L1 help, designing it from scratch

[JoePfeiffer]

I'd move the rear rail guide back towards the rear of the rocket.

Otherwise, build it, and launch

There is no aerodynamic reason for the second rail button or guide to be aft of the center of pressure. Once the first guide has come off the rail, the rocket rotates around the second one (not the center of gravity) until that one comes off too.

To whatever extent a single rail guide behind the CP makes any difference to the flight
(and if it makes any significant difference your rocket is going much too slow exiting the rail) it will act to increase the rocket's angle of attack, which isn't good. Talking about leaving the second guide on as long as possible is a red herring.

For many rockets it ends up being convenient to put it at the very aft end because it's easy to put it there and it really doesn't matter, but if it's just as easy (or as in this case easier) to put it farther forward, do it.

 

[Handeman]

There is no aerodynamic reason for the second rail button or guide to be aft of the center of pressure. Once the first guide as come off the rail, the rocket rotates around the second one (not the center of gravity) until that one comes off too.

To whatever extent a single rail guide behind the CP makes any difference to the flight
(and if it makes any significant difference your rocket is going much too slow exiting the rail) it will act to increase the rocket's angle of attack, which isn't good. Talking about leaving the second guide on as long as possible is a red herring.

For many rockets it ends up being convenient to put it at the very aft end because it's easy to put it there and it really doesn't matter, but if it's just as easy (or as in this case easier) to put it farther forward, do it.

Absolutely nothing wrong with having the bottom button/rail guide further up the rocket. Many Estes rockets have worked great with a single launch lug near the CG. Of course, as rockets get bigger and motor thrust variers more, this becomes more of an issue.
The biggest reason I know of for having the buttons/guides as low as possible, is to be able to take as much advantage of the rail length as possible if the motor is marginal, and/or the winds are strong. Having them low gives you more rail and more time to get up to speed.

 

[Saint_Tiki]

Disclaimer, I'm not as experienced as most of these folks.

That being said, I think you're going too high for a L1. I'd aim for no higher than 600m (2000') but closer to 400m (1300') is best. You want to be able to keep eyes on the rocket. Ways to fail L1 are to lose the rocket because it went too high and lost sight of it... or have it drift too far into powerlines and fry... or lose it in trees and never recovery it, etc.

To prevent having it drift too far, you can use a smaller chute but then you risk damaging it on recovery. Could also use a Chute Release to help bring it back closer to the site but then you're adding complexity to your cert flight. And the chute release is only necessary because you didn't make changes in the design stage. Best to keep it low with a good sized chute.

I'd consider going for a 3" diameter rocket instead of 2.6" like you've got now. That'll bump up the weight and the drag and reduce your altitude.

I like a bit of negative sweep on the aft end of the fins so that when it lands while drifting, the retainer or aft centering ring/tube takes the impact, not the corner of the fin. Look at the PML Intruder fins, that's what I mean. (https://cdn.shopify.com/s/files/1/0568/7489/3503/products/IntruderJerry300t_900x.jpg?v=1633696020) I also like big parachutes for a majestic gentle landing.

My L1 cert flight went to about 2400 feet. Higher than I wanted but the motor vendor didn't have the motor I picked as ideal so I went with a backup choice. My chute release pack job failed and the chute deployed at apogee instead of staying packed up tightly until 600'. It drifted over a mile and narrowly missed power lines. Was more stress than necessary and I got lucky it all worked out. My 2 cents.

 

[smstachwick]

Disclaimer, I'm not as experienced as most of these folks.

That being said, I think you're going too high for a L1. I'd aim for no higher than 600m (2000') but closer to 400m (1300') is best. You want to be able to keep eyes on the rocket. Ways to fail L1 are to lose the rocket because it went too high and lost sight of it... or have it drift too far into powerlines and fry... or lose it in trees and never recovery it, etc.

To prevent having it drift too far, you can use a smaller chute but then you risk damaging it on recovery. Could also use a Chute Release to help bring it back closer to the site but then you're adding complexity to your cert flight. And the chute release is only necessary because you didn't make changes in the design stage. Best to keep it low with a good sized chute.

I'd consider going for a 3" diameter rocket instead of 2.6" like you've got now. That'll bump up the weight and the drag and reduce your altitude.

I like a bit of negative sweep on the aft end of the fins so that when it lands while drifting, the retainer or aft centering ring/tube takes the impact, not the corner of the fin. Look at the PML Intruder fins, that's what I mean. (https://cdn.shopify.com/s/files/1/0568/7489/3503/products/IntruderJerry300t_900x.jpg?v=1633696020) I also like big parachutes for a majestic gentle landing.

My L1 cert flight went to about 2400 feet. Higher than I wanted but the motor vendor didn't have the motor I picked as ideal so I went with a backup choice. My chute release pack job failed and the chute deployed at apogee instead of staying packed up tightly until 600'. It drifted over a mile and narrowly missed power lines. Was more stress than necessary and I got lucky it all worked out. My 2 cents.

