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Old Dec 30, 2014, 08:22 PM
When in doubt, bail out!
United States, FL, Palm Bay
Joined Oct 2013
84 Posts
Build Log
Quatinus 60" Twin Boom Pusher

This has been a long term project that I never got around to making a build log for. My last year at college got very very busy, so I put RC on hold for some time. So I'll start at the beginning. First off the name is latin for "How far", because the goal is eventually to get into long range FPV. I based the design heavily off of Experimental Airlines' "Ozone" but made it slightly smaller.

I will be linking to my other builds here, mainly for my own sake, but also in case any of you are interested.


Quatinus V1.
Wingspan: 60"
Chord: 7" with 2 " ailerons (9" total)
Designed to carry at least a 3s 5000mAh battery and FPV equipment.
-Motor is an NTM prop drive 28-36 1000kv
-11x4.7 prop.
-40A HK Blue ESC.



I painted it green after seeing the L-3 Grasshopper and thinking it looked cool. I had dark green paint leftover from some projects and put it to use.





1.72 pounds without batteries.
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Old Dec 30, 2014, 08:23 PM
When in doubt, bail out!
United States, FL, Palm Bay
Joined Oct 2013
84 Posts
Quatinus V2.


I Have designed and started building V2. After the not so successful maiden of V1 I tore it apart and decided to change some things. The fuselage was way too flimsy, and deflected a lot, including when hand launching, which made it very difficult. Instead of 4" square, it is not a 2x4" rectangular tube. I also decided that the booms had no reason to be foam board and changed to 1/2" round dowels in order to cut down the flex and cross wind resistance. I decided to go with an inverted V-tail after reading some good things about them such as proverse roll in turns and 2 surfaces has less drag than 3, but mainly because it is more sturdy and looks cooler.



This shows the nose, it hinges up and the electronics tray slides out. The nose is also "disposable", it is meant to be a crumple zone in impacts. It is angled in a way that should make the plane not dig in as much in all but the worst nose dives. We will see if this causes nose up issues at speed.


I used some pieces of plastic bottle to reinforce the edges where the rubber bands are.
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Old Dec 30, 2014, 08:23 PM
When in doubt, bail out!
United States, FL, Palm Bay
Joined Oct 2013
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Old Dec 30, 2014, 08:25 PM
When in doubt, bail out!
United States, FL, Palm Bay
Joined Oct 2013
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Old Dec 31, 2014, 12:24 AM
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Canada, NT, Yellowknife
Joined Nov 2012
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Looks interesting. Let us known when you've flown it.
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Old Dec 31, 2014, 08:38 AM
When in doubt, bail out!
United States, FL, Palm Bay
Joined Oct 2013
84 Posts
Will do. The first one already had its maiden. It was too tail heavy and porpoised the whole time. On V2 i moved the fuselage forward two inches. Got all the servos mounted and pushrods made. It is setup with ruddervator mix and flaperons for some slow speed flying. Just need to mount the battery and get some paint on it.
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Old Jan 14, 2015, 10:26 AM
When in doubt, bail out!
United States, FL, Palm Bay
Joined Oct 2013
84 Posts
Two weeks of storms and high winds... I haven't bothered painting it until I know it flies in some respectable manner. Weather forecast for this weekend looks better.
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Old Jan 14, 2015, 02:09 PM
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For V2: Have you calculated whether or not you will have sufficient yaw stability?
The vertical surface of that shallow v-tail looks pretty slim.

Also, your "fuselage" is quite flat and long and will actually provide some lift at even slight AOA. So CG calculation should take it into account.

