Tapering fins? Leading, Outer, Trailing? Just Leading?

[Michael L]

When I tapered the fins on my LOC IV I "winged it" (pun intended). The only edge that I didn't taper was the root. I'm working on an Apogee Aspire and I'm to the point of tapering the fins. The Aspire fins are smaller than the LOC fins and made of balsa vs plywood, said Captain Obvious.

Should I taper the leading, outer, and trailing edges of these fins (hoping for a no). Just the leasing edge? If just the leading edge what about the outer edge transition, how important is that? I really don't want to screw these up. Yup, I could just cut out new ones but I don't have stock and I'd rather just do it right the first time.

Did you know that there are tons of videos (and opinions) and tapering fins? Me too...

 

[BABAR]

Goals?

if you want multiple flights, round every edge except obviously the root which stays flat. This is best compromise of durability and performance

If you are going for altitude, I am not sure since Aspire can break Mach. That said, not sure what percentage of flight is supersonic vs subsonic. Subsonic most efficient is tapered trail, rounded forward and lateral. The high power guys likely can speak more toward supersonic, I think there it is taper forward and aft , probably lateral as well.

tapered edges are less durable on landing and during transport and handling.

 

[Funkworks]

If by "outer edge" you mean the fin tip, I'm not so sure it should be tapered or rounded. I think there are in fact different opinions on this. I'm just butting in here to emphasize it might an open question in need of a specialist.

 

[samb]

IMO any way you choose you cannot screw it up. As BABAR said, the specific flight regime of a particular model may dictate a specific fin edge profile. If building a kit, check the instructions. Square edges are always an option. An ugly option, but an option.

FWIW I learned how to build model rockets by religiously following the model rocket manual (yellow pages) included in the 1969 Estes catalog. I've tried many times to leave square edges on a model's fins but I always end up rounding them.

 

[Michael L]

Goal #1 - For the first flight I'm flying it in a club competition (60 N-s or less and highest altitude wins). I selected an Econojet F42-8T (55.0 N-sec). I'm going to use an Easy-Mini and deploy a drogue at apogee with that and deploy the chute at 820'-ish agl with it as well.

Assuming it survives that I think I'll go for 5,000' later. We have a huge area to fly in (miles in diameter) so finding it without a tracker makes me a little nervous.

 

[David Schwantz]

A 90 degree edge has the most drag. I like to round or taper all the exposed edges, think they look much cleaner. A razor sharp edge on a balsa fin will be very easy to ding. I would stay away from that.

 

[Michael L]

IMO any way you choose you cannot screw it up. As BABAR said, the specific flight regime of a particular model may dictate a specific fin edge profile. If building a kit, check the instructions. Square edges are always an option. An ugly option, but an option.

FWIW I learned how to build model rockets by religiously following the model rocket manual (yellow pages) included in the 1969 Estes catalog. I've tried many times to leave square edges on a model's fins but I always end up rounding them.

View attachment 470531

Yeah... the instructions vary with this rocket. The Aspire (check Apogee's website) was made to fly fast and/or high. It's s little rocket that can fly on an F motor and achieve Mach or 5,000 (F10-8). Personally, now that I've built and modified one, I wish I had built it first (prior to L1 cert). It's a good intro to some high power "things" (like electronic deployment)

 

[samb]

Decisions... decisions, whatcha gonna do ? This Apogee newletter has alot of info on fins:

Peak of Flight #305

 

[samb]

Based on goal #1, symmetric airfoil would be my choice. I've never tried a radial taper but I think you would need a jig to pull it off.

 

[Michael L]

That's what it looks like to me too. I wonder if I could 3D print a radial taper jig (and if it's worth the effort).

 

[samb]

That's what it looks like to me too. I wonder if I could 3D print a radial taper jig (and if it's worth the effort).

The aerodynamics that Tim presented in the newsletter has been pretty well proven. Whether it's worth your effort will be seen if you win the contest !

 

[OverTheTop]

For balsa I generally just round the leading and trailing edges but I am not trying for optimised flights in LPR/MPR. The outside edges, parallel to the airframe, are left square which slightly improves lift (correctional forces) when the rocket is not traveling straight into the airflow.

 

[JoePfeiffer]

Contest rocket => taper.

I don't fly contests, so my fins stay square.

 

[BABAR]

Goal #1 - For the first flight I'm flying it in a club competition (60 N-s or less and highest altitude wins). I selected an Econojet F42-8T (55.0 N-sec). I'm going to use an Easy-Mini and deploy a drogue at apogee with that and deploy the chute at 820'-ish agl with it as well.

Assuming it survives that I think I'll go for 5,000' later. We have a huge area to fly in (miles in diameter) so finding it without a tracker makes me a little nervous.

not too deep in the dead letter box…figgered I’d check up.
how did you do with this one?

 

[Blast it Tom!]

We have a huge area to fly in (miles in diameter) so finding it without a tracker makes me a little nervous.

<sigh> Oh, you guys out west... If I can get 1000' in one direction it's a red-letter day on the calendar.. Well, that does it. Today is the day I contact a utility company for permission to fly at a couple of tree-free square miles that used to be a settling pond. Could be the best thing to happen to model aviation of all sorts in Western PA in a very long time if it works out.

