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Feb 15, 2017, 09:27 AM
Sonoran Laser Art
Thread OP
Build Log

Tarantula Hawk 2M RES


I have wanted to build an Allegro Lite for a long time but I thought it would be difficult from scratch. So I started re-designing the Allegro the way I want to build it. Every part has been drawn and cut files created for each size of material.

The wing uses the AG35-36-37-38 air foil with a single spoiler. Thank you Mark Drella for the airfoils and the Allego Lite. The spar is .375x.060 straight the entire length. On the first build I am using .030 CF caps epoxied to 1/32 bass top and bottom. I realize I don't need this much carbon but at this point I prefer less complexity and bullet proof. Since the wing tapers all the spar core block and shear webs are cut and etched with numbers and letter to identify where they go. I think its critical to laser everything to make sure each part is accurate and it goes together quick with minimal tweaking. The ribs are cut at the rear so that 1/16 balsa sheeting can be used for ease of assembly. On the this first build the wing is one piece with dihedral braces at each joint. With the straight spar it would be pretty easy to add a few ribs with holes for 3/8 brass tubes should it need to come apart.

I do not want to mess with a composite pod and I want it to be woody F3RES legal. I need the flexibility to change it for intended use. I belong to a great electric club in Mesa so the first one is designed for a Turnigy SK3 2830 motor (mount cut to match from the rear). Its just wide enough for a 800 Mah battery under the spar. It should not be too tough to make some changes for bungee or winch launch.

The tail has a 2 piece stabilizer/Elevator from 1/8 balsa and some 1/64 ply reinforcement at the mounting area. The fin is 1/4 cut to fit over the end of the Goodwinds Allegro boom. I designed small mount for the stab from 1/8 ply and balsa for shaping. The mount pad has a hole for thread insert so the stab can be removed. The balsa slab tail pieces will be hand sanded for the airfoil. After I find out how it balances I will add lightening holes if needed.

The build plan sheet is printed, parts are all cut and the build is started. As I go I am writing instruction and making any needed minor changes to the cut files if something does not fit just right.

Here are some pics for look at. I hope you enjoy
Last edited by CloudSniffer; Feb 22, 2017 at 08:33 PM.
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Feb 15, 2017, 11:43 AM
F3-RES is fun!
Ur Wingman's Avatar
When is a rib kit or kit available? I'm liking what you did to the center spar!
(Drela's BD/Allergo wings are amazing. I have one BD I bought that was "Totaled" by a radio failure. It's now called "Old Number7" since the wing has been damaged 7 times(2 by me), yet still takes a full pedal winch and flies great!)
Can we pre-order?
Cheers,
Jim
Feb 15, 2017, 01:36 PM
Sonoran Laser Art
Thread OP
I would like to get through the build a little more so I don't ahead of myself. I will likely take some pre-orders in the near future . The only way to keep the cost down is to order enough material to either get free shipping or some discounts. If I order materials for 1-2 at a time the freight would be a killer. If I had wood I could cut kits now, but I want to make sure everything is good. So far just some minor sanding adjustments, then go back and adjust the cut file where needed. I am thinking when I am close I would like to 5-10 kits together and get some feedback from guys that will start building when they get them.
Feb 15, 2017, 01:43 PM
F3-RES is fun!
Ur Wingman's Avatar
Well, please put me down as a definite "pre-order" on your list!
I work from home and slow weeks (like this week) allow me to "play", and right now, I'm almost done with an AndREaS F3-RES.
Cheers,
Jim
Feb 15, 2017, 01:46 PM
Sonoran Laser Art
Thread OP
So far so good. Each tip with the polyhedral braces is 20 grams uncovered. The AL shows tips at 24 grams. On these I only have carbon on the top and two pieces of 1/32 bass epoxy'd together for the lower spar cap. No load on the tip. These are very solid. They need to be completely assembled and sanded pretty close to cover ready before attaching them to the mid panels. I have the mids assembled and ready for tips so that will be next.
Last edited by CloudSniffer; Mar 02, 2017 at 07:50 AM.
Feb 15, 2017, 02:05 PM
Sonoran Laser Art
Thread OP
Will do Jim, thank you
Feb 16, 2017, 02:22 AM
Registered User
Why the need for this solidity, excessive, imo...
Sheeting is way too wide for the structural resistance requirements in that area.

My F3 RES model whole extreme panel is 69 grams covered, 58 structure (including joiner rod) + 11 covering, and this is at the heavy side of the weight range...
Feb 16, 2017, 03:25 AM
supreme being of leisure
ZAGNUT's Avatar
Quote:
Originally Posted by renatoa
Why the need for this solidity, excessive, imo...
Sheeting is way too wide for the structural resistance requirements in that area.

