Boeing 727-200 scratch build

[viper1990]

Finally!
It have been almost 3 years since I last posted my scratch-build aircraft.

While I was still in the army,NTU Aerofest was just around the corner ,infact it was just 3 weeks after I ORD. While still busy in the army I did some planning first and placed orders on the electrical parts. When the parts arrived, I was only 1 week away from the NTU Aerofest competition! I only had 5 days to build, Monday to Friday as Saturday was the competition day itself. I knew I have to rush to come out with something elegant in flight with a "cool" factor in it. I thought of Boeing 727,something old but looks like a unique aircraft at that point of time. Painted with Singapore airline livery. With Thrust reversals and retracts! But please do not expect the finishing of the aircraft to be detailed as I was building the aircraft at a very hasty speed with minimum sleep while eating on the job!

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

Video from cameraman #1

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.

[viper1990]

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 Artfriend, 2" 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.

[viper1990]

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 and 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!

[viper1990]

Next was cutting out the engine pod holder, well, basically it's a strong point that holds the 2 engines 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 had ended up saving up to 150grams on my whole aircraft!

[viper1990]

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.

[viper1990]

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 was unless i build another 727 with the 3rd engine next time round!

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.

[viper1990]

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 got the CG spot on 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.



Boeing 727 next to Boeing 787

[viper1990]

Saturday morning, I haven't got time yet to maiden this aircraft. I took a couple of photos before heading off to NTU aerofest.

Time was running out, initially I wanted to maiden it Woodlands or Tuas but I have decided to test fly at the venue itself. I brought it to NTU few hours before the competition to maiden the aircraft. Attracted quite a few people which gather round my aircraft before I brought it to the skies!

It wasn't a safe place to fly maiden the aircraft, especially when there are so many poles around!, soccer nets, trees and especially 4x stadium spot lights all around the area! I had to avoid so many obstacles during take-off and landing, it think was as difficult as landing at the old hong kong Kai Tak airport with it's infamous and dangerous landing approach.

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 centre line 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.

[viper1990]

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 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.

Here are the pictures of the Boeing 727 during the NTU Aerofest 2012, Enjoy! Apologise if I use some photos from other photographer's picture without asking!



Thanks for reading through,thats all for now!

[VinCopter]

Vary nice scale look and flight.

[joe yap]

Good job! Can you share some pictures of the thrust reverser system rigging?

[viper1990]

Thanks Vincopter and Joeyap!

Sure, i would like to share,

In the next picture, it shows the rear cowling of the engine pod. Within the rear cowling, i embedded miniature bent push-rods into the foam. Those pushrods will than "hook" onto the icecream stick,where i pre-drilled 1mm holes in them. The little end where the pushrods are bent 90degrees will be the point of rotation for each of the cowl. The icecream stick simply holds the 2 cowls in place whether it's in open or close position.

In the following picture, shows the movement of the engine cowls from the close to open position. The servo is embedded into the rear of the fuse on the other side. Only 1 servo controls each engine pod which have 2 movable cowls.

Note there is a plastic tubing which is extruded outwards at the rear end of the engine pod,the exhaust outlet was kept near to the closed position of the engine cowling,but not too close whereby it blocks most of the airflow,so there is an optimum distance to keep. (I have build a test rig just to test the trust reversal position for optimum thrust blowing towards the front) .This is done so that minimum air will be leaked from it's side producing useful thrust blasting air forward 45degrees both up and down to push-back the aircraft. The push-back effect will be felt at 3/4 to full throttle, and it moves back really slowly,like a baby crawl.

[viper1990]

Here is the video taken by my dad at NTU aerofest 2012. (Video is taken from a different angle compared to the video at the first post)

[dt2133]

Great design, great build, great plane and great pilot. I enjoy it very much. Thank you for sharing.

[rayonnair]

Beautiful, thanks for sharing. Landing looked a bit hot, it was scary for a moment there!

The commentary was pretty good too