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Post by dennisp on Feb 4, 2009 19:35:48 GMT 8
A bit of History Back in June 2006 I ordered a Baby Boomerang as my first turbine model, which from all accounts was a good stable aircraft and had a wide speed of operation namely 15 mph to 140 mph. The model was to be powered by a Jet Cat P-60 turbine with a maximum thrust of around 12lbs for a model that weighed dry (no fuel) on board 16lbs with fixed gear and increased weight with retracts. Being my first venture into this side of the hobby I decided that when I visited my daughter in the UK in July I would sign up for 1 days training at the Paul Heckles flight school on the P-60 Boomerang to get to know the habits of the model and also the possible changes in flying techniques that are required with a turbine model. Although expensive it was worth every English pound as the training was first class and every aspect of the flight envelope was explained and executed. The Baby Boomerang when assembled is BIG with a span of 76” and total length of 71” however the ability to remove the booms, outer wings and stabilisers makes the model ideal for transportation in my Volvo car and for storage at home and very easy to work on the bench when these parts are dissembled. I was interested to hear recently that Boomerang jets has now sold over 1,000 Boomerang models worldwide which is quite something for a turbine model. On my return to Singapore in 2006 construction fever set in and the airframe was quickly assembled into the classic Boomer twin boom shape, the next step was not so quick in the installation of the turbine and all the associated accessories as it was soon found that fitting all these items, air systems, fuel systems that bit fuselage was err just not big enough..! After several redesigns of the systems trays everything was finally squeezed in and we were ready to burn kerosene.    In March of 2007 I was all set for my first light up of the P-60 turbine, but had problems with the TRIM brake valve and I was not keen to explore the taxing of the fuselage with that kerosene blow lamp just in case....!!    The P-60 started first time and I was a happy chap to say the least, the faulty brake valve was returned to Trim in Australia and the endless wait then occurred for the replacement brake valve. The Boomer was put in the corner of the workshop and eventually the stores as other projects had taken priority, time passed and as we know the opportunity to fly turbine models has sort of vanished in Singapore so I had this big model stored with the MOHA declaring war on the state of my stores at the apartment. While surfing the net as one does, there was a thread on could the Baby Boomerang be converted to EDF, Jim Phelps had done a conversion using a Schubeler 120mm fan which was encouraging but it did not look too great a conversion with the big NACA scoop in the top of the fuselage and a big hole cut in the wing from top to bottom to get the air into the Schubi fan.   I had received my StuMax 110 fan and also the Tam Jets TJ-100 fan and the desire to get this model flying was raised to priority # 1 in the project status and would be used as valuable experience for 2 other large EDF projects that I have lined up for 2009. The Tam Jets TJ-100 seemed to fit in the space where the Jet Cat P-60 was located so this seemed to be the fan to use as the StuMax is that extra 10mm bigger but has more thrust. Before committing to the removal of all the turbine equipment I needed to have some level of confidence that a 12 lb thrust EDF was going to haul this 16 lb plus model around the skies. The homework was done and several Excel spreadsheets were created to try to understand what could or could not be done..!, needless to say the sheets were only guide lines but offered some degree of confidence in that if the conversion was possible. While doing all my homework and research a Fai Bao L-39 weighing a similar weight to the Boomer had successfully flown in the USA on a TJ-100 fan so things were looking more positive. Next step – Design and Conversion considerations. |
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Post by derrick on Feb 4, 2009 19:59:39 GMT 8
Oredi........... Subsribed!
