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Author Topic: Wot 4 turbo prop  (Read 1716 times)

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Offline JimG

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Wot 4 turbo prop
« on: June 10, 2017, 20:15:25 PM »
This board has basically became a spam sit for one posters videos (aren't they meant to be put in FuelTube?).To bring it back to what it used to be I will show the conversion of a Wot4 extreme to turbo prop power.
Having retired last Christmas I ended up with a bit more money than expected so decided to give myself a present of a Wren 50i Turbo prop. I now needed a plane to put it in so looked around for one to suit a similar sized petrol. The most obvious ones like a Tucano or P21 would give me problems in transporting them due to the fuselage length. (At present I carry my models on a trailer towed by a motorcycle which does limit size. I had previously looked at the Wot 4 extreme for an MVVS 45 I have and decided to buy one and convert it to the turbo prop. Ripmax give a recommended engine size as a 55 petrol and Wren give the turbo prop as an 80cc petrol equivalent, however the turbo prop can easily be downrated by restrictng the maximum turbine revs.

I don't intend to show the full build as the Wot is just another ARTF (just  a bit bigger than most) and goes together like any other ARTF. I just intend to ducument the modifications needed to convert to the different power system.

Jim
« Last Edit: June 10, 2017, 20:30:44 PM by JimG »
Jim Gill
Dundee Model Aircraft Club


Offline JimG

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Re: Wot 4 turbo prop
« Reply #1 on: June 10, 2017, 20:26:57 PM »
The first step was to make a hole in the firewall to take the turbo prop. A template is provided by Wren for this although I found that this had been copied slightly undersize (96%), this was copied with a slight zoom (1.04 times) to make it the right size.
After marking the firewall the hole was chain drilled then cut out with a keyhole saw and sanded to size with a Dremel.
The compartment behind the firewall has a plate for the throttle and choke servos so the mounting blocks for this were removed leaving a clean compartment. A removeable top hatch is part of the kit making it easy to access here.

Wren recommend a 1.5l tank so room had to be made to fit a Sullivan 50oz tank. Part of ythe wing doublers at the fuselage top had to be removed first then the original tank mounting floor was also removed. A new tank bay floor was fitted to bring the tank up to fit the former between the tank bay and the front compartment.

The fuselage insides were then given a coat of epoxy to seal them.

Jim
Jim Gill
Dundee Model Aircraft Club

Offline JimG

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Re: Wot 4 turbo prop
« Reply #2 on: June 10, 2017, 20:40:57 PM »
Once the epoxy had hardened the tank could be shoehorned in. It needs to be low to stop it clashing with the starter motor on the turbine. The pipes into the tank even had to be bent slightly downwards to give them more clearance.

The turbo prop unit was them fitted temporarily, I just used screws at the moment as I am waiting for the proper bolts and blind nuts to make the proper fitting.


The front compartment is just long enough for the turbine to fit. A spacer could be fitted to the front of the firewall to move it forward but I have left it as it is to allow for the fitting of the cowl.




Jim
« Last Edit: June 10, 2017, 20:48:14 PM by JimG »
Jim Gill
Dundee Model Aircraft Club


Offline JimG

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Re: Wot 4 turbo prop
« Reply #3 on: June 10, 2017, 20:47:51 PM »
The next step will be to fit the supporting hardware for the turbine. This is still at the planning stage so may change over the next few days.
There is a radio tray at the rear of the wing opening which has the rudder servo and receiver at the moment. It would be a tight fit for all of the rest of the equipment so I will probably be fitting a ply plate over the top of the tank for much of this. I am not sure where I will fit the batteries (3 2S lipos, one for the turbine and two for the radio.) but this will need to wait till all of the rest is finished and the CG checked.


Jim
Jim Gill
Dundee Model Aircraft Club

Offline Charlie C

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Re: Wot 4 turbo prop
« Reply #4 on: June 10, 2017, 22:25:06 PM »
Mmmmmm,

Brilliant stuff, keep it coming chap :af

Charlie C
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Offline JimG

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Re: Wot 4 turbo prop
« Reply #5 on: June 13, 2017, 12:08:21 PM »
The next step was to start fitting the hardware for the turbine. The instructions for the fuel pump say that it should be mounted vertically with the pump outputs downwards. This is so that if the pump should leak it keeps fuel out of the motor. They also give a minimum distance from the pump to starter motor of 100mm, this puts it behind the tank bay where there are convenient slots in the mounting plate . The first step was to print a suitable mount for the pump.

