Dave’s Discount Motors sells a Walbro WT-990 carb with a sealed ball bearing mod on the throttle shaft. An idea I really liked so I installed one of those as well. For good measure I replaced the spark plug with an Iridium plug and the air cleaner element as well.

Upon teardown I realized the engine was running much richer than I had suspected. The spark plug was black and wet with oil as was the top of the piston and the top of the combustion chamber. The piston ring had some varnish but wasn’t clogged or stuck. The air gap of the magneto was a little tight on one side. Total flight time was about seven and a half hours on the engine. I should have checked the spark plug before now but I mistakenly didn't think it was that rich.

I’m very happy with the new carburetor. With the ball bearings it’s butter smooth and a very tight air seal between the throttle shaft and the carb body; this corrects one of my biggest gripes about carburetors.

In the flight video you can hear the tone of the engine is very consistent now and the tail is almost perfectly steady. Engine acceleration (with the blades off) is very good. I’ve flown it for about an hour now and it’s a lot more fun to fly with a good running engine and a steady tail. Needle settings are 1-1/16 high and 1 turn low. Full power has always been good with this engine and with the new carb it is the same.

Here is a picture of the new spark plug now after flying for an hour.




On a different subject you may have noticed in previous pictures I’ve always been using a “T” fitting with a plug in the return fuel line for fueling. I think I’ve read in other posts that people just unplug the lines from the carb to fuel or de-fuel and I finally tried that and sure enough it is a whole lot easier than fooling with the plug. So, no more T fitting. Another lesson learned.


Video after engine work with new carburetor.

[joecass2]

What oil are you using and what ratio?
Looks like there is a lot of blow by. Mybe the ring was stuck from all the carbon build up. Glad you got it fixed though.

[The Mechanic]

Hi,
Using 4 oz per gallon of Husqvarna synthetic blend with premium gas. Ring wasn't stuck and compression seems pretty good. The amount of carbon buildup wasn't as bad as it looks in the picture but I was surprised there was any at all. Should have been looking at the spark plug sooner. Really happy with how it runs now.

[rbort]

But its lean. Needles for the 990 should be around 1/8 L and 1/4 high with a 27 motor.

If its super smooth then the cue is "something is not right", might be lean. Needs to burp a little in normal mode and clean up in idle up 1/2.

If too lean it won't make as much power, if too rich it won't make as much power. It needs to be right on. These are gassers not nitros, so run them on the edge of perfect.

I hardly ever look at plugs but I can see with yours its grey (lean/hot), should be brown.

-=>Raja.

[The Mechanic]

Hi Raja,

It's a G290RC engine. I've been running at 1-1/4 H for 2 years and you can see the results. I always fly in idle up and now for the first time it has a solid note at all speeds but idle. The last nitro I flew was a P40 Warhawk control line plane when I was a teenager. Fox .15 engine; still have it. So I couldn't tell you much about adjusting those except that Fox engine ran good.

The color of the plug looks brown to me. Pictures are hard to faithfully reproduce colors. Base of spark plug temp on last 10 minute flight ran about 180F. Ran great.

[rbort]

Yes I can see you've been running it lean the past 2 years hence why all the black burnt piston. That is an indication of it running hot, there shouldn't be any black on the sides of the piston. You're not in good shape doing that.

But OK if you think its good then go with your gut about it. I just gave you my thoughts from what I'm seeing.

All the best wishes for a Happy New Year and some nice flights to come!

-=>Raja.

[joecass2]

Yea be careful I Seized up the top end of my TRM300 trying to get my tail perfectly smooth. I had a tail oscillation that was in the air frame. I stacked 2 bottom plates together and that got ride of it.

I noticed also if any of the bolts that hold the engine to the frame are loose you can get a tail oscillation from that.

[The Mechanic]

Thanks Raja,

Best wishes and a Happy New Year to you too.

Just an FYI for anyone who is reading along on this thread; The Zenoah engine in my helicopter is a stock Zenoah G290RC. It hasn't been modified by a third party. The Zenoah manual specifies carburetor mixture adjustments as 7/8 to 1-3/8 turns open for the high needle and 1 to 1-1/2 turns open for the low needle depending on local altitude, air temperature and probably variations in carburetors. The first carburetor that came with my engine just ran a little rich; thus the carbon build up.

