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        Discussion Boeing 727-200 Quick build in exactly 5 days

#1 viper1990 Oct 02, 2012 12:36 PM

Boeing 727-200 Quick build in exactly 5 days
 
*Note that i took exactly 5 days to build, 16 hours of work each day excluding the time spent on eating and toilet breaks and sleep. That's a total of 80 hours spent building the aircraft. Do also note that building that fast, i didn't have much time to pay much attention to the finishing such as the paint job.The building time span was from the 24th to 28th September.

The reason for building that fast is because i finally got sometime for myself to do some scratch-building at home and there's a deadline to meet for a under 1.5m flying competition which is to impress the judges so i have to come out with something elegant and cool. That's when i thought of a Boeing 727 with retracts and thrust reversals.

The venue of this competition will be a stadium, with obstacles such as soccer goalpost, nets, tennis courts,basketball courts and 4 gigantic field lights which towers roughly 50meters up. There is no room for error when flying this 1.5m wingspan model during takeoff and landing!

Specification of the scratch build aircraft:
1.5meter wingspan
1.4kg AUW
500-600grams of static thrust (figures will be different in flight)
Wingloading of 17oz/sq ft
4400Mah 3s lipo

Boeing 727 at NTU Aerofest 2012 (with thrust reversals)* (2 min 33 sec)


[New video taken in Year 2015]
RC Boeing 727-200 Singapore Airlines (2 min 59 sec)

#2 viper1990 Oct 02, 2012 12:43 PM

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Now with a brief history on the Boeing 727 Singapore Airline (extracted from a website)
The Boeing 727s were first delivered on 30th august 1977, Singapore airlines bought 10 of the aircraft and it's service duration was from 30th august 1977 to 6 march 1985. If I'm not mistaken, it was initially flown from Paya Lebar Airport at that time, flying short and medium haul flights to neighbouring countries.

#3 viper1990 Oct 02, 2012 12:49 PM

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Monday

The designing and modifying of the aircraft was done on Autocad, of course with some reference from the Boeing website where they provide full scale plans on the various aircrafts that have.

I started cutting out the templates first, will be used for hot wiring later on. The foam was all bought from my local DIY store, 2 inch thick typical EPS foam, I started on the fuselage first, Cutting out the shape I want before hollowing out the middle where all the electrical wiring will run through later on.

#4 viper1990 Oct 02, 2012 12:56 PM

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Tuesday

I have chosen Haoye 55mm ducted fan, for no particular reasons, probably it has 7 blades which produce more static thrust than achieving high efflux velocity as i'm not going for speed. I'll run it at a lower kv compared to other EDF of it's class, at 4000kv. Its blade at it's root is measured close to 70degrees! Of course, once the plane starts picking up speed, the blade from a stalled AOA will un-stall itself as soon as higher airspeed enters the inlet. I spent the next 2hours balancing the blades to give it the "wooshing" sound that everyone likes to hear with minimum vibration.

The engine pods are designed slightly bigger than the real aircraft (else I'll need a 35mm edf to make it look scale!) I've added thrust reversals on the engine pod too! Won't be elaborating much on this, its just simple mechanics and linkages pushing and pulling the cowl, picture will says it all!

#5 viper1990 Oct 02, 2012 12:59 PM

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Tuesday

Next was cutting out the engine pod holder, well, basically it's a strong point that holds the 2 engine pods where it will be embedded into the rear section of the aircraft. I find plywood a suitable material to do this job fairly well. It was one big bulky piece when I first cut it out, wasn't happy with its weight, so I further cut rectangular holes into the structure to lighten it up and save 8 grams. A little weight reduction here and there end up saving up to 150grams on my whole aircraft!

#6 AirX Oct 02, 2012 01:00 PM

Nice work.

Cheers,
Eric B.

#7 viper1990 Oct 02, 2012 01:01 PM

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Wednesday

Fixing the retracts was slightly difficult for me as I was handling mechanical retracts for the first time ever! I thought of servo-less retracts at first but mechanical retracts are lighter as I was trying to save as much weight as I possibly can. The nose gear have doors that open and close along with the wheel, all the mechanism is done under one servo, and of course it's steerable. As for the rear landing gears, it doesn't have any doors that cover the wheels after it is retracted.

