Fins & Hanger

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Need for Speed
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Fins & Hanger

Post by Need for Speed » Mon Oct 03, 2005 11:35 am

Need help on placement of fins and hanger.

Do you place fins in 3 divided sections with the hanger in front of one? That gives you two fins down. Or do you place hanger by itself to give you one fin down?

Do you set fins like an airplane?

I know less is best with 1/8 '' being min. on walls. We are down to 15 grams on weight now. Would a real good paint job give strenght to the walls to go less?

First trip down the line. Please give us some help

:? :? :?


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Re: Fins & Hanger

Post by jrz_dad » Wed Oct 12, 2005 7:39 am

We've always used three fins - one directly behind the hangar and the other two set like airplane fins but slightly angled upwards with the hopes it raises the rocket off the line "ever-so-slightly-to-decrease-line-friction". We like to make sure the fins are very small in surface area but still lift the rocket. Can't say it always works cuz we win some and we lose some...



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Re: Fins & Hanger

Post by Need for Speed » Fri Oct 14, 2005 8:29 am

Thanks jrz-dad.

I have also been thinking of no fin. The hanger acts like a fin as is. That would be even less weight. Just not sure. We are building a test track. Should have a few rockets to test in the Den. Will test a few this weekend.


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Re: Fins & Hanger

Post by M7 Racing » Thu Nov 16, 2006 10:11 am

We just had our derby and we had about a half dozen thin designed well built rockets. All of these rockets were pretty close in speed, however one of them in this group dropped and lost both of the wings that they had on the side. During the next race it blew everyone away and took the championship. Before this happened I would of guessed that it would of came in around 4th or 5th. Definately by not putting the fins on the rocket was lighter.

Do you think the wings really help or does it just add weight?



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Re: Fins & Hanger

Post by gpraceman » Thu Nov 16, 2006 12:39 pm

I have wondered about the real benefit of the fins. Since the rocket runs on a guide wire, it seems that the fins are not really helping to guide the rocket. So, it seems that they are merely decorative.


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Re: Fins & Hanger

Post by M7 Racing » Thu Nov 16, 2006 1:51 pm

I didnt see how the ships where hanging on the hangers but I thought the reason for the fins was to stop the ship from spinning around. I think the hanger might hold it in place fine and the fins might be decorative. Unless the hanger has some flex and you want to keep the ship straight.



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Re: Fins & Hanger

Post by gpraceman » Thu Nov 16, 2006 2:04 pm

4Racers wrote:I didnt see how the ships where hanging on the hangers but I thought the reason for the fins was to stop the ship from spinning around.
The weight of the rocket will keep it from doing loop-to-loops around the guide wire. If the rocket was made to be extra ultra light (which I can't see how you could trim weight down that far), then maybe that would be an issue. However, if that were the case, I don't know that fins would be of much help.


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Re: Fins & Hanger

Post by gpraceman » Thu Nov 16, 2006 2:15 pm

Here's a photo of the rockets and their track hangers.

Image


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Re: Fins & Hanger

Post by M7 Racing » Thu Nov 16, 2006 3:24 pm

Well then I guess if decreasing the weight is a major factor not having fins seems like a great way of reducing it without losing performance.



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Re: Fins & Hanger

Post by billbillb » Wed Mar 07, 2007 12:36 pm

I can speak from personal experience that I think fins are definitely needed if you end up building a very thin (walled) lightweight rocket. We sanded down both the interior and exterior of the rocket and it ended up being slightly more than 1/8 th inch thick all around.

To keep the weight down, we put small fins on the back...about 1 inch tall and 1 inch long. We had 2 rubber bands and 100 winds.

Well it was an absolute bullet down the track to the point of being slightly embarrassing compared to the rest of the field.

The real surprise was that it also did a barrel roll down the track. On another run, it went down the entire track at about the the 9 o'clock position until it hit the finish line. The torque from the propeller and rubber bands was significant

Needless to say, we won the pack championship.

I do not think I would want a heavier rocket with thicker walls, but fins with more surface area for better stability and control would be better.



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Re: Fins & Hanger

Post by Jthompson » Sun Feb 10, 2008 10:38 pm

The 3 fin sheets that BSA kits have weigh approximately 4.07 grams uncut. Large fins can add significant weight to the rocket. Reduce the fin size proportionally, and you can calculate the approximate weight of the fins.

The plastic fins are difficult to attach for you Scouts. Cutting through the rocket body with a hobby knife can damage the rocket or worse, cut the child.

I recommend abandoning the plastic fins and using balsa wood from the kit. When you glue a body together, simply bandsaw a thin slice off the side and use this for the fin material. You can shape this and glue the fin directly to an unpainted body using super glue for balsa wood. These fins can be shaped, are lighter, and much stronger than the fin material that came with the BSA kits.


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Re: Fins & Hanger

Post by GravityRacer » Sat Mar 22, 2008 1:36 pm

I made a rocket so thin you can see through some areas. I had to add material back on at the plastic dowel area or the thing would have split. I didn't bother with fins, I just angled the nose hole so the prop pointed away from "straight" to counteract the propeller torque.

If you want fins, the optimum steering effect would be one large one pointing straight down- that's where the longest moment arm is, for steering torque. This has the added benefit of being the best place for weight, as well, if you needed it for some reason. It'd be kind of weird looking. Maybe paint the rocket like a fish, and paint the fin like a...fish fin.



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