Ogive not that good.

[Senior Space Cadet]

If you go to buy nose cones, most are going to be ogive. In some tube sizes you can't find anything else, at least not in plastic.
I've been researching the drag of the different nose cone shapes, for subsonic rockets, and ogive doesn't seem to be that good.
Or, at least, there are better choices. Ogive may be a waste basket term for a variety of shapes. Some vendors may be calling a nose cone ogive that is really some other variation.
There are some minor contradictions' or variations in the conclusions arrived at, but here are a couple examples of what I'm finding. I haven't found too many direct comparisons between an ogive and hemispherical (my golf ball idea) but, from what I've seen, it has a similar drag to ogive. With dimples, maybe lower drag than ogive.

 

[rocketman4h]

Read this report it may give you better information
https://www.offwegorocketry.com/userfiles/file/Nose%20Cone%20&%20Fin%20Optimization.pdf

 

[Senior Space Cadet]

Read this report it may give you better information
https://www.offwegorocketry.com/userfiles/file/Nose%20Cone%20&%20Fin%20Optimization.pdf

I'm not an idiot, but I've been working in a grocery store for that last 44 years and have no formal engineering training, so there is a little smoke coming out of my ears.
Thank got for the summary. I did glean some useful information. Thank you. It confirmed some of the ideas I already had.
I'd like some clarification on the fineness ratio, five seeming to be a good all around number. Is that the length to root chord ratio?
I thought the comment, that the nose cone choice might have an impact on the optimal fin design, was interesting. One of the things I've found true in my other pursuits is that changing one thing often changes everything.

 

[Funkworks]

According to today's wikipedia article, the fineness ratio is:
"the ratio of the length of a body to its maximum width".
https://en.wikipedia.org/wiki/Fineness_ratio

 

[Senior Space Cadet]

According to today's wikipedia article, the fineness ratio is:
"the ratio of the length of a body to its maximum width".
https://en.wikipedia.org/wiki/Fineness_ratio

That's kind of what I figured. Thank you.
I might want to change the nose cones I have on some of the rockets I plan to launch this weekend.

 

[Steve Shannon]

That's kind of what I figured. Thank you.
I might want to change the nose cones I have on some of the rockets I plan to launch this weekend.

Unless you have optimized everything else on your rockets the difference might not be noticeable.

 

[gna]

You could run sims in OR and see what difference it makes. Or you could fly the same rocket with different nose cones and see how it performs. The different nose cones may weigh different amounts, so it might require a small weight adjustment to make it as even as possible.

I simmed a rocket with an elliptical nose cone and an ogive cone. The ogive cone went 13 feet higher. I adjusted the weights so they were the same, but the ogive cone still went 6 feet higher. I didn't really get into fineness ratio or trying to find the best shape, but it could be an interesting experiment.

 

[rharshberger]

Motor performance variation will probably affect altitude more than an ogive in the subsonic range.

 

[heada]

Motor performance variation will probably affect altitude more than an ogive in the subsonic range.

And surface finish in the supersonic range.

 

[rharshberger]

And surface finish in the supersonic range.

Yep, the thing about motor variation is its the one thing as builders and fliers we cannot control.

 

[Charles_McG]

While researching information about the Terrier Malemute sound rocket for my scale build, I came across a discussion in a research paper about how they had both 5:1 and 3:1 ogive nosecone options, but selected the 3:1 because it had more useable room for payload with what they considered to be a small performance penalty.
The Terrier Improved Malemute is usually pictured with an 11° Total Angle Cone, which is about a 5.5:1 simple cone. I was told that shape does better at super (hyper?) sonic speeds.
I certainly don’t fly rockets that need that kind of performance edge. I go for the look I want.

 

[lakeroadster]

Kind of a drag...

