Fin Shape Poll

[PunkRocketScience]

Hey all-

Just curious. I seem to spend a heck of a lot of time shaping my fins while I see a lot of rockets at our local launches and pics here on TRF of fins that are square/flat edged.

How do you shape your fins?

 

[wwattles]

For me, it depends on the type of rocket. If it's going for speed, then I go airfoil and polish them with 1000 grit automotive sandpaper. If it's supposed to just look decent, then I generally stick with rounded. If I'm just building/flying for the heck of it, then just leave 'em square and launch that bad boy!

WW

 

[Bushmaster]

If I'm helping the kids with thier rockets I don't do anything to the fins, I leave it up to them to do something with thier fins (they always stay nice and square ) with my rickets I typically will taper both leading and trailing edges (I'm looking more for drag reduction than lift)

 

[flying_silverad]

Depends on the design. The overall look of the model is what the drives the fin shapeing for me.

 

[Rocket Guy 1317]

I just sand the fins smooth and then leave the fins with square edges to lazy to round them.

 

[KermieD]

I always tend to just bevel the edges. Gives 'em a small touch of attitude and only takes a couple minutes total to do for all the fins dragging them over a sheet of sandpaper on the workbench.

 

[Micromeister]

Originally posted by PunkRocketScience
Hey all-

Just curious. I seem to spend a heck of a lot of time shaping my fins while I see a lot of rockets at our local launches and pics here on TRF of fins that are square/flat edged.

How do you shape your fins?

Of your choices I use the last three depending on the models end use, saving the tapered airfoiled combinations for Altitude comptetition or Hi performance models.
but the very simple act of rounding the leading and tailing edges will increase any models performance by about 25 or more percent. so if nothing else at least round those areas.
By the way; it's better to leave the fin tips square to reduce the vortex created at this area. Reducing the vortex size at the fin tips will reduces the amount of induced drag, which will also help overall performance.
Hope this helps

 

[Rocketjunkie]

For most rockets I just round the edges. Tip edges parallel to the body I leave square. For high performance, supersonic rockets will get beveled edges.

 

[dbarrym]

Todd, you've seen my rockets, all of them have airfoiled or beveled fins, even the low n' slow ones.

A square edged fin makes a lot more drag than a simple rounded edge. At the low speeds and RN's we fly most LPR's at a fully airfoiled fin doesn't necessarily gain much. And on a trans-sonic or supersonic HPR the best shape changes radically depending on the average or sustained speed. I do try to match the fin shape and airfoil to the intended 'mission' of each rocket.

But the main reason is pride of ownership, etc... it shows craftsmanship, skill, knowledge, etc...And it really doesn't take more than a few minutes to do, so why not?

Just my $0.01....

PS - I DID learn not to sharply bevel the TE/corner of swept-back fins after dropping my 2.1" Mini-BBX (with 1/16" G-10 fins) on my foot....the tip of one fin went through my tennis shoe and about 1/4" into my foot! Ouch.

 

[Stymye]

I like to round the fin edges a bit.
however, I always leave the outer edge square , according to stine's book this is far more aerodynamic with than a rounded edge, so no extra work there

 

[cjl]

Airfoiled and filled carefully for LPR.

HPR: beveled.

 

[LFLekx]

Originally posted by KermieD
I always tend to just bevel the edges. Gives 'em a small touch of attitude and only takes a couple minutes total to do for all the fins dragging them over a sheet of sandpaper on the workbench.

Same here. They're easiest to apply fiberglass to, as well.

 

[RimfireJim]

Originally posted by dbarrym

But the main reason is pride of ownership, etc... it shows craftsmanship, skill, knowledge, etc...And it really doesn't take more than a few minutes to do, so why not?

Same reason here. I round leading edges, taper trailing edges, leave tip edges square. With balsa fins and the right sandpaper on a sanding block, I can do a set in a few minutes. The label paper I use over the balsa adds a lot of support for the thin trailing edge.
Whether it makes any difference or not on my 'low and slow' rockets doesn't matter to me - it just 'looks right'.
-Jim

 

[jcsalem]

On balsa, I usually round leading and trailing. I'll sometimes taper the trailing, but it takes more time and makes that edge weaker.

On plywood, I'll usually round the edges using a belt sander. Tapering takes to much time.

I do nothing on G-10 fins (I've only used up to 1/16" G-10).

I'm definitely not a perfectionist in my builds. If it looks good 30' away on the pad and it goes up, I'm generally pretty happy.

-- Jim

 

[Rock_It]

.

 

[geof]

Originally posted by stymye
I like to round the fin edges a bit.
however, I always leave the outer edge square , according to stine's book this is far more aerodynamic with than a rounded edge, so no extra work there

That's fascinating. Can anyone whip up some Rocksim results showing the difference, and post a text table here?