By the way: Some simple mechanical aileron differential will give some additional help with pro-verse yaw.
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Old Jan 14, 2015, 06:07 PM
When in doubt, bail out!
United States, FL, Palm Bay
Joined Oct 2013
84 Posts
I haven't calculated yaw stability, mainly because I don't know how haha. I assume I need to shift the CG forward to compensate for the lift from the fuselage? Do I need to generalize the AoA and just assume it'll fly a few degrees nose up?
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Old Jan 14, 2015, 09:29 PM
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Wolf,

Haha, I'm with ya, I don't know how to calculate that stuff. What I believe nuteman is getting at is that the inverted v tail design isn't a very common one. And the way you have it setup doesn't look like it will give you much vertical control area, and therefore yaw stability. The planes I have that are similar to that size have a standard vertical fin that is about twice that size. Eye ing up your plane right now it looks like you have a horizon stab that is deflected up at 2 angles, and no real vertical stab to speak of. It might fly fine, but I personally would be studying others models similar to yours that fly well, and then copying their designs.

Don't mean to be discouraging at all, but I've made my fair share of planes that were frustrating to fly.

Just so you know, it also looks like your wing is drooping downwards. This known as anhedral.. It is used to make airplanes more maneuverable , or another way to put it is less stable. So your plane might not stay stable as you fly it and keep requiring inputs. That could be tied to the wing anhedral.
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Old Jan 14, 2015, 09:59 PM
When in doubt, bail out!
United States, FL, Palm Bay
Joined Oct 2013
84 Posts
In those pictures the spar wasn't in and the wing nuts that secure the wings weren't fastened. Hopefully with the two carbon arrow shafts in the wings the droop will be gone.

Off the top of my head the spscing between booms is 17", each section of the tail is 10" long and the top angle is very close to 120 degrees. The math says It should be 4.8 inches total height. 4" HStab surface with 2" ruddervator. Anyone know a typical VStab area for a 60" wingspan foamie?
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Old Jan 14, 2015, 10:13 PM
When in doubt, bail out!
United States, FL, Palm Bay
Joined Oct 2013
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After some quick searching I found a rule of thumb that the Vstab should be 10% of the wing area. Idk if this works but looking at it from the side(imagine each diagonal surface is a vertical surface of the same total height), I have a(maybe two?) 4.8" tall Vstab with 6" chord(28.8 sq in). Wing is 60x9", so 540 sq. in. If both count it would be right in that 10%, otherwise roughly half.

All of this is speculation and I'm not sure it applies.
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Old Jan 15, 2015, 12:16 AM
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With spars in and fastened I'm sure the wing will be a lot more rigid without anhedral. Should be good.

Looks like you've done more math that I have. Hopefully you're vertical control surface area is enough. It looks like you should have decent aileron authority, and decent elevator authority, (it might be a little pitch sensitive with such a short tail moment) I would anticipate fairly weak yaw control though. Even if the math is correct. Not that it matters. But I have built enough scratchbuilts, not from plans, I always love to study a plane and try to guess how it is going to handle before its first flight. Then do a maiden, then see if my hunches were correct. So I'm having fun guessing how's yours might handle.

I also think there is a good chance you'll have good or even very sensitive pitch control with such a huge motor blowing air directly over your very close tail surfaces. The only reason that might not be true is if the model is very nose heavy. But if it's balanced well that pitch control should provide very positive, if not downright exciting.
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Old Jan 15, 2015, 12:21 AM
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Nuteman

By the way: Some simple mechanical aileron differential will give some additional help with pro-verse yaw.

What does this mean? What is proverse yaw? And how do you set up differential aileron to fix it?
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Old Jan 15, 2015, 04:54 AM
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Quote:
Originally Posted by Nwtlakes View Post
Nuteman

By the way: Some simple mechanical aileron differential will give some additional help with pro-verse yaw.

What does this mean? What is proverse yaw? And how do you set up differential aileron to fix it?
Hi All,

All the things I discussed are elaborated upon in great detail or very succinctly in other posts and on other sites - and presented much better than I could in a few sentences (they have pictures, videos, etc.). A quick search using the search feature of this site, or just a simple google search will give you what you need to know about these topics.
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