Post by dennisp on May 11, 2009 22:51:50 GMT 8
Background
The Velox is a twin boomed model like the Boomerang but a lot sleeker and with a better aerodynamic shape, all my contacts advised me not buy it as it had a reputation to “Cobra” at low speeds and high “alpha” angles of attack. Some research on the web revealed that the Cg as published was too far back and once moved forward then the Velox was tamed, double checked this with my Cg programs and it looks like the way to go with caution.!!
The construction of the model as supplied is a composite fuselage and booms with balsa wings and stabilizer that are glassed, with a total weight with a turbine fitted of 8Kg this was going to be a real challenge on weight control and any sort of performance regardless of how aerodynamic the model shape was. I started to have some second thoughts as to was this really possible to convert to EDF so with the aid of an aeronautical engineer from Beechcraft in the USA a spreadsheet was created to see whether this brick would really fly on the current 6Kg fans that are available. The theory seems to indicate that it should fly well on 11S and even on 10S but I suspect it would need the length of the TPE to get airborne, 12S however there should be no problems at all but we are adding extra weight to an already heavy model. At this stage of the project the estimated weight of the model was 8.49Kg..!! with 12S packs and 8.37Kg with 11S packs.
As with most China models there are no instructions provided so a search on the web to the US distributor showed that they had done a manual for the Velox. The manual is like a Great Planes one 52 pages of pictures on how to build the turbine version. The basic assembly of the retracts and servos was completed as per the manual so I had a raw airframe all set for the conversion process.
The original plan was to use a StuMax SM110/52 fan but this became impractical once I discovered the upside down mount of the turbine would not allow the SM fan to fit without some major surgery to the model to clear the fan fixing mountings. So like the Boomerang conversion this will be powered by TAM Jets TJ-100 fan with a 1515-3D motor which should allow the use of 12S packs.
To further save the packs based upon the experience gained on the EDF conversion of the Boomer the Capt. Kindly obtained some 30C 5,000mA 5S and 6S packs for me, which needless to say are slightly larger than the TP V2 packs that I had used on the Boomer conversion and also a tad heavier.
Conversion begins
The next big step was to make a tray to carry these large packs inside this shapely fuselage, the curvature of the fuselage does not lend itself to big “brick packs”, several dry runs were performed before the initial layout was determined. I also wanted to mount the packs on their sides so should there be any “bloating” of the pack from the high currents they would not wedge themselves sort of permanent in the model. As it turned out this orientation of the pack also allowed the pack to fit further into the curvature of the fuselage.
The original tray was too high to get the packs in so a new tray was fabricated with the associated support beams for same.
Needless to say as the conversion proceeded there would be further modifications to the battery tray, a second tray would be required for the avionics (receiver, BEC and the data logger). The data logger will be used to validate the theory with practice and will apart from the usual power monitoring include logging of altitude and air speed of the model, may also help if the beast does decide to do a “Cobra” after all.
With the packs using all the available space there was no room for a the air services valves and gauges so a sub panel was fabricated to hold these items and was mounted in front of the nose retract.
The next item to receive attention was the avionics tray, the tray was designed so the centre of the tray should be clear for the data logger and also the big 10AWG power cables.
Loads of pipes already and fortunately the avionics tray would be at the same level as the tray would be for a turbine model, it also provided room as the build progressed to hide all the pipes and wires.
With very limited clearance under the battery tray the air pipes had to clipped into place to ensure the brake and gear servos did not squash same.
At the same time I have learnt from experience that all trays must be removable for MRO or fixing things that go wrong…!!, so the pipes and wires have to be long enough to allow this but at the same time have sufficient space to hide the slack wire and pipes.
The battery in the service position
The tray lowered into the fuselage.
Being a rear mounted turbine sport jet the only additional work here was the making of the inlet ring for the fan and the paper template for the fan cover.
Both trays were then fitted to see how things were or not as the case may be…?
If you look closely at the pictures above and below you can see the static air pressure port on the side of the fuselage and the ASI probe on the wing root held with tape while the glue sets.
