Roban AH-1W Cobra 700 Size Scale Helicopter

[PawPaw]

Just thought of another question for you guys, if y’all don’t mind? I’m trying to make peace with the blade balancing proceedure that seems to be the current accepted practice nowdays. What is the reasoning behind accurately locating & matching the cg points between blades? I’m not understanding why a static cg is important on a blade that will be clamped in a rotor grip on one end for flight? Obviously the blades must weigh the same to be dynamically balanced in rotation around their axis but I can’t see why it’s more beneficial to add more weight to the cg point than the less weight required to balance at the tip for the same blade?

[DCORSAIR]

Sorry to hear about the health issue, DC! Hope everything resolves quickly & life gets back to normal for you. Good news on the expansion project, sfc...sure wish I had more room here but came to the realization I’d just fill up more space with more projects anyway. Other than a couple of quick low hover hops my Cobra just sits on top of a bookcase awaiting this Gulf coast monsoon season to pass. Hopefully will have more Cobra news soon.....

Thanks, I hope to get back to normal as well, I thought I would reach out to you guys that were building the Cobra, it is still on my list to have, only thing is, I can't decide between the camo or gray.

[F106DeltaDart]

I've been still receiving parts for detailing mine. Got some new skids from Mike Spinner over on scalerchelis, and a bunch of 3D printed cockpit parts from Tyler Grey Models. Hopefully I'll get the mechanics up in the air soon.

[RCjetdude]

Just thought of another question for you guys, if y’all don’t mind? I’m trying to make peace with the blade balancing proceedure that seems to be the current accepted practice nowdays. What is the reasoning behind accurately locating & matching the cg points between blades? I’m not understanding why a static cg is important on a blade that will be clamped in a rotor grip on one end for flight? Obviously the blades must weigh the same to be dynamically balanced in rotation around their axis but I can’t see why it’s more beneficial to add more weight to the cg point than the less weight required to balance at the tip for the same blade?

The rotational forces will not be balanced if the span wise CG's are not the same even if both blades weigh the same. If the span wise CG's are the same but one blade is heavier then you would want to add weight to the CG of the light blade to keep the CG's equal but make them both weigh the same. If your CG's are not equal you would add weight to the tip or the root of the lighter blade. If the blades weigh the same but CG is off you would add the same amount of weight to each blade depending on which direction the CG needs to move. Take it to an extreme and suppose you have two blades that weigh the same but the CG of one is 3" from the tip and the other is 3" from the pivot bolt. The rotational forces will exert more outward force on the blade with the CG 3" from the tip because it is moving at a higher rotational rate.

[sfcfury]

The rotational forces will not be balanced if the span wise CG's are not the same even if both blades weigh the same. If the span wise CG's are the same but one blade is heavier then you would want to add weight to the CG of the light blade to keep the CG's equal but make them both weigh the same. If your CG's are not equal you would add weight to the tip or the root of the lighter blade. If the blades weigh the same but CG is off you would add the same amount of weight to each blade depending on which direction the CG needs to move. Take it to an extreme and suppose you have two blades that weigh the same but the CG of one is 3" from the tip and the other is 3" from the pivot bolt. The rotational forces will exert more outward force on the blade with the CG 3" from the tip because it is moving at a higher rotational rate.

I agree... and with my limited experience, it seems the bigger the blades, the overall balance seems more important. I followed the videos for the center line balance for the 500 size stuff, and that seems to work fine. On the cobra, (which is actually a 750mm blade), I did that and got the weights to match on each blade, and that just didn't cut it. It was a good starting point, but when I put them on the prop balancer, I clearly had a heavy blade. So I added tape to the light blade (which ended up being about of gram of weight if i remember correctly) till it balanced. What's crazy is that there is about 1 gram weight difference between the blades now (the heavier blade being the one without tape... go figure), but when the motor is running, I have definitely killed like 95% of my vibration issues.

[DCORSAIR]

Just thought of another question for you guys, if y’all don’t mind? I’m trying to make peace with the blade balancing proceedure that seems to be the current accepted practice nowdays. What is the reasoning behind accurately locating & matching the cg points between blades? I’m not understanding why a static cg is important on a blade that will be clamped in a rotor grip on one end for flight? Obviously the blades must weigh the same to be dynamically balanced in rotation around their axis but I can’t see why it’s more beneficial to add more weight to the cg point than the less weight required to balance at the tip for the same blade?

Good question, all these yrs flying helis, I don't have the answer for you, allI I know is, I use to only tip balance, now I balance on the CG piont and things seem so much smoother.

Someone will have our answer I'm sure, or at least explain it better than I can.

[DCORSAIR]

The rotational forces will not be balanced if the span wise CG's are not the same even if both blades weigh the same. If the span wise CG's are the same but one blade is heavier then you would want to add weight to the CG of the light blade to keep the CG's equal but make them both weigh the same. If your CG's are not equal you would add weight to the tip or the root of the lighter blade. If the blades weigh the same but CG is off you would add the same amount of weight to each blade depending on which direction the CG needs to move. Take it to an extreme and suppose you have two blades that weigh the same but the CG of one is 3" from the tip and the other is 3" from the pivot bolt. The rotational forces will exert more outward force on the blade with the CG 3" from the tip because it is moving at a higher rotational rate.

Thank you sir, I thought it was something like that but I just couldn't put it into words.