 

[OzHybrid]

What is this data? Drag at 39 MPH... What rocket flies at that speed. This data in the graph is meaningless unless you plan to manufacture a car for driving in an urban environment. People, please...... for rockets flying at a speed you'd expect for a rocket, Use Von Karmen 5:1 or higher. I used 7:1 Von Karmen and got 26k instead of 24k. We've all had this discussion. If you're sub sonic there is no point in going to the trouble of making ANY ratio of ogive curve nosecone. And doing a comparison of 3:1 nosecones where your military objective is to deliver a warhead is also pointless. That's not us. Let's see a comparison of sub,trans and super sonic speeds for various nosecones. 39 MPH..... What are you thinking about. Mainly meaningless and distracting to those that like shiny objects.

Oh look a shooting star........

 

[lakeroadster]

What is this data? Drag at 39 MPH... What rocket flies at that speed.

Nearly every rocket ever launched flew 39 mph at least twice during each flight.

Let's see a comparison of sub,trans and super sonic speeds for various nosecones. 39 MPH..... What are you thinking about. Mainly meaningless and distracting to those that like shiny objects.

Oh look a shooting star........

Your name is Rocket Scientist... post up the data instead of bloviating... or do you just like to read your own prose?

 

[beeblebrox]

Nearly every rocket ever launched flew 39 mph at least twice during each flight.



Your name is Rocket Scientist... post up the data instead of bloviating... or do you just like to read your own prose?

Or maybe it was a typo, and was supposed to be 390MPH... I think the difference would be relatively the same until you got close to supersonic, I.E. less than MACH 0.8

If someone has a wind tunnel...

 

[gna]

Motor performance variation will probably affect altitude more than an ogive in the subsonic range.

That's what I was thinking when I posted that OR data. Motor variation or a gust of wind could affect altitude more than nose cone shape with a sport rocket.

 

[dr wogz]

this kinda reminds me of the fat guy who buys the carbon fiber & titanium bike..

"Cuse it's carbon fiber & titanium, it's super light, so it'll go fast & far!!" (Regardless of the extra 50+lbs the cyclist is permanently carrying around with him...)

 

[manixFan]

I've been flying high performance rockets for several years and have done a fair amount of research on how to do better. My rockets are carbon fiber, min diameter, well finished, and tower launched. What I've learned is there are two big things that affect overall performance: optimization during boost and optimization during coast.

For boost, the smaller the 'wetted area' (overall surface area), the lower the drag, and the better the overall performance. Nose cone shape, launch lugs, etc., do matter, but reducing the length of the rocket as much as possible seems critical to reducing drag and has a large effect on performance. On smaller rockets, things like launch guides and fin root size may also have a large effect, though I suspect those items become less important as rocket size increases and the ratio of those items to the overall rocket size decreases.

For coast, there is an optimum weight, based primarily on the characteristics of the motor. A long burn motor needs a light rocket to achieve maximum altitude since most of its gain comes during boost, whereas a fast burn, high impulse motor needs a heavier rocket to coast after motor burnout.

And of course the overall finish can have a large effect as well.

You can test some of this in OpenRocket. Using the Rocket Optimization tool, you'll find that with some motors you need to add weight to get max altitude. But in almost every case, the shortest rocket that is stable will provide the max altitude.

For nosecones that operate in both sub and supersonic regions, the Von Karman ogive is widely considered to be a good compromise.

Not a rocket scientist by any means, but lots of reading, building, and flying.


Tony

 

[H_Rocket]

Use whatever nose cone floats your boat. In the end these are, for the most part, essentially toy rockets.

And Tony, until you can tell us just exactly what motor is in the rocket, we will just hold judgement on the rest...

 

[mbeels]

Some say "Ogive not that good".

Confucious say, "Ogive not that bad."

 

[SecondRow]

Nearly every rocket ever launched flew 39 mph at least twice during each flight.

I once launched a rocket that hit 39 mph exactly three times.

 

[jrap330]

Read this report it may give you better information
https://www.offwegorocketry.com/userfiles/file/Nose%20Cone%20&%20Fin%20Optimization.pdf

Thanks for the slides...very interesting.

