Fun shape and speed

[bikefxr]

My son wants to do a science project on fin shape to see if that effects the top speed of the rocket 10 rockets and 20 different shapes.. any ideas if this would work using the same body tube diameter and same nose cone but with different fins

 

[Nytrunner]

Great idea!
He must be careful though, if changing the fin shape changes the mass of the rocket, then the data is not pure.

To keep all else equal, he must ensure each rocket weighs the same on launch.

Maybe 5 fin shapes tried in 3, 4, and 5 fin configurations. As long as all the 3 fin rockets weigh the same as each other (and same for the other number of fins), the experiment should be sound.

Honestly, your biggest hurdle will be buying motors. A nose cone or 3 can be shared among the rockets to save cost, and balsa sheet is relatively cheap at hobby lobby.

 

[mdnehez]

As far as gathering the data:

PerfectFlight makes the pnut, and I'm pretty sure it records speed & altitude and will fit in bt-50 for sure, maybe bt-20.
https://www.perfectflite.com/pnut.html
Jolly Logic AltimeterTwo is also pretty small
https://www.apogeerockets.com/Electronics-Payloads/Altimeters/Jolly-Logic-AltimeterTwo

Many companies offer bulk packs of rocket kits for classes:
https://www.asp-rocketry.com/ecommerce/ASP-Educational-Bulk-Pack-Model-Rocket-Kits.cfm?cat_id=11
(These guys might do a deal where the fins were not precut, and just included the balsa for each rocket, can't hurt to ask)

the wholesalers sell bulk packs of motors:
https://www.acsupplyco.com/estes/bulk.htm
https://bellevillehobby.com/

Hope this helps,
-Mike

 

[jlabrasca]

My son wants to do a science project on fin shape to see if that effects the top speed of the rocket 10 rockets and 20 different shapes.. any ideas if this would work using the same body tube diameter and same nose cone but with different fins

Interchangeable fins might be tough, but ten versions of a swappable fin can+motor mount should be doable.

For what parameters will you control as you vary the fin shape?

Will you compare fins with the same span, or the same area, or the same leading edge length, etc?

Whatever, you are going to have to do a little bit of geometry.

Also do some fiddling around with sims to get the same COP for the different configurations.

 

[bikefxr]

Thank you for all the great ideas and the help this project is making me a BAR can’t wait to hit the launch pad again

 

[BABAR]

Hobby lobby sells bulk packs of 24 motors.
With the 40% off coupon you can get n your phone, may help out.

Anybody know the variance of Estes motor proplleant? I recall reading the ejection charges were supposed to be plus or minus one second, so I would imagine some variability in propellant loads.


Neat project, you may need a lot of motors to get reliable data.

Consider either forward swept fins, or at least not extending posterior to the motor. Less chance of fun breakage, especially since you are going to do a LOT of flights.

Also a bit daunting to try 20 different shapes. Maybe start with one shape, 3, 4, and 5 fins (three styles), get some flights and data. If you can’t separat 3 styles with this data, you ain’t gonna make it with 20.

Consider A engines and streamer recovery. Faster turn around and less likely to lose a rocket.

Straight trails!

 

[Rex R]

the Estes Viking would probably make a good rocket to 'play' with fin shapes, what with those cardstock fins. biggest problem with this idea is being able to separate meaningful data from the 'noise' as the variation from shape will be rather small.
Rex

 

[BABAR]

No I don't work for Hobby Lobby nor do I get any commission but they also often have a bulk pack of Vikings for a very reasonable price particularly when you get the 40% off coupon

 

[BABAR]

Rex's idea the Viking is really good given it comes with pre-cut cardboard fins Therefore your fin sizes and shapes will be consistent across three and four and five fin models and you also will have relatively consistent finishing. As opposed to having to sand your Balsa fins and determine if you're going to taper them or around them or whatever.

 

[jqavins]

Please don't let me discourage you, but be aware that there are a lot of variables that affect both the top speed and altitude, and some are more important than the shape of the fins.

• Keep the CPs all the same, which has been mentioned.
• Keep the weights all the same, which has been mentioned. You can do this by weighing the heaviest and using clay to bring the others up. but do it with clay in the fin can, not the normal nose weight, in order to keep the CG the same in all the configurations.
• Keep all of the taper and airfoil profiles the same with all the fin shapes. The simplest (and probably the only practical) way to do that is to use no taper or airfoil at all, which is less than optimal for performance.
• Keep the surface finishes all the same. Whatever level of effort your son puts into finishing - anything from none at all to perfectly glass smooth - should be consistent. And were I in his shoes, I'd be likely to work harder on the first one or two than I would on the last, so encourage him to not go overboard from the start.
• Keep the fillets the same.
• Motor variability, already mentioned, you can't do anything about.

Since some of these can't be controlled perfectly, make note of them as sources of error in the report on results. Many seem minor, but to be honest the effect of fins shape will also be minor, and all of these combined except motor variability might well be swamped by that one factor alone. That means, for really valid results, flying each version a bunch of times and averaging, while being careful to either have one single date code for all motors or the same mix of date codes for each version.

 

[jlabrasca]

My son wants to do a science project on fin shape to see if that effects the top speed of the rocket 10 rockets and 20 different shapes.. any ideas if this would work using the same body tube diameter and same nose cone but with different fins

How old is the kid?

We all seem to be interpreting fin shape to mean the outline of the fin.

