2 stage Quest Bright Hawk

[ronhill]

Attached is a pic of a custom designed 2-stage Quest Bright Hawk. Hobby Lobby had their 50% sale on rockets a couple of months ago so it made sense to buy two. The original kit is designed so no finishing or painting are required, but once the weather improves, I plan to do it up right. It’s just plain ugly without paint.

There is no stage coupler. I recessed the upper stage body tube forward in the upper stage fin can so the lower stage body tube slides into the upper stage can. It’s a tight fit so I’m still sanding down the BT. It uses “pop and go” staging, but the two engines are in contact so I could tape them also. I’m debating that point. Any ideas on whether taping combined with pop-and-go is really necessary?

I don’t know if it’s stable. I’d guess that it’s not stable (any thoughts on that?), and I’ll likely have to add some nose weight. I will RockSim it but measure the CG directly with engines in place.

 

[the unknowen]

being a two stager yes i would add a little nose weight
you could also do a swing test just to make sure it stable

looks good though

 

[Fore Check]

HMMmmm....

On the stability thing.

You *are* doubling the weight of the engines (more or less) which will move the CG further aft. However, you are also doubling the fin area. If I was guessing, I'd say the CP is within an inch or two of the leading edges of the sustainer fin can.

 

[powderburner]

Come on guys, this IS supposed to be rocket science. It is NOT supposed to be trial and error.
At the risk of sounding like a lecture (which it probably is anyway), this is exactly the kind of thing that should be checked pre-flight (or even pre-construction) by cardboard cutout, or by Barrowman equation (they are posted free on-line, you don't even have to buy a copy of Stine's handbook or anything), or by using the free on-line trial version of rocsim.
There is no reason to have to doubt whether your design will be stable. None of these calculations require anything more than grade-school-levels of intelligence (because grade-school kids can DO them). Put your rocket away, and get your pencil out!

Whew, I feel better now.

 

[ronhill]

Thanks for the replies. This does look like it's going to be fun.

Powerburner: Note my last paragraph in which I said I will RockSim it. I've had version 8 since it came out and use it religiously on all scratch-builts. My query was to simply get folks talking about it. You're right that it is easy to do the calculations, but there is some joy in speculating before running the numbers.

Ron

 

[powderburner]

ron,
I am sorry, you are completely correct. You did clearly mention running a stability sim in your first post and I missed it clean.
I think I 'lumped' your notes into a category of other posts that I see way too many of: someone wants to modify a rocket or design his own, doesn't have a clue how to do this safely, but is charging full steam ahead anyway and intends to use live testing (sometimes even with high-power motors) to find out. You can see that I am greatly concerned about the safety (or lack thereof) of this approach.

 

[ronhill]

Powderburner,

That's not a problem at all. I fully understand and agree with your ideas. We've all seen the approach employing "let's see if it works" and had to duck to avoid the consequences. We didn't even have an excuse in the early 1960s--there were tools even in those days to check stability. I cut out a lot of profiles in cardboard!

Your concern is well justified.

Now that I'm back from all my travels, I'll run the sim and let everyone know how it works out.

Ron

 

[Balltip]

Hello! Just curious... Have you gotten round to run any sims? Me for one would like to know what data you might have come up with.

Per

 

[ronhill]

Originally posted by Balltip
Hello! Just curious... Have you gotten round to run any sims? Me for one would like to know what data you might have come up with.

Per

I sure did. With a C6-0/C6-7 combination, it has a stability margin of 1.41 with an altitude (with a bit of wind) of about 1,600 ft. That's with no nose weight.

But I don't quite trust those figures, and I'm going to do some weighing in the next few days and enter the data in the mass/CG override portion of Rocksim. While I think I sim-ed it fairly well, I know I didn't get the mass of the plastic fin cans right. They're heavy and will shift the CG aft. Further, I'm usually heavy on the adhesives in building. It's also best to do the final weight and balance after the paint is on. Once I get the mass/CG data entered, I'll give you another report.

By the way, the fin cans are intentionally upside down to shift the CP a bit more aft.

If the Ohio weather is agreeable today, I plan to prime it. I may be able to paint it (orange and white) later in the week. Next weekend is our scheduled launch so perhaps it will fly then--likely with a B engine in the upper stage rather than a C engine.

 

[ronhill]

Originally posted by Balltip
Hello! Just curious... Have you gotten round to run any sims? Me for one would like to know what data you might have come up with.

Per

Per,

By the way, I visited Sweden a few years ago on a joint Swedish Air Force-USAF technology tour. It's a beautiful country with lots of friendly people. Got to see the new (at least it was new then) JAS-39 Gripen up close and personal.

We also took an excursion to a locale north of the Arctic Circle. It was impressive during the summer. Glad I wasn't there in winter.

Ron

 

[doug_man_sams]

Originally posted by ronhill
I sure did. With a C6-0/C6-7 combination, it has a stability margin of 1.41 with an altitude (with a bit of wind) of about 1,600 ft. That's with no nose weight.