This was mounted to the pump with a touch of glue to keep it secure. It was then screwed to the radio plate with the pump through the plate, the pipes were brought up through an adjacent slot.


A ply plate was then mounted over the top of the tank which had been held down with ties. The tank is now semi permenantly fitted as it would be difficult to remove. The valves were mounted to this plate and could be plumbed into the pump. An air trap was fitted to the top of the main tank and the rest of the plumbing completed. The vent from the main tank is still needing fitting to a pipe through the side of the fuselage. The air trap tank is held down with velcro but once the wing is on it will hold it securely.


Jim
Jim Gill
Dundee Model Aircraft Club

Offline JimG

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Re: Wot 4 turbo prop
« Reply #6 on: June 13, 2017, 12:22:44 PM »
The Fadec was now mounted between the pump and the Rx and the connections from the pump, valves and throttle set up.

I am intending to use 2 2S Lipos as power for the radio and have fitted a Powerbox Systems Baselog to the model. This will provide regulated power to the receiver and has a high enough current output to drive the high torque digital servos fitted. There are also 2 power outputs to the Rx to help provide the power. An extra ply upright was fitted to the side of the fuselage and the Baselog fitted with servo screws (mountings with grommets were provided for this.

The remote switch was then fitted to the fuselage side under the front of the wing. This allows one or both batteries to be switched on and will failsafe to its last setting, possible switch failure in fligh will leave the radio on.
ila_rendered
The last step will be to fit the turbo prop , check the CG and fit the batteries. An air intake will also need to be fitted to provide cooler air for the turbine, this will be either on top of or below the turbine compartment.

Jim
Jim Gill
Dundee Model Aircraft Club


Offline JimG

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Re: Wot 4 turbo prop
« Reply #7 on: June 16, 2017, 14:20:16 PM »
A quick check on CG showed that the batteries would need to be as far forward as possible. This meant fitting them in the same compartment as the turbine. To keep heat away from the LiPos a divider would need to be fitted between the batteries and turbine,
The first step was to cut a hatch in the bottom of the nose for access to the batteries.

This was sized to allow the 2200 2S Lipos to be easly inserted but keep as much of the bottom as possible. The original platform for throttle and choke servos for a petrol engine was re purposed as a turbine compartment floor above the batteries. It was painted with BVM Heat Shield as a protection. The holes were left to allow airflow from a scoop on the bottom and provide cooling air for the nose compartment.

The batteries were mounted in the bottom using velcro and high density foam packing and are nice and secure.
The front of the hatch cover was raised to form an intake to provide cooler air while the engine is running.



Jim
Jim Gill
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Offline JimG

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Re: Wot 4 turbo prop
« Reply #8 on: June 16, 2017, 14:37:33 PM »
To make sure that there is a good flow of air to the turbine the top hatch had an opening cut. This was covered with metal mesh to make the opening less obvious. While the hatch is held down at the rear with magnets there is a hold down screw as well making it secure in flight. Having this opening at the top should help with cooling airflow once the turbine is shut down and after the cooling cycle stops.


To give some airflow over the gearbox at the front a couple of intakes were made in the front of the cowling.

The plane is now basically ready for the engine to be run however before flight it will need to be balanced. Initial measurement using a Xicoy CG system showed that it will need quite a bit of noseweight to get the CG correct.

Just a couple of comments about the model itself. Overall the quaility is quite good but the covering was badly shrunk when it arrived, most of it needing going over with a covering iron to remove wrinkles and bubbles. The clevises will all be replaced before flight. There are reports of the clevises provided witrh the XL and large Acrowot being loose on the rods, with some pulling free from the rod with a strong tug. These clevises are tight fitting on the rods and I couldn't pull them loose but so far two of them had the clevis pin break free. These pins are just a tight fit in the clevis and not rivetted like the better quality ones. They will all be replaced with SLEC versions brfore it will be trusted for flight.