I can understand how modified engines would be sensitive to failure as they are being operated at power outputs beyond OEM design specifications but the stock engine should be pretty robust.

[joecass2]

The modified engines are very robust. Just got to make sure you have the right needle settings

[The Mechanic]

Since my last update I’ve flown about another hour and 45 minutes and I’m still happy with how the engine is running. Still very smooth and good power.

I’ve made some more improvements that I’m really happy with. I keep thinking ok, everything is perfect now; it doesn’t need anything else. But there always seems to be a little something better.

First is my bubble level. Since the Spirit FBL gyro needs to have the helicopter as level as possible when booting up to calibrate the rescue I found these very small bubble levels on Amazon. They’re surprisingly accurate. At first, I was just setting the level on the tailcase when I booted up and then putting the level back in my pocket. Then; you can see this coming; then I took off with the level just sitting on the tailcase. I didn’t realize I had forgotten until I got home and started putting things away. It was the last flight of the day I left it on. I don’t know how or when it fell off but it could have easily gotten jammed in the main gear at full rotor speed while taking off. THAT would’ve been real cool to watch!!!!

It gets better. That was last summer I lost it. This thing is the size of a dime. On February 15th I’m back out to the flying field on a nice day; and I look down; and there it is… just laying there on the grass. That is dead grass because it’s winter. What are the odds!

So even though I didn’t really want to I’ve bonded the level to the helicopter with 3M VHB tape. The level being permanently on there isn’t as obvious as I thought it would be. In fact, I’ve put one on the 450L too. But it has helped a lot with the Spirit calibration being dead on every time instead of just guessing… “oh, that looks pretty level.”



I love the look of the T-Rex 470L and I put the tilted landing skids from that heli on the 450L I built last year. I liked it so much I put the tilted skids from the 700X on my 700. I was concerned I might not have enough clearance for the recoil starter; and it’s real close; but it works. Landing and taking off doesn’t seem to be any harder and it keeps the tail blades out of the grass a little better as well as just looks cool!



So the 3 most popular questions people ask me:
Number 1: Does it have a camera?
Number 2: How far (high) will it go?
And number 3 is always: How fast will it go?

I’ve always kinda’ wondered myself how fast the 700 can go but I’ve had way more important things to worry about. So now that I’m getting more comfortable with day to day flying of the 700 and I was thinking one day last February I wish I had a radar gun to see how fast the 700 was going flat out. And then I realized; I don’t have a radar gun but I do have a chronograph (stupid phone) in my pocket! So I requested the assistance of a couple of the guys at the field if they would time me while I flew the length of the runway. After that it’s just some math.

They agreed and after I measured the length of the runway (just shy of 100 yards) they positioned at each end and used hand signals to mark the passing of the 700 at the far end of the runway. First call… 2.0 I’m flying the helicopter so I don’t really understand what he’s saying. Then he calls 2.1

After I land my friend with the chrono comes over and says 2.0 seconds and 2.1 seconds. I’m like what? Two seconds! It doesn’t seem that fast when I’m totally focused on flying. I pull out my stupid phone and ask, “how fast is 100 yards in 2 seconds.” The first hit reads 50 yards per second equals… 102 MPH

I process that for a little bit. In my Phoenix simulator I use a Raptor 90 Nitro customized to the specs for my 700 Gas. Full out simulated speed with that is about 80 MPH. I honestly didn’t think my 700 could go 80 MPH. Looks more like about 50 or maybe 60… but 102!!!

So I get home and do some figurin’… With Google maps I confirm the length of the field is just shy of 100 yards. OK; what if it actually took 2.5 seconds to go the length of the runway? About 80 MPH. Yeah; that sounds a little more realistic. But, my curiosity is peaked. I research what a GPS sensor costs and decide it’s a little pricy at $99 but I can justify it because if my heli ever runs away on me I can go find it. Of course it’s impossible for that to happen because I have a spring loaded NC kill relay rigged so if I lose radio contact, or battery power or if I simply flip the kill switch that’s as far as she’s gonna’ go. But hey, it’s a flimsy excuse to get the GPS!







