"Finless" Rocket Design - Ram Air Intake Stabilization?

[rstaff3]

Whereas the long one may be stable without the vents, the stubby probably won't be. Hopefully the vents blow and don't suck

 

[KenECoyote]

Cute!

Looks almost harmless!

Whereas the long one may be stable without the vents, the stubby probably won't be. Hopefully the vents blow and don't suck

Actually, I've done a swing test and it is stable; however I needed nose weight when adding in the motor (I put in the biggest motor planned for now which was a 1/2A3-3T). There's a blizzard on the way, so I'll likely have to put this on the backburner; however I'd like to finish building the longer Mini, additional shrouds and possibly launch the short mini in my backyard on Sunday. I'll update if anything new comes up.

 

[rstaff3]

Looks almost harmless!



Actually, I've done a swing test and it is stable; however I needed nose weight when adding in the motor (I put in the biggest motor planned for now which was a 1/2A3-3T). There's a blizzard on the way, so I'll likely have to put this on the backburner; however I'd like to finish building the longer Mini, additional shrouds and possibly launch the short mini in my backyard on Sunday. I'll update if anything new comes up.

Oh really? I am surprised. Where is the CG? BTW, I have had a couple of rockets that passed a swing test but still were unstable. Some don't like crosswinds, some have their fins occluded by low pressure areas when the rocket goes fast etc etc. Anyway, I would fly it as is and see what happens.

 

[GlenP]

so, based on your initial swing tests, it was unstable with engine but stable with nose weight? that is a very good starting point. To add to that body of knowledge, I would suggest doing some more swing tests where you tape off the fin slots completely, then progressively remove larger portions of the tape, like 0%, 25%, 50%, 75%, 100% open fin slot regions. Maybe try taping over 3 fin slots, does one single fin slot make an impact? Lots of possibilities to find the boundary of stability with respect to the fin slot effectiveness with a good swing test model. Can you make the balanced model go unstable again by covering up the air fin slots? Have fun with it.

 

[KenECoyote]

Oh really? I am surprised. Where is the CG? BTW, I have had a couple of rockets that passed a swing test but still were unstable. Some don't like crosswinds, some have their fins occluded by low pressure areas when the rocket goes fast etc etc. Anyway, I would fly it as is and see what happens.

Good point! However it's still a good start. I likely shouldn't have started with such a short version (was the only BT5 I could find initially). The CG is right about in the middle...2.5" from tip (motor sticks out the back a bit for taping or easier removal).

so, based on your initial swing tests, it was unstable with engine but stable with nose weight? that is a very good starting point. To add to that body of knowledge, I would suggest doing some more swing tests where you tape off the fin slots completely, then progressively remove larger portions of the tape, like 0%, 25%, 50%, 75%, 100% open fin slot regions. Maybe try taping over 3 fin slots, does one single fin slot make an impact? Lots of possibilities to find the boundary of stability with respect to the fin slot effectiveness with a good swing test model. Can you make the balanced model go unstable again by covering up the air fin slots? Have fun with it.

Great suggestions! Yes, I was originally thinking of doing the same and I figured the smaller models would make things easier. I also wanted to see the effects of the different size outlets as well as closed. I didn't think about closing off a slot though...I would think that's bad...much like a rocket losing a fin. Thanks!

 

[neil_w]

Great suggestions! Yes, I was originally thinking of doing the same and I figured the smaller models would make things easier. I also wanted to see the effects of the different size outlets as well as closed. I didn't think about closing off a slot though...I would think that's bad...much like a rocket losing a fin. Thanks!

Speaking of losing a fin, I think you should spend several posts describing your filleting technique for this rocket.

Also, I think tomorrow would be a good day to go outside and do some more swing tests. I'll be looking forward to the updates.

Oh, and the "closing off a slot" test will really reveal what effect the fin slots are actually having. I think that's a really good one to try.

 

[KenECoyote]

Speaking of losing a fin, I think you should spend several posts describing your filleting technique for this rocket.

Also, I think tomorrow would be a good day to go outside and do some more swing tests. I'll be looking forward to the updates.

Oh, and the "closing off a slot" test will really reveal what effect the fin slots are actually having. I think that's a really good one to try.

Nah...all that is secondary to my next round of important groundbreaking tests...making it whistle! :grin:

 

[mbecks]

When does the launch happen? Some cars use body vents like the picture for ground force, I'm sure the same concept will work if done properly. This is such a cool idea!

 

[KenECoyote]

When does the launch happen? Some cars use body vents like the picture for ground force, I'm sure the same concept will work if done properly. This is such a cool idea!

Just a slight issue of a "historic" blizzard making things a bit difficult for me.

My area received about 20+" of snow in one day. Worse yet, I had one of my vehicles blocking the snowthrower (long story) and the city plows buried my car in place...plus my neighbor broke his snowthrower so I had to figure out other ways to get mine out. Regardless, I managed to clear everything and also managed to get in some quick flights off the frozen/"slushy" lake in my back yard...life proves to be quite challenging to me at times!

 

[kcobbva]

Wow Ken, I've completely missed this thread! very interesting concept! I look forward to seeing what the report is when it goes up and performs PERFECTLY!

