Articles
| Elan Build Review | ||||||||||||||||||||||
By Peter CarsonA few weeks ago I was looking on Al's hobbies website when I came across the new Boomerang Elan. At 82.5” wingspan and 80” in length this model fits in between the Boomerang Intro and the XL in the range. I took a look at the videos on the bottom of the page and watched as this big model was taken out of the back of a small car, quickly assembled and flown like a pattern ship. I was hooked. The order was placed with Sandor from Digitech Turbines, and although the maximum size turbine recommended is a P80 with 20lb thrust, I went for the JetCat P120SE at 28lb thrust. I did this for two reasons, first the throttle response of the SE engines is much faster than that of the non SE turbines, and second, I wanted an engine that could power a wider range of models in the future. While using the 120 either the maximum RPM and therefore thrust can be lowered via the ground support unit (GSU) or good throttle management carried out during the flight. So far I have selected the second option as this way I still have max power for unlimited vertical performance.
The airframe arrived on Thursday 5th June but as we were in the middle of preparing for the display we were doing on Saturday 7th, the kit remained untouched until the evening of Monday 9th. As the second package had not arrived, and this one had everything else in it, turbine, servos, extension leads, undercarriage, etc., all I could do on Monday and Tuesday was to connect the control surfaces and attach the control horns. It was on Monday evening that Ian said “If the turbine arrives on Thursday, as expected, there is no reason why you couldn't have this flying on Sunday. WHOLLOP The gauntlet hit the floor. OK I thought, let's go for it. The second package arrived on Wednesday 11th and as I was on a half day I had a chance to have a quick look at the turbine and do an inventory of the second package, servos, tank, extension leads, etc. I had asked Sandor to supply everything required to complete the build and he had provided a very complete package. Due to circumstances I was unable to do any work on the Elan on Wednesday. I took another half day on Thursday and started work on the model at 2 pm. I began by installing the servos onto the servo hatches, but as the servos were slightly too long a bit of sizing was required to fit each servo. Next I ran the extension leads through the booms and labelled them as I went, to make life easier later and at the airfield. I didn't like the push rods supplied with the kit (although Alan, the designer, has over 100 flights on the prototype using this type of push rod.), so I selected to go with 3 mm threaded bar with metal quick links, secured with nylon lock nuts. Better to be sure with a model that has been clocked at 210 mph.
I finished work on Thursday night at 2.20am. I was off on Friday so work began at 9 am. I finished installing all the servos but ran into a problem with the flap push rods. These were so short that the quick links I was using were too long so I had to come up with another solution and this took a while as I tried different options. At 7 pm I relocated the model up to Ian's workshop where the model remained until it was completed. The next job was to install the main gear. The inflatable tyres were a good fit in the wheel wells but due to the trailing links they were unsuitable, but Sandor had foreseen this and supplied a smaller tyre (thank you Sandor), so the Elan got a tyre change from inflatable to solid. The air system for the gear and wheel brakes was installed next. Ian did some pipe work while I fitted the second main gear. Work finished on Friday night at 3.30am. Saturday morning I was in the workshop by 11am. Chris had finished the work he was doing on his Hawk and give me a hand. I installed the nose gear and servo, and while I was cutting the retract hatch access hole, Chris connected the steering cables. The Elan has a large access hatch on the bottom that removes to give you more room to fit the nose gear. Then the hatch is secured by 8 screws. I thought this was a tad unsightly so Chris and I added a ply locating tongue to both the front and back ends of the hatch, and secured the middle with concealed screws. From the outside the hatch is invisibly held in place.
Now I had a Working undercarage complete with wheel brakes. We had installed the pipe work for the undercarriage with over length lines to get it working and as Ian tidied these up I installed the extension leads into the main body and labelled them. Next I routed the servo extension leads to the front of the model and installed the receiver and the on/off switch. This is of the JR heavy duty lockable type. Now we were ready to begin the turbine installation. It was now 9.51 pm. The Elan is designed for 14 – 20 lb turbines so the P120 is physically larger than the model was ever intended for. As a result the normal 10 minutes to position the turbine and install 4 screws took about 3 hours and involved a lot of fettling by Ian. Once the turbine was secured into the body we turned our attention to the on board systems required to make this model operate.
The connecting cables from the turbine were installed along with the kerosene start pipe work. The time was now 2.23 am. Next we were faced with the problem of where to put everything. At first glance this is a big body with loads of space for the gear, but the fuel tank, all 2.5 litres of it, takes up a lot of space. After some thought we installed the fuel pump and the ECU (Electronic Control Unit) at 4.22 am.
The next items required are the valves and filters for the turbine. As this is a kerosene start engine we need two valves and two filters. The tank was plumbed and fitted along with the turbine lipo battery, located under the tank. I had read on the internet that the model can be nose heavy so I put everything as far back as possible. Next the ECU was located and the JetCat LED board temporally connected. A fuel safety cut off valve was fitted and the tank filled. The air was purged from the fuel lines and we took the body outside for the first start up. Time check, 6.02 am.
The turbine burst into life and even thought we were in a remote location we shut the engine down again without giving it some throttle, tempting as it was. Work finished on Saturday night (Sunday morning) at 6.10 am. I got home at 6.30 am and got up again at 8.45 am. Who needs sleep anyway? Sunday saw me in the workshop by 10.05 am. Not much had changed unsurprisingly. There were a number of important final tasks required, not least of which was a C of G check. The model balanced just a few millimetres behind the required position but relocating the Rx battery from the top of the fuel tank to the nose beside the Rx put the balance in the right spot. The JetCat LED board was permanently secured and the whip aerial fitted. I programmed the transmitter with the mixes required and Ian adjusted push rods to get everything centred. A vent pipe hole was drilled in the floor of the body and pipe fitted. I had fitted the canopy to the top hatch the previous night so now it was time to fit the booms and wings, and fit the bolts that secure the wings in place. As the wings were a little loose on the main spar, the heat shrink supplied in the kit was shrunk onto the spar and this give the wings a nice snug fit It was now time for a quick photo opportunity. Time check, 12.43 pm.
We relocated to the flying site and after range checks with and without the turbine running it was finally time for take off. I taxied out and turned into wind, wheel brakes on, throttle forward to about two thirds and brakes off. The Elan shot into the air and after a few clicks of trim she was flying straight and level. A few low passes were made for the camera and a few rolls, which the Elan performed beautifully, then a practise approach. With no flap deployed she came in fairly fast so on the second approach I selected half flap. This was only meant to be a practise approach but it looked so good that I continued down to a nice smooth touch down and then applied the brakes to shorten the roll out.
Was I a happy bunny or what! Time check 3.35 pm. I estimate the build took about 62 hours, with two people working on the model for some of that time. I want to say a very big thank you to Ian and Chris for helping with the building and with pitting for the test flight, and of course for the late nights and long hours.
I also want to say thank you to Sandor for his help with selecting the necessary extension leads and other internal items. And to the Boomerang Designer, Alan, for a fantastic model. One very happy jet pilot. Peter Carson Some other pictures from the build
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Langford Model Aviation 2010