I bought the Spektrum SPMA9587 and I was a little concerned that this GPS sensor would either take forever to get acquired or the rotor blade spinning right above it would drive it squirrely or something. Neither was the case. First time powered on this thing locked on in seconds while sitting on the dining room table inside the house! (I’ve since found that it can take a minute or two when in the house but I didn’t expect it to work in the house at all !)

Out to the field and I’m ready to do my speed runs. I bring my computer because I thought I would have to pull the SD card out of the DX9 and read the log file to find out what the fastest speed was. After I land I realize that the GPS data for speed is recorded on one of the telemetry displays and it shows maximum and minimum speed since last boot up. It reads… 88 MPH

Oh, did I grin. That’s a bunch faster than I thought it would be. Not as cool as 102 but certainly faster than I thought it would be! The 700 is so big it just doesn’t look that fast. Note; the wind on this day and the day I had the timed runs wasn’t a factor. So when I get home I read the log file and I see the GPS data is very consistent and the readings are what I would have expected. I don’t think being under a spinning rotor blade has any detrimental effects for the sensor. And of course, being outside, the GPS locks on immediately after boot up. It doesn’t work inverted though and I can hear the DX9 call “GPS acquired” after I roll upright again.

I exported the log file to Google maps and had it plot my flying path over the sat image of the flying field. Just something else cool you can do with the data. Oh, and the highest I flew (question number 2) was about 300 ft. I was a little surprised at how far out I was on wide turns but considering how much I underestimated my speed it only makes sense the helicopter is also traveling farther than I thought as well.



The one other thing I learned while bench testing the GPS, is my flight batteries don’t have much reserve amperage at storage voltage. I was getting a telemetry warning about low receiver voltage when I’m at about 7.8 volts. I thought what??? The batteries were Turnigy 2200 25C LiPos. The plain blue ones. They’re only 6 months old and the IR was less than 10 per cell. They’ve been working great at the field; I’ve flown almost an hour on one charge. But now here’s this low voltage warning “receiver voltage 5.1 volts” (I was moving the servos around now to test it). I look down and it’s reading 7.8 maybe 7.7 I do an experiment charging the battery and testing it. After the at rest voltage was above 8 volts I stopped getting the warning. I’m usually not below 8 volts anyway but after my Lion Power battery catastrophe (a long story) I’m now a lot more cautious about my batteries.

So I ordered Align 30C batteries (made for the 700N) from Amain and when they show up they’ve got like 20 gauge power leads coming out of them! That ain’t gonna’ happen. So I sent them back and for once the Turnigy Nano-Tech 2250 65C batteries (with 12 gauge power leads) were in stock. I did the same test with the Nanos at storage voltage. No warnings. The old batteries went in the trash. You can see the new battery in the picture with the GPS. So I should be all good to go now.

But let’s see… about that camera???

[Dawiev]

d4.

[The Mechanic]

So I went to the Schiller Park (IL) Fun Fly again this year and as I’m walking in, one of the pilots there said “I see you brought the chain saw”; I like that nickname; “The Chainsaw!” It was a good day and one of the other pilots had a new USA flag theme canopy on his 700X. I raved about it and he told me I could get one too on ebay they have them for all the T-Rex 700s. I ordered one on my phone right there. I really like it. It’s for a 700 Nitro Pro not the DFC but it fit without any modification. I didn’t even have to make a cutout for the throttle linkage or the fan air. I did have to add a bushing to the rear canopy mounts to move them out about a quarter inch but that’s all. Cool



So…. the first day I fly with my new canopy (see above pictures), July 11, everything was working great. The tail still had that little side to side bounce every so often and when I did a high-speed pass, 104 MPH! (downwind), the tail wagged ever so slightly. But, a real good flier as far as I was concerned. Engine running real smooth and strong.
But then I did the absolutely most stupid thing I’ve ever done with a helicopter… last flight of the day; I messed up a flip and hit the rescue switch… and hit the throttle hold by mistake at the same time. I shut the engine down to idle while flying and then stood there in stunned denial like a deer in the headlights while my rotor blades slowed down. My DX9 diligently announced “throttle cut!” and I just froze and stood there for at least 2 seconds. I could, and should have kicked the throttle hold back off but I wasn’t sure I could find the switch in time to save it so I just thought “fly the plane!” My attempt at an auto resulted in landing on the skids really hard. This is the funny part; as I’m walking across the field out to my heli I think, oh yeah, I guess I can shut the engine off now, and hit the engine kill switch on the TX. So… after 3 and a half years and 12 hours, 18 minutes of flight time logged on the 700 I had my first damage. Wow was I disappointed in myself. That was some really P poor piloting. Truth be told I didn’t hit the rescue switch I lashed at it in a flurry of panicked fingers. I don’t know why I was so scared that day but I was scared of crashing and see what happened. Total over reaction to a simple problem I’ve faced many times.

