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Helicopter recovery

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Rktman

Eric
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Hopefully I'm posting this to the correct group. My question is: does curving the rotors (perpendicular to the grain along the narrow axis) on a helicopter recovery rocket take the place of carving/sanding airfoils on those rotors?
 

Gary Byrum

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If you're looking for an alternative to sanding airfoils, might I suggest something much easier? This was given to me and I've used it on two heli jobs with great success. In the pic, you see a diagonal line in the prop. This is a cut line. You'll only want to cut 1/4th - 1/3rd of the way through the wood. Take a dowel 1/16th - 1/8th inch, place it under the prop on the other side of the cut line and carefully bend the sides of the prop down. You may have to manually mess with it a bit, but you can shape it to a point where it doesn't spring back. While you have the prop bent over the dowel, put several dots of medium CA about 1" apart from each other. Set the CA or just let it dry. Your want your bend to be around 10*. That's why I suggested different size dowels. Once the CA has set, run a bead of your preferred wood glue all the way down the cut line. Smooth with your finger and let dry completely. You might have to use some weights to assure the bend stays in place. Once that is dry, fill with wood putty so you can sand a smooth curve to the cut. You'll want your bent side of the prop to fold toward the vehicle when you install it.

Cloud Chopper Prop.jpg
 

Rktman

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Hi Gary, sorry I didn't see your post till now. Still learning to use the forum but normally it sends me an email when anyone replies. Don't know why it didn't this time. Thanks for the tip, this is much easier and far less time consuming than sanding in an airfoil (less messy too). It can take me hours to do a single rotor, especially if I decide to go with basswood instead of balsa. Much appreciation.
 

Gary Byrum

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My approach to this is for simple heli recovery. I found it more suitable to my needs. Airfoiling is the TRUE way to do this, especially if you're doing competitions. Since I'm not, I like the simple plan better. Glad to help. Hope to see a video of your flight.
 

Steve Shannon

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modeltrains

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If you're looking for an alternative to sanding airfoils, might I suggest something much easier? This was given to me and I've used it on two heli jobs with great success. In the pic, you see a diagonal line in the prop. This is a cut line. ...
Interesting. :) Will note that idea for potential future use.
 

Rktman

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My approach to this is for simple heli recovery. I found it more suitable to my needs. Airfoiling is the TRUE way to do this, especially if you're doing competitions. Since I'm not, I like the simple plan better. Glad to help. Hope to see a video of your flight.
My avatar pic is of my scratch-built 'copter, concepted when I initially became a "born again rocketeer" last December after many many years away. Not having known just how far the sport had progressed, I wanted to create something "original, something no one had ever thought of". Unlike the earlier attempts which were largely body tubes with large fins and flaps that deployed to spin them down, I wanted a true set of dedicated "rotors". Hah! Fast forward a few weeks only to discover that not only did helicopter recovery already exist, there were even NAR events dedicated to this genre!

Never been able to get a video, things happen too fast even on just a C engine. Maybe I could borrow a true videocam, one that can track and zoom real good so I can stand way the heck back.

For a first attempt the thing boosts ridiculously straight and I have to admit airfoiling the rotors really made a difference. It actually comes down slower than a rocket with a chute. Plus, well...it looks cool too.

Just started on a featherweight eRockets kit model (Heli Roctor) that employs the same slice and bend technique. I'm curious to compare the spin and descent rate of this vs my airfoiled one. Granted the eRockets model weighs in at 26 grams and mine at 57grams (with engines installed), allowing for scale, I think the lift generated by both rotor designs will have a large effect.
 

Rktman

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Semroc makes a helicopter kit as well.
https://www.erockets.biz/semroc-flying-model-rocket-kit-heli-roctor-kc-02/
Its not too difficult to build.
It's actually a simple build...when you don't have fat fingers and big hands like me. It's a downscaled featherweight model that uses the 13mm mini engines and trying to get in and between all the (to me) small parts and pieces is a challenge for me. If you have nimble fingers and steady hands, it's a snap to build.

One caveat: there's a notch on the root edge of the fin that the rotor fits into. The notch is very close to the root edge and tends to break off easily while sanding or handling (due to the grain direction). If you or anyone else decides to build this kit, just be aware of this.
 

Rktman

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They are working on a G powered version too. The prototype has flown and it is impressive to watch.