And yes, like @BABAR, I'm wondering how it worked out for you!

 

[brockrwood]

<sigh> Oh, you guys out west... If I can get 1000' in one direction it's a red-letter day on the calendar.. Well, that does it. Today is the day I contact a utility company for permission to fly at a couple of tree-free square miles that used to be a settling pond. Coule be the best thing to happen to model aviation of all sorts in Western PA in a very long time if it works out.

And yes, like @BABAR, I'm wondering how it worked out for you!

As a middle-schooler in the mid-1970’s I flew my rockets on my uncle’s tobacco farm in south central Virginia. It was plenty of open space EXCEPT you had better have seen EXACTLY where the rocket came down in the tobacco field. Once it lands in the middle of 6 feet tall tobacco plants, you can forget finding it until all of the tobacco leaves are “primed” (removed) and the tobacco plants are stripped bare.

 

[brockrwood]

Oh, you guys out west... If I can get 1000' in one direction it's a red-letter day on the calendar.

It is great in the West except that you can never fly because of fire bans due to the hot, dry and windy conditions.

 

[bjphoenix]

With balsa I usually round the leading edges and trailing edges. With plywood I may do more of an airfoil shape. Depending on the fin shape I might round the outside edge or keep it square, I consider it sort of a matter of style. There is another thread about rounding fin edges, certainly with balsa I round them as a compromise between looks and durability.

 

[Blast it Tom!]

As a middle-schooler in the mid-1970’s I flew my rockets on my uncle’s tobacco farm in south central Virginia. It was plenty of open space EXCEPT you had better have seen EXACTLY where the rocket came down in the tobacco field. Once it lands in the middle of 6 feet tall tobacco plants, you can forget finding it until all of the tobacco leaves are “primed” (removed) and the tobacco plants are stripped bare.

Yes, that's rough. But my torture has been seeing my carefully prepared handiwork in plain site, only 30' off the ground or so! Of course, many other here have dealt with trees.

It is great in the West except that you can never fly because of fire bans due to the hot, dry and windy conditions.

Yes, very true. I had a colleague out there that was going to try to get back into it as well. I know he worked for the USBR in Denver, but hhe was almost always on the road so I don't know how close to Denver that he lived.

And more pertiniently to the thread - how would he taper his fins?

 

[jqavins]

As most of know, a round leading edge, sharp trailing edge, smooth curve in between airfoil is best for subsonic flight, with bullnose leading edge, flat majority, and tapered trailing edge being quite nearly as good.

As most of us know, a diamond airfoil is best for supersonic flight, with tapered leading and trailing edges and flat fin in between being pretty nearly as good.

What I could never find out, here or anywhere that Google sent me to, is what about in the transonic regime? That's where things are the worst, and where I couldn't find an answer.

A few years ago I had the opportunity to ask an aerodynamics expert who designs wings for jets. He told me to go with the diamond.

 

[brockrwood]

What I could never find out, here or anywhere that Google sent me to, is what about in the transonic regime? That's where things are the worst, and where I couldn't find an answer.

That would be the F-111 and F-14, no? Just “swing wing” it when you want to go from subsonic to supersonic? Just get through transonic as fast as possible?

 

[Hobie1dog]

another thread like this one, started recently:
https://www.rocketryforum.com/threa...t-the-leading-edge.173241/page-2#post-2289285

 

[jqavins]

That would be the F-111 and F-14, no? Just “swing wing” it when you want to go from subsonic to supersonic? Just get through transonic as fast as possible?

I think he's a little young to have done those. F-14 first flight 1970. F-111 first flight 1964. My former coworker is in his forties, more or less.

We worked together on Lockheed Martin's proposal for the MQ-25 unmanned aerial refueling vehicle. He was the aerodynamics lead and wing specialist. I was the electric power subsystem guy. He bacame a manager, I moved back east, and Boeing got the contract.

 

[brockrwood]

I think he's a little young to have done those. F-14 first flight 1970. F-111 first flight 1964. My former coworker is in his forties, more or less.

We worked together on Lockheed Martin's proposal for the MQ-25 unmanned aerial refueling vehicle. He was the aerodynamics lead and wing specialist. I was the electric power subsystem guy. He bacame a manager, I moved back east, and Boeing got the contract.

The MiG-17, it seems, was a “high subsonic” airplane. The top speed was 711 mph and the speed of sound is about 767 mph. I would assume that the MiG-17 had a wing shape that was well suited to the “transonic” speed range?

https://en.m.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-17

 

[jqavins]

Oy vey, that's a tough realm to live in!

The speed of sound varies with altitude, to a minimum of about 593 mph from about 36,000 to 65,600 feet. So 767 mph is anywhere from 0.93 to 1.20 mach depending on altitude. There's no single boundary number between transonic and supersonic, as it depends on an object's shape, but a decent rule of thumb is 1.2.

That thing must have drunk fuel at an alarming rate.

 

[lakeroadster]

John Coker's Fin Beveling How To