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Post by dennisp on Feb 4, 2009 21:25:05 GMT 8
Conversion and design considerations From my homework and research it seems that a magic figure of 150 Watts / pound is required for an EDF model and 200 + Watts / Pound if you wish to be a “Top Gun” pilot. Boomer is no sleek fighter jet and really has quite a high drag airframe but the P-60 turbine version was capable of the claimed 140 mph which is more than fast enough for me and my aging eyes...!! Simple calculation we need 150 Watts for every pound weight so with a 16 lb dry model we need 2,400 Watts OMG, a check on the Tam Jets web site showed that there was no technical performance data like that published by Schubuler or StuMax so a little bit of confidence was lost on the possibility of achieving the conversion. One positive was the Boomers wing is quite thick and semi symmetrical so would provide good lift, reverting back to the TAM TJ-100 all I could find was that it could provide 12 lbs of thrust on 10, 11 or 12S again no solid definitions. After some meditation I decided to press on and address the next real major the ducts, if you look at the first part of this thread you will note that there is a plastic “Shrek” ear by the turbine for the air entry. There was no way that this would work for a EDF just not enough area, based upon Jim’s conversion I decided to go for the inlet ring solution and no fancy glass ducts but this still left me with question how do I get more than 100% FSA into the fan.? As we no longer have a giant kerosene tank I could make giant slots in the side and that should be enough.... umm..? Back to the spreadsheets once again.. the FSA of the TJ-100 is 9.82 sq.” and we are going to need more than that for a non ducted fan, at 150% FSA we need 14.30 Sq.” and with the potentially horrible routing of the air to fan my hunch was that this would not be enough either. With a side inlet in the fuselage 7.00” x 1.50” would give me 10.50 sq.” Per side of inlet area into the old kerosene tank area. If I were to make side ducts like say a F-15 I would then be constrained by the inlet hole of the duct to the hole in the side of the fuselage, looking at things and making bits of cardboard up to see what was possible I was able to make the side inlet duct 4.50” x 2.25” which would give me 10.125 sq.” of intake area. Getting close which was good news, downside is the wing has curvature (obvious) so the area shrinks a little as goes further down the wing. Oh dear and I am not lover of cheater holes but we may need a very small one so the top of each duct would have a small by-pass cheater (aka F-15) giving me another 1.50 sq.” of air inlet, so my best case inlet area is now 11.625 sq.” so with the two ducts I am over 200% FSA best case and probably about 180% FSA taking the curvature of the wing into consideration.... I will go with that. So much for the rudimentary theory can we make these ducts...? the widest balsa I had in the stores was 4” so that is the first reduction in area but not too much so I will live with that. So now we have the other issue to address and that AUW of the model with packs and the unknown parameters of the TJ-100 fan, do I do it or not ha-ha that is question...? As I had nothing to lose and potentially everything to gain and a fair chance of success based upon my simple arithmetic time to hit the “GO” button. First job was to remove all the turbine specific equipment and of course the turbine, and weigh this big pile of expensive equipment  AIYO all this kit works out at 2.418Kg and the bit for the EDF version (excluding the packs) weighed in at 1.70 Kg. So I am down on weight by 0.718 Kg. which is a good start. If we now compare the weight of the fuel in the main tank and also the UAT tank to say 2 x 10S pack we get the following numbers. Kerosene weight 1.593 Kg. and 2 x 5S 5,000ma packs 0.940 Kg so I am on the winning side by another 0.65 Kg so heavy packs are possible. If we consider the Dry weight specified for the model was 16 lbs or 7.25 Kg the weight of the fuelled Boomer would be 8.78 Kg. and the planned EDF conversion 7.47 Kg. This all sounds good in theory so now we have to put theory into practice and achieve a AUW of 7.5 Kg. Max (including the packs) and then hope that the TJ-100 will have enough puff and Watts / lb. to get this bird flying on either 10 or 11S packs and as last resort 12S. So having removed all the turbine parts all we have to install is the fan the ESC is in the tail cone of the fan (more on this later) , two air valves and the receiver this is too simple to be true...  Next step – Design and making the ducts |
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Post by dennisp on Feb 5, 2009 18:20:49 GMT 8
Design and making the ducts So far too much maths, now time to get myself in trouble with the MOHA making the ducts and loads of saw dust around the house.... One of the criteria I set myself was to be able to fully build and cover the new ducts before final gluing to the model which did not prove to be a big challenge in the end, it also allowed me to make minor changes as the duct was built up. A cardboard template to get the contour of the wing and the anticipated shape of the duct drawn on same, the maximum width balsa I had was 4” wide as I mentioned before and as I had a stock of 3/16” and 1/8” in the stores this would be used to make the ducting. Looking at the L-39, Bae Hawk, F-14 and F-15 they all have a splitter plate between the fuselage and the inlet duct. Knowing these are not put on aircraft to look pretty and serve a useful purpose decision made to do the same. The cardboard template was checked against the fuselage to get an idea what could or could not be done as the case may be and as I had hope I could use one template to make the three inlet duct sides that were required for each inlet.     