 

[mbeels]

I once launched a rocket that hit 39 mph exactly three times.

Twice on the way up, once on the way down?

 

[Zeus-cat]

The rockets flown by the Most Interesting Man in the World only hit 39MPH ONCE!

 

[manixFan]

Use whatever nose cone floats your boat. In the end these are, for the most part, essentially toy rockets.

And Tony, until you can tell us just exactly what motor is in the rocket, we will just hold judgement on the rest...

I don't understand your point? My point was to choose whatever motor you want and run the sims yourself, with your rocket. What judgement is there to withhold? I'm just stating basic aerodynamics.

But to answer your question, the two most common motors I have flown in my MD CF rockets are the CTI L265 and the CTI L935. The L265 needs a much lighter rocket than the L935 to achieve max altitude. Both benefit from the shortest possible rocket vs. a longer one of the same weight.

Pick any motor you want and just run the sims, no judgement needed.


Tony

 

[OzHybrid]

Nearly every rocket ever launched flew 39 mph at least twice during each flight.



Your name is Rocket Scientist... post up the data instead of bloviating... or do you just like to read your own prose?

1 is good, 4 is not as good.
There you go. Data at realistic rocket speeds, but this comparison above does not include fully blunt cylinders as a nosecone.

Also included https://www.offwegorocketry.com/userfiles/file/Nose%20Cone%20&%20Fin%20Optimization.pdf which was linked to earlier.

But as already said. If YOU like the look of it and it's safe to fly, passes a basic stability test, go with the shape you like.

Data presented for a range of speeds that we don't operate in just confuses people.

Also the previous data presented seems to be experimental data. Perhaps someones personal tests. The drag in grams, is in very small numbers of grams. The variation between the best and worst is even smaller and there is no information on the measurement accuracy that would give me any confidence to use it for anything rocketry related.
The results above, here, although there was a lot of discussion years ago, have been validated by actual launches. Once you're through the atmosphere and there is no atmospheric drag, you could have a house brick as a nosecone. That's not generally where we fly either though some have. And well done those that made it there.

 

[lakeroadster]

View attachment 425759
1 is good, 4 is not as good.
There you go. Data at realistic rocket speeds, but this comparison above does not include fully blunt cylinders as a nosecone.

Also included https://www.offwegorocketry.com/userfiles/file/Nose%20Cone%20&%20Fin%20Optimization.pdf which was linked to earlier.

But as already said. If YOU like the look of it and it's safe to fly, passes a basic stability test, go with the shape you like.

But data presented for a range of speeds that we don't operate in just confuses people.

Link to thread where the nose cone chart originated from some good data there too.

 

[gna]

Apogee sells a set of nosecones for science projects. I didn't think it was that great a project, as the science has already been done, but still could be fun for kids. I also thought he had a video of one of his daughters setting up rockets in a wind tunnel, but I can't find it.

From the Wikipedia Entry on Nose Cone Design, which is linked to in above referenced thread:

For aircraft and rockets, below Mach .8, the nose pressure drag is essentially zero for all shapes. The major significant factor is friction drag, which is largely dependent upon the wetted area, the surface smoothness of that area, and the presence of any discontinuities in the shape. For example, in strictly subsonic rockets a short, blunt, smooth elliptical shape is usually best. In the transonic region and beyond, where the pressure drag increases dramatically, the effect of nose shape on drag becomes highly significant. The factors influencing the pressure drag are the general shape of the nose cone, its fineness ratio, and its bluffness ratio.

So unless you're approaching Mach 1, it shouldn't make much difference.

 

[SecondRow]

Twice on the way up, once on the way down?

RIP Estes Fletcher. You hit your last bullseye.

 

[OzHybrid]

A conical nosecone will give you the minimum WEIGHT for any nosecone shape. It has the lowest surface area so has the potential to produce the lowest weight nosecone. This is also dependant on your construction method. Less weight in the nose may or may not be a good thing. If you've already got a lot of electronics up there(and they fit) there may be an advantage.