Jim
Jim Gill
Dundee Model Aircraft Club


Offline retflyer

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Re: Wot 4 turbo prop
« Reply #9 on: June 17, 2017, 13:39:54 PM »
Good to see this, I almost did it myself. I had a 44 turboprop in 3 different models over a 9 year period but after down sizing my car I sold my last big model.
Looking forward to hearing how it flys, you will enjoy running the engine.
Barrie

Offline JimG

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Re: Wot 4 turbo prop
« Reply #10 on: June 18, 2017, 20:26:56 PM »
Took the plane down to the field today to give the engine a run. I didn't have time to get the CG set so no chance to give it a test flight, still tail heavy. It was also rather windy so it wouldn't have been the best day to test fly it.




I left the cowl off for these test runs to make sure that the gearbox kept cool, it was a rather warm day.
<a href="http://www.youtube.com/watch?v=4ViPm3927Q0" target="_blank">http://www.youtube.com/watch?v=4ViPm3927Q0</a>

Jim
Jim Gill
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Offline JimG

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Re: Wot 4 turbo prop
« Reply #11 on: June 23, 2017, 20:18:35 PM »
Bought some lead flashing so was able to set the CG. sheets were epoxied and bolted to the sides of the front engine bay with some smaller sections fitted to the top hatch at the front. In all around 1000g of lead was added to give the CG a couple of mm in front of the rear position. (there is 10mm difference between the front and rear CG positions). The CG was set using the Xicoy balancer then checked using fingers under the wing. The total weight is 9.99Kg with an empty tank.


The CG position is further forward than I had expected, oround 27% of chord at the rear position not the usual 30 to 33% . Waiting now for some decent weather to give it it's test flight. Forecast for this weekend is rather windy (up to 20mph) :banghead: (no heatwave up here this week)

Jim
Jim Gill
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Offline Alan H

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Re: Wot 4 turbo prop
« Reply #12 on: June 24, 2017, 10:48:19 AM »
Interesting project, I hope the test flight goes well. Look forward to the report on it (and possible video?)

Offline JimG

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Re: Wot 4 turbo prop
« Reply #13 on: June 24, 2017, 19:56:46 PM »
With 2 servos per wing half this means that 4 wires have to be plugged into the Rx everytime the wing is fitted. If there is any wind this becomes quite awkward as around 10 sq feet of wing acts as a good sail. It also leaves 4 wires hanging loose inside the fuselage. I therefore decided to try and simplify the wiring using MPX plugs, this also allowed the extra battery connector from the Powerbox Baselog to be connected straight to the wing servos, not sending power through the Rx. As the wings can't be kept in one piece but must separate for carrying this needed a second MPX plug to link the wings together.

To reduce the number of wires needed 3 of the servos only used the signal wires, no plus or minus needed as there is a separate power supply to the wing servos. The 4th servo uses all the wires.
Plug holders were printed to take the MPX plug and these were screwed to the wing. I kept the plugs horizontal so there is no downward pull from the wires although MPX plugs are tight fitting.


The wires from the RX were tie wrapped together to give a single harness.

With only a single plug to fit on the wing this will now make it much easier to set everything up at the field and reduce the number of possible loose wires inside the radio compartment.

Jim
Jim Gill
Dundee Model Aircraft Club

Offline JimG

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Re: Wot 4 turbo prop
« Reply #14 on: July 24, 2017, 19:29:22 PM »
I took the opportunityof some good flying weather to take the Wot down to the field today to test fly it. With a light wind almost down the runway things were looking good for flight.I fitted a 22 x 10 prop which gave around 2750 revs on the ground and plenty of thrust. FIrst flight it was a bit slow off the deck and proved to need quite a bit of up trim for level flight, probably around 50% trim. Looks like I might be able to remove some of the nose weight. I found it flew with around 1/3 to 1/2 throttle and was using 70% rates on elevator and full rates on ailerons, roll rate was about right with this. I didn,t try any looping manouvers at this stage so can't confirm if the lower rate on elevator is right although it felt OK for normal flying. I checked the flaps out and found little attitude change and no need for flap / elevator mixing.
After around 5 minutes it was time to land and the first approach was without flaps, it came in a little fast and wasn't settling down after cutting throttle so I tried full flap to slow it down. All this did was add lift so full throttle was given to go around again, power coming on just before running out of room and reaching hte fence at the end of our runway. Full power does give as good climb rate so it ended up OK. The next approach I started from further out and was able to slow it down better so once over the threshold power was cut and it settled down to the runway with a little bounce when the wheels touched (the undercarraige legs do have some spring in them).
It was flown for a second flight later on with a bit stronger wind which helped it slow down better for landing.
I found that taxying was a bit tricky at times, getting the right amount of throttle to taxy was not easy and if too much was given there is a delay between lowering throttle and prop revs reducing. It proved to be easy to get a bit of a runaway on taxy, perhaps this is where brakes could come in handy.
A friend took a video of the first flight with his phone and I am waiting for him to send it to me so will make this available when I can.
One thing very noticable  was that the flight was very quiet compared to what you might expect from such a large model, most of the noise was due to the prop and gearing, not the turbine.