Strictly speaking, landing in a place that precludes recovery is not necessarily a failure, so long as the rocket can be inspected in place and confirmed to not have damage. Drifting out of the specified range would be a DQ however.

This is true under Tripoli rules anyway; NAR simply says that recovery will “be considered when evaluating the safety of the flight”, which permits a more strict interpretation.

 

[Saint_Tiki]

Strictly speaking, landing in a place that precludes recovery is not necessarily a failure, so long as the rocket can be inspected in place and confirmed to not have damage. Drifting out of the specified range would be a DQ however.

This is true under Tripoli rules anyway; NAR simply says that recovery will “be considered when evaluating the safety of the flight”, which permits a more strict interpretation.

I more meant that it drifts outside the usual recover area so you never even find it... But good points about inspection.

 

[Handeman]

I think you should fly the rocket you want for your cert flights. Don't listen to the nay-sayers about low altitudes, small motors, etc. If it doesn't work out, you learn something and try again. There is nothing wrong with failing an attempt. It happens all the time and the world hasn't ended yet.

The way I did mine was completely against all the TRF "wisdom". I scratch built the whole thing from mailing tubes, including a homemade nose cone, rolled my own av-bay tube, and used DD. After years of flying AT Hobbyline, I used my first Loki snap ring case with a I110 moonburner to 4200 ft. for the cert. It all worked out, but if it hadn't, I would have just picked up the pieces and tried again. Not a big deal.

If a failed L1 attempt is that much of a big deal, you probably should find a new hobby.

Just my opinion...

 

[bad_idea]

I completely agree with @Handeman A cert flight is just another flight. If you have problems with it, fix those problems just like you would with any other failed flight. If you want to fly high on big motors, fly high on big motors. That's pretty much how I flew L1 (including having problems, fixing them, and reflying later).

I will say if you're going to eschew "low and slow," invest in a tracker. I find it hard to track rockets when they get smaller than 1 or 2 arc minutes in anything but a perfect sky.

 

[OzHybrid]

Fly what you want, however....
Cloud comes in at about 5000ft and can affect the ability to be able to launch. If you cannot launch, you cannot certify. Once you certify you can launch what you want. High, low, whistling dixie... Don't let the go for it brigade push you into doing something that has a higher chance of failing.
It's your choice. Your risk. It can be very expensive going to a launch in the middle of nowhere multiple times and not being able to launch due to cloud.
Once youve cert'd you would probably attend a launch with multiple options, just in case. Before then, you tend to only have a single ootion cert rocket that may not be able to be launched.
My 5c ( inflation)

 

[bad_idea]

Cloud comes in at about 5000ft and can affect the ability to be able to launch. If you cannot launch, you cannot certify.

That's a good point. Depends where you are, and what your goals in flying are. I am fortunate to have a high power launch scheduled within a three hour radius just about every weekend, so weather's not a huge factor when I'm designing rockets.

 

[tsmith1315]

Fly what you want, however....
Cloud comes in at about 5000ft and can affect the ability to be able to launch. If you cannot launch, you cannot certify

Indeed. I’m considering building a quickie large diameter backup rocket in case of low ceiling on cert day.

 

[Handeman]

Fly what you want, however....
Cloud comes in at about 5000ft and can affect the ability to be able to launch. If you cannot launch, you cannot certify. Once you certify you can launch what you want. High, low, whistling dixie... Don't let the go for it brigade push you into doing something that has a higher chance of failing.
It's your choice. Your risk. It can be very expensive going to a launch in the middle of nowhere multiple times and not being able to launch due to cloud.
Once youve cert'd you would probably attend a launch with multiple options, just in case. Before then, you tend to only have a single ootion cert rocket that may not be able to be launched.
My 5c ( inflation)

Norman,

I guess I'm in the go for it brigade!

I do understand where you're coming from and don't disagree with your point. Someone that has bought their L1 cert motor already is pretty much locked into a flight profile and whatever altitude they will reach and the recovery designed into the rocket. Field conditions can certainly make or break that flight. Not just the cloud level, but surface wind speed, winds aloft, and wind direction, depending the field configuration. Definitely something an aspiring L1 candidate should consider. It is also something they will learn a lot more about as they start flying motors in their cert level.

I don't know the travel requirements in Oz, but here in Virginia, I have 4 - 5 fields within a 3 hour drive, that can be a long day trip, so travel expense isn't too bad on the east coast. That may be quite different west of the big muddy and where you are. It's not something I think about much but can certainly be a consideration.

As far as doing something with a higher chance of failure, I don't think that should be a primary concern. I think that is kind of subjective and depends mostly on the rocketeer. Some fly low and slow and still take 3 tries, other use a large motor, new electronics and personal best altitudes and cert on the first try. I think it is more about the rocketeer than a type of rocket and flight profile.

