powderburner
Well-Known Member
- Joined
- Jan 17, 2009
- Messages
- 7,398
- Reaction score
- 15
I saw something alarming on a website yesterday that has me wondering if anyone else thinks this is as much of a problem as I do, and if anyone wants to join me in warning the site owners.
At ALLEXPERTS they have a website set up for people to post questions and other volunteer experts to post answers (sound familiar?). One of the subject categories is model rocketry. At least one of the self-appointed experts is posting answers that are badly wrong. So whats the big deal?
People using the posted info are being misinformed. If they actually use this advice, they will very likely have crashes instead of successful flights. This might only result in some beginner rocketeers being discouraged and quitting the hobby, or it might result in an unsafe rocket hitting and injuring someone. I dont think we need either of these outcomes, or anything in between.
Three of the first four posts that I saw had something that was wrong enough to catch my attention and make me concerned. ALLEXPERTS uses feedback/complaints from other users to determine which experts to keep and which to get rid of, but this system requires more than just one of me sending complaints. So, I am asking for a few others to also critique these posts and get this website back on track.
Example 1: Mr. P implies that adding fins to the front of a rocket might improve stability, with which I strongly disagree.
Expert: Todd Panico
Date: 10/17/2007
Subject: rocket fins
QUESTION: I was thinking of adding fins just behind the nose cone apart from the rear fins. Will it increases the stability or simply increase the drag.
ANSWER: Hello Veerendra - The answer is both. Most likely it will add more drag than the benefit of stability. If the rear fins are well designed and properly applied, they offer all the stability that is needed.
If you like, check this post for yourself at:
https://en.allexperts.com/q/Model-Rocketry-2312/rocket-fins.htm
Mr. P does not qualify his remarks by talking about a configuration that might be over-stable, but (I think) leads most readers to think that adding forward fins is a good thing stability-wise for rockets in general (other than perhaps adding a little drag). Where do they find these people?
Example 2: Mr. P shows more brilliance and even admits that he does not know and is guessing, but does not stop there and shut up. He rambles around (and completely misses an obvious misconception on the part of the questioner) and ends up making a feeble indication to go ahead and try it, which I find more than a little alarming.
Expert: Todd Panico
Date: 8/6/2007
Subject: Estes engine ignition
Question: Todd, I see you are a source for Estes 'A to D' engine rockets, but I'll take a flyer here on a question about and E engine:
My son and I have built a multi stage rocket from Estes parts. It is designed to use D boosters (1 to 3) and have an E engine in the main body, final stage. Can we count on reliable ignition of the E engine from the D booster charge? I ask because I see that E engines require a higher energy electrical ignition system than other Estes engines. Thanks
Answer: Hello Paul, I would think it would be reliable. Just as any staged rocket, the distance from one engine to the next would be the biggest variable that would affect 'light off'. But, I do not have a lot of experience with staged rockets. My launch sites are not big enough for safe recovery. My only experience with staged rockets are with C engines. I have never had a failure with one stage lighting the next. These have been Estes kits, I have not designed one myself.
On the other hand, Estes does not make an 'E' engine booster, that I know of. There might be a reason for that. Might be an altitude issue, maybe a light off issue or a weight to thrust issue.
So, to answer the question you asked. I don't know :-D my GUESS would be yes.I would like to hear what you experience if you give it a try.
If you like, check this post for yourself at:
https://en.allexperts.com/q/Model-Rocketry-2312/Estes-engine-ignition.htm
I believe the questioner has confused the launcher set-back distances (for ignition on the ground due to the various impulse classes) with the ability to pyrotechnically stage different motor sizes. This is a completely different subject, and should have been explained to him. Then Mr. P goes on to wonder about Estes E boosters the expert sounds like he might need more help than the questioner. I just love his technical terminology (i.e., light off instead of the really-difficult-to-learn ignition).
Example 3: Mr. P is almost half on-track with his basic discussion of vehicle weight effects on performance and then blows it by admitting the basis of his knowledge is trial and error testing (which gives me warm fuzzies all over). He goes on to completely mis-define the cord (sic) of the fin, apparently confusing the chord of a lifting surface with the half-span. He recommends thinning white glue with alcohol (will those two even mix?) instead of using the much-easier and much-more-readily-available water. And for fins on model rockets (most all of which are solidly SUB-sonic) Mr. P recommends that the leading edges be sanded to a sharp point and fails to recommend anything for shaping the trailing edges.
Expert: Todd Panico
Date: 5/9/2007
Subject: Fins Design & Pain
QUESTION: Should the root edge of our fin be exactly twice the diameter of our body tube? If so, will it make a lot of difference if the fins are slightly less? Also, what is the absolute best paint to use for altitude purposes?
ANSWER: Hello Sindy,
I have never heard that the root edge needs to be twice the diameter of the body tube. I can't even think why that would need to be. So, in my opinion, slightly less would be fine. The best paint is a high gloss enamel paint. The trick with getting the most altitude is weight. So, you will need to apply as little paint as possible. The more paint the more weight. The reason for a high gloss enamel is drag. Generally speaking, shiny paints are smoother which would have less drag and allow the rocket to fly higher. I have to say in all my trial and error testing rocket designs, I could never measure the minute distance gained by different paints on rockets. Again, if the highest altitude is what you are after, find a way to reduce weight.