Things are finally getting sorted most of the wires have homes to go to and the same applying to the air-pipes which was good news not to have any spare ones, every wire has an id at both ends so as to reduce errors at connection time and every air pipe function is a different color pipe so it was just as case of join the same colors together….!
The 10AWG power cables surface through a small hole in the fan area, I am getting good at fishing for wires and pipes from building this model. Again I learnt the easy way to do this… piece of cord / string tie a ¼” wheel collet on the end and drop down the hole a few shakes and bingo you have a draw string.
I made from the paper template a plastic card cover and with my low skill spraying managed to get the colors close…
So now for the 1st assembly of the brick….., OMG it is a big model….., perhaps it is a concrete block..?
The push pull steering wires connected to the steering servo and this was the start of several problems..
I originally planned to use a servo reverser to get the two rudders and NLG steering to all go the same direction, after the initial power up I discovered I did not need a servo reverser and could use “Y” leads. Easy to adjust the rudders but there is no adjustment on the steering wires….. back to drawing board again…
After a while I found some turnbuckles which could be used with the 2-56 clevis and the problem was resolved..
The next disaster was the receiver pack would not slide under the NLG retract, Ooop’s where to put….?, the steering problem solved this one for me as I can then locate the receiver pack where the servo reverser was located. Umm have to pull a few wires here and there to match this new location….
The next problem to hit the conversion was the nice fan cover..! the intake of the TJ-100 has no support and is quite thin carbon fiber and the load of the 1mm plastic fan cover when it was fitted actually distorted the front of the fan casing just to get a very light rub. So once again back to the drawing board for a new solution…
I decided to chop the original composite turbine cover and just fit as a cover over the fan without the nice snug fitting around the fan, not elegant but there is no stress or loads on the fan casing.
Time to fit the data logger in place and this seemed to go to plan with the power cables running down through the center of the fuselage, the white bullet sleeves are the anti-spark connections, essential for 10S upwards.
So it is time for the set up and Cg checks…… stay tuned for the next step…
The Velox is a twin boomed model like the Boomerang but a lot sleeker and with a better aerodynamic shape, all my contacts advised me not buy it as it had a reputation to “Cobra” at low speeds and high “alpha” angles of attack. Some research on the web revealed that the Cg as published was too far back and once moved forward then the Velox was tamed, double checked this with my Cg programs and it looks like the way to go with caution.!!
The construction of the model as supplied is a composite fuselage and booms with balsa wings and stabilizer that are glassed, with a total weight with a turbine fitted of 8Kg this was going to be a real challenge on weight control and any sort of performance regardless of how aerodynamic the model shape was. I started to have some second thoughts as to was this really possible to convert to EDF so with the aid of an aeronautical engineer from Beechcraft in the USA a spreadsheet was created to see whether this brick would really fly on the current 6Kg fans that are available. The theory seems to indicate that it should fly well on 11S and even on 10S but I suspect it would need the length of the TPE to get airborne, 12S however there should be no problems at all but we are adding extra weight to an already heavy model. At this stage of the project the estimated weight of the model was 8.49Kg..!! with 12S packs and 8.37Kg with 11S packs.
As with most China models there are no instructions provided so a search on the web to the US distributor showed that they had done a manual for the Velox. The manual is like a Great Planes one 52 pages of pictures on how to build the turbine version. The basic assembly of the retracts and servos was completed as per the manual so I had a raw airframe all set for the conversion process.
The original plan was to use a StuMax SM110/52 fan but this became impractical once I discovered the upside down mount of the turbine would not allow the SM fan to fit without some major surgery to the model to clear the fan fixing mountings. So like the Boomerang conversion this will be powered by TAM Jets TJ-100 fan with a 1515-3D motor which should allow the use of 12S packs.
To further save the packs based upon the experience gained on the EDF conversion of the Boomer the Capt. Kindly obtained some 30C 5,000mA 5S and 6S packs for me, which needless to say are slightly larger than the TP V2 packs that I had used on the Boomer conversion and also a tad heavier.