My decision depends a little on the intended looks, and a lot on the material. Usually:
Balsa: round
Basswood or thin ply: a sort of ogive profile with slightly unsharp tip
>=1/8 ply: bevel
G10: fine bevel

 

[Stymye]

For general sport flying it's probably not that detrimental to the fun

If your building an altitude ,speed demon or competition model than it would make sense to airfoil them and streamline the rocket for top performance

 

[RoyGreen]

At least a rounded LE and TE, with the tip square. But for looks (not always performance) I like to taper the TE. You have to be careful though, because a bad taper will cause an asymetrical airfoil and you'll induce spin. Not always a bad thing, but I really enjoy watching a rocket with a spin rate of < 1 per flight. I used to have a Der V3 that was rock solid on ascent -- no roll at all.

 

[Loon]

On my models with cardstock fins, I create a fairly sharp leading edge and a sharper trailing edge. By folding the cardstock skin over the cardstock/cardboard frame.

This is more due to the construction technique than design, not the most efficient airfoil for LPR.

 

[by basher]

I'm happy just to get them all the same size.

 

[bigone5500]

I like rounding mine. But may sometime in the future start trying to airfoil them. I'm just too lazy at the moment to do it.

 

[Chicagonative17]

Shaping the fins on a large, draggy rocket won't really help much. However, if your rocket is closer to the high performance kind, it will help a lot. An aerofoil fin shape is the best for high performance applications.

 

[bigrocketman]

For me I ask a couple questions to myself,
1. HPR
2.Do I want sleek aerodynamic rocket
3.Altitude

Those three questions make pretty good fin designs.All the best

 

[eastvolt]

Bevel them for HPR. At least this is what i did . . .

 

[new2hpr]

Depends...

Quick build on a kid's rocket, square.

General use LPR and HPR, round leading and trailing, square tip.

Performance (subsonic), airfoiled with square tip.

Performance (supersonic), tapered leading and trailing, square tip.

My $0.02.

Ken

 

[powderburner]

Bevel them for HPR.

If your HPR rocket spends a 'significant' part of its ascent (like half or more) in transonic or supersonic flow, then yes, a beveled leading edge can be good. It needs to be sharp, smooth, and have a uniform bevel angle root-to-tip.

If your rocket spends most of the ascent while still well into the subsonic range (generally less than M 0.85-0.9) then sharply beveled fin leading edges are usually a bad thing. Honestly, most HPR designs spend half (or more) of the ascent fighting gravity while trying to accel to higher speeds, and spend most of the ascent at subsonic speeds. For subsonic speeds, a round LE profile is better. It too needs to be smooth and uniform from root to tip. It has lower drag (and can even generate a small bit of aerodynamic thrust), keeps the airflow smoother over the rest of the fin, and thus helps the overall fin function better to keep your rocket on a straighter path. Less wobble = more altitude.

 

[richalex2010]

It depends a lot on what I feel like doing, and am capable of doing; on 1/64" plywood, I just run it over very fine sandpaper a couple of times; I couldn't even see an airfoil without some sort of magnifier
On big rockets, if they have G10, I just leave 'em as is. On thicker plywood I don't usually bother either, unless I can find someone to help with the belt sander (a handheld one) for rounding or beveling.
On balsa and thin plywood, sometimes I'll bevel, sometimes round, sometimes just leave them square. On my Madcow Rocketry Little John (which survived a month in a tree, with the only damage being to the tip of the nose cone--good materials, and heavily overbuilt), I left the 1/8" plywood square, because I wasn't going for scale, just a nice, 24-29mm, AP-only mid-power rocket (really needed one of those; everything else is too small to not loose with AP, or much larger).

-Jake

 

[DaveCombs]

Round leading and trailing edge on LPR unless it's a scale kit (like my SCUD or Merc Redstone). Occasionally I'll bevel the trailing edge.

On my HPR, I've used a sanding drum on my Dremel to round the leading edge and bevel the trailing edge of the plywood. The cool thing about ply is that, like in eastvolt's picture, you can see when you've got it right.

I leave the tips square.

 

[Chicagonative17]

shaping the outside edge of the fin doesn't matter too much but it looks good. I find that aerofoiling fins is easier than beveling all the way around. All you do is round the LE and taper the TE, and do nothing with the outer edge.

 

[uncle_vanya]

shaping the outside edge of the fin doesn't matter too much but it looks good. I find that aerofoiling fins is easier than beveling all the way around. All you do is round the LE and taper the TE, and do nothing with the outer edge.

I don't think of this as "airfoiling". True airfoiling would require a much more specific shape with a longer taper than what this implies. Maybe I'm being silly - but real airfoiling is a real pain - I typically round the front and taper the back - but I don't call this airfoiling.

I have airfoiled fins for a D-Streamer duration bird.