Mega Mosquito help

Hi folks, first post here and feeling a little guilty immediately asking for some guidance...

I'm in the process of building the Mega Mosquito and I'm having an issue with the fin tabs mating with the motor mount. When I dry fit the fins they are all about 1/8" short of touching the motor assembly. I can determine this because when I attached the motor assembly inside the body tube, I only glued in place the upper centering ring and retainer ring (the ring that slides over the engine hook) with the engine mount tube. The lower centering ring was dry fit in place to align/support the motor assembly while the upper CR glued. (geez I hope I have these acronyms right)

Anyway, since I have access to the fin tabs I can clearly see a 1/8" gap between all three fin tabs and the MMT. The gap 'steps' with the notch in the tabs to accomodate the retainer ring.

I can also tell that the fin tabs are touching the upper CR and will also contact the lower CR. My question (finally!) is this: will the fin tabs not touching cause an issue during flight? I'm worried about properly supporting these heavy fins. I can put fillets inside and outside the BT and I can fillet the fin tabs to the upper CR, but should I try to get something between the motor assembly and the fin tab? If so, what type of material (i.e. epoxy) would be structurally sound while spanning that distance?

Thanks
Matt

Hi, and welcome to the forum.

You can sand or use an xacto knife to trim down the root edges of the fin that will be glued to the airframe. Go a little at a time until the tab touches the motor mount tube.

...Fudd

1) Welcome to the forums
2) I'd suggest gluing some "strakes" to the MMT (Motor Mount Tube). These strakes would be strips of balsa 1/8" thick that would compensate for the gap, then you'd dry fit each fin (number them, and the slot it fits in), and shave any excess from the bottom of the fin tab. Once the fins fit, glue them in, and create some epoxy fillets for the internal joints. It might not be the absolute strongest fins you could have, but it allows you to use what you have. Bob's your uncle.

[EDIT] In reflecting on this, I'd change my suggestion to gluing stips of 1/8" thick balsa to the bottom of the fin tabs, and then shave away what is needed to get the fins to fit properly... Still do the internal fillets.

To strengthen the assembly further, try papering the fins. I have a tutorial on a method that is IMHO foolproof.

Fuddrucker said:

Hi, and welcome to the forum.

You can sand or use an xacto knife to trim down the root edges of the fin that will be glued to the airframe. Go a little at a time until the tab touches the motor mount tube.

...Fudd

Click to expand...

I've built 4 of these in the past year and I agree that sanding or using a knife to cut away the root edge is the key to getting the tabs long enough. If you have a palm sander that would make it go faster than sanding by hand, and still be slow enough that you don't overdo it. Of course if you DO overdo it slightly you can always shorten the tabs.

Definitely put glue fillets inside all around all edges of the fin tabs.

When I built mine, I was lazy and used 2 pieces of balsa from the outer fin frame to put a piece on each side of the fin tab to the motor mount.
breaking off the frame

Cut to length

Glue in Place on either side of the fin tab after insertion through the body tube. Body tube left out for clarity.


Lucky for you I have one in the build pile.

I also have made one of these this year, and found the same issue... tabs not being glued to the motor mount tube. (I also was concerned about the layers of the fins not lining up, so I made the outer edges of the fin match, and let the tab be uneven. Later I was told that was the reverse of what I should have done.)

As a result, having not done one of these before, I glued in both the top centering ring and the bottom centering rings, positioned exactly right at the top and bottom of the slots in the body tube. I was able to drip glue down a stir stick from the top(throat) of the body tube after the fact, to create a fillet on the top centering ring.

Several people suggested drilling holes carefully in the centering rings to dribble glue down the tabs to create fillets where the fins impacted the motor mount. But after some deliberation, I opted to redouble my fillets between the outer body tube and fins as there was a gap there. Though some told me I wanted to glue everything to everything to make he most secure rocket possible, I decided drilling holes would introduce other weakness or flaws. And if necessary, I could do that later as well.

SO, I decided to hedge my bets. I finished the Mega Mosquito without gluing the fins to the motor mount. (But I also ordered a second Mega Mosquito to "do right" in case of the first one failing.) To my great delight, the first rocket has not failed with more than six flights on the D12-3. (Now the older hands at the club flight are urging me to skip an E-motor flight, and insert and F motor or something MUCH more powerful, but I'm aware of the internal construction and prefer taking smaller steps. Plus, they've got nothing to loose... they might enjoy a spectacular flight, successful recovery or not!)

