Sanding Rotor Airfoils

[JAL3]

I am currently looking at a plan by George Gassaway for a rocket called the Tasmanian Devil. It has fixed (as opposed to hinged) helicopter rotors that are supposed be sanded into airfoils.

What is the best way to go about doing this? Somehow the idea of me taking a piece of sandpaper and applying it to a rectangular prism in order to obtain the desired shape is ludicrous.

Are there any good methods for this out there?

 

[MarkII]

John,

I'm not sure that the airfoiling is a real requirement with this design. The spin tabs are what are supposed to make the Taz autorotate (on the way up as well as down), right? Airfoiling might improve the performance somewhat, but this is not a high performance design, nor is it meant to be. It is meant to be a fail-safe design to achieve a qualifying flight in competition heli events.

The technique that I have used for sanding airfoils is to measure how far back from the leading edge of the wing or rotor you want the "high line" (the thickest part) of the airfoil to be, and then place a strip if 1/8" to 1/4" wide masking tape along this line. The width will depend on the width of your wing or rotor. Use your best judgement; the area that this covers will be the thick part of the contour. Place another strip of masking tape on the bottom of the piece along the leading edge so that it is even with the edge, and place another one along the trailing edge, if applicable. Taping the leading and trailing edges on the bottom side will help to keep these edges intact and prevent them from getting frayed as you sand in the airfoil.

Now sand in a curve on the leading edge on the top of the wing or rotor. Have it curve smoothly from the edge of the tape on the bottom side to the front edge of the tape on the top side. This is really no different than rounding the edge of a fin, except that you do all of the rounding on one side.

Now sand an even bevel from the back edge of the tape on the top side down to the trailing edge. After you do that, remove all of the tape. On the top side, lightly blend in the forward and back edges of the strip where the tape was, but don't do too much to it. Just take off the sharp edges, if there are any. One or two light strokes with the sanding block should be all you would want to do on them. After that, you are done.

Hope this helps.

MarkII

 

[JAL3]

John,

I'm not sure that the airfoiling is a real requirement with this design. The spin tabs are what are supposed to make the Taz autorotate (on the way up as well as down), right? Airfoiling might improve the performance somewhat, but this is not a high performance design, nor is it meant to be. It is meant to be a fail-safe design to achieve a qualifying flight in competition heli events.

The technique that I have used for sanding airfoils is to measure how far back from the leading edge of the wing or rotor you want the "high line" (the thickest part) of the airfoil to be, and then place a strip if 1/8" to 1/4" wide masking tape along this line. The width will depend on the width of your wing or rotor. Use your best judgement; the area that this covers will be the thick part of the contour. Place another strip of masking tape on the bottom of the piece along the leading edge so that it is even with the edge, and place another one along the trailing edge, if applicable. Taping the leading and trailing edges on the bottom side will help to keep these edges intact and prevent them from getting frayed as you sand in the airfoil.

Now sand in a curve on the leading edge on the top of the wing or rotor. Have it curve smoothly from the edge of the tape on the bottom side to the front edge of the tape on the top side. This is really no different than rounding the edge of a fin, except that you do all of the rounding on one side.

Now sand an even bevel from the back edge of the tape on the top side down to the trailing edge. After you do that, remove all of the tape. On the top side, lightly blend in the forward and back edges of the strip where the tape was, but don't do too much to it. Just take off the sharp edges, if there are any. One or two light strokes with the sanding block should be all you would want to do on them. After that, you are done.

Hope this helps.

MarkII

I appreciate the tips on sanding the airfoils. I really do. They make sense except for the part about ME doing it.

I don't think we're talking about the same plan though. The one you describe is one I think I remember as a spot landing model. This one does not use tabs. I've included the PDF to see if we're talking about the same thing.

View attachment Taz.pdf

 

[MarkII]

I forgot to mention that on a wing, rotor or fin that is irregularly shaped, so that the trailing edge is not parallel to the leading edge, keep your airfoil parallel to the leading edge. This means that as you sand the back end of the contour down to the trailing edge, it will intersect that back edge rather than run parallel to it. That's OK; that's the whole idea with these wing shapes. Do not try to "twist" the contour around along the surface so that it stays parallel to both edges. That will defeat the purpose.

Also, always use a sanding block when you sand, and do the shaping by making long strokes with the block, going in one direction only from one end of the wing/rotor to the other.

MarkII

 

[MarkII]

I don't think we're talking about the same plan though. The one you describe is one I think I remember as a spot landing model. This one does not use tabs. I've included the PDF to see if we're talking about the same thing.

Nope, that's the one. The "tabs" that I was talking about are the rotors on the bottom of the "fins." To have them cause the Taz to autorotate without having to sand airfoils into them, glue them to the bottoms of the fins at a slight angle (8-10°), not perfectly perpendicular to the bottom edges. Just make sure that the angle goes the same way for all three rotors.

MarkII

 

[Micromeister]

John:
The Taz is a very funny little "Qualifier" heli-roc.
Sanding Airfoils on rotors and Glider wings is one of those skills that takes a little time to develop.
As Mark said layout the high point of your airfoil and always sand with a sanding block, the longer the better really. The High Line should be about 1/4 to 1/3 of the rotor or wing width.
To that end I generally us a 12" or 18" block to "T" bar depending on the length of the Rotor or wing.
I've also found one of the most important tools as a solid sanding surface. I use an 12" x 24" piece of 3/4" Plate glass as a dead flat surface the doesn't move easily and doesn't flex at all
To keep the rotor or wing in place while sanding I use a strip of Double faced masking tape that has been somewhat de-tac'ed to hold firmly but will release the sanded piece with the help of a Plastic pallet knife.

