How to lower expected apogee?

[GottaGoFast]

Hi y'all

I'm planning on flying a Level 2 in the next few months, but the rocket i've been designing and building is simed to go to 4000ft AGL. This is no good since the field closest to me has a waiver of up to 3000ft. I can drive the 3.5 hrs up to a field with a 10kft waiver but gas is expensive.

I was planning on 3d printing my nosecone and some E-bay parts, I was already going to reprint them to be heavier and make a flat top nosecone to increase drag. This gets me to about 2850ft but I would like to bring it down further incase there is wind that day.

Does anyone have any tricks they have tried and used? I've thought about attaching some streamers to my fins but I think they would count as flight critical and would need to survive the flight.

 

[Steve Shannon]

Make the nosecone bigger diameter.

 

[dhbarr]

Drag plate, doesn't even have to be permanently attached. Use the base drag hack for your sim. Won't be super accurate, but should keep you in the ballpark.

Depending on your motor choice, either more or less weight could be helpful, but heavier means more recovery gear and a higher chance of damage on landing.

 

[kjhambrick]

@GottaGoFast --

What @dhbarr said ... see @Rschub's Thread: Minnie-Magg drag mods for Level 2?

It's an ingenius gadget and he might have some additional recommendations after his L2 Flight ?

-- kjh

 

[tsmith1315]

It's an ingenius gadget and he might have some additional recommendations after his L2 Flight ?

I’ll be curious to hear how much effect they had.

@Rocketjunkie did some great field work using drag plates. This particular post in his thread outlining his results really demonstrates the extreme effect of drag on a single rocket/motor combination. (Hint: 85%)

https://www.rocketryforum.com/threads/variable-drag-project.157027/post-2320053

 

[kjhambrick]

Thanks for the Link Tim !

That'll cost me another day

-- kjh

 

[thzero]

Build a different rocket?

 

[Rschub]

@GottaGoFast --

What @dhbarr said ... see @Rschub's Thread: Minnie-Magg drag mods for Level 2?

It's an ingenius gadget and he might have some additional recommendations after his L2 Flight ?

-- kjh

I am waiting for the parts to be shipped, my printer had a delay. Still have time, our next launch is 8/27.

 

[ljwilley]

look at this thread about drag plates!!
Variable Drag Project

 

[Rschub]

look at this thread about drag plates!!
Variable Drag Project

Yes, that thread was the inspiration for my project.

 

[kjhambrick]

Yes, that thread was the inspiration for my project.

@Rschub --

Yes, Tom Binford's tube fin project with variable numbers of drag plates is ground breaking.

I am still absorbing that thread ... but I like the look of the flight profiles in his videos -- I can definitely see where the rocket slows very quickly after the motor burns out.

I would sure like to see the flight data from a logging accelerometer

What I like about your approach is that you are retro-fitting air brakes to your existing Mini Mag and that the air brakes can be removed if you ever want to fly smaller motors without them or fly higher or ...

Good luck with your L2 flight whenever it can happen and please let us know how it goes !

-- kjh

 

[JoePfeiffer]

Build a different rocket?

That's certainly the most fun answer!

 

[tsmith1315]

What I like about your approach is that you are retro-fitting air brakes to your existing Mini Mag and that the air brakes can be removed if you ever want to fly smaller motors without them or fly higher or ...

Exactly!

If your ceiling drops and you still want to fly, this would be a simple adjustment. Not everyone’s budget allows a stash of motors for all occasions.

I’m working up an alternate L2 rocket for this purpose. Larger diameter, low & slow. But a set of plates or rings added to the rocket that’s already been built would be a much more convenient and less expensive option.

 

[Back_at_it]

Add weight or increase drag. I built and flew a Warlock for my level 1 and have extended it to fly for my level 2. In all, I've added a touch over 4 lbs to the rocket so that will help kill some altitude.

You could also add drag by attaching flat pieces to the trailing edge of each fin. I've seen this done with 1/4" plywood strips that were 1.5" wide screwed to the trailing edge of a T-LOC. My buddy got his level on a J435 and flew less than 1000ft.

 

[86mustang408w]

You could add weight... Some guy build a 3D fin jig that would be great to add drag. I wish I had that picture....

 

[GottaGoFast]

@dhbarr @Rschub @tsmith1315 @kjhambrick

Thanks for all the answers guys, I'm part of the rocketry club for my university and I'm trying to get my L2 to help us get to competition. I leave my rockets fairly modular to allow for **** like this. COVID left our club pretty ravaged and I'm the only member with a cert and I'm L1. There is a field "near" me that has a 10kft ceiling but that's 250 miles one way. RIMRA is only 100 miles away from me but they have a 3kft ceiling.

Both Nosecone and AV-bay have 3D printed parts and I have been re-printing them much heavier, Nose cone went from 150g to 400g including an Eggfinder GPS tracker.

I'll take a look at the drag plate, I was trying to stay away from airbrakes since I don't know how they would interact with my fins, and the last thing I want is the thing to go sideways after it leaves the rail. But if I implement it I'll be more than willing to give out the data.

I have a homegrown flight computer I plan on flying on this rocket one day so when that happens I should be able to characterize a Cd for it.

Edit: Now that I'm working on the AV-bay I have a 1/2in hole for a camera, will this affect my vent holes, I saw someone mention that static/vent holes can be oversized

 

[Buckeye]

Edit: Now that I'm working on the AV-bay I have a 1/2in hole for a camera, will this affect my vent holes, I saw someone mention that static/vent holes can be oversized

I don't think the big hole is a problem for the altimeter. I did the same.

https://www.rocketryforum.com/threads/corrupt-video-file-from-runcam2.153842/post-1904071

 

[GottaGoFast]

I don't think the big hole is a problem for the altimeter. I did the same.

https://www.rocketryforum.com/threads/corrupt-video-file-from-runcam2.153842/post-1904071

Ironically I'm using a RunCam too. I have the RunCam Split 3 Lite, bought one of the last in stock when they discontinued it. I plan on getting some split 4's soon.

 

[OzHybrid]

[USER

Edit: Now that I'm working on the AV-bay I have a 1/2in hole for a camera, will this affect my vent holes, I saw someone mention that static/vent holes can be oversized

An oversize vent hole can lead to false apogee triggering with older flight computers. Most modern ones will be ok. Check with the manufacturer rather than relying on people's anecdotal advice. They designed it and know the capabilities. The larger hole creates buffeting just like you get if the drivers window is open fully, but you don't get it if all the windows are open just a little bit. This is why there are recommended quantity and sizes of vent holes for a given AvBay volume.
Additionally, the barometric sensors are very sensitive to sunlight. They only have a tiny hole in them for pressure sensing, but if sunlight hits that hole you could have a deployment accidentally. With a 1/2 " hole, you have a larger chance of this and if it lets sunlight in and hits the hole, mystery altitude gets hit..... This is a known issue and why manufacturers don't print a shield over the sensor, is beyond me. Or design the board so it's on the underside and cannot see the sun.

You say you plan to build your own flight computer. You'll need to be able to filter that buffeting out.

 

[Buckeye]

An oversize vent hole can lead to false apogee triggering with older flight computers. Most modern ones will be ok. Check with the manufacturer rather than relying on people's anecdotal advice. They designed it and know the capabilities. The larger hole creates buffeting just like you get if the drivers window is open fully, but you don't get it if all the windows are open just a little bit. This is why there are recommended quantity and sizes of vent holes for a given AvBay volume.
Additionally, the barometric sensors are very sensitive to sunlight. They only have a tiny hole in them for pressure sensing, but if sunlight hits that hole you could have a deployment accidentally. With a 1/2 " hole, you have a larger chance of this and if it lets sunlight in and hits the hole, mystery altitude gets hit..... This is a known issue and why manufacturers don't print a shield over the sensor, is beyond me. Or design the board so it's on the underside and cannot see the sun.

You say you plan to build your own flight computer. You'll need to be able to filter that buffeting out.

It is not a gaping 1/2" hole. The camera lens fills most of it, flush to the airframe, mitigating some of the wind and sun effects. I also use 2 additional "normal" sized holes in the ebay for pressure equalization.

Most baro sensors are indeed on the bottom of the board - RRC3, SLCF, Raven - to name a few.

 

[OzHybrid]

It is not a gaping 1/2" hole. The camera lens fills most of it, flush to the airframe, mitigating some of the wind and sun effects. I also use 2 additional "normal" sized holes in the ebay for pressure equalization.

Most baro sensors are indeed on the bottom of the board - RRC3, SLCF, Raven - to name a few.

Not everyone is using the latest and greatest, which makes it better to check that the barometer port is not facing the sun.
The latest MARSA33 is on the side with the connector which would tend to be the front. BPS on the front. I'm certain there are others. So not everyone is putting it on the back in their new production.. Then there are the people who want to make a flight computer and don't know what they don't know. So your blanket statement that most are on the bottom, may or may not be true but by stating that you may mislead people.

As the OP is asking for information, the why is important. Once they know that, they can make a decision.

 

[GottaGoFast]

Here Is the front and back of the Av-Bay, Right now I have a SLCF on top and an RRC2+ on the bottom. The big rectangular hole is what I call the Computer Control Housing (CCH), the only reason I have it right now is for future flights with my custom computer since I plan on having a Diagnostic port for it in the CCH.

The CCH has a cover panel and a TPU gasket just for ***** and giggles really. I doubt it would have any effect, but this will be my highest and fastest launch (4000ft AGL, 420mph), I figure I should pull out all the stops on my design.

As for the hole in the back, I could always try to shove a Film over it to prevent buffeting. But as @Buckeye said, the camera is going to be right next to the hole, about 1-2 mm back for clearance for my sled to slide in. The camera should act as enough of a baffle to reduce buffeting in my opinion.

I'm doing my final revisions so the Camera Port is likely moving up and to the right so I planned on dropping three 1/8 in static ports around the center of the AV bay. The total volume is around of the AV bay is 68 in^3. That is a 2.88in internal diameter and 10.5 in long internal length (bulkhead to bulkhead). Online calculators say that three 1/8 in ports are right on the upper end of what I need.

Also @RocketScientistAustralia, my altimeters are up and away from the ports on the vehicle so I should be okay from sunlight, but that is a good fact to know going forward, never even considered that.

 

[OzHybrid]

If it sits 1mm back you have a cross-sectional area of 1*12.7*3.14 which is the equivalent of a 7mm hole if it's 2mm that's the equivalent of a 10mm hole. So still a big opening. It's a small gap, but a big cross-sectional area because the gap is at a large diameter.
It may be no problem. Ask the altimeter manufacturer, or isolate the camera more with a U of EVA foam on the inside of the coupler for the camera to mate to and a U of EVA around the camera on the opposite side to slide into the other. Let me know if you need clarification.
You're not going fast enough to melt anything. Good luck with the flight.

 

[techrat]

FInd a bigger piece of tube and make a ring fin for your rocket. Adds a ton of drag, and makes your rocket more stable as well.

 

[GottaGoFast]

If it sits 1mm back you have a cross-sectional area of 1*12.7*3.14 which is the equivalent of a 7mm hole if it's 2mm that's the equivalent of a 10mm hole. So still a big opening. It's a small gap, but a big cross-sectional area because the gap is at a large diameter.
It may be no problem. Ask the altimeter manufacturer, or isolate the camera more with a U of EVA foam on the inside of the coupler for the camera to mate to and a U of EVA around the camera on the opposite side to slide into the other. Let me know if you need clarification.
You're not going fast enough to melt anything. Good luck with the flight.

I can throw some bulkheads to isolate the two computers and just drill static holes for each of them. I'll figure something out or just ground the camera for the first flight, I dont know yet. Thanks for all the info!

 

[OzHybrid]

Multiple smaller ports around the diameter are better than 1. If you get a gust of wind on the side you can get false triggering. But 1 can work. Watch out for a gusty day.
All of rocketry building is about knowledge and compromises. You use your knowledge to build the best you can.