So, I guess I'm telling you that it's possible to over-think these things, and that you CAN fly the rocket without having EVERY possible fillet or intersection glued. (I know that is contrary to the opinions expressed by others posting above me, but I've not found a problem yet...and I love my Mega Mosquito!)

Thanks everyone for the advice. As I am new to this forum I will share that I was very impressed with the quality of the guidance I received and how quickly commenters jumped in. You all have a great community here!

Now on to the path forward...

I considered the ideas of trimming/sanding the root edges, but I had concern about being able to maintain consistency around the entire fin. I wasn't confident I could sand the skins along the fin tab without creating other issues. The idea holds merit; it was more a matter of my own confidence/skill level that made me go against this option. I wonder if a small shoulder plane would help in that type of trim work.

I really liked the idea of the strakes, but when I started working this up I realized I wasn't going to get this dialed in to my level of satisfaction. The strakes have to be stepped to follow the pattern on the fin tab, which is not a problem if you get the strakes to the perfect thickness as a single piece prior to cutting and attaching. If the strakes are too thick (hint: mine were) then they need to be trimmed to meet the stepped contour of the MMT. This brought me back to trimming multiple planes that are dependent on each other for their final positioning along the MMT, which I just couldn't get right.

So after scrapping the work I did there I went with RochonRockets' 'lazy' fix. I used the scrap balsa to fit twelve runners. Four per fin, two per side, with each rooted to the MMT and standing independent of each other on the step in the MMT. With the fin tab inserted, it acted as a nice guide to get the position and alignment perfect.

So that's it. I'm really happy with the stability of the connection to the MMT. This fix did add a little bit of weight to the final product, but I'm not particularly concerned with that. Onward and upward!

Thanks again to all commentors, I learned something from each of you. Perhaps I learned the most from Kirk G, whose thoughts were echoed by my wife. I think her exact comment was "You're this obsessed with an $8 rocket?!?"

Crash-N-Burn,

I'm not convinced that I'm completely out of the woods yet. I haven't flown on any E's yet, and we'll see if those stresses come at a price.

It's not wrong to want to go slow and check out options with others before proceeding. I posted here on TRF several times as I proceeded and compromised what I chose to do. (This was my first slotted body tube construction, and I learned a bit... understanding how it's going to come together helps to anticipate and allows you to make improvements even while following the steps.)

Some have urged me to go faster....and experiment. ("There are no rules!") You can learn from your failures, if you can afford the replacements.

Anyway, have fun.

PS: I sped up the whole sanding process by borrowing my wife's orbital sander...and boy, with fresh sandpaper on it, it really makes short work of wood quickly!

Thickened epoxy is your friend.

mine flies nicely on E18-4s.
Rex

What kind of altitudes are you seeing with that motor Rex ? I kinda want to skip the D motor for first flight on mine.

aww, the little kids really enjoy the low and slow flights , at a guess somewhere between 900 - 1100'(probably closer to 900')/
Rex

Rex R said:

aww, the little kids really enjoy the low and slow flights , at a guess somewhere between 900 - 1100'(probably closer to 900')/
Rex

Click to expand...

Actually just about what Im looking for- what brand E18-4 'S - Im guessing whatever it is I choose- a short delay (3-4) is in order ??

Sorry for the hi-jack btw CNB

I *was* going to launch a Mega Mosquito at an outdoor wedding as a surprise to the guests on a Aerotech E15W-4. I bought two MMs, built one just quick and dirty, no sanding, no paint, to test and see how high, loud, and smokey it was. Then the plan was to finish the other one pure white with the names of the bride and groom, the date, etc. and shoot it at their kiss at the end of the ceremony.

Then they decided to call off the ceremony and do a court house wedding.

So... I'm stuck with 4 Aerotech E15W-4s and a couple of spare Mega Mosquitos that I don't care if I lose. Woo-HOO!!!

the Aerotech E18-4w is a reload for the '24/40' RMS motor case*, the E18 is also available with a 7 second delay(you do not want that for the mega mo) Aerotech also makes an E15, E20, and E30 in single use.
*other loads include the D9, D15, F12, F24, and the F39. the F24 will put the mega out of sight. the E18-4 is a popular reload, great for the heavier Estes birds that struggle on D12-3s(like the intercepter-e or the Big Daddy)
Rex

Yeah I only have a 29-3 Cessi case so Im stuck with Estes motors for now- To bad I cant shorten the delay on the pile of E9-8's I fly in the Magician lol

Has anyone contacted or heard from Estes about this being a design defect or just a limited number of defective cuts?