Align the edge of the rotor with the front edge of the glass. Sand the leading edge first then pop the rotor up with the pallet knife and reverse on the glass to sand the tailing edge leaving the line almost intact. this can then be eased with fine grit paper after the piece has been removed for the tape. another thing is to sand in one direction only, keeping constant pressure on the block. this will take a little time to perfect but once you've sanded a couple rotors you'll get the hang of it

Tasmanian devil isn't a great performer no matter how well built or what scale, I have a 13mm model and two different micro models that get nearly identical flight times on 13mm A's and Micro motors! it's amazing!!! Funny as all gee-wiz also LOL

 

[JAL3]

Nope, that's the one. The "tabs" that I was talking about are the rotors on the bottom of the "fins." To have them cause the Taz to autorotate without having to sand airfoils into them, glue them to the bottoms of the fins at a slight angle (8-10°), not perfectly perpendicular to the bottom edges. Just make sure that the angle goes the same way for all three rotors.

MarkII

OK.

Again, I do appreciate it. I spent some time looking last night and finally found the one I thought you were referring to. Taking a look at it will show you what I mean.

View attachment moonsat.pdf

 

[JAL3]

John:
The Taz is a very funny little "Qualifier" heli-roc.
Sanding Airfoils on rotors and Glider wings is one of those skills that takes a little time to develop.
As Mark said layout the high point of your airfoil and always sand with a sanding block, the longer the better really. The High Line should be about 1/4 to 1/3 of the rotor or wing width.
To that end I generally us a 12" or 18" block to "T" bar depending on the length of the Rotor or wing.
I've also found one of the most important tools as a solid sanding surface. I use an 12" x 24" piece of 3/4" Plate glass as a dead flat surface the doesn't move easily and doesn't flex at all
To keep the rotor or wing in place while sanding I use a strip of Double faced masking tape that has been somewhat de-tac'ed to hold firmly but will release the sanded piece with the help of a Plastic pallet knife.

Align the edge of the rotor with the front edge of the glass. Sand the leading edge first then pop the rotor up with the pallet knife and reverse on the glass to sand the tailing edge leaving the line almost intact. this can then be eased with fine grit paper after the piece has been removed for the tape. another thing is to sand in one direction only, keeping constant pressure on the block. this will take a little time to perfect but once you've sanded a couple rotors you'll get the hang of it

Tasmanian devil isn't a great performer no matter how well built or what scale, I have a 13mm model and two different micro models that get nearly identical flight times on 13mm A's and Micro motors! it's amazing!!! Funny as all gee-wiz also LOL

That information helps as well.

I wasn't counting on good performance. It just looks like it might be something interesting.

Thanks

 

[gpoehlein]

One caveat - if you are using it for NAR competition as a qualifier, use the absolute shortest delay possible - even a booster if available. I flew it in competition with a B4-2 and it almost landed before the ejection went off, which would have DQed the flight. For B Helicopter, I use B6-0 in the thing now. Obviously, with A right now, you're stuck with an A8-3 (at least until and unless Estes brings back the A8-0). That said, the Taz is a hoot to fly and a definite crowd pleaser!

 

[mjennings]

We did planes out of blue insulation foam and foam lunch trays as a project in college. Gluing some foam lunch trays or foam board together for air foil sanding practice, might give you a little bit of confidence before going to the thin balsa. Plus you could use the practice wings on some hand toss gliders.

 

[JAL3]

One caveat - if you are using it for NAR competition as a qualifier, use the absolute shortest delay possible - even a booster if available. I flew it in competition with a B4-2 and it almost landed before the ejection went off, which would have DQed the flight. For B Helicopter, I use B6-0 in the thing now. Obviously, with A right now, you're stuck with an A8-3 (at least until and unless Estes brings back the A8-0). That said, the Taz is a hoot to fly and a definite crowd pleaser!

I'll keep that in mind. I'm really looking forward to the return of the A8-0 as well.

That said, I'm not really looking to be a competitor. I just want to try this design.

 

[MarkII]

OK.

Again, I do appreciate it. I spent some time looking last night and finally found the one I thought you were referring to. Taking a look at it will show you what I mean.

Well, that looks like a good one, too!

MarkII

 

[MarkII]

I'll keep that in mind. I'm really looking forward to the return of the A8-0 as well.

That said, I'm not really looking to be a competitor. I just want to try this design.

I agree; it might be more interesting as a sport model.

But I still want you to keep building rockets that drift out of sight on their chutes.

So that I can send my minions out to scarf them up. :dark:

MarkII

 

[JAL3]

I agree; it might be more interesting as a sport model.

But I still want you to keep building rockets that drift out of sight on their chutes.

So that I can send my minions out to scarf them up. :dark:

MarkII

One of the reasons I too often post about repairing fins is that I have a habit of substituting streamers or the next chute size down just to avoid the minions...and avoid excess exercise. :neener: