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?
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Roban AH-1W Cobra 700 Size Scale Helicopter
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Originally posted by PawPaw View PostSorry 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.....
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Originally posted by PawPaw View PostJust 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?
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Originally posted by RCjetdude View Post
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.
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Originally posted by PawPaw View PostJust 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?
Someone will have our answer I'm sure, or at least explain it better than I can.
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Originally posted by RCjetdude View Post
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.
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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.
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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.
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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.
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Got some new skids from Mike Spinner over on scalerchelis, and a bunch of 3D printed cockpit parts from Tyler Grey Models.Roy Mayoral
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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!!
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Originally posted by sfcfury View PostHey! 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!!
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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.
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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.2 Photos
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Originally posted by DCORSAIR View PostHey 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 ??
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Originally posted by F106DeltaDart View PostYes, 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.
So why didn't you use the stock blades, just curious?
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Originally posted by DCORSAIR View Post
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?
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