But I don't quite trust those figures, and I'm going to do some weighing in the next few days and enter the data in the mass/CG override portion of Rocksim. While I think I sim-ed it fairly well, I know I didn't get the mass of the plastic fin cans right. They're heavy and will shift the CG aft. Further, I'm usually heavy on the adhesives in building. It's also best to do the final weight and balance after the paint is on. Once I get the mass/CG data entered, I'll give you another report.

A couple of points: It's good you plan to re-sim with actual mass figures. The estimated numbers can be all over the place.

The important data for now are the CP's: both the 2-stage and sustainer figures. Keep in mind that the CP and CG will both shift forward at staging. Some rockets can become unstable then, so you need to allow for that, although it's more typical with large finned boosters. In your case, my swag is that it gets more stable after staging (since the booster fins are no larger than the sustainer fins).

All you need for stability checking is the CP's. Once you start prep'ing for flight, you can balance the rocket - both single and 2-stage configurations - on your finger to determine the CG and hence the stability margin.

I like to mark both the Rocksim and Barrowman CP's. That way, I have a range of comparison. If the Barrowman margin is a little tight (eg, 0.85 calibers) but the Rocksim is good (eg, 1.5), then I won't worry about noseweight.

Once you know the CP's, and have done the finger balancing, you know whether it's stable. After that, the main thing Rocksim tells you (via simulation) is how long the sustainer delay should be so that you don't strip the chute or zipper the airframe.

I usually look at rod speed, too, just in case I'm flying something heavy that might be slow off the rod. Using the wind input to estimate landing spot doesn't do much good until you know the wind speed/direction, and you won't know that until you're at the field, at which point it's highly unlikely that I'm running sims.

The chute sizer/descent rate estimator is also useful.

I've gotten kinda OT here, but my main point is that you only really need the CP for stability. Your finger is as good at finding the CG as any computer.

Doug

 

[Balltip]

Hey Ron!
Living on the west coast of Sweden, this time of the year usually means above freezin', almost no snow or no snow at all. This morning it was 20 centigrade below, and even though it is clear skies outside at the mo, snow is still falling...
I don't see where it comes from!

And on behalf of all us Swedes I'd like to say "Thank you!" for your kind words about this little country!

Per

 

[ronhill]

Doug,

Excellent points. Thanks for the observations and guidance.

You're absolutely right about the CP. That's not going to change regardless of the mass distribution, and Rocksim pegs that well. It's just a simple matter of balancing the determine the CG yielding the distance between the measured CG and the calculated CP.

I got a little obsessive because moments of inertia can play a part, but it's probably negligible in this case. I'm suffering from a a classic case of "cutting it with an ax and measuring it with a micrometer."

I used used the Rocksim CP for the 1.41 margin, but I have taken a look at the Barrowman CP. Barrowman does, indeed, appear to be more conservative, i.e., indicating a lesser degree of stability.

The 7-second delay worked surprising well for the C/C engine combination. I've zippered a few in the past.

We've got a very soft field so I use a streamer if at all possible. That portion of RockSim is fun to play with.

Again, thanks for the thoughts.

Ron

 

[ronhill]

Originally posted by Balltip
Hey Ron!
Living on the west coast of Sweden, this time of the year usually means above freezin', almost no snow or no snow at all. This morning it was 20 centigrade below, and even though it is clear skies outside at the mo, snow is still falling...
I don't see where it comes from!

And on behalf of all us Swedes I'd like to say "Thank you!" for your kind words about this little country!

Per

Per,

One of my fellow researchers introduced me to Sweden. He'd lived there all of his life before taking a sabbatical in Texas. I fell in love with Sweden while he opted to stay in Texas forever! At least I know he's warm in Texas while I'm shivering in Ohio.

Ron

 

[Balltip]

Originally posted by ronhill
Per,

One of my fellow researchers introduced me to Sweden. He'd lived there all of his life before taking a sabbatical in Texas. I fell in love with Sweden while he opted to stay in Texas forever! At least I know he's warm in Texas while I'm shivering in Ohio.

Ron

Ron! I am not gonna turn this into a debate about weather, but I really can't hold myself back...
In the summer of -94 the world championships in track and field were held in Gothenburg. It was a really hot summer - so hot that the brazilian tv team reported back home that "this is a lovely place but don't go here in the summer because it is awfully hot!"
LMAO!
(Just to clarify to all of you who hasn't been here in the winter I can tell you that right now it's freeeeeeezing outside, and that about every other summer seems to be nothing but 3 months of rain...)

OOOWWWW!
What?! Oh that was just me putting my fingers in the socket to jolt myself back on track....

Ron, I am really looking forward hearing about how that staged Bright Hawk performs. It looks like a very good idea to me as I do happen to fly some over frozen ground at the mo. Balsa or basswood ain't as tough as those plastic fin cans. And in the "...BAD rocket kits...." thread I got warned about the Moon Goose having weak body tubes.
So here there might be something for Quest to consider as a kit? If so, I'd buy one! (But until then I'll just wait 'til I hear how this turns out, and then get myself a pair of Bright Hawks!)
How about calling it "Dual Hawk"?

Per

 

[ronhill]

Per,

Sounds like Dallas--hot in the summer and cold in the winter--the best of all possible worlds. All I recall is that August in Sweden was mild during the day and cool at night. Farther north it was cool during the day and cold at night. Of course, the saunas and the heavy partying north of the Arctic Circle made that quite pleasant. The Swedish Air Force knows how to entertain!