I want that one! Working on tiny models is a headache. Maybe I'm just naturally clumsy but I always feel like I'm handling spiderwebs with tweezers. Larger models tend to use sturdier materials as well (it's irritating when an engine tube creases or wrinkles after inserting engines after awhile, for example).
 

Gary Byrum

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I want that one! Working on tiny models is a headache. Maybe I'm just naturally clumsy but I always feel like I'm handling spiderwebs with tweezers. Larger models tend to use sturdier materials as well (it's irritating when an engine tube creases or wrinkles after inserting engines after awhile, for example).
Then build a big one. I have the specs for this BT 70 version.

100_1112.jpg
 

TheAviator

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Hopefully I'm posting this to the correct group. My question is: does curving the rotors (perpendicular to the grain along the narrow axis) on a helicopter recovery rocket take the place of carving/sanding airfoils on those rotors?
It takes the place of MOST of the airfoil sanding, you'd still benefit from rounding the leading edge and tapering the trailing edge. Personally, I just round the leading edge and call it a day. The nice thing about doing to the curved warp is that the twist it gives you is a lot more optimal than just a flat airfoiled blade, and I would guess (haven't done the analysis) that it more than makes up for the lack of an airfoil.
 

Rktman

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It takes the place of MOST of the airfoil sanding, you'd still benefit from rounding the leading edge and tapering the trailing edge. Personally, I just round the leading edge and call it a day. The nice thing about doing to the curved warp is that the twist it gives you is a lot more optimal than just a flat airfoiled blade, and I would guess (haven't done the analysis) that it more than makes up for the lack of an airfoil.
Love the feedback here. You obviously know a whole lot more about aerodynamics, physics, engineering principles and fluid dynamics than I do so I'll take that as gospel. I can handle rounding edges and bending a twist far better than laboriously sanding with a block and files with a dust mask on for hours.
 

Rktman

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In fact I'm currently receiving build videos of this kit. Looks like a challenging, but well designed kit.
I designed and constructed my scratch-built (my avatar image) before I even realized helicopter rockets even existed (I've been away a loooong time). Interestingly the top portion ended up looking almost identical to the Heli-roc because I got a little carried away with the exhaust ports and had to reinforce the body tube with balsa strips.

I knew nothing of retention and deployment methods so I created a sliding piston system to retain/release the rotors. Maybe a little more complex than a burn string but in 7 flights it's never failed to deploy. My rotors are hinged at the rear and uses the rocket's ring fin as a dihedral stop. The reason was to reduce drag from the fins during rotation as well as protecting them from damage from rough landings. I prefer nose-down landings. I soaked my nosecone in wood hardener and laid on a layer of CA (I know, overkill) and it's never sustained any damage other than scuffed paint even after landing on the only concrete walkways for miles.

I like the Heli-roc's simpler deployment system but the model is on the small side. I'm finding building the Heli-Roctor a challenge because of the tiny components, so I'm looking to go larger, to sizes more suited to my handful of thumbs.
 

Gary Byrum

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Spectacular! Can you send me a link to it? Thanks!
2 things to know about this rocket. You probably wont find a nose cone for a BT 70 that even comes close to this. I have a lathe and turned it myself. 2nd, my heli's have a tendency to come in upside down / nose first. This usually doesn't present a problem though. My nose cones are usually kinda tuff.

Now....I do have a drawing of a BT 60 size bird that you can sport a 60 AH nose cone with. It'll top out at 2' 4". Let me know which way you wanna go with this and I'll lay the drawings on you. The templates will be to scale and in a pdf file. Generally you can just print them off and go with it.
 

Rktman

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2 things to know about this rocket. You probably wont find a nose cone for a BT 70 that even comes close to this. I have a lathe and turned it myself. 2nd, my heli's have a tendency to come in upside down / nose first. This usually doesn't present a problem though. My nose cones are usually kinda tuff.

Now....I do have a drawing of a BT 60 size bird that you can sport a 60 AH nose cone with. It'll top out at 2' 4". Let me know which way you wanna go with this and I'll lay the drawings on you. The templates will be to scale and in a pdf file. Generally you can just print them off and go with it.
Gary Byrum Thanks Gary, the BT-6o version sounds like the way to go. I don't much worry about nose cone damage since I started soaking them in wood hardener and/or CA before painting.
 
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