Just brigadethink!

 

[bad_idea]

Indeed. I’m considering building a quickie large diameter backup rocket in case of low ceiling on cert day.

When I was trying once to design a rocket to fly on the widest feasible spread of alphabet motors, I considered a removable ring fin and a ballast bay to add drag and mass and still maintain roughly the same stability. I never ended up pursuing that rocket, but it would be a way to keep a high-flyer down a bit.

 

[OzHybrid]

Norman,

I guess I'm in the go for it brigade!

I do understand where you're coming from and don't disagree with your point. Someone that has bought their L1 cert motor already is pretty much locked into a flight profile and whatever altitude they will reach and the recovery designed into the rocket. Field conditions can certainly make or break that flight. Not just the cloud level, but surface wind speed, winds aloft, and wind direction, depending the field configuration. Definitely something an aspiring L1 candidate should consider. It is also something they will learn a lot more about as they start flying motors in their cert level.

I don't know the travel requirements in Oz, but here in Virginia, I have 4 - 5 fields within a 3 hour drive, that can be a long day trip, so travel expense isn't too bad on the east coast. That may be quite different west of the big muddy and where you are. It's not something I think about much but can certainly be a consideration.

As far as doing something with a higher chance of failure, I don't think that should be a primary concern. I think that is kind of subjective and depends mostly on the rocketeer. Some fly low and slow and still take 3 tries, other use a large motor, new electronics and personal best altitudes and cert on the first try. I think it is more about the rocketeer than a type of rocket and flight profile.

Just brigadethink!

Australia,
The NSW HPR launch site has 2-3 launches a year-5 1/2 hour drive from Sydney 14,000 AGL limit. Can get cloudy but not often. The Victoria site is a 10 hour drive from Sydney 4-6 launches a year 25k max. Suffers regularly from cloud issues, had to cancel my L2 once and my L3 once. ( before we got the NSW site) WA site is a flight away plus shipping to the site. etc. it's like living in NY and launching in LA as your best option. Same distance......

Fully for people doing what they want to do, just make sure you can do it, and that includes the logistics which frequently get forgotten in the race to space.
My lucky chums in the US have a lot more options, but, y'know, make sure you think all your options through.
Norm

 

[Saint_Tiki]

A "cert flight is just another flight" only really applies to those of us that have done it and aren't under the pressure of trying to cert ;-) I agree but that is said with perfect hindsight on this side of the process, not the (self-induced) pressure of trying to be successful bearing down on you. My recommendations were merely things that can help increase the chance of success on the first try and hopefully reduce some of that pressure. If your launch site has a motor vendor, immediately go buy a motor after your cert and launch it as high as you like.

Regardless of the "safe and easy" versus "do whatever you want on your cert" debate, I don't really think an apogee of 2800 feet with motor deploy and no chute release is a good plan on any flight, cert or not, unless you like chasing your rocket across the state or fishing it out of the trees.

 

[thzero]

Build the rocket, be safe, fly the rocket, be safe!

 

[Scott Tung]

Hi guys, I have my final design here, crossing fingers and building it tomorrow

 

[86mustang408w]

I like it, I'm putting together my first L1 build now, well planning it for 10 years. But picked out everything pretty scratch from Rocketryworks, then Amazon and a few other places. Laid it out last night and out it into OpenRocket(which I'm still reading). My heads been spinning with info, I got back into this about 5 weeks ago and just said one Alpha III kit, and a few motors. Goimg to get my good collection hopefully 2morrow. So that will be a thread I'm happy to share. Gonna open the holy grails from 10 years ago, several unopened Estes Pro-Series II kits, Aerotech G-Force, etc its in my signature. But ill be watching!!

 

[OzHybrid]

I like it, I'm putting together my first L1 build now, well planning it for 10 years. But picked out everything pretty scratch from Rocketryworks, then Amazon and a few other places. Laid it out last night and out it into OpenRocket(which I'm still reading). My heads been spinning with info, I got back into this about 5 weeks ago and just said one Alpha III kit, and a few motors. Goimg to get my good collection hopefully 2morrow. So that will be a thread I'm happy to share. Gonna open the holy grails from 10 years ago, several unopened Estes Pro-Series II kits, Aerotech G-Force, etc its in my signature. But ill be watching!!

Rearward facing fins reduce your chance of examination success. Breaking a fin is a fail. Rearward fins fail more than non rearward facing fins. You can reduce the chance of breaking by using fiberglass or CF.

Good luck with your flight.

 

[86mustang408w]

Im building a L1 for a H motor, but got to my old collection yesterday. Now have a MDRM, Aerotech G-Force, Mercury Enginering Integrator, and a few more. My choices just got bigger!