Actual functional rollerons would be awesome to kill the corkscrewing of my bellyfloppers.
Are Fins Over-Engineered?
- Thread starter sr205347d
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Duncan's spreadsheet is not correct. He dropped a "square root" term from the NACA equation which
causes an underestimation in the fin flutter velocities. So you have super conservative numbers.
You'd probably have to "spin up the rollerons" while the rocket was on the pad.... and that would be awesome!
UK MoD reports of Russian soldiers armed with shovels sounds almost as absurd as Russian propaganda saying the UK is eating squirrels, but somehow I believe it. (The shovels thing, not the squirrels)
Maybe it’s my bias showing, but I would believe Russian soldiers are eating squirrels.
tsmith1315
Not a shrubber
Thanks for that shot!
tsmith1315
Not a shrubber
A little canned air and a good bearing...
There was an article in HPR magazine years ago where they did just that. It should be around here somewhere...
Please do not share finsim on this website. The owner or developer does not want it shared here:
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To read more:
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rharshberger
Well-Known Member
....and twisted....I'll vouche for him.. He knows "warped"
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We had some conversations about this recently related to someone wanting to build a fairly large bullet bobby- they wanted the fins removable so it would be easier to transport. I recommended making the mounts from small pieces of aluminum angle such as what you can get at HomeDepot. One leg of the angle is bolted through the airframe, the fin goes between the 2 outstanding legs and then you bolt through them.
Just don't do really stupid stuff that will anger the fin flutter gods...Like Big Wing fins with clustered tractor motors.
Cheap, squishy Hobby Lobby balsa quickly covered with 3M lable paper. Any decent engineer will see the problem; if they can get past the horror of the claw fins and kite tail. Yes Mr. RSO, It will hold together long enough. It will naturally find the breaking point and then it can be repaired with a fin tab and some CA. Better, faster, stronger.
Don't design your rocket without fins and a wobbly body that really flutters under power.
Strong, stiff body tubes and fins are the way to go!
And the flutter from telescopic tube fins will put any anti-flutter engineer over the edge.
Especially when one of the strings break! Run away!
Going through life without flutter is to be safe and sound!
Cheap, squishy Hobby Lobby balsa quickly covered with 3M lable paper. Any decent engineer will see the problem; if they can get past the horror of the claw fins and kite tail. Yes Mr. RSO, It will hold together long enough. It will naturally find the breaking point and then it can be repaired with a fin tab and some CA. Better, faster, stronger.
Don't design your rocket without fins and a wobbly body that really flutters under power.
Strong, stiff body tubes and fins are the way to go!
And the flutter from telescopic tube fins will put any anti-flutter engineer over the edge.
Especially when one of the strings break! Run away!
Going through life without flutter is to be safe and sound!
To be clear and transparent, cwbullet is correct. Copyright infringement is serious business. This is NOT open for discussion or debate.
My employer was accused of copyright infringement a few years ago (we didn't). Just defending ourselves from the (false) accusation involved lawyers and a months-long argument between our lawyers and and their lawyers, and was a colossal headache. TRF doesn't need that. Defiance of this policy will result in bans or lengthy vacations from the forum. Do not test us on this.
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Sweet Christmas, his postings on that page really are... out there.
Yup, but his product is pure genius. Remember, everyone has their own brand and he might think you are out there.
"Both sides" is a pretty stupid argument to make about factual (or in this case, counter-factual) claims.
Just making a statement that there many views that do not make him right or wrong. I simply acknowledge the quality of his product.
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tsmith1315
Not a shrubber
Everyone has the same right to their own personal perspective. Whether or not it makes sense to others is beside the point.
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I know a couple people who could reasonably be judged mentally ill and generally disconnected from reality. That does not mean they don't have keen intellectual insights into certain topics from time to time.
Not defending the viewpoints in question, just pointing out the general case that a person can be a wacko in some areas and also highly functional in others.
Not defending the viewpoints in question, just pointing out the general case that a person can be a wacko in some areas and also highly functional in others.
Time for a little culture...
boatgeek
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[pushes glasses up nose] Well ackshully...
I would dispute the premise of the question. Most fins aren't over-engineered because they're not engineered to begin with. Except for a few cases where people use FinSim or the like, people generally say something like "1/8" plywood should be fine" or "I should really paper these balsa fins so they hold up." Those statements come from our own and other people's experience breaking things. They're valuable, but they're also not exactly engineering. I would definitely agree that most fins are stronger than they need to be, whether that's because of collective wisdom (you must tip to tip if you go supersonic!) or because we don't want to break another @#%%^! fin if the rocket falls off the tailgate.