From now on it's called the Dual Hawk. The only thing unique about the design is the way the lower stage body tube slides into the upper stage fin can--about 0.75 inches. It took some sanding to make it slide smoothly. I'll send pictures of the parts when it's all painted. That feature occurred simply because I couldn't find a stage coupler to fit. I'm concerned that the ejection debris from the departing lower stage will damage the naked inside of the upper stage fin can, but that's a small issue.

Plastic film cans are quite useful. I sometimes buy rockets just for the can--the one-pieced cans, not the glue together cans. Fin cans are being discussed in another thread now. We all have to finish wood fins, but plastic has some major advantages. Too bad there is not an affordable source of various diameters.

I'm afraid there was no painting today. But the weather is supposed to be reasonable later this week.

Ron

 

[ronhill]

Per,

I loaded up everything and measured the CG. It actually improved (was more forward) over the RockSim calculations. The margin is about 2.0. No nose weight is required.

I've only primed it because the weather has been disagreeable for painting. It won't fly this weekend even if the weather is good.

Ron

 

[Balltip]

Good to hear! Will be great hearing 'bout how it flies once you get round to that!


If I spray paint anything this weekend, then it will be in the basement. Too cold outside... And if I do, the fumes will only spice up the weekend a bit

Be safe!
Per

 

[ronhill]

Originally posted by Balltip

If I spray paint anything this weekend, then it will be in the basement. Too cold outside... And if I do, the fumes will only spice up the weekend a bit

I've gotten very close to doing some limited spray painting in my basement when it's cold, damp, and ugly outside. I've read all the articles about buidling a simple spray booth with an exhaust fan ducted through the window, but that requires a lot of time and room.

 

[ronhill]

Per,

Here is the completed Dual Hawk. We had a couple of decent days in Ohio this week.

The finish came out quite good although it's hard to tell it in this photo. It has a couple of the obligatory cat hairs embedded in the white paint. Of course, in my house cat hair is in or on everything.

The conventional wisdom is "warmer is better" for painting, but for the last month or so, between 40 and 50 degrees F has produced some excellent paint results--deep, smooth finishes and no running. Maybe it also has something to do with the low humidity.

I may opt to junk this up with some white trim (stick-on monokote) on the fins and/or a band of orange near the top of the fuse, but simple may be better in this case.

Our next launch dates are Saturday and Sunday. If one can trust a 5-day forecast, it will get a test flight.

Ron

 

[ronhill]

Well, I was sure the photo was attached to the last message, but here's another attempt.

 

[Balltip]

Hey, that looks good!
And when it comes to cat hair I don't know a thing. But try dog hair...

I really like the idea of plastic fin cans so this might be my next project. I just want somebody else to do the test run first

Per

 

[Balltip]

Ron, any news? Just qurious...

Per

 

[ronhill]

Originally posted by Balltip
Ron, any news? Just qurious...

Per

Per: Not yet, but the weather this weekend sure looks good. I'll get it off either Saturday or Sunday.

 

[NUBlackshirts]

Ron-

I feel your pain on the pet hair issue....try 2 cats and a dog. I paint my rocs outside, but bring them inside to dry. At that point, all bets are off.

 

[ronhill]

Originally posted by Balltip
Ron, any news? Just qurious...

Per

I'm about to do some traveling, but I wanted to give you a brief report. The flight was perfect. I used a C6-0/B6-6 combination, and it was just about right. There was little wind, and the flight was straight with no tip off at staging. It made a nice, loud pop. It certainly went higher than I expected.

I wish all of my flights today went as well at the Dual Hawk.

Ron

 

[ronhill]

Originally posted by NUBlackshirts
Ron-

I feel your pain on the pet hair issue....try 2 cats and a dog. I paint my rocs outside, but bring them inside to dry. At that point, all bets are off.

There is a little cat fur in every one of my rockets!

 

[ronhill]

BTW, the gases from the lower stage did smudge the inside of the plastic fin can of the upper stage, but it was easy to clean out. Didn't seem to melt the plastic at all.

A streamer sure worked well especially with the tough plastic fins.

I'll use a C6-0/C6-7 combination if the winds are agreeable at the next launch?

Ron

 

[Micromeister]

OH man every time I hear someone talking about a Brighthawk, I immediately think of the North Coast rocketry Brighthawk. Particularly my converted BrightHawk. I don't fly AP so I clustered the model into a 5 D12 Large model rocket, Added some LEDs and other stuff as a Great Night flyer.
Quests is a very nice model and I'm sure your gonna have a great time flying and finding it and it's booster... but I can't help but take pause whenever I hear the name to think about this Great flying Bird. It likely would have been great fun Staging it also but I'm more the cluster freak

Sorry for the interruption I'll return you now to your program in progress

 

[ronhill]

Micromeister ,

Thanks for giving us that perspective. Rocket names get recycled, but your pics sure present a mighty interesting model. The Quest model is about as simple as they come, but I agree with you--clustering is a real pleasure.

Ron