---------- FOLLOW-UP ----------
QUESTION: Thanks Todd for your expertise, but just one problem with the whole weight factor. In my grade 11 physics class we have 3 trials. Therefore, I cannot just have a small weight because it accounts for low stablity. How do I maximize my height without making sure my fins snap?
Answer: I am not sure I understand what you mean by small weight accounts for low stability. If your center of gravity (CG) and center of balance (CB) are correct, your rocket could weigh less than a gram and still be stable. But lets talk about fins. Your fins can be very strong if you cut then right. You want the grain of the balsa to run with the cord of the fin. In other words, the grain of the wood should be parallel with the leading edge of the fin. Not only does this create a strong fin, it gives you a very strong glue bond to the body tube because some of the glue gets soaked up into the fin. You can also strengthen the fin by mixing up some alcohol and white glue(50/50) and paint your fin with it. This will add weight though. You should also sand the leading edge into a very fine edge.
If you don't want to reduce weight, the only other thing you can do is to make sure your rocket flies as straight as possible. Any twisting or wobbling reduces it final altitude. Do you get to choose your engines? If so, choose an engine with a very long delay for it's ejection charge. This way you can coast upwards for more altitude.
Good luck!
If you want to see the original post, check:
https://en.allexperts.com/q/Model-Rocketry-2312/Fins-Design-Pain-1.htm
Clearly, Mr. P has never learned about optimum mass and the effects of weight on coasting flight. He also makes the shaky recommendation to select a motor with the longest possible ejection delay .so it will coast all the way into the ground? (How about checking into motors recommended by the manufacturer?) And what the heck is a center of balance? (yes, I know he meant CP)
I think his final comment (Good luck!) is a completely valid one with help like this, the questioner is really going to need it.
My thinking is this: if there are this many screwy answers in the first few posts I looked at, how badly messed up is the rest of this website and how many newbies are getting advice that runs from bad to disastrous. If we want to attract and keep more new rocketeers, should we try to straighten out these errors?
No, I do not want to sink their website (although these people really SHOULD be redirected to TRF) or tell them off or anything like that. I dont have anything against Mr. P, despite all my pithy comments here. I certainly do not aspire to become an expert on ALLEXPERTS although I think I will start posting there soon. I just want people with questions to get proper and useful answers, and for them to stay safe in the process of learning more about rocketry. I do want to see these questions answered correctly.
So, am I going to be jousting this windmill alone, or is anyone with me? Or are there too many of these screwball websites out there to try to help them all?
At ALLEXPERTS they have a website set up for people to post questions and other volunteer experts to post answers (sound familiar?). One of the subject categories is model rocketry. At least one of the self-appointed experts is posting answers that are badly wrong. So whats the big deal?
People using the posted info are being misinformed. If they actually use this advice, they will very likely have crashes instead of successful flights. This might only result in some beginner rocketeers being discouraged and quitting the hobby, or it might result in an unsafe rocket hitting and injuring someone. I dont think we need either of these outcomes, or anything in between.
Three of the first four posts that I saw had something that was wrong enough to catch my attention and make me concerned. ALLEXPERTS uses feedback/complaints from other users to determine which experts to keep and which to get rid of, but this system requires more than just one of me sending complaints. So, I am asking for a few others to also critique these posts and get this website back on track.
Example 1: Mr. P implies that adding fins to the front of a rocket might improve stability, with which I strongly disagree.
Expert: Todd Panico
Date: 10/17/2007
Subject: rocket fins
QUESTION: I was thinking of adding fins just behind the nose cone apart from the rear fins. Will it increases the stability or simply increase the drag.
ANSWER: Hello Veerendra - The answer is both. Most likely it will add more drag than the benefit of stability. If the rear fins are well designed and properly applied, they offer all the stability that is needed.
If you like, check this post for yourself at:
https://en.allexperts.com/q/Model-Rocketry-2312/rocket-fins.htm
Mr. P does not qualify his remarks by talking about a configuration that might be over-stable, but (I think) leads most readers to think that adding forward fins is a good thing stability-wise for rockets in general (other than perhaps adding a little drag). Where do they find these people?
Example 2: Mr. P shows more brilliance and even admits that he does not know and is guessing, but does not stop there and shut up. He rambles around (and completely misses an obvious misconception on the part of the questioner) and ends up making a feeble indication to go ahead and try it, which I find more than a little alarming.
Expert: Todd Panico
Date: 8/6/2007
Subject: Estes engine ignition
Question: Todd, I see you are a source for Estes 'A to D' engine rockets, but I'll take a flyer here on a question about and E engine:
My son and I have built a multi stage rocket from Estes parts. It is designed to use D boosters (1 to 3) and have an E engine in the main body, final stage. Can we count on reliable ignition of the E engine from the D booster charge? I ask because I see that E engines require a higher energy electrical ignition system than other Estes engines. Thanks
Answer: Hello Paul, I would think it would be reliable. Just as any staged rocket, the distance from one engine to the next would be the biggest variable that would affect 'light off'. But, I do not have a lot of experience with staged rockets. My launch sites are not big enough for safe recovery. My only experience with staged rockets are with C engines. I have never had a failure with one stage lighting the next. These have been Estes kits, I have not designed one myself.
