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Dec 16, 2018, 10:42 AM
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Build Log

Airtronics Jetfire ultra-micro replica


Up till now, my only personal experience with the Airtronics Jetfire design has been in stories of legend. Freind, Andy Kunz, is on a Jetfire kick recently. You can see one result in a thread by Gary Wright where a prototype of the 20-size with electric power is being documented. I've been building up the test sample of the first ever (to my knowledge) ultra-micro size version.

At this point, the airframe is finished. Covering will start soon. I've sent the revision notes to Andy for plan and parts updates. Short-kit availability should be soon. Some slight variations might be noticed in the photos here. I'll note my own build preferences where appropriate.

In the meantime, a historic photo and image of the bare bones airframe are attached.

Thank you for your interest.
Last edited by MichaelR.; Dec 22, 2018 at 08:56 PM. Reason: revisions and additions
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Dec 16, 2018, 05:23 PM
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Plan


Hey Andy! Please post the plan when you feel it's ready for release. In addition, please let us know when the short-kit is available. Thanks!
Dec 16, 2018, 08:14 PM
AndyKunz's Avatar
Will do. Gary flew his big one today.

Andy
Dec 16, 2018, 09:37 PM
Senior to who? Member
crossup's Avatar
I have to ask, if this is ultra micro, what would a 6" WS version be? femto ? or do we need more than 15 zeros?
Regardless, nice design
Dec 16, 2018, 09:58 PM
Wabi-Sabi
coriolan's Avatar
Its 50% of the Jetfire-20 per picture in the OP:
https://static.rcgroups.net/forums/a...6-IMG_4730.JPG
The original "Jetfire-20" had a wingspan of 45"
https://outerzone.co.uk/plan_details.asp?ID=7037
Dec 16, 2018, 10:20 PM
Registered User
An Ugly stick, albeit with rounded edges A proven airframe.
Dec 17, 2018, 07:56 AM
AndyKunz's Avatar
Quote:
Originally Posted by Bare
An Ugly stick, albeit with rounded edges A proven airframe.
Even better:

When I was working on the CAD for the 20" version, for some reason it felt familiar. So I pulled down my Bridi T-20 off the wall, and sure enough the wing was an EXACT match for chord and span, the tail moment was within 1/2" (probably 1/4"), and the horizontal stab was identical in root chord, tip chord, and span (the T-20 is a tapered tail; the Ugly Stick is a rectangle). The nose moment was very close as well.

So while it might look like an Ugly Stick because of the flat shoulder wing, it's more of a T-20.

In other words, the numbers just work.

Andy
Dec 17, 2018, 09:04 AM
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GWRIGHT's Avatar
Quote:
Originally Posted by AndyKunz
Will do. Gary flew his big one today.

Andy
I wouldn't say "big",.. it's a little .20 size plane and only uses 4s/2200. From what I saw today, a 3S setup would be more than adequate for 99% of the pilots.
Latest blog entry: blog
Dec 17, 2018, 09:56 AM
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What you need to build an ultra-micro Jetfire 180


Recommended Jetfire 180 Accessory List
Motor: E-flite BL180 brushless outrunner, 2500–3000Kv (EFLUM180BLB/2)
Spinner: UMX Beast 3D 2-blade spinner (EFLU4851 )
UMX P3 Revolution Spinner (EFLU5051) optional
Ultra micro ICON A5 3-blade spinner (PKZU2308) optional
Propeller: E-flite 5 x 2.75 2-blade electric propeller (EFLUP050275)
3.95 x 3.95 3-blade electric propeller (EFLUP3953953B) optional
Prop adapter: E-flite UMX propeller adapter (EFLU4067)
Receiver: Spektrum DSMX 6Ch Brushless ESC and Receiver with AS3X (SPMAS6410NBL)
Spektrum DSMX 6Ch Brushless ESC and Receiver (SPMAR6410LBL) optional
E-flite DSM2 6Ch Ultra Micro AS3X Receiver BL ESC & Servos (EFLU4864)
Servos: (2) Spektrum 2.3-gram performance linear long throw servos (SPMSA2030L)
Micro-light covering (UltraCote ParkLite recommended)
Wheels: UMX MiG-15 landing gear set (EFLU1655), or similar


Jetfire 180 Hardware List
0.047-inch music wire for nose and main landing gear
(2) 1/8-inch O.D. mixing straws as pushrod guides
0.032-inch music wire for z-bends
0.040-inch carbon fiber for pushrods
2mm heat-shrink tubing for pushrod joiners
(4) 1mm x 5mm landing gear screws
(2) 4-40 nylon bolt (wing mount)
(2) -inch square/round hatch magnet
(1) 1/8 x 24-inch carbon fiber rod (wing leading edge)
(1) 2-inch length of 4mm carbon tube (motor mount)


Jetfire 180 Short-Kit Materials list
Andy Kunz, Jetfire 180 laser-cut short kit available from Manzano Laser Works
(1) Full sheet of 1/8 x 3 inch balsa (hatch stack, wing tips, spars and fuselage stringers)
(1) 1/32 x 3 inch balsa sheet (wing and fuselage sheeting)
Last edited by MichaelR.; Dec 19, 2018 at 07:13 AM. Reason: Addition
Dec 17, 2018, 10:54 AM
Registered User
Jetfire 180 Specifications
Wingspan: 22 1/2 inches
Length: 19 3/4 inches
Wing Area: 101 sq/in
Flying Weight: 80-90 grams
Motor Size: 180 BL, 2500–3000Kv
Radio: Ultra-micro
Servos: (4) linear-type
Battery: 180–280mAh
Propeller: 5 x 2.75 two-blade – 3.95 x 3.95 three-blade
Spinner: 1.00 inch foam
Dec 18, 2018, 10:18 AM
Registered User

The wing


The ultra-micro with a wing that retains the "bulletproof" status of the original Jetfire. The recommended leading edge material is a 1/8-inch carbon fiber rod. Given the time, I would have used a carbon tube to save some weight (even an aluminum tube might be lighter). Since balsa dowel rods don't exist (please prove me wrong), a lightweight rod made of bass will work too as long as it's dead straight like the carbon.

Webbing is optional. I believe it makes the wing significantly stronger and less dependent on covering to keep it from being "twisty".

Support the trailing edges of the ribs during assembly with a strip of 1/4 square balsa pinned to the board at the front line of the trailing edge sheeting shown on the plan. This support is also helpful to get a perfectly straight trailing edge by moving it directly under the sheeting and weighting down the entire length while the glue sets.

Instead of blocks or a stack of lightweight balsa, my wingtips are simply the profile shape made from 1/8-inch sheet material. Lightening holes here are optional.
Dec 18, 2018, 10:27 AM
AndyKunz's Avatar
Thanks for that post, Michael.

With regards to the leading edge, I wanted it to be a single piece end-to-end for strength, and it needed to be STRAIGHT and stay that was, and I was not successful in finding a source for 24" rods of approximate size needed except the Midwest item.

In the "please prove me wrong" vein, I would welcome input for sources for 3.2-3.5mm rod or tubing at least 24" (610mm) long that are readily available in the USA. I can find Chinese 500mm products easily, as they fall into the size of packaging that the USA subsidizes postage from China.

Andy
Dec 18, 2018, 02:11 PM
Going back to balsa
Quote:
Originally Posted by AndyKunz
I would welcome input for sources for 3.2-3.5mm rod or tubing at least 24" (610mm) long that are readily available in the USA.
You can get .125" / 3.175mm from Goodwinds:

https://goodwinds.com/composite-rods...ded-tubes.html
Dec 18, 2018, 02:37 PM
AndyKunz's Avatar
Thanks. I will have to work that link into the plans.

I bought the rods the day I gave the kit to Michael, and now I see that MID5701 is discontinued at Horizon Hobby.

If you can find another source for the Midwest #5701, use it - it's quite a bit cheaper.

I'll make sure both are on the plans for future reference.

Andy
Dec 19, 2018, 06:28 AM
Registered User
GWRIGHT's Avatar
Balsa dowels do exist Michael

http://www.specializedbalsa.com/products/dowels.php
https://www.amazon.com/Balsa-Wooden-.../dp/B01K4X113W
https://www.amazon.com/BALSA-DOWEL-l...s=balsa+dowels

probably more sources, but here are three
Latest blog entry: blog


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