Jim
Jim Gill
Dundee Model Aircraft Club

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Re: Wot 4 turbo prop
« Reply #15 on: July 24, 2017, 21:04:38 PM »
Hi Jim, nice to hear the test flights went well. The taxying problem is always there with a turboprop even on full size, brakes can help but the risk of tipping onto the nose is greater. Your prop sounds a bit small, I always ran mine on a 24 x 12 and Mike at Wren said that was only just enough.
Barrie

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Re: Wot 4 turbo prop
« Reply #16 on: July 25, 2017, 13:44:14 PM »
Hi Barrie
you might be right about the prop size, just checked the tacho and it was set to the wrong number of blades so don't know the actual ground rpm. The turbine is still set to lower max rpm as it is still below the 1 hour running in time. I do have a 22 x 12 prop which I can use and will check this weekend when next at a flying field. Both props are within the range given in the instructions. In flight there was no sign of over revving and virtually allow of the fights were less than half throttle so unlikely that it reached more than the maximum rpm in the air.

Jim
Jim Gill
Dundee Model Aircraft Club

Offline Neil Byrne

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Re: Wot 4 turbo prop
« Reply #17 on: July 25, 2017, 17:01:57 PM »
Hi
Nice turbine !
What setting was the tacho?
Regards
Neil B

Offline JimG

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Re: Wot 4 turbo prop
« Reply #18 on: July 25, 2017, 17:55:05 PM »
Hi Neil

when I checked it today it was on a 5  blade setting. A little bit of arithmatic gives a litlle under 7000 revs on the ground, this should still be under the 9000rpm max in the air.  The 22 x 12 prop I had tested earlier worked out to around 5500 revs which would be well under the max in the air.

Jim
Jim Gill
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Re: Wot 4 turbo prop
« Reply #19 on: September 24, 2017, 17:01:11 PM »
Hi Jim,
How is the Wot 4 going, fully wrung out now I expect. I am still thinking of doing this myself, could you tell me the overall length from tip of prop shaft to tip of tail, need to know it will go in my car.

Barrie.

Offline JimG

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Re: Wot 4 turbo prop
« Reply #20 on: September 24, 2017, 19:46:40 PM »
Hi Barrie,
still flying well, it was flown this afternoon down at the club field. Not flown enough yet to be fully wrung out but I am at ease with flying it. There is a short video on the Dundee clubs facebook page https://www.facebook.com/dundeemodelaircraftclub/videos/vb.1567111516914087/1786837868274783/?type=2&theater although it only shows the takeoff not the rest of the flight.
The length is 185cm or about 72 3/4 in. I don't know how well it fits in cars as mine travels on top af a small trailer towed by a motorbike.

Jim
Jim Gill
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Offline JimG

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Re: Wot 4 turbo prop
« Reply #21 on: September 25, 2017, 10:12:07 AM »
Hi Barrie
a bit more size information.
Tailplane span is about 30 in or 76cm.
Fin Height  is 20 in or 50.5cm from fin tip to bottom of tailwheel.
Fuselage height at the main wheels is 17in or 43.5cm.

Jim
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Re: Wot 4 turbo prop
« Reply #22 on: September 25, 2017, 19:44:13 PM »
Thanks for that, will check if it will fit.

Barrie

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Re: Wot 4 turbo prop
« Reply #23 on: September 30, 2017, 19:20:39 PM »
Wot 4 is too long, so I have decided to refit the Turbo into my Graupner Taxi where it started out almost 10 years ago. The Taxi has been flying with a 30cc petrol for the last 8 years.


 

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