With the sweep of the leading edge it is important to ensure that at a later stage of the assembly the bottom lip of the duct can be added and at the same time the taper of the outside edge of the duct would match up after bending to the fuselage side pieces.  With these checks out of the way it was time to mate the two inside pieces of wood with the fuselage and chop the hole in the side of the fuselage to make the main air entry to the fan. The triangle on top of the wing will be used as a locating piece between the inside duct formers.  My that is a big hole was my initial reaction but better larger than smaller....!, the next step entailed using the MOHA’s window cleaner and soaking the outer inlet panels and bending these into shape.  First trial fit of all the pieces to the fuselage using clamps and “T” pins with jigs made to get the correct spacing of the ducts.  The next step was the gluing of the actual formers inside the ducts and the top and bottom inside ramps to help direct the air into the fuselage.  Top of the duct added with the additional cheater hole  Yet another trial fitting....!, with the front alignment jig added to allow the fitting of the outer panel of the duct.   All glued up with the front jig still pinned in place.  While all the PVA glue was setting it was time to make up the three pieces for the intake ring for the front of the fan from 3/16” x 4” balsa.  With the PVA fully set time to add the rear covers of the duct and sand some shape into the entire duct assembly.  Both ducts were now ready for covering, one of the nice things about the Boomer kit is you get spare covering film in the kit so this was used to cover the ducts with a nice colour match to the original.    |
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Post by dennisp on Feb 5, 2009 19:05:03 GMT 8
Time to fit the FAN As always a trial fit was performed to see if there were going to be any problems and apart from shaving off a little wood form the original turbine mounting plates the TJ-100 should just pop in.    The intake ring was sanded down to the correct shape and then trial fitted to the fan.  It was now time to do some MRO before I fitted the fan, I was never happy with pencil thin ROBART legs and had during the “dust collection” period obtained some Jet-1A legs designed for the Boomer which had bigger wheels and were the trailing link variety which are designed for better handling on grass strips. As always MRO is a pain as the legs were shorter than the ROBART ones which required the retract units being moved in closer and of course the bigger wheels meant enlarging the wheel well holes. Not exactly stressful a task until the mating of the legs to the Spring Air’s was attempted, AIYO the Spring Air’s were Imperial 3/16” and the Jet-1A’s were 5mm, which is a difference in diameter of some 0.25mm. It does not sound a lot but the shaft rocked about inside the leg like a drunken sailor. After much hunting around I managed to get some 5mm o/d brass tube which just slipped over the steel 3/16” leg shaft, some metal Epoxy was used to secure the brass tube to the steel rod. A word warning when using steel Epoxy if you have to do any grinding or drilling do this after 1 hour as the Epoxy will be semi cured and still possible to grind after the full time of 24 hours you stand no chance what so ever as this glue goes mega hard. With the MRO out of the way it was time to fit the fan and the inlet ring, which would need some trimming to fit inside the Boomer fuselage. Trying get cuts on a circular ring that are parallel is a real pain so another jig was made to ensure this could be achieved.   From the picture you can that the base is a square piece of plywood with a vertical line and a load of lines at right angles, you lay the ring on the jig and mark where you want to chop and rotate as necessary and you can get the right angle of the chop position and then it is onto the jig-saw for the cutting. With all the cutting of the inlet ring completed some fine sanding down and then a coat of PVA paste with a drop of food colouring (that is why it is that awful yellow colour...!) then sand again and repeat the process 4 times to get a nice smooth inlet ring. Although the colour is terrible it was a good guide when doing the sanding as it enabled the high and lows done by yours truly to be corrected. I made possibly a big mistake in that I decided to fit the inlet ring to the fuselage former rather than to the fan, it not impact the fitting of the fan but was going to bite me at a later stage.   With the major part of the fan fitting out of the way time to fabricate the exhaust tube, which is 85% of the fan swept area, the tube was made of clear plastic sheet with packing tape re-enforcement at the fan and exhaust ends. The fan end has ½” wide single sided sponge tape to ensure a good seal on the fan casing. A quick spray of gun metal and another job completed.   We are now on the home straight with not a lot more to be done, here are some pictures of the fan installed in the Boomer’s fuselage.    |
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Post by dennisp on Feb 5, 2009 19:26:55 GMT 8
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Post by dennisp on Feb 5, 2009 20:05:38 GMT 8
