Century E640 finally done and test flown

[distructor]

Yesterday was one of those days I should just have packed it up while I was ahead. I was off the other three flights, but decided to try just one more.

The lower part of slide channel spit off. I don't know how it can even happen with the pin in place...which it wasn't when I picked up my hurt bird. Would think the pin would take a lot of the force. How does the pin even disappear? I can only blame it on operator error. Lesson learned. On days like that, quite while you are ahead.

I have spares for all but the frames. I'm going to try and repair it, Will let you know how it works out.

[Dennis P]

Hope you are back up and running distructor ! I have gotten several more flights on the stretch and several more on my 10s 640 .They are different helis and they have a different feel to them for sure.I am not one for high headspeeds and that being said I am really liking the 690 with 1660 headspeed more every flight.The one thing that really does make me wonder though is how fast it is.This bird will power around a huge loop at amazing speed for it's headspeed but I do have 12 deg's of pitch available.The other thing about it is how quiet it can be.I am getting use to it but being slightly deaf (some say more than slightly ) it would go silent with light pitch when it was out aways,this would cause a little concern for a sec or so sometimes.It is just a joy for me to fly .Is anyone else on here flying a stretch? Sure would like to hear your input? I know it may not be for everyone but I think there are many of use that do not want a 10 horse 700 running 50 rpm shy of shedding all it's blades .
I know this is a different brand but look at what is capable at 1000rpm.It is a very similar setup to a stretched E640 being a very light 700 class heli. I do just love this flight.They say he can fly 25 minutes on one charge? Update .I have some more info on his setup.He is running his 5000mah 5s packs in parrallel so 5s 10,000mah pack.He has a headspeed range of 780-1380 .Flight times 20-25 minutes depending on headspeed.

[ame]http://www.youtube.com/watch?feature=player_embedded&v=yntueog1KYU[/ame]

[rotorsport]

Nice sound
I like the slow head speed!

[karl k]

Now that I have the 10 tooth pinion installed, I flew on 620mm blades at 1750rpm on Monday.

Even at 9lbs 9.5oz, it still had plenty of pop. The roll rate was crisp and the tail held solidly.

I've installed the HW phase sensor and enabled the Skookum governor since that flight. I'm planning on 1600, 1750 and 1950 rpm for headspeeds. Seeing how little current I pulled from the packs at 1750, I may be able to either extend my flight times to 8-10 min using the 3300 packs or move down to some 2600 packs to make it light. If I really want to drop the disk loading, I could install 640mm blades, or even stretch it like Dennis.

Looking forward to more testing. This thing should be unboggable with a 9.4:1 gear ratio.

[Dennis P]

Hello Karl,glad to hear you are enjoying playing with some of the slower headspeeds.I fly my 640 with 620's allot at 1730 and as you say it can flip and roll stationary down fairly low with no issues.I think sometimes people have everything set up for very high headspeeds and do no adjusting to control response when they try lower headspeeds.The FBL has made switching back and forth allot easier though as paddle size and weight is of no concern anymore. Have fun.

[karl k]

What weight did yours come in at? Mine sits at 9lbs 9oz RTF.

[Dennis P]

Hello Karl my E640 is 9lbs 7oz and I plan on sheeding some of that shortly though.

[karl k]

Care to share some weight loss plans?

[Dennis P]

Eat less bacon ,walk more,

I will let you know what I do .
Dennis

[joallen001]

Had a successful flight on the n640 this past weekend. This heli seems to be really nice and smooth. I was going over everything tonight to make sure everything is still tight. I noticed one issue that I am not sure on what to do. I will do my best to explain the issue. With full positive and negative collective the elevator servo works perfect. Elevator works perfect at mid stick also. But when I go to full positive and/or negative and give elevator the ball link bottoms out on the servo arm(the round part that goes over the servo gear). The only way I can see to fix this is by spacing the linkage balls more than the manual suggests?

[Dennis P]

Originally Posted by joallen001

Had a successful flight on the n640 this past weekend. This heli seems to be really nice and smooth. I was going over everything tonight to make sure everything is still tight. I noticed one issue that I am not sure on what to do. I will do my best to explain the issue. With full positive and negative collective the elevator servo works perfect. Elevator works perfect at mid stick also. But when I go to full positive and/or negative and give elevator the ball link bottoms out on the servo arm(the round part that goes over the servo gear). The only way I can see to fix this is by spacing the linkage balls more than the manual suggests?

There are a few options.The first one to check is to see if when this is happening is the swash plate binding also? If so set the cyclic ring up on the FBL controller SK540 in your case.This will limit the amount of cyclic at full pitch so it will not bind.The next option depends on your servo shape size ect.I am running Airtronics 94774 servos and I sanded the bottom of the servo holder down to within a few thou of the bottom of the servo case so I could mount the balls on the upper side of the servo arm as with the airtronics servo the linkage hit the case.We generally should not be full collective at full pitch unless we are in a oh crap situation in which cause a little less cyclic may actually help us

[joallen001]

Originally Posted by Dennis P

There are a few options.The first one to check is to see if when this is happening is the swash plate binding also? If so set the cyclic ring up on the FBL controller SK540 in your case.This will limit the amount of cyclic at full pitch so it will not bind.The next option depends on your servo shape size ect.I am running Airtronics 94774 servos and I sanded the bottom of the servo holder down to within a few thou of the bottom of the servo case so I could mount the balls on the upper side of the servo arm as with the airtronics servo the linkage hit the case.We generally should not be full collective at full pitch unless we are in a oh crap situation in which cause a little less cyclic may actually help us

I had the same issue with the linkage hitting the servo. I changed the linkage balls on the servo arm. The century ones had more of a standoff on the ball. So this fixed that problem. I am not getting any swash plate binding. I am using the torq servos and I noticed I could sand a little off of the servo holder (very little though). I thought of trying to mount the balls on the topside of the arm but was worried about the angle of the linkages. I do agree that during flight the elevator servo may never bottom out, but then I think what if it is! Paranoid I guess after the maiden flight crash. here is a photo but its kinda hard to see. I think I took that mid stick, if not close to it. You can see if I was full positive or negative pitch and pulled back on elevator or pushed forward the link would hit the servo arm.

