It FLEW! Flight Report: The Slipstream, 3FNC, 3 Swept Fins spaced at 120 Degrees

[BABAR]

Skip to Post 22 for Flight Report

In my continuing exploration of asymmetric fin designs (perhaps better described as "How NOT to build a rocket") I came up with a modification of the basic 3FNC design. This is the SlipStream (alternative name was WhackJob, that just didn't have the ring I was looking for.)

The question was, if I did the standard 3 fins, spaced 120 degrees from each other, but put ALL of them on one side of the rocket, would it fly, and would it fly well? For those who think I wouldn't post this if it DIDN'T fly well, I'd have to say they need to look at a few of my past attempts (the Stinker was particularly well named.)

Anyway, feel free to vote in the poll or not. I'll give it a few days, and then post the flight report.

As always, comments (positive and negative) appreciated.

 

[rbelknap]

I think this could work, if the CG (and CP?) is in the right place in relation to the thrust vector. In any case, I'm interested in seeing the result...

 

[astronwolf]

Photo 2 (doggie hiding in car) is the best one.

 

[adrian]

In my continuing exploration of asymmetric fin designs (perhaps better described as "How NOT to build a rocket") I came up with a modification of the basic 3FNC design. This is the SlipStream (alternative name was WhackJob, that just didn't have the ring I was looking for.)

The question was, if I did the standard 3 fins, spaced 120 degrees from each other, but put ALL of them on one side of the rocket, would it fly, and would it fly well? For those who think I wouldn't post this if it DIDN'T fly well, I'd have to say they need to look at a few of my past attempts (the Stinker was particularly well named.)

The main concern would probably be that with almost all of the drag and perhaps a significant portion of the mass off to the side from the line of thrust, it will arc over. If the fins aren't quite properly lined up then it may roll or corkscrew instead.

 

[Daddyisabar]

It would be cool to get the dog an RSO vest and hat. MacGruff the RSO dog barks out everything that is wrong with the design

 

[dave carver]

The main concern would probably be that with almost all of the drag and perhaps a significant portion of the mass off to the side from the line of thrust, it will arc over. If the fins aren't quite properly lined up then it may roll or corkscrew instead.

Yep, thinking the same thing, asymmetrical drag. Some kind of camber on the motor to counteract the drag, and weight for that matter, will be needed or a looping flight could be expected. Angling the motor slightly toward the fins' centerline. The two centerlines should intersect at some point above both.

The forces here are kind of complex and worth further research. Keeping it from looping is just the start. I think a misalignment or even uneven fin sanding causing lift will make it pivot on an axis doing a spiral on the way up. A straight up boost will deserve a cheer :wave:

 

[Daddyisabar]

Power and nose weight are your only friends and with plenty of each you will be fine. Had a bit of the same problem on the B 58, but it few nice and straight with the nose gear evening things out in the drag department.



When you reach the point where asymmetrical drag pulls over your nose you will know real quick. Launch in calm conditions with a long rod!

 

[astronwolf]

 

[BABAR]

View attachment 251076

Maybe if I soaked my rockets in beef broth she'd bring them back. At the moment, she is a retriever in name only.

 

[adrian]

Power and nose weight are your only friends and with plenty of each you will be fine. Had a bit of the same problem on the B 58, but it few nice and straight with the nose gear evening things out in the drag department.

Power and nose weight are the solution to an otherwise unstable design, e.g. that B-58, but its drag is, as you say, fairly balanced thanks to the undercarriage and nacelles.

I was worried about unbalanced drag on my Trabant boost glider, so its motor mount is angled a bit, the exact angle being determined by the classic TLAR system (*). It does sometimes fly off at a bit of an angle but that is as likely to be simple weathercocking as unbalanced drag or thrust.