Mushtang said:

I *was* going to launch a Mega Mosquito at an outdoor wedding as a surprise to the guests on a Aerotech E15W-4. I bought two MMs, built one just quick and dirty, no sanding, no paint, to test and see how high, loud, and smokey it was. Then the plan was to finish the other one pure white with the names of the bride and groom, the date, etc. and shoot it at their kiss at the end of the ceremony.

Then they decided to call off the ceremony and do a court house wedding.

So... I'm stuck with 4 Aerotech E15W-4s and a couple of spare Mega Mosquitoes that I don't care if I lose. Woo-HOO!!!

Click to expand...

Are you suggesting that you might be willing to sell off your un-needed Mega Mosquitoes, or your E15W-4s?

Stan said:

Has anyone contacted or heard from Estes about this being a design defect or just a limited number of defective cuts?

Click to expand...

I think it has more to do with getting the sandwich stacked correctly. I think we all stacked it so the curved end was even on all of them instead of stacking it so the body edge was lined up. If I stick the core layer in the slots it reaches the motor mount on the one in my build pile.

Kirk G said:

Are you suggesting that you might be willing to sell off your un-needed Mega Mosquitoes, or your E15W-4s?

Click to expand...

The Mega Mosquitoes are built. One just glued together quickly for testing with no sanding or painting, and the other built with care the right way all the way to the primer stage, no paint yet.

But no, I'm not selling them. The E15W-4s will be used with a big smile on my face as I watch the rockets disappear. If I'm lucky enough to recover any I'll keep shooting them until I'm either out of Mega Mosquitoes or E15s.

RochonRockets said:

I think it has more to do with getting the sandwich stacked correctly. I think we all stacked it so the curved end was even on all of them instead of stacking it so the body edge was lined up. If I stick the core layer in the slots it reaches the motor mount on the one in my build pile.

Click to expand...

I was very careful about aligning the skins on the root edge of the core fin, which led to some overhang on the curved edge. I've seen discussions about this overhang in other threads. I used a granite surfacing plate and a Starrett square during glue-up, so I am confident that I had the skins properly registered to the root edge. Rochon has the right idea, though. If I build another one I would dry-fit each core fin to ensure it registers properly to the MMT and tube, then scribe a line on the core fin along the BT to use as a better reference point for the skins. This would require numbering the fins and slots to ensure you place them properly later on.

Stan said:

Has anyone contacted or heard from Estes about this being a design defect or just a limited number of defective cuts?

Click to expand...

I'm wondering if this is why Estes placed so many of the Mega mosquitoes on their sales this year. I wonder if they are aware of this.
Certainly, it has helped to introduce this wonderful staple to many of us who had overlooked it.

I had been advised by many to sand the leading edge of all my rocket fins to try to earn or eek out those extra tens of feet in height during liftoff...and so, I just assumed that I was supposed to feather the leading edge of each of the three sandwich fins for the Mega to reduce wind resistance.

It never occurred to me that by aligning the curved outer edge that I: 1)was going to have to sand a lot more material away. 2) That the contact with the motor mount tube was going to be compromised. or 3) That I should have left the leading edge uneven, as I would be sanding most of that uneven edge away to create the feathered/knifes edge later.

What do you think?

Kirk G said:

It never occurred to me that by aligning the curved outer edge that I: 1)was going to have to sand a lot more material away. 2) That the contact with the motor mount tube was going to be compromised. or 3) That I should have left the leading edge uneven, as I would be sanding most of that uneven edge away to create the feathered/knifes edge later.

What do you think?

Click to expand...

Having built 4 of these in the past year or so I will say that in my experience the root edges should be lined up at the tab and the outer edges should be uneven at the time of gluing. After the glue is dry, you're expected to sand the leading, trailing, and rounded end so all three layers are even. Whether or not you round over the leading edge is up to you and it may indeed add a couple feet to your apogee. I prefer not to round them since it looks more like the original small Mosquito that is bigger. The leading edges on those weren't rounded.

Kirk G said:

It never occurred to me that by aligning the curved outer edge that I: 1)was going to have to sand a lot more material away. 2) That the contact with the motor mount tube was going to be compromised. or 3) That I should have left the leading edge uneven, as I would be sanding most of that uneven edge away to create the feathered/knifes edge later.

What do you think?

Click to expand...

I think #3 was their design intent.

Works great with a 29mm mount . But forget what G it went on . The fins had a t2t one layer of glass

I've just glued the fins together, and as far as I remember, all the edges lined up perfectly all the way around. I can look again when I get home tomorrow.