Conversion begins
The next big step was to make a tray to carry these large packs inside this shapely fuselage, the curvature of the fuselage does not lend itself to big “brick packs”, several dry runs were performed before the initial layout was determined. I also wanted to mount the packs on their sides so should there be any “bloating” of the pack from the high currents they would not wedge themselves sort of permanent in the model. As it turned out this orientation of the pack also allowed the pack to fit further into the curvature of the fuselage.
The original tray was too high to get the packs in so a new tray was fabricated with the associated support beams for same.
Needless to say as the conversion proceeded there would be further modifications to the battery tray, a second tray would be required for the avionics (receiver, BEC and the data logger). The data logger will be used to validate the theory with practice and will apart from the usual power monitoring include logging of altitude and air speed of the model, may also help if the beast does decide to do a “Cobra” after all.
With the packs using all the available space there was no room for a the air services valves and gauges so a sub panel was fabricated to hold these items and was mounted in front of the nose retract.
The next item to receive attention was the avionics tray, the tray was designed so the centre of the tray should be clear for the data logger and also the big 10AWG power cables.
Loads of pipes already and fortunately the avionics tray would be at the same level as the tray would be for a turbine model, it also provided room as the build progressed to hide all the pipes and wires.
With very limited clearance under the battery tray the air pipes had to clipped into place to ensure the brake and gear servos did not squash same.
At the same time I have learnt from experience that all trays must be removable for MRO or fixing things that go wrong…!!, so the pipes and wires have to be long enough to allow this but at the same time have sufficient space to hide the slack wire and pipes.
The battery in the service position
The tray lowered into the fuselage.
Being a rear mounted turbine sport jet the only additional work here was the making of the inlet ring for the fan and the paper template for the fan cover.
Both trays were then fitted to see how things were or not as the case may be…?
If you look closely at the pictures above and below you can see the static air pressure port on the side of the fuselage and the ASI probe on the wing root held with tape while the glue sets.
Things are finally getting sorted most of the wires have homes to go to and the same applying to the air-pipes which was good news not to have any spare ones, every wire has an id at both ends so as to reduce errors at connection time and every air pipe function is a different color pipe so it was just as case of join the same colors together….!
The 10AWG power cables surface through a small hole in the fan area, I am getting good at fishing for wires and pipes from building this model. Again I learnt the easy way to do this… piece of cord / string tie a ¼” wheel collet on the end and drop down the hole a few shakes and bingo you have a draw string.
I made from the paper template a plastic card cover and with my low skill spraying managed to get the colors close…
So now for the 1st assembly of the brick….., OMG it is a big model….., perhaps it is a concrete block..?
The push pull steering wires connected to the steering servo and this was the start of several problems..
I originally planned to use a servo reverser to get the two rudders and NLG steering to all go the same direction, after the initial power up I discovered I did not need a servo reverser and could use “Y” leads. Easy to adjust the rudders but there is no adjustment on the steering wires….. back to drawing board again…
After a while I found some turnbuckles which could be used with the 2-56 clevis and the problem was resolved..
The next disaster was the receiver pack would not slide under the NLG retract, Ooop’s where to put….?, the steering problem solved this one for me as I can then locate the receiver pack where the servo reverser was located. Umm have to pull a few wires here and there to match this new location….
The next problem to hit the conversion was the nice fan cover..! the intake of the TJ-100 has no support and is quite thin carbon fiber and the load of the 1mm plastic fan cover when it was fitted actually distorted the front of the fan casing just to get a very light rub. So once again back to the drawing board for a new solution…
I decided to chop the original composite turbine cover and just fit as a cover over the fan without the nice snug fitting around the fan, not elegant but there is no stress or loads on the fan casing.
Time to fit the data logger in place and this seemed to go to plan with the power cables running down through the center of the fuselage, the white bullet sleeves are the anti-spark connections, essential for 10S upwards.
So it is time for the set up and Cg checks…… stay tuned for the next step…