 

[KenECoyote]

I don't have too much time, so I'll spare you guys the details of the building; however I managed to build two other smaller test rockets. So I now have three! Of note is that I had built them in a rush since my launch window was very narrow and closing...with the warmer weather predicted coming, the ice on my lake (which may be questionable at the current time) would likely be melting, thus closing my backyard launches for a bit.

Here are the three stooges:

#1 "Look! No Fins!" - Stubby mini with wide outlet and shroud covering much of the rocket- tumble recovery.
#2 "Well De-Finned" - Long mini with narrow outlets and shroud only on bottom third of the rocket - streamer recovery.
#3 "RAIS'N Heck" - 18mm with narrow outlets and shroud on bottom third - streamer recovery.

In my swing tests, the narrow longer slots seemed to get the rocket stable more quickly, so I thought that was the better design...however...

 

[KenECoyote]

Wow Ken, I've completely missed this thread! very interesting concept! I look forward to seeing what the report is when it goes up and performs PERFECTLY!

Ha! In my dreams! :wink:

 

[KenECoyote]

So after I got my snow clearing duties out of the way, I had 2 hours to quickly get my stuff and launch before it starts to get dark. Additionally, with all the snow, the shrouds were likely to get water damage as they were. Given this, I decided to spray them with waterproofing spray. I don't know if it was really necessary or even if it really worked, but I figured it was worth a shot (spray I had was a mess...sputtered stuff out and made the shrouds look stained. Oh well.

Okay, I got out on the frozen ice...I was the one brave soul to claim the honors of "first man on ice" in my area this year...I had tested it Friday and it seemed good and likely the first time this year it was thick enough to hold my weight; however it's hard to tell what happens once snow goes over it. So I marched out there with a life vest on as well as improvised "ice claws" (almost like handheld spikes to allow you grip on slippery ice so you can pull yourself out). Ice was fine; however it was a bit slushy.

First up was the longer mini. I figured it would be more stable than the stubby and also had streamer recovery, so it was more likely to land nearby.

 

[CrazyOB]

Here is the finished short shroud. Notice the fronts of the vanes are air foiled.


You'll also see that I have the shroud bottoms cut (what a pain cutting all those little circles out by hand!). I've also glued on the black bottom stop ring to the motor tube.
ARRGH! I used a blade with the tip already broken off since I would usually have them break when cutting circular patterns in cardboard anyway.

Ken, try one of these to cut these rings: I understand you can get them a number of places.[h=1]OLFA 9911 CMP-1 Compass Circle Cutter[/h]

 

[KenECoyote]

#2 "Well De-Finned" launch report:

I decided to launch this first since I thought it would be more stable than the stubby one. Motor used was an A3-4T - I had used this motor to set the motor block and it became glued in place (did I mention I was rushing the build?), so by default it would be the motor for launch!

First I had the usual "first launch of the winter" pains such as recording video 3 times of failed ignition...check everything and determine it's a weak batter, go back into house for a screwdriver and new battery...etc. Then launch and forget to video. Of course.

Once I got everything set...3-2-1 Launch! Rocket went up...that's good...swirly rear...not good. After boost, it nosed down and recovery came out about 30' from the deck and landed somewhat far away. Oh well, might as well test the ice in the center! LOL

Rocket was fine; however it had plowed itself into the snow and the shroud had packed ice inside. Sure glad I used the waterproofing!

 

[KenECoyote]

Ken, try one of these to cut these rings: I understand you can get them a number of places.OLFA 9911 CMP-1 Compass Circle Cutter

Thanks for the tip! Looks like it would save my fingers some pain.

 

[rstaff3]

Thanks for the tip! Looks like it would save my fingers some pain.

I got mine at either Michaels or Hobby Lobby, with a coupon of course. They do work well. Tip: On thicker stock, just cut part was through and then stick a hobby knife through the slit. You can then quickly work your way around using the circle cutter rut as a guide.

 

[rstaff3]

#2 "Well De-Finned" launch report:

I decided to launch this first since I thought it would be more stable than the stubby one. Motor used was an A3-4T - I had used this motor to set the motor block and it became glued in place (did I mention I was rushing the build?), so by default it would be the motor for launch!

First I had the usual "first launch of the winter" pains such as recording video 3 times of failed ignition...check everything and determine it's a weak batter, go back into house for a screwdriver and new battery...etc. Then launch and forget to video. Of course.

Once I got everything set...3-2-1 Launch! Rocket went up...that's good...swirly rear...not good. After boost, it nosed down and recovery came out about 30' from the deck and landed somewhat far away. Oh well, might as well test the ice in the center! LOL

Rocket was fine; however it had plowed itself into the snow and the shroud had packed ice inside. Sure glad I used the waterproofing!

I read that: it didn't skywrite but headed in the wrong direction.

 

[CrazyOB]

Dick, Great tip I hadn't thought of that. RE: circle cutter

 

[KenECoyote]

Well, after rocket #2 was what I considered a failure, I was hesitant to launch the stubby one...oh well, I'm out there and already warned the family to be heads-up, so YOLO! (You Only Launch Once!). :grin:

Launch 2: #1 "Look! No Fins!"