But wait! This update is going to end with a happy ending! Believe it or not my stupid mistake may have saved my helicopter! I’ll explain.

The tear down.



When I walked up to the 700 there was only a few obvious problems like the right landing skid broken off, a broken rotor blade, the fuel tank was pulled out of the frames!, all 6 servo rods to the swash bellcranks were bent. But I feared much hidden damage. As it turned out, the most “devastating” damage had nothing to do with the crash landing; it was excessive wear and tear to the tail drive torque tube. I just didn’t know it was there; yet.





As you can see, I was about 80% of the way to losing my tail drive. The front umbrella gear and the mating torque tube splines had extreme wear. Had I kept flying it would have only been a matter of a few more hours before I could have really lost control of the helicopter when the plastic splines in the gear wore through. I never would have guessed there would be that much wear that fast. In my opinion it’s Align’s fault because the torque tube is too short; it was fully engaged with the aft umbrella gear (which was fine) but only half engaged with the front gear. Too short by about 1/8 to 1/4 inch. The new parts were exactly the same so I made sure to equally distribute the gaps front and rear upon re-assembly. Oh, and one of the 2 screws that hold the rear tail case to the boom was broken in two. I don’t think that happened in the crash (tail case, tail blade grips, fin, etc. didn’t have a scratch; one tail blade got flung back and had a nick in the trailing edge) I think I over tightened them a long time ago and the screw that broke just fatigued. That one’s on me.

The other point of interest was the control shaft that holds all the swash bellcranks. It’s made out of aluminum and was severely worn. I used an extra shim when I re-assembled to reduce vibration damage in the future but I’ll have to keep a closer eye on that too. Note the chew marks on the right end of the shaft in the picture are from taking it apart. It was stuck in the bearings pretty tight.



There are just too many details to cover here but some things that were interesting. I mentioned the swash servo push/pull link rods were all bent. They were all “bowed” the same way; that is down. That is just weird because when one rod is under compression its mate is under tension. They all bent as if they were under compression which doesn’t seem possible. The ProModeler 420 oz/in swash servos are real troopers; only one of the three felt like it could have gear damage. I replaced the gears in that one but the old gears looked fine. I kept them for spares.

When I removed the canopy (undamaged by the way) to unplug the battery after the crash the battery was already unplugged; but the battery hadn’t moved even a little bit from its normal secure position; also weird.

As expected the engine was ruined. The impact to the recoil starter bent the fan case/crankcase and the crankshaft was probably bent from high Gs of the flywheel. New engine is “only” $220 so not too bad.
None of the Helibug parts were damaged so a big help there. Them are some tough frames!!!

The graphite/aluminum tail boom looked straight; until I rolled it across the kitchen counter. $36 for a new graphite tail boom with a new sexy matt finish. I already had the spare aluminum tail boom that came with the 700N kit but I wanted the graphite. It looks real good.

So while I had the ship disassembled and my credit card warmed up I sprung for the MKS HBL880 tail servo to replace the ProModeler I’ve been using. I wasn’t sure it would make any difference but I felt I had to try as my unsettled tail, as minor as it was, was triggering my OCD. As it turns out, that was an excellent decision as the tail is now absolutely rock solid as it is on my 450 and 250 also with MKS tail servos. Love the MKS servos. I probably will never buy another servo that isn’t an MKS. Just outstanding performance.

So as I write this I flew the 700 in all its new glory for 26 minutes last Saturday. The new engine; which I tore down and re-assembled with new gaskets, Permatex #2 and the sealed bearing modified carburetor from the first engine ran perfectly smooth. Great performance from the new engine. This is how she looked before I took it out.

The Chainsaw!