[Dennis P]

Well I am getting some flights on the stretch.I have gotten in 8 flights over the last 2 days and it is working well.I put KBDD lime dampers in the head and that got rid of a little play in the spindle.It seems to be a little less noisy in pitching manuvers .But no big change ,the big thing that has happened is it is finally warm enough to fly in some wind and I have finally had the tail blow out 4 times now.Two times in fast backwards fight and 2 times in funnels.A couple where poor pilot issues but they would not have blown out on my E640 with a bit higher headspeed or on the 690 without wind but we do fly in wind .This got me thinking and looking about on the parts wall ect.I realized that the Gassers and the N640 use a 21 tooth tail transmission gear where as the E640 uses a 24 tooth.So a little calculating and I see that the 24 tooth is a 4.0-1 ratio and the 21 is a 4.57.This translates into a tailspeed at 1700 headspeed of 7769 for the gasser gearing and 6800 for the electric. I had 104mm KBDD on for the first two flights today and RotorTech 105mm on for the second 2 .The RotorTech where better but I needed more to hold in the wind .So apart it came and I fitted the 21 tooth and slid the transmission in to see how much elongating of the holes will be required to set the mesh.It was just under a half a hole so lets say 1.5mm.I worked slowly as I wanted it to be a slide forward and the mesh is correct fit.I was not slow enough as I have a slide forward zero backlash fit Close but not perfect.I am really thinking that this gearing change should fix me up.It may not be a perfect setup but it is going to increase the tail power allot I am sure being a 13% increase in speed with the 105mm blades that it should be a huge increase in authority A E640 running 2300 rpm with the stock 4.0-1 tail ratio has the tail spinning at 9200 rpm and at 2000rpm it is spinning at 8000 rpm .So my 1670 headsped will be 7632 so it should be decent.We shall see tomorrow

[MotorRotor]

Well thought out Dennis.

As the trend to higher rotor speeds increased, the gear ratio for the tail rotors where lowered to help keep the tail rotor power consumption reasonable (remember power consumption is not a liner function relative to rotor speed, as a doubling in tail rotor speed will result in a four times increase in power consumption) and to also keep the tail rotor response within the working parameters of the gyro systems they may be used with.

As you are now running LONGER blades and LOWER rotor speeds your solution of increasing the t/r ratio is a good one.

To maintain similar yaw power, one can also increase the length of the blades, but this will only increase the power of the tail rotor in a linear manner rather then the higher return using an increase in tail rotor speed.

[distructor]

Looking forward to hearing the test flight report. I'm been playing with 12s 2600ma batteries running 1600-1800 rpm 640mm mains and 104 tail. I've had a couple tail kick outs at 1600. Nothing to bad, but it does undermine the confidence a bit.

[Dennis P]

Well all I can say is the results could not be better.About the same wind today and fast backwards flight turning fast into the wind no issue but good howl from the tailblades. Fast backwards loops sideways in the wind no issue at all and funnels zero issues.Kind of crappy sky's to see in today so it was not a brutal test but not even a slight sign of the tail getting close to a blow out and it did get pushed harder than yesterday which had 4 blow outs.I would have to say that the gearing change is a great success but it has moved my boom forward just that little bit which has put my mains into possible stricking distance of the tailblades !!
May have to make a new boom that is about 3mm longer now.

[distructor]

Originally Posted by joallen001

I had the same issue with the linkage hitting the servo. I changed the linkage balls on the servo arm. The century ones had more of a standoff on the ball. So this fixed that problem. I am not getting any swash plate binding. I am using the torq servos and I noticed I could sand a little off of the servo holder (very little though). I thought of trying to mount the balls on the topside of the arm but was worried about the angle of the linkages. I do agree that during flight the elevator servo may never bottom out, but then I think what if it is! Paranoid I guess after the maiden flight crash. here is a photo but its kinda hard to see. I think I took that mid stick, if not close to it. You can see if I was full positive or negative pitch and pulled back on elevator or pushed forward the link would hit the servo arm.

I cut the left side frame to make room to flip the ball/control arm arrangement around.

[Dennis P]

I cut the left side frame to make room to flip the ball/control arm arrangement around.[/QUOTE]

That looks like it worked out really well distructor , a very nice fix. By the way what did you do frame wise with the battery slide?

[distructor]

Originally Posted by Dennis P

I cut the left side frame to make room to flip the ball/control arm arrangement around.

That looks like it worked out really well distructor , a very nice fix. By the way what did you do frame wise with the battery slide? [/QUOTE]

I ended up removing all the plastic part of the slide from both sides. Milled delrin channels, and drilled and tapped it to align with the existing holes. Didn't turn out as good as I had hoped but it does the job.

[Dennis P]

Oh well as long as it holds the packs in there and you did not end up buying new frames.How do you like the magnetic canopy mounts? I have done everything to blow my canopy off and it is always in position when I land.I am amazed how well those magnets hold along with the screw that goes in the hole.Sure nice for pack changes also !