Motor: 1/2A3-3T

Sorry...I forgot to take a pic. I have video; however it's the annoying "only got the rocket shooting off the pad and then landing somewhere" shots.

Crossed fingers and launched...#1 shot off the pad quickly and very straight and fast! It was so fast both my wife and I missed it! From what I saw, the rocket zoomed straight up without any noticeable instability nor any tail wiggle/waggle. Coast also seemed good and event popped out the motor and the rocket came down into the snow. Unfortunately this one got a lot of snow crammed well into the shroud and the front edge of the shroud was also a bit dented and mushed. Still, it was what I considered to be a good flight and worthy of more follow up tests. :grin:

 

[KenECoyote]

I read that: it didn't skywrite but headed in the wrong direction.

Actually #2 rocket boosted upwards (no cartwheels/skywriting); however it had a swirly/spirally upward path...somewhat similar to my cup rockets.

 

[KenECoyote]

Okay, since I've managed to launch two of the minis without anyone running for the hills or bodily harm, I figured I'm out there I might as well try the 18mm, right? To be honest, I had a thought in my mind that after the first launch, it would probably be best for me to go back into the house and cut the slots bigger; however I didn't know if I had time for that and I wanted to see if the first flight was an anomaly, so onto the pad it went (note it's getting darker already)!

Launch 3: #3 "RAIS'N Heck"

Motor: A8-3

Launch conditions: Frosty and slushy with some feeling of being on thin ice.

Good ignition; however that was likely the only nominal part of the flight. Shortly after lift off, the rocket went unstable and started a slow odd sort of tumble under power. It was basically a cartwheel, but like a lobbed cartwheel (hard to describe and I haven't seen such a flight before). It still remained in the air and event about 15' AGL.

Post-flight examination revealed I had made a big error...I had initially built this one with a motor hook planned, so for the shroud bottom, I used one of the motor centering rings with the notch cut into it for that; however I ditched the hook since it wasn't working out and...I forgot to plug/cover the hole on the bottom. Worse yet - while I used a bottom stop ring on the other two rockets (which would've blocked some/most of the hole), I decided to just use tape as a stop on this one (did I mention I built these in a rush?). So this test was like one of the ones GlenP suggested...what happens when one "air fin" is somewhat blocked...not good. Two of the outlets had full air effect but the third had less flow...this meant the other two were pushing the rocket bottom off-side and also explained the very usual flight I witnessed.

This one definitely was raising heck and it was the only one I called "heads-up!" on after launching.

 

[CrazyOB]

Ken, nice work so far. Goddard certainly didn't get it right the first time.
Now you need another set of flights and then can start working on the math. Relation between tube length/dia, etc... Then you build a rocket based on the math to validate your results. Hey more building!

I know why you want finless you really really really hate sanding!

 

[KenECoyote]

These tests were interesting and it seemed like I had one bit of success; however I'll need to do more tests. I think the tricky part here is the large amount of variables going on. Basically I have what is a amalgamation of a tube fin, air fin, cone base and regular finless design. Add to the mix the width and length of the shroud as well as it's ratios in relation to the main rocket body tube, the ratio of inlet to outlet as well as the dimensions of the outlet. Boy, that's quite a lot going on!

I think that I should get wider shrouds with the shorter wider outlet given these prelim results (also note that one successful flight is likely not enough to judge this design as being successful). Unfortunately for me, with the week looking warmer, I'll be losing my backyard launch spot for a while, so I'll have to wait to do more testing. Future possible builds include one where the base of the shroud is cone-shaped so it can more efficiently funnel the air to the slots (may also help with just a bit of GDS). I'd also like to try one where the shroud is covering the entire body tube as well as one where the inlets are in the nosecone itself.

It's been fun so far! Thanks for sharing the journey!

 

[KenECoyote]

Ken, nice work so far. Goddard certainly didn't get it right the first time.
Now you need another set of flights and then can start working on the math. Relation between tube length/dia, etc... Then you build a rocket based on the math to validate your results. Hey more building!

Thanks for the encouragement CrazyOB!

I know why you want finless you really really really hate sanding!

Haha! I love that! :rofl:

 

[kcobbva]

You rock Ken! Got out in the Snow and Ice and launched those cool concept rockets! Guess you need a real "mini" cam to strap on the side of that. Bet it'd be cool!! Regardless of the outcome, it's quite a success!!

 

[KenECoyote]

You rock Ken! Got out in the Snow and Ice and launched those cool concept rockets! Guess you need a real "mini" cam to strap on the side of that. Bet it'd be cool!! Regardless of the outcome, it's quite a success!!

Haha! You're much too kind Kevin, but thanks for the great support!

 

[K'Tesh]

Looks almost harmless!

In the grand scheme of things, I'm sure that this is "Mostly Harmless".

 

[rstaff3]

I'd say that they WERE totally harmless. Three points don't predict the future, however.

 

[rstaff3]

Hey, I stole one of your photos for my blog. If that's bad, tell me to take it down!