That first taxi and the first disaster...! Well things did not go as planned and Murphy’s and Sod’s law struck with a vengeance... to avoid temptation I had just brought the fuselage for the taxi set so there was no chance of flying which turned out to be a very wise decision. Everything installed Tx ON, Rx ON, main power ON, the “GO” stick was moved and the TJ-100 spun into life albeit a very short one two quick blips to ½ throttle and the CC 110 decided it had enough of this and that was the end of the show no taxi just a short power up. The ground crew tried everything to get the CC110 to co-operate but without success and always thanks guys it was a splendid effort, so the Boomer returned to the workshop with a dead “donk” (airline slang for engine). The fan was removed and as I mentioned at the start of thread the tail cone was removed from the TJ-100 to get at the ESC, no signs of any burning just a “duff” ESC, I re-assembled the fan and then contemplated what the next step should be. The obvious was to return the fan to Tam Jets but that could take weeks or fit a new ESC from the stores. With Chinese New Year fast approaching I was placed in detention for making far too much saw dust in the house..., but I had decided that OK let us mount the ESC external to the fan and if it should need replacing it would not be a major task. I should point out that the fitting of the CC110 inside the tail cone of the fan is a work of art..! The CC-110 ESC is quite big and where to mount this in the fuselage caused the brain to work overtime especially as I was on limited pass for any sanding, sawing or drilling with CNY just a few days away. The obvious was needless to say staring me in the face why not put the ESC in the “Shrek” ears hole that was now blanked off but the new ducts.? By sheer luck it fits like a glove and enlarging the “Shrek” holes to take the ESC was an easy job with little mess (brownie points for yours truly from the MOHA). Needless to say you win some and lose some ....! the inlet ring would have to be removed and trimmed to clear the height of the ESC AIYO.  The next instant problem was how to hold he ESC in place as it was in the inlet area of a 12lb suck from the fan.... Again the obvious move the fan forward ¼” and then use the inlet ring to restrain the fan, this presented another set of problems in the fan mountings would need to be replace as the new holes that would be required just happened to be where the fan mounting rings were located. Too late now to go back so a real big pile of saw dust was created removing the old mounts, making new ones and as the fan was closer the former in front of the fan the centre of this former was removed... yep you guessed MOHA withdrew all my brownie and points and I was in a negative state and deep you know what for the dust that I had created.. While doing the Cg tests I determined the model was nose heavy so the receiver battery was located under the exhaust as far back as possible.  With all the mess making completed and two days to CNY it was time to re-assemble the fan in its new location.   I had some odd ball thoughts (you get these when you older) there was something wrong with the Cg as the Boomer is known to be tail heavy, once again the Cg was rechecked and my thoughts proven correct, so the receiver pack was removed from the back to the front and we were back in business once again. The Jet-Tronik valves were giving me agro so I decided that for the first flight forget about brakes and retracts as we have an EDF model and not a hot blow lamp one, which could injury if it went out of control on taxing. One last set of checks and the packs were charged ready for the repeat of the taxi tests. |
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Post by dennisp on Feb 5, 2009 20:41:30 GMT 8
The second taxi and the first flight... So you are all wondering how heavy is the model now?, well the initial weight estimates proved almost spot on at 7.3Kg (2 x 5S packs installed) or 16.09 lbs just over the dry weight of the turbine model so I was lighter by the fuel load of the turbine version and I was fitted with retracts and brakes.... good result. With the packs charged we were all set to go for testing, taxing proved OK with the taxi packs although a crosswind made tracking a little challenge, the ground crew checked everything out and it was time go for that big jump into the skies or not as the case may be. The ground then checked and rechecked the Cg with the two 5S 5000mA and there were no more reasons not to go. So it was ¼ flap for take-off “Go” control advanced and about 50 meters later she was airborne and climbing away nicely. Yes from fading old brain she flies just the turbine one which was very good news. I had set the Tx timer to 4 minutes as a best guess and the beeps were soon coming loud and clear and the Boomer was returned to mother earth. As I advised my brain totally failed as forgot to give one of the ground crew the Cannon to shoot the Boomer in the sky on 10S drat and double drat... So I can only show you the model after that first flight but there will be some in flight pictures coming very soon...    Special thanks to ground crew (DT, ER and Capt. Harn) for making the first flight a success. |
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Post by dennisp on Feb 5, 2009 21:02:40 GMT 8
On the return to the hanger the Watt-meter was connected to see just what was going on and with the used packs the Input Amps were 62 and the power just over 2KW. The good news is that this confirms that 2,000 / 16.09 = 124Watts / lb which is below the 150 criteria I had hoped for this big model will fly. Probably with fresh packs the Watts will be higher so this is a key check for the next flight. I shall probably go for a 11S configuration as this is the normal requirement for a TJ-100. I shall also be checking just how much energy was used from the packs when I re-charge then which will be another useful piece of information to have.
An update will be provided after the next flight....., coming soon..., so stay tuned to this channel.
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Post by dt8666 on Feb 5, 2009 22:09:19 GMT 8
Fantastic detail build! Welldone and Keep it coming Dennis!
And congratulations to the successful maiden and you EDF conversion!
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