I'll go further out on a limb and say that the vast majority of hobby rockets don't need engineering either. Again, except for relatively extreme edge cases, calculating out minimum flutter speeds or "dropped rocket" loads is unnecessary. Not to mention very difficult, especially if you're making your own materials. I'm a practicing engineer with 25 years of experience in structural work and I'd have to think really hard about how to go about calculating a minimum fin thickness or fillet size to protect a rocket dropped off the back of a tailgate. I could come up with a dozen different answers with a dozen different entirely reasonable entering assumptions. (landing on sod or concrete? landing on one fin or two? etc. etc.)
I would dispute the premise of the question. Most fins aren't over-engineered because they're not engineered to begin with. Except for a few cases where people use FinSim or the like, people generally say something like "1/8" plywood should be fine" or "I should really paper these balsa fins so they hold up." Those statements come from our own and other people's experience breaking things. They're valuable, but they're also not exactly engineering. I would definitely agree that most fins are stronger than they need to be, whether that's because of collective wisdom (you must tip to tip if you go supersonic!) or because we don't want to break another @#%%^! fin if the rocket falls off the tailgate.
I'll go further out on a limb and say that the vast majority of hobby rockets don't need engineering either. Again, except for relatively extreme edge cases, calculating out minimum flutter speeds or "dropped rocket" loads is unnecessary. Not to mention very difficult, especially if you're making your own materials. I'm a practicing engineer with 25 years of experience in structural work and I'd have to think really hard about how to go about calculating a minimum fin thickness or fillet size to protect a rocket dropped off the back of a tailgate. I could come up with a dozen different answers with a dozen different entirely reasonable entering assumptions. (landing on sod or concrete? landing on one fin or two? etc. etc.)
Yeah, "over-engineered" is not a good term here. But, it makes a good headline!
My premise, or rather conclusion, is that a "dropped rocket" mishap (from whatever altitude) should be repairable quickly in the field rather than requiring major surgery, or worse, euthanizing the patient.
Bolt on fins with frangible attachment parts could do it. The attachment is what is over-done, not the fin itself. I don't expect anyone to actually engineer a solution. Rapid iteration until something works is my hobby version of engineering. See my thread on Bellyflop Recovery. I am still iterating on that. https://www.rocketryforum.com/threads/bellyflop-recovery.175503/
My premise, or rather conclusion, is that a "dropped rocket" mishap (from whatever altitude) should be repairable quickly in the field rather than requiring major surgery, or worse, euthanizing the patient.
Bolt on fins with frangible attachment parts could do it. The attachment is what is over-done, not the fin itself. I don't expect anyone to actually engineer a solution. Rapid iteration until something works is my hobby version of engineering. See my thread on Bellyflop Recovery. I am still iterating on that. https://www.rocketryforum.com/threads/bellyflop-recovery.175503/
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Pem Tech
Notorious Member
Keep your fins and motors at the back of the rocket. Surface prep is key. Good technique on fillets. DO NOT OVERPOWER YOUR ROCKET WITH TOTALLY AWESOME, HIGH AND QUICK THRUST MOTORS!
Wing warping fins is very bad.
View attachment 565922
Shaping fins in flight with fire is very bad.
View attachment 565924
Keep on the straight and narrow path of sound engineering and your Low and Mid Power fins will be fine. Over engineering for high and ultra high power as your motor sizes slide down the backside of the alphabet is...
TOTALLY AWESOME!
That is flippin' incredible! Is that an Albatross? Wow, just wow.
To heck with engineering. I just can't take anymore damage or failed, unstable flights or shredded rockets. So embarrassing. BULLET PROFFING RULES!
That's why the initial edge bond is always considered temporary. The real strength of a surface mount is in the fillets. "Everyone" knows that, and "always" has.
How do you ensure glue gets into the holes? They look pretty tiny, and I would bet the glue won't run into them without help.
But back to the original question, I'd say the answer, for LPR, is yes. Sometimes. TTW attachment is very rarely needed, but it's nice for a little extra security. Papering is rarely necessary for strength, but it's nice for a little extra security, and what the heck, it's nice for finishing too. Interlocking fin tabs with centering rings is really over the top, but it's nice for a little extra...
You can build a low power rocket as if it's a mid power rocket, and it might not even cost you much, but it's usually not really beneficial (unless it provides peace of mind).
Good construction technique is many times more important than are the design "upgrades".
But the mods are so cool and hip. You can discuss all the over engineering for hours with the fellas. Yes. I have an indestructible low power rocket out on the pad. Glassed, ttw, internal fillets, dual deploy and a very expensive composite motor in there. Total peace of mind. If you think my rocket mods are cool, just look at the tuned pocket rocket I drove to the launch, totally rad. Build light, build strong...boring! Balsa and dope are for the last century.
