Development of a compact batchrocket core.

Matt Todd wrote:@Peter van den Berg  
Do you think it would be alright to put the final exhaust opening on the BACK side of the riser instead of the front?

Yes, Glenn is right, it can be done. The lower riser part should be different, the pictures of the French bench build are quite clear how it should be done, in my opinion.

Peter van den Berg wrote:

Matt Todd wrote:@Peter van den Berg  
Do you think it would be alright to put the final exhaust opening on the BACK side of the riser instead of the front?

Yes, Glenn is right, it can be done. The lower riser part should be different, the pictures of the French bench build are quite clear how it should be done, in my opinion.

Alright, so a simple matter of moving the "riser liner" to the back wall instead of the front. I was afraid that this decrease in port depth would have an effect on the design, but I see now that you have tested this and found it satisfactory. The flames still enter a square space to form the vortex before expanding in the wider top half of the riser. Thanks for confirming!

Peter van den Berg wrote:Both a core and door drawing is available, please find them here

Thank you so much for sharing!

This is the core lovingly named Shorty?!

Pros: compact, large window, no secondary air channel necessary, very forgiving at reloading, a choice of core exhaust directions, highly resistant to fuel overload
Cons: less initial draw

Correct me if I'm wrong please.

EDIT: adding the pros Peter listed

Benjamin Dinkel wrote:This is the core lovingly named Shorty?!

Pros: compact, large window, no secondary air channel necessary
Cons: less initial draw

Correct me if I'm wrong please.

The pros could be extended with: very forgiving at reloading, a choice of core exhaust directions, highly resistant to fuel overload.

So, your very brief description is correct, including the lovingly name.

Peter van den Berg wrote:
The pros could be extended with: very forgiving at reloading, a choice of core exhaust directions, highly resistant to fuel overload.

On the dutch batchrocket site (great that you were able to find the time to update, many thanks!), I saw you mentioned the shorty could also be exhausting in the 'roof' of the afterburner. In that case, where is the port located? Are there running references? I'm interested because flow-wise this may be more interesting for my own application.

Julian Adam wrote:On the dutch batchrocket site (great that you were able to find the time to update, many thanks!), I saw you mentioned the shorty could also be exhausting in the 'roof' of the afterburner. In that case, where is the port located?

Using a top exhaust, the opening should be at the top front side. It is done and measured towards the end of the development phase.

Julian Adam wrote:Are there running references?

Yes, there are, see this link.

Julian Adam wrote:I'm interested because flow-wise this may be more interesting for my own application.

It's one of the possibilities, use those if it fits your purpose. Please, stay within the current specs, it's a sensitive core that's easily disturbed.

Thanks for replying, Peter. I didn't realize you re-tested the top exhaust at 70% of chimney CSA riser port at later stage. I'm assuming building this out of 50 or 60 mm thick bricks will also be OK. Should the front wall then be continued upwards to the top of the roof, or should only the roof itself be added? (Leaving the front wall a bit lower as in your link).

Hello everbody,

some questions came to my mind while making plans for my upcoming Shorty build. I hope it´s fine to ask them here. I searched the forum but didn´t find these questions asked.

- The V-shaped floor, is it essential? Coaling down is faster with the V-shaped floor, as I understood, right? Since I am planning to build a small core due to size restrictions, this floor design would make the burn chamber even smaller. And I don´t like to cut refractory too much...

- How do you guys take out the ash out without pushing it into the port of the burn chamber?

- Is the Shorty core prone to smoking back into the living room? If so, might a bypass higher in the bell (above the endport) help?


I have refractory slabs available of 250x120mm and 300x150mm and I found out, that a small 131mm system size core can be build with very few cuttings using this dimensions. Looking forward to start my build soon.

Thanks, Mat

Hi Matthias;
No, the angle-cut bricks on the floor are not required.
I do not use them in my stoves.

I use a short handle scoop and pull ashes to the front.
I use my gloved hand to pull any ash from the port.
Inside the riser, I use a vacuum.

Shorty does use a bypass high in the bell until it is warmed up for the season.