The landing gears and wheel configuration was fully customized so that the scale replicates the real aircraft.

#8 viper1990 Oct 02, 2012 01:04 PM

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Thursday

Finally my plane was beginning to take shape! What's left was the horizontal and vertical stabs to build which is also one of the hardest part to construct because the middle engine have to be blended in nicely with the vertical stab. I'm aware that the 3rd engine was functional on the real aircraft but constructing the S duct pose a very hard challenge for me, especially I do not have much time to build it ,Somewhere in Rcgroups states that efficiency & flight performance drops when the 3rd engine is added on, not too sure how true it is though.

For my aircraft,The 3rd engine was simply a hollow tube of foam being attached to the vertical stab. After which I cover it with 1mm thick depron panels which blends the engine nicely with the vertical stab.

#9 viper1990 Oct 02, 2012 01:05 PM

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TGIF!

This was the last day of the build, one more day to the competition. I was rushing to complete the decals, its not that pretty, but I?ll make do with it. I use a printer to print out the windows. On my previous build, 777 and 787 , all the 80 windows was hand cut out by hand and pasted one by one onto the fuselage!

A battery hatch was cut out slightly forward from the leading edge of the main wing which is to house the 2x 2200mah 3s battery.

At this point of time, I wasn't sure whether I hit the CG correctly even though I use various CG calculators online. I decided to go for 20% static margin, or simply it meant nose heavy. I rather maiden it to fly with mushy and less sensitive control than being tail heavy which is very twitchy in flight and might be a problem when comes to landing, especially at slow speed.

#10 viper1990 Oct 02, 2012 01:09 PM

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Saturday morning

I haven't got time yet to maiden this aircraft. I took a couple of photos before heading off for my flying event.

Time was running out, initially I wanted to maiden it at some nearby flying site but I have decided to test fly at the venue itself. I've Attracted quite a few people which gather round my aircraft before I brought it to the skies!

I did a pushback using the thrust reversals and taxi to the runway. Once lined up, I gradually increase the throttle from 3/4 to full over a few seconds as it rolled down the centreline of the runway, or lane number 4 of the running track! It took a couple of seconds to accelerate before it rotates and off it goes! As predicted by the CG calculator, the plane was nose heavy, but controllable, I was quite excited with it's performance, I flown the plane round the stadium a couple of times before bringing the plane to land on the grassy patch. Moments before I touched down, I hit the retract switch to keep the landing gears else it'll be ripped off from the underbelly.

Now that my plane was airworthy, I readjust the CG and now waits patiently for the event to start!

Unfortunately I do not have pictures of it's maiden flight.

#11 viper1990 Oct 02, 2012 01:14 PM

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The Boeing 727's 2nd flight was now much more stable than previous, everything working well as it should except for the retracts, as I guess I have damaged it during the 1st belly landing so I kept it down all the way. As for the landing, I manage to hit the runway centre but veered off to the side as I didn't apply much rudder to control it's ground steering. I applied reverse thrust to bring the aircraft to a complete stop before taxing back to my position.

That's all for my scratch building post, thanks for looking through!

#12 abroadhurst94 Oct 02, 2012 02:06 PM

Amazing work there, viper1990! :D
5 days! That's incredible, keep up the great work.

Alex.

#13 jdlilfan Oct 02, 2012 02:09 PM

Looks great! Looks like it flies good as well! Love those clamshell reversers. Can you take a pic of how you installed the servo and its actuation to the thrust reverse? Curious how you did it?

#14 brett1984 Oct 02, 2012 03:55 PM

Wow:eek: that looks amazing, thanks for the pictures i enjoy seeing how other people design there aircraft:) *note to self must try thrust reversers on one of my ailrliners:D

#15 demondriver Oct 02, 2012 11:27 PM

Awsome Work Viper! Your 727 is smok'In Hot!:D


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