On the other hand, Estes does not make an 'E' engine booster, that I know of. There might be a reason for that. Might be an altitude issue, maybe a light off issue or a weight to thrust issue.
So, to answer the question you asked. I don't know :-D my GUESS would be yes.I would like to hear what you experience if you give it a try.
If you like, check this post for yourself at:
https://en.allexperts.com/q/Model-Rocketry-2312/Estes-engine-ignition.htm
I believe the questioner has confused the launcher set-back distances (for ignition on the ground due to the various impulse classes) with the ability to pyrotechnically stage different motor sizes. This is a completely different subject, and should have been explained to him. Then Mr. P goes on to wonder about Estes E boosters the expert sounds like he might need more help than the questioner. I just love his technical terminology (i.e., light off instead of the really-difficult-to-learn ignition).
Example 3: Mr. P is almost half on-track with his basic discussion of vehicle weight effects on performance and then blows it by admitting the basis of his knowledge is trial and error testing (which gives me warm fuzzies all over). He goes on to completely mis-define the cord (sic) of the fin, apparently confusing the chord of a lifting surface with the half-span. He recommends thinning white glue with alcohol (will those two even mix?) instead of using the much-easier and much-more-readily-available water. And for fins on model rockets (most all of which are solidly SUB-sonic) Mr. P recommends that the leading edges be sanded to a sharp point and fails to recommend anything for shaping the trailing edges.
Expert: Todd Panico
Date: 5/9/2007
Subject: Fins Design & Pain
QUESTION: Should the root edge of our fin be exactly twice the diameter of our body tube? If so, will it make a lot of difference if the fins are slightly less? Also, what is the absolute best paint to use for altitude purposes?
ANSWER: Hello Sindy,
I have never heard that the root edge needs to be twice the diameter of the body tube. I can't even think why that would need to be. So, in my opinion, slightly less would be fine. The best paint is a high gloss enamel paint. The trick with getting the most altitude is weight. So, you will need to apply as little paint as possible. The more paint the more weight. The reason for a high gloss enamel is drag. Generally speaking, shiny paints are smoother which would have less drag and allow the rocket to fly higher. I have to say in all my trial and error testing rocket designs, I could never measure the minute distance gained by different paints on rockets. Again, if the highest altitude is what you are after, find a way to reduce weight.
---------- FOLLOW-UP ----------
QUESTION: Thanks Todd for your expertise, but just one problem with the whole weight factor. In my grade 11 physics class we have 3 trials. Therefore, I cannot just have a small weight because it accounts for low stablity. How do I maximize my height without making sure my fins snap?
Answer: I am not sure I understand what you mean by small weight accounts for low stability. If your center of gravity (CG) and center of balance (CB) are correct, your rocket could weigh less than a gram and still be stable. But lets talk about fins. Your fins can be very strong if you cut then right. You want the grain of the balsa to run with the cord of the fin. In other words, the grain of the wood should be parallel with the leading edge of the fin. Not only does this create a strong fin, it gives you a very strong glue bond to the body tube because some of the glue gets soaked up into the fin. You can also strengthen the fin by mixing up some alcohol and white glue(50/50) and paint your fin with it. This will add weight though. You should also sand the leading edge into a very fine edge.
If you don't want to reduce weight, the only other thing you can do is to make sure your rocket flies as straight as possible. Any twisting or wobbling reduces it final altitude. Do you get to choose your engines? If so, choose an engine with a very long delay for it's ejection charge. This way you can coast upwards for more altitude.
Good luck!
If you want to see the original post, check:
https://en.allexperts.com/q/Model-Rocketry-2312/Fins-Design-Pain-1.htm
Clearly, Mr. P has never learned about optimum mass and the effects of weight on coasting flight. He also makes the shaky recommendation to select a motor with the longest possible ejection delay .so it will coast all the way into the ground? (How about checking into motors recommended by the manufacturer?) And what the heck is a center of balance? (yes, I know he meant CP)
I think his final comment (Good luck!) is a completely valid one with help like this, the questioner is really going to need it.
My thinking is this: if there are this many screwy answers in the first few posts I looked at, how badly messed up is the rest of this website and how many newbies are getting advice that runs from bad to disastrous. If we want to attract and keep more new rocketeers, should we try to straighten out these errors?
No, I do not want to sink their website (although these people really SHOULD be redirected to TRF) or tell them off or anything like that. I dont have anything against Mr. P, despite all my pithy comments here. I certainly do not aspire to become an expert on ALLEXPERTS although I think I will start posting there soon. I just want people with questions to get proper and useful answers, and for them to stay safe in the process of learning more about rocketry. I do want to see these questions answered correctly.
So, am I going to be jousting this windmill alone, or is anyone with me? Or are there too many of these screwball websites out there to try to help them all?