[PawPaw]

Thanks, RC! I completely understand the importance of matching blade weights to facilitate rotor balance and note that full size heli mechanics will balance blades both spanwise, as we do, AND chordwise (usually 25% chord) which we don’t do. This will be a good later project when I read up on this IKON 2 data logging feature: vibration with matched cg blades vs vibration without matching cg but overall balance.

[RCjetdude]

Chord-wise CG used to be more critical back when we used the wooden blades as they were more prone to twisting forces if the center of lift was ahead of the center of mass which caused fluttering. With today's fiberglass blades it is typically not an issue because they are built with more mass towards the leading edge and made from more rigid materials.

[DCORSAIR]

Boy do I ever remember those wooden blade days, flutter was an issue that's for sure, now we can almost bolt them on and go fly, well except for these Roban blades, have to say though, this 5 blade set I got with my Magnum PI was really good, I checked them, all were good weight wise, very close on the CG, so I bolted them on and flew them, they track good and no vibes, think I got a lucky set.

[Heli143]

Got some new skids from Mike Spinner over on scalerchelis, and a bunch of 3D printed cockpit parts from Tyler Grey Models.

Mike Spinner is my go to guy for scale skids. Tyler Grey Models is the best in my opinion to buy 3D printed parts from. When he didn't have a part I wanted he designed the part for me and it was perfect.

[PawPaw]

Any updates on your AH-1W, sfcfury? How about the 600 you were waiting on?

[sfcfury]

Hey! Kinda slowed way down... still finishing up my lil hobby area... it's like i'm kinda half ass packed up in sense (from spreading heli parts all over the house during the covid 'break') waiting to finish up the room... Got a cabinet and few other storage items that should be in tomorrow actually to finish out the storage... all that and I've been pretty much back to normal work routine (plus some) for a month now. The Funkey fuselage finally made it in... I had really wanted to go with the phoenixtech 600 mechanics, but they seem to be on a indefinite TBD shipping status at the moment. Might have to look at the 550X/L mechanics route... To be honest that's kinda my routine tho... I go at it hard in spurts... then slow way down. I get on here pretty much every day tho to see what everyone is talking about. I see your 407 is coming along very nicely!!

[DCORSAIR]

Hey! Kinda slowed way down... still finishing up my lil hobby area... it's like i'm kinda half ass packed up in sense (from spreading heli parts all over the house during the covid 'break') waiting to finish up the room... Got a cabinet and few other storage items that should be in tomorrow actually to finish out the storage... all that and I've been pretty much back to normal work routine (plus some) for a month now. The Funkey fuselage finally made it in... I had really wanted to go with the phoenixtech 600 mechanics, but they seem to be on a indefinite TBD shipping status at the moment. Might have to look at the 550X/L mechanics route... To be honest that's kinda my routine tho... I go at it hard in spurts... then slow way down. I get on here pretty much every day tho to see what everyone is talking about. I see your 407 is coming along very nicely!!

Scaleflying.de in Germany has the Flasher 600 mechanics for the Roban and Funkey fuselages, they are like Phoenixtech and Chaos mechanics, just a clone, you will have to wait awhile for them to get to the USA, might be worth ordering a set.

[PawPaw]

That makes perfect sense now that you mentioned it. I keep forgetting everybody’s back to semi-normal work status these days, except me. I’ve been retired since 2006 but was working 4 days/month on the ambulance, until COVID. Just not worth the risk at my age. Glad to hear you got the Funkey, at least. Maybe we’ll see these OOS items restock soon.

[F106DeltaDart]

Finally got my mechanics up in the air yesterday. Since then, I've gotten around 6 flights on them and have gotten the Spirit pretty well dialed in. Next step is to get the Geolink GPS module installed on the boom and start figuring that out. That, and start cleaning up the ugly wiring mess on the testbed.

[DCORSAIR]

Hey Delta,, looking good, is that the mechanics for the 700 Cobra? I had another guy that is building one on another site, he said that the Cobra mechanics were hard to set up or should I say dial them in ??

[F106DeltaDart]

Hey Delta,, looking good, is that the mechanics for the 700 Cobra? I had another guy that is building one on another site, he said that the Cobra mechanics were hard to set up or should I say dial them in ??

Yes, these are the Cobra mechs. I didn’t really have any issues getting them setup and dialed in, seemed pretty smooth out of the box. Running 1300 rpm with Align 760mm blades. Trying to fit those blades was the hardest part and required a bit of tweaking to things.

[DCORSAIR]

Yes, these are the Cobra mechs. I didn’t really have any issues getting them setup and dialed in, seemed pretty smooth out of the box. Running 1300 rpm with Align 760mm blades. Trying to fit those blades was the hardest part and required a bit of tweaking to things.

Oh okay, I might do a Cobra after I get my OH-6 flying, it's not here yet, it's shipped but with this Covid thing, it will be awhile coming from Germany.

So why didn't you use the stock blades, just curious?

[F106DeltaDart]

Oh okay, I might do a Cobra after I get my OH-6 flying, it's not here yet, it's shipped but with this Covid thing, it will be awhile coming from Germany.

So why didn't you use the stock blades, just curious?

Nice, will be looking forward to seeing your report on the OH-6. I went with the Align blades for the shape. The stock blades are almost like Huey blades, with a flat tip. I wanted the more rounded and swept look of the full scale machine. I’m sure the stock blades would have been flown fine though.