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#1) 
 Post subject: Durafly Spitfire EP
PostPosted: 19 Nov 2010 16:24 
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Here's my latest "baby"....a Durafly Spitfire! (courtesy of Hobbyking and my Dad as a b'day gift!). :D She's a big 'un for a foamie: 1.42m (55.9'') wingspan, 1.65 kg, Retractable Landing Gear :shock:

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My Dad actually needs to take almost all of the credit for this one, you can't see it but he has done a LOT of work on her before maiden. The stock prop has been upgraded, the aileron servos that were in the wing roots operating through an inefficient bellcrank system have been moved outboard to directly actuate the ailerons, and all stock servos (apparently a bit of a weak point) have been exchanged for Hextronic HXT-900s. It is currently running a 3S 2600 mAH Lipo, and I've put in a new Spektrum AR600 (This model was the tipping point for "forcing" me to upgrade to a DX6i ;) )

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I've had to wait a bit as one of the servos operating the gear (a standard servo) failed almost immediately out of the box, but finally got the geometry right on the new replacement servo (a "retract" servo). The gear mechanism itself is a nice one with a sliding pin arrangement that locks at both ends (which unloads the servos) and mounted on good solid wheel wells that should be pretty beefy for landings. Looks better set up than the FMS setups!



I just need to finish up some wiring tidy ups and fit some belly skids (I'm not sure I'm quite going to be able to get away with gear down landings at my local flying field....we'll see). Flight report hopefully coming soon! :)
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#2) 
 Post subject: Re: Durafly Spitfire EP
PostPosted: 19 Nov 2010 18:55 
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Location: Salisbury, England
Ooh nice one Ben! :D Pretty much the same size as the FMS one I was looking at the other day in my LHS, I've also heard negative things about their retracts but I also heard that they'd done something about it on the later models.
I'm still thinking about getting one - probably seeing the flight vid of yours will convince me :)

Hats off to your dad for the work done ;)

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My site is rc-airplane-world.com, a beginners' guide to radio control flying.


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#3) 
 Post subject: Re: Durafly Spitfire EP
PostPosted: 19 Nov 2010 19:31 
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Location: Lake Charles, Louisiana
Good looking plane Ben, Looks like you have taken care of the weak points. Good luck with the first flight.

Dave F


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#4) 
 Post subject: Re: Durafly Spitfire EP
PostPosted: 19 Nov 2010 21:05 
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Pete wrote:
Ooh nice one Ben! :D Pretty much the same size as the FMS one I was looking at the other day in my LHS, I've also heard negative things about their retracts but I also heard that they'd done something about it on the later models.
I'm still thinking about getting one - probably seeing the flight vid of yours will convince me :)

Hats off to your dad for the work done ;)


Thanks guys! :) Pete, Dad's now got the FMS P-51 and FMS P-47 and he's had a couple of niggling issues with the landing gear on these. These are set up with servoless retracts which mount directly onto the foam wing. It probably works OK on surfaced or cricket pitch like grass, but in the more uneven stuff has not fared as well. The P-51 broke a main bolt on one of its retract drives after landing with 1 wing a bit down. Been about 8-10 weeks on back-order for replacement units but nothing as yet.

With the P-47, because the gear mounting is into foam, it started pulling out from the wing from the whole unit wanting to "twist" backwards from ground drag. The geared mechanism can also be a little prone to binding and the motor not have enough grunt to overcome this leaving the gear hanging down, partially retracted (the gear motors cut-off after a couple