My F3 RES model whole extreme panel is 69 grams covered, 58 structure (including joiner rod) + 11 covering, and this is at the heavy side of the weight range...
the AG3x foils use top sheeting past the spar to control covering sag...but then a lot of very successful models use the same foils without any sheeting at all.

i will say that the spars look wider than they need to be since the D-box is handling torsion. the baba jaga and others are using 3,4,and 6mm wide by 1mm thick carbon strips with only balsa webs between them, no other wood in the spar. these are also thinner foils. this carbon is available for very, very cheap compared to the wider/thinner stuff used on the allegro. would be a good way to significantly reduce the kit cost....if buying in bulk for ~20 kits the cost might be $6 per kit.
Feb 16, 2017, 08:56 AM
Sonoran Laser Art
Thread OP
Zagnut you are correct on the sheeting as it follows the AG3x design profile. I am not second guessing that. The spar core width is .375" the full length with .125 shear webs and polyhedral joiners. That's why it looks wide. The lower sheeting slides up to the front webs so I chose to keep sheet line straight. The Allegro has 1/2" wide spars in the center, then 3/8, then 1/4. Weight wise I think it's a wash but will see. I wanted it strong enough for a hard winch launching. One could easily eliminate the shear webs and wrap the spar with Kevlar. I am considering offering different spar cap options depending on intended use. Could be .030 carbon and bass top and bottom, or .030 just on top with bass or spruce bottom. National Balsa does not have spruce the size I need so I need to research that a bit more. I am sure there will be a lot of opinions on the spar make up. I think it comes down to intended use and builder choice. So working in a .375x.060 Window those opinions are welcome at this point. Remember it's a thin section so what worked in the old days with thicker wings will not apply. The other area I am interested in thoughts on is my spar cap being pre assembled with 1/32 bass and .030 CF. I have done this in the past and never failed a spar with hard winch launch and ping. In doing this you can really weigh down the carbon on the bass with weight on a bench. Then sand the edges or the bass if the material comes a little thicker than spec which i finding is common. Then when you epoxy the cap with the bass facing the balsa core you get a good joint being wood to wood. If you just epoxy CF to the spar core I think it is more susceptible to voids and adhesion issues unless you wrap it which I want to stay away from for an easier build. Again builder choice. Thoughts from experience and preference for this type of airfoil?
Last edited by CloudSniffer; Mar 02, 2017 at 07:51 AM.
Feb 16, 2017, 09:10 AM
Sonoran Laser Art
Thread OP
Please keep one thing in mind. I have heard for years about people that want Allegro kits. Also how the build is a challenge. V mounts and Kevlar pods are tough to find or make and can add a lot of cost. The double angle joiner boxes seem complicated for most to get right. My goal is a plane that flies as good, similar weight, EASY to build, with the lowest cost possible. I plan to have an E pod, a RES pod, and later a full wood fuse. The wing stays with Mark Drella's airfoil.
Feb 16, 2017, 09:14 AM
Registered User
I agree, then why not get the best from each german F3-RES model and lego your close to perfect model ?
If Allegro is so difficult to build, why choosing as a start ?
Feb 16, 2017, 09:37 AM
Registered User
Quote:
Originally Posted by CloudSniffer
The spar core width is .375" the full length with .125 shear webs and dihedral joiners.
Why wouldn't you double taper the spar? A constant width spar across the entire span is structurally inefficient = unnecessary weight.

Double tapering everything, IMO, is also vitally important to reduce inertia and ensure good yaw performance. Therefore the leading and trailing edge stock should also be tapered.

Cheers-
Dave
Feb 16, 2017, 10:41 AM
Sonoran Laser Art
Thread OP
Dave, your suggesting I use tapered Carbon cap strips?
Feb 16, 2017, 10:44 AM
Registered User
Quote:
Originally Posted by CloudSniffer
Dave, your suggesting I use tapered Carbon cap strips?
The point I was trying to make is that the spar should not have a constant width (from the top view) across the entire wing. It should be tapered in thickness, in addition to height (which happens "naturally" as the chord goes down).

CF is a different thing. IMO not a bad idea, but depends what your goals are.

-Dave
Feb 16, 2017, 10:59 AM
Sonoran Laser Art
Thread OP
It tapers in thickness. I chose the same width to make the sections easy to join trading off some complexity. My goal is to balance assembly and performance. I agree taking some weight out as it progresses toward the tips would be a good thing and wouldn't compromise my goals. There are a few ways I can do that so need to think about what would be best. Thanks


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