But re-reading, I am not sure how to parse "10 rockets with 20 shapes" I wonder if you might have meant edge profile (rounded versus square). 10 different rocket designs, each with two different fin profiles?

• Motor variability, already mentioned, you can't do anything about.

While it cannot be controlled it can be controlled for. The worry is that there is a lurking variable -- some systematic lot-to-lot variation in motor performance that would be mistaken for a fin-related effect. Motors come in packs of three. Do a 3 x 3 x 3 matrix. Three fin shapes, three launches each using a motor from a different packages. Also, heep a record of the date codes on the motors as part of the data.

 

[jqavins]

While it cannot be controlled it can be controlled for. The worry is that there is a lurking variable -- some systematic lot-to-lot variation in motor performance that would be mistaken for a fin-related effect.

Agreed, up to a point. It's not just systemic lot-to-lot variation that concerns me, but random motor-to-motor variation even within a lot. That can only be controlled for by averaging quite a few (more than three) flights, and the lot-to-lot variations have to be controlled for at the same time (for example by expanding the 3×3×3 matrix to 3×3×10 or more). And while I don't have data, my concern is that the motor-to-motor variation adds noise to the data that swamps out any systemic shape-to-shape difference unless lots of flights are used. And that means getting in lots of flights without damaging or losing the rocket, which is why something with A motors (previously mentioned) is a good idea.

 

[jlabrasca]

Agreed, up to a point. It's not just systemic lot-to-lot variation that concerns me, but random motor-to-motor variation even within a lot. That can only be controlled for by averaging quite a few (more than three) flights, and the lot-to-lot variations have to be controlled for at the same time (for example by expanding the 3×3×3 matrix to 3×3×10 or more). And while I don't have data, my concern is that the motor-to-motor variation adds noise to the data that swamps out any systemic shape-to-shape difference unless lots of flights are used. And that means getting in lots of flights without damaging or losing the rocket, which is why something with A motors (previously mentioned) is a good idea.

This is why I asked about the age of the kid.

If this is for primary school science fair, then my advice would be to test something with an effect size larger than the expected motor variability. Make the fin shapes REALLY different.

If this is for a kid in middle school, and the funds are available, then he can burn a large number of motors in the same rocket to collect the variability. In his conclusions he can then assess whether the differences between particular fin shapes are detectable above the motor performance noise.

Regardless of the child's age I would, of course, require a full reporting of z-scores, p-scores, and a full-factor analysis with pairwise applications of Student's t-Test.

 

[kuririn]

My son wants to do a science project on fin shape to see if that effects the top speed of the rocket 10 rockets and 20 different shapes.. any ideas if this would work using the same body tube diameter and same nose cone but with different fins

You might be interested in this:
https://www.apogeerockets.com/Rocke...periment-Kit?zenid=29udg9krkj1tq58ksqd6s3p1r6
Cheers.

 

[Mushtang]

From a statistical standpoint I would recommend at least 10 flights of each configuration in order to see how accurate the data is.

For example, if you fly 10 times and get speeds of 90, 110, 80, 102, 120, 83, 115, 122, 101, 118 you may average them and use 104. But if you only flew once and your one single flight happened to be the 80, or the 122, you'd have very different conclusions.

 

[bikefxr]

He is in middle school .. he is now wanting to 10 rockets... different shapes 3-4- and five fin configuration on each shape .. but the apogee science kit looks like it might just be the ticket and a jolly logic altimeter 2.. thanks for all the feed back in the project

 

[kuririn]

Don't mention it. Hope you and your son have fun!

 

[jlabrasca]

He is in middle school .. he is now wanting to 10 rockets... different shapes 3-4- and five fin configuration on each shape .. but the apogee science kit looks like it might just be the ticket and a jolly logic altimeter 2.. thanks for all the feed back in the project

That's a lot of graphs to fit onto a tri-fold... but then again, you didn't say this was a school project. Is this for a science fair/school report, or is he just ambitious?

 

[bikefxr]

It’s a science fair project

 

[BABAR]

He is in middle school .. he is now wanting to 10 rockets... different shapes 3-4- and five fin configuration on each shape .. but the apogee science kit looks like it might just be the ticket and a jolly logic altimeter 2.. thanks for all the feed back in the project

That apogee kit looks like it might be perfect for you. Again rcommendation, if you use the funny curvy fins, put them on so the pointy lateral tip is forward, not backward. I know, it will look “wrong” but just say you are going to the coolness factor, and from the description Tim says the fins are oversized so your rocket is gonna be stable anyway. This will give you less chance of fins breaking on recovery.

Unfortunately looks like the Apogee kit minimum engine is a B. ( says B6-2 or B6-4). Too bad as HobbyLobby usually has the A8-3 bulk packs.

I have occasionally seen B6-4 bulk packs at hobby lobby but that’s uncommon. Worth checking, if they have it with the 40% off coupon it’s a steal.

Hobbylinc.com (not Hobby Lobby) does sell a bulk pack of 24 B6-4s us for $56 plus shipping. That’s about 1/2 what it will run you from APOGEE. Apogee is a great company, just a bit on the pricey side.

You son will learn a lot from this. One thing he should learn is economics. you say he wants to do 10 rockets, but say you want 10 flights each rocket, that’s 100 flights, that’s likely over $200 just for motors.......$400 if you buy from Apogee.

 

[bikefxr]

I am looking forward to hitting the launch pad again building a big Bertha for my self now