I've built a few models with unbalanced drag because they look like aircraft so they have horizontal wings in the middle and one tail unit above the rear end, but the imbalance is not as severe as if the whole fin assembly is off to one side. This older version of the Feuerlilie F25, for example, flew without any noticable tendency to tip over.
View attachment 251114

(*) That Looks About Right

 

[mjennings]

Very interesting, can't wait to see the flight report. It would also be interesting to try inverting the fins, vaguely as shown in the poor ASCII diagram below.
/
|---O
\

 

[boomtube-mk2]

I’m not going to even take a guess at what this rocket is going to do once it leaves the rod; but I’ll go out on a limb and say it won’t be anything good.

My guess is that the Center of Pressure on this model is located somewhere near your dog’s left ear and that’s assuming it actually has anything approaching a real Center of Pressure to begin with.

Now as for your dog recovering your rockets; beef broth isn’t going to cut the mustard. You are going to have to rub the rocket against something along the lines of a dead Possum, easily found along most rural highways.

I stress the need to use dead Possums as live ones are. . .well, lively and don’t especially like being rubbed against rockets.

A Dead Skunk can be used if a dead Possum is unavailable but your fellow rocketeers won’t thank you for that particular substitution.

 

[Cookie the Dog's Owner]

A Dead Skunk can be used if a dead Possum is unavailable . . . .

Crossin' the launch area late one night
He shoulda looked left an' he shoulda looked right
He didn't see the launch rod or the B.A.R.
The skunk got cooked and there you are

You got yer dead skunk in the middle of the pad
Dead skunk in the middle of the pad
Dead skunk in the middle of the pad
An' it's stinkin' to high heaven.

 

[Bat-mite]

I voted, and then when I saw the results, I was comforted to know that the majority voted with me. Now, whether or not we were right remains to be seen....

 

[fyrwrxz]

I wuz gonna vote fer the dead possum with a 4 second delay...wait...whut wuz the question????

(It's not really true anything will fly with enough power, but it WILL shred...)

(Hmmm-shredded possum with barbeque sauce, but I digress...)

(Not true I have ADD...SQUIRREL! Now a Squirrel on a G80-4 (or barbeque sauce)....that's either a good launch or a good lunch)

 

[Bat-mite]

I wuz gonna vote fer the dead possum with a 4 second delay...wait...whut wuz the question????

(It's not really true anything will fly with enough power, but it WILL shred...)

(Hmmm-shredded possum with barbeque sauce, but I digress...)

(Not true I have ADD...SQUIRREL! Now a Squirrel on a G80-4 (or barbeque sauce)....that's either a good launch or a good lunch)

It's time for your meds, Mr. Wrxz.

 

[fyrwrxz]

I knew I wuz forgetting sumpthin'....LOL! I am feeling much better now the pre-frontal lobotomy has worn off....

 

[boomtube-mk2]

It’s better to have, a-bottle-in-front-of-you, than a pre-frontal lobotomy.

 

[jmattingly13]

Well, you presumably have a non-coaxial CG and CP, so you'll presumably have some funny moments at various points in the rocket. Never mind the flight report--hook up a strain gauge or flex gauge to the airframe and let's see how much it bends in flight!

 

[BABAR]

(Not true I have ADD...SQUIRREL! Now a Squirrel on a G80-4 (or barbeque sauce)....that's either a good launch or a good lunch)[/QUOTE]

Hmmm, I guess I'll have to upscale.........

https://www.rocketryforum.com/showthread.php?69006-Squirrel!&highlight=squirrel!

 

[fyrwrxz]

(Not true I have ADD...SQUIRREL! Now a Squirrel on a G80-4 (or barbeque sauce)....that's either a good launch or a good lunch)

Hmmm, I guess I'll have to upscale.........View attachment 251153View attachment 251154View attachment 251155View attachment 251156

https://www.rocketryforum.com/showthread.php?69006-Squirrel!&highlight=squirrel!

For all you guys who think I'm crazy...the defense rests...

 

[BABAR]

Flight Report
Unfortunately it was so cold on the initial flight day that my fingers wouldn't work and I messed up the video, so I re-shot it today.
First flight was on Quest B6-4. Boost seemed pretty straight, maybe a bit of rotation but not much corkscrew on BOOST, then when it went to coast a very pronounced corkscrew. I am guestimating hit about 300 or 400 feet. Winds were about 5 MPH, enough to blow it about 100 yards. Overall a very enjoyable flight, I liked the corkscrew bit at the end.

Today winds also light, probably 4-5 mph.
Quest A6-4
Mild roll versus corkscrew on boost, again corkscrew on coast. Videos here:
Long Version: [video=youtube;TE6I3OxmNqo]https://www.youtube.com/watch?v=TE6I3OxmNqo[/video]
SloMo CUT Version: [video=youtube;PANSGRGr4LQ]https://www.youtube.com/watch?v=PANSGRGr4LQ[/video]

Quest B6-4
Minimal roll or corkscrew on boost, again corkscrew on coast
Long Version (Narration is wrong, this is B6-4 engine, NOT A6-4 as described): [video=youtube;F3sILvTNzsA]https://www.youtube.com/watch?v=F3sILvTNzsA[/video]
SloMo CUT Version: [video=youtube;6tbNd-84FSk]https://www.youtube.com/watch?v=6tbNd-84FSk[/video]

Quest C6-5
Appreciate input on this, started straight, about 20 feet up sharply changed trajectory (? wind gust) "sort of" into wind, then almost a straight horizontal flight out of site (not recovered)
Long Version: [video=youtube;SFabEwOq8Zs]https://www.youtube.com/watch?v=SFabEwOq8Zs[/video]
SloMo CUT Version: [video=youtube;YTGTCEsjCRE]https://www.youtube.com/watch?v=YTGTCEsjCRE[/video]


I am guessing the C6-5 engine weight may have made this initially unstable then stabilized as it came up to a bit more speed.

Regarding the poll, my "pre-flight" guess was that this would corkscrew throughout. I'll let you guys be the judges as to whether on the A6 and B6 it was "corkscrewing" on the boost or just having a little bit of minimal rotation. On the FIRST flight (again no video on that one) I thought it was flying pretty darn straight.

Some posts expected a "St. Louis Arch" where the asymmetry consistently deviated the rocket in one direction, sort of leaning over and over and over and doing a half loop into the ground. Nothing close to that. I also don't think there was enough rotation or corkscrew on the boost to counter that, although I guess it is possible.

The design did not incorporate any additional nose weight (this MIGHT have saved the C6 flight). Also there was no "fin angle" adjustment for the asymmetric fins. I just did everything I could to make sure everything was lined up straight relative to the axis of the body tube.

 

[AstronMike]

Had a feeling this would boost straight under power, then start to 'act up a bit' once the thrust stopped, mainly due to the asymmetrical drag. I did not vote on your poll, because it was not known/declared that all the fins were exactly straight and aligned. That's a biggie.

Think about gliders like Bomarcs (sans ramjets) and SkyDarts, especially larger ones with thicker wings/tail. Notice that these have ALL of their 'flat' *above* the BT?? And, 40 years of flying these tells me that if you have all said 'flats' aligned right, they tend to boost pretty straight (CG correct, of course).

Neat project, can't wait to see what you're going to do next....

 

[rbelknap]

I can't see the long versions of the A6-4 and C6-5 videos. The youtube player is telling me they are private.

Neat project, glad it flew.

UPDATE: videos are working for me now. Thanks! (Also - July 10th 2015... the C6-5 flight is FROM THE FUTURE! :wink: )

 

[Daddyisabar]

Well I got it right in the poll, straight up up corkscrew on coast in calm conditions. Any wind acting on that big asymmetrical fin and the resulting lift will cause all kinds of trouble. I assumed your fins were straight given your prior projects. Now it is time to go real crazy. That nice big tail is reminding me of a C-141 tail. Get out some BT 60 or 2.6" with a round plastic cone, glue on some wings, multiple motor mounts in the jet pods, get some center line thrust from a couple of crazy motor placements in the landing gear pods or out the cargo bay or both. Put the landing gear down. Your RSO will love it. Just say you have given in to the bad influences from the forum and gone over to silly oddrocs.

 

[tim cubbedge]

Nice!

 

[Zebedee]

Was the arc to the left of picture off the rail due to weathercocking or the off center thrust? Which way was the wind blowing?

 

[BABAR]

The sharp turn about 15 or 20 feet above the pad was roughly (but not exactly) into the wind direction. I'd appreciate input of more experience rocketeers on this one, cuz rather than a smooth arc into the wind, it was a sharp immediate deviation, followed by a surprisingly straight trajectory. Rocket was not recovered. I am doubting a structural failure, as I would not expect a deviation followed by an almost arrow straight trajectory. On other flights where I have suspected weather cocking with other rockets seemed like a more smooth deviation into the wind. I did not notice any gusts of wind, but it is possible. Had it not been for that deviation I am guessing I would have gotten 600 or 700 feet altitude out of the rocket.

I liked the lines on this bird, and will build another one with the same plans (well, I'll have to approximate, but it was pretty simple, hopefully I have the template for the fins "somewhere" in my pile.) I will stick with A and B engines (or put nose weight in to keep CG just a BIT ahead of the CG for a B engine. The "just a bit" forward is my fudge factor for the fact that since the rocket weighs more with the C engine it may have bit lower acceleration of the pad.)

Other modifications will the T-bird, One fin sticks straight out from the Body Tube and one "cross-bar" like the top of a capital "T".
Could also try Michael Jennings' idea of "Slouch" version, sort of like the T but with the cross bar fin (or in this case fins) drooping laterally toward the Body Tube.

I have already done a true planar "two fin" rocket successfully.
https://www.rocketryforum.com/showt...s-and-a-nose-cone-The-Lucky-7&highlight=lucky

 

[Daddyisabar]

Reminds me of the old commercial from Continental Airlines. "At Continental Airlines we really move our tail for you!" It just went a bit airplane on you, luckily it had some height from a bit of vertical flight off the rod. Wind was blowing enough on the big fin to tip the nose slightly off vertical, moving the angle of attack on the big fin to where it's lift took over and pointed the nose where it wanted to go, just flying on a wing and a prayer. If there is any breeze I always point the wing into the wind, well very slight breeze because you can't fly in more than a puff. I tell them not to worry, I am flying the nose and the rest of the rocket will follow behind for show. I won't let those wings take over because it is a rocket, not an airplane. Vertical, not horizontal refreshment is what the oddroc flier desires. More power, more nose weight, less wind! Or maybe less craziness. Proven, traditional 4FNC design and no big. asymmetrical surfaces way off the center line. That is the cure I am told.

 

[tab28682]

Well I got it right in the poll, straight up up corkscrew on coast in calm conditions. Any wind acting on that big asymmetrical fin and the resulting lift will cause all kinds of trouble. I assumed your fins were straight given your prior projects. Now it is time to go real crazy. That nice big tail is reminding me of a C-141 tail. Get out some BT 60 or 2.6" with a round plastic cone, glue on some wings, multiple motor mounts in the jet pods, get some center line thrust from a couple of crazy motor placements in the landing gear pods or out the cargo bay or both. Put the landing gear down. Your RSO will love it. Just say you have given in to the bad influences from the forum and gone over to silly oddrocs.

It will work for sure.

I need to post pictures of the MD-80 D powered boost glider I designed back in the 1990s. Perfectly straight boost with the t-tail and some sheet balsa wings. Motor center in 2" tubing (old oddbal tubing from NCR that was used for the shuttle solids boosters on their shuttle kit.