An "R"-powered rocket build

[dhbarr]

I'd have to defer, he's scrapped more fin designs than I've sketched ^_^

 

[Rail Dawg]

I'd have to defer, he's scrapped more fin designs than I've sketched ^_^

Good point!

I think I'll let Mike at Binder Design tell me the fastest fin he can build with the tooling available.

These fins ain't coming off lol.

Chuck C.

 

[Paulb06]

Binder Design says he thinks he can build a 12" 6061 aluminum fin can but the root length would be limited to 24".

Based on that can you give the measurements or something close to the Max Q design? I just plug those into the "free form" fin size on Open Rocket I assume.

I can play with the length of the rocket to keep the CP and CG where they need to be.

Chuck C.

If the root chord is limited to 24" and you want the height at 12"" then all you can play with is tip chord and sweep angle....so....make the tip chord 4.5" and the sweep angle 55 deg....bout as close as you're going to get

 

[Paulb06]

If the root chord is limited to 24" and you want the height at 12"" then all you can play with is tip chord and sweep angle....so....make the tip chord 4.5" and the sweep angle 55 deg....bout as close as you're going to get

Binder Design says he thinks he can build a 12" 6061 aluminum fin can but the root length would be limited to 24".

Based on that can you give the measurements or something close to the Max Q design? I just plug those into the "free form" fin size on Open Rocket I assume.

I can play with the length of the rocket to keep the CP and CG where they need to be.

Chuck C.

Good point!

I think I'll let Mike at Binder Design tell me the fastest fin he can build with the tooling available.

These fins ain't coming off lol.

Chuck C.

One last thing...if you want a fast design and you're willing to spend the money for a fabbed up aluminum fin can, why not go with a 8" airframe?.... if you did that the 24" root limitation is no longer a problem...

 

[RocketFeller]

One last thing...if you want a fast design and you're willing to spend the money for a fabbed up aluminum fin can, why not go with a 8" airframe?.... if you did that the 24" root limitation is no longer a problem...

The motor case is 9”.

 

[Rail Dawg]

One last thing...if you want a fast design and you're willing to spend the money for a fabbed up aluminum fin can, why not go with a 8" airframe?.... if you did that the 24" root limitation is no longer a problem...

Yeah like Dan said it's a 9" case.

I'm going with 12" diameter because the 12" G-12 airframe and couplers are readily available.

Since I've got my nifty new router I'll make all the centering rings and such.

Thanks though!

Chuck C.

 

[Ez2cDave]

Binder Design says he thinks he can build a 12" 6061 aluminum fin can but the root length would be limited to 24".

Chuck C.

Chuck,

Another possibility might be a two-piece fin can ( up to 24" long for each section ), with an upper and lower section ( "partial" fins on each section ). Construction and alignment would have to be dead perfect. It would allow a fin root up to 48" long. After the two sections are built, they would be mated, welded together, ground smooth, and given a final finish to your specifications. Once completed, it would be "one-piece".

"Adapt & Overcome" !

Dave F.

 

[Paulb06]

Yeah like Dan said it's a 9" case.

I'm going with 12" diameter because the 12" G-12 airframe and couplers are readily available.

Since I've got my nifty new router I'll make all the centering rings and such.

Thanks though!

Chuck C.

Ahh... I see that...my bad....Performance Hobbies does list some 9" in carbon fiber...its pricey...$200 / ft ...Madcow gets $125/ ft for its G12 - 11.67".... performance also lists 9" glass.... out of stock $90/ft

 

[Rail Dawg]

Ahh... I see that...my bad....Performance Hobbies does list some 9" in carbon fiber...its pricey...$200 / ft ...Madcow gets $125/ ft for its G12 - 11.67".... performance also lists 9.25" glass.... out of stock

Well there are some interesting finds!

A minimum-diameter "R" rocket.

Holy cow I've never built anything like it but talk about a great experience.

That 9" carbon... if the motor could just slide up into that...

What do you guys think though... I just don't see a straight carbon tube being able to handle this much stress.

It's why I'm considering G-12 with couplers along the whole length.

Chuck C.

 

[Paulb06]

Binder Design says he thinks he can build a 12" 6061 aluminum fin can but the root length would be limited to 24".

Based on that can you give the measurements or something close to the Max Q design? I just plug those into the "free form" fin size on Open Rocket I assume.

I can play with the length of the rocket to keep the CP and CG where they need to be.

Chuck C.

You don't need the " free form fin"....just open the trapezoidal fin box and plug in the numbers

 

[Rail Dawg]

Chuck,

Another possibility might be a two-piece fin can ( up to 24" long for each section ), with an upper and lower section ( "partial" fins on each section ). Construction and alignment would have to be dead perfect. It would allow a fin root up to 48" long. After the two sections are built, they would be mated, welded together, ground smooth, and given a final finish to your specifications. Once completed, it would be "one-piece".

"Adapt & Overcome" !

Dave F.

Interesting Dave!

I've taken a totally trashed stainless steel prop to a prop guy and the thing has come back looking brand-new.

Props and fin cans have some similarities... combining two sections ain't a bad idea. Have to run that by Binder...

Chuck C.

 

[Rail Dawg]

You don't need the " free form fin"....just open the trapezoidal fin box and plug in the numbers

OK I'm working it that way.

Love rocket designing like the rest of us but still learning the software.

Thanks.

Chuck C.

 

[Rail Dawg]

Still working with the trapezoidal fin set.

The English definition of a trapezoid: "a quadrilateral with only one pair of parallel sides"

The fin on the far left below has NO parallel sides. I can't get that first edge after the leading edge to angle inward.

Chuck C.

 

[dhbarr]

Draw it like the right fins, not the left.

 

[Rail Dawg]

Draw it like the right fins, not the left.

Which fin design do you guys think are most super-sonic capable?

Are they all 4 equal?

Of course I need to toss the question to Binder and let Mike tell me what's best.

Thanks.

Chuck C.

 

[Paulb06]

Well there are some interesting finds!

A minimum-diameter "R" rocket.

Holy cow I've never built anything like it but talk about a great experience.

That 9" carbon... if the motor could just slide up into that...

What do you guys think though... I just don't see a straight carbon tube being able to handle this much stress.

It's why I'm considering G-12 with couplers along the whole length.

Chuck C.

Call them, it looks like they probably build the to order....as far as carbon being strong enough.....it all has to do with the layup thickness....if they build to order...getting some glass or kevlar added shouldn't be a problem, nor should making it thicker...an existing nosecone wouldn't fit...but there are no 9" nosecones...the nosecones a little trickier...I think PML is the only one making an 11.67" nosecone...a 9" would have to be custom made.....

 

[MClark]

There are Hott Rockets 9" nose ones out there, I have one.
There is no way I would use a commercial cone for an R motor, it will collapse.
I used a cone made in the Hott Rockets mold using carbon fiber for a P motor project (Max. velocity M2), but we are talking four times the power here.
You need to determine the maximum velocity to know what materials, thickness and shape for all the components. To do this the final design of the motor is needed. To design the motor the case needs to be hydro tested.

 

[Theory]

Chuck,

Another possibility might be a two-piece fin can ( up to 24" long for each section ), with an upper and lower section ( "partial" fins on each section ). Construction and alignment would have to be dead perfect. It would allow a fin root up to 48" long. After the two sections are built, they would be mated, welded together, ground smooth, and given a final finish to your specifications. Once completed, it would be "one-piece".

.

I second this idea. finding a person who you trust to tig this together might be a challenge though, as excess heat will cause the fins to warp, and a poor weld will result in a spectacular failure of the fin.

however, should the welding work out you will have a fin can with a optimal fin design.

 

[RocketFeller]

If you end up going true MD the 9” fincan would have less than 24” root chords.

 

[BDB]

I second this idea. finding a person who you trust to tig this together might be a challenge though, as excess heat will cause the fins to warp, and a poor weld will result in a spectacular failure of the fin.

however, should the welding work out you will have a fin can with a optimal fin design.

Or you could do a split fin design. I'm thinking upscale Madcow Frenzy! (Seriously, I wouldn't play games with this much power in a minimum diameter design. But it's fun to imagine.)

 

[Theory]

Or you could do a split fin design. I'm thinking upscale Madcow Frenzy! (Seriously, I wouldn't play games with this much power in a minimum diameter design. But it's fun to imagine.)

couldn't agree more. not saying that I would play games at any power level (seen a few really scary 'I' and 'J' class flights in my day that were clearly not well thought out)

are there any issues to a split fin design at these speeds? curious if there is a pressure wave that would build at the leading edge of the second fin that may pose issues. I really have no idea

 

[Paulb06]

There are Hott Rockets 9" nose ones out there, I have one.
There is no way I would use a commercial cone for an R motor, it will collapse.
I used a cone made in the Hott Rockets mold using carbon fiber for a P motor project (Max. velocity M2), but we are talking four times the power here.
You need to determine the maximum velocity to know what materials, thickness and shape for all the components. To do this the final design of the motor is needed. To design the motor the case needs to be hydro tested.

It seems like most commercial nosecones available are mostly gelcoat...and the airframe tubing is mostly filament wound...in commercial wall thicknesses it's not the strongest stuff either, might be a good substrate for additional layup... not sure you'd save over having a tube made....

 

[MClark]

Since the launch site has changed to Black Rock use aluminum tubes.

 

[OverTheTop]

Or you could do a split fin design.

That just went through my mind as well!

 

[viciouspeanut]

Imagine the whistle from the split fins on that motor!

 

[numbo]

Use high drag fins (tube, cone, grid) to keep the altitude down as originally intended.

 

[Rail Dawg]

Lots of great ideas!

This is going to be a fun journey.

Glad you guys are a part of it.

Chuck C.

 

[Andrew_ASC]

I’ll remotely volunteer some compressible gas dynamics knowledge to you for this project. I just graduated with a BSME and have some design experience with supersonic md multistage. Need to know final Max Mach number for sims and radius/length of nosecone once finalized initially. This will give you a very rough idealized thermodynamic temperature on this nosecone with oblique shocks computed for supersonic flow. This techique was good enough for spacecraft hypersonic flow theoretical problems by hand methods. That way thermally you’ll have a better idea of what you are up against in respect to aero heating.

I can also attempt to do aerofinsim naca4197TN flutter analysis once you’ve designed the fin shape geometry. Limited to flat plate profiles and solid single core materials. Need to know final max Mach, root, tip, span, fin thickness, body tube diameter, and sweep length. Also any epoxies if chosen or a tensile strength for max design angle of attack computations and if through wall or butt joint and fillet radius.

Only offering that assistance as it would be something I would consider helpful in materials and epoxy selection. I’ll leave the material selections and design geometry up to you. It’s better to know than not know in my opinion. There are other engineers on this forum with way more actual experience than me who should be more fully capable with structural questions.

I preferred the delta trapezoidal fins on rockets for stability but I’m not an aero engineer. When you increase the sweep angle you decrease induced drag and reduce weak shock strength from oblique shocks. View it as I’m arming you with some knowledge to make decisions with as a friend would help a friend.

The size and scope of this project is still daunting to me and there are hobbyists with better recommendations than mine by flight experience.

 

[Andrew_ASC]

Which fin design do you guys think are most super-sonic capable?

Are they all 4 equal?

Of course I need to toss the question to Binder and let Mike tell me what's best.

Thanks.

Chuck C.

They are not equal. The fin geometry determines aerodynamic stability and characteristics. The span and thickness along with material affects fin flutter when it harmonically vibrates and fails. The angle of the fin is at play with compressible flow above Mach 0.3. I know the sweep angle affects induced drag through oblique shock behavior for supersonic flight. More sweep angle is less drag. The fin area and aspect ratio is physically at play here. Lateral stability will change with sweep angle too. A delta trapezoidal on the right is more stable than a delta pure right triangle configuration. I’m not an aero engineer and you need to consult more serious scholarly texts and experienced people for hard answers. With certain equations these aero guys optimize the sweep angle for a specific Mach number. It was an inverse sin with respect to mach optimizing for cruise with shock effects. Don’t remember the specifics atm. I think it’s a few algebra lines. I wish I could find that ch.5 wing design book I used last year on the net. I’ll get back to you if I find it. The stability characteristics were covered in design of fighter jet wings. I’m not certain of the behaviors of the ones with swept sharp corners on the left you have sketched. But I’ve attempted to answer your question. Hope an Aero dork or Mike answers it better.

 

[Ez2cDave]

Or you could do a split fin design. I'm thinking upscale Madcow Frenzy! (Seriously, I wouldn't play games with this much power in a minimum diameter design. But it's fun to imagine.)

I advise caution here . . . Split-Fins and Supersonic flight ( maybe Mach 2 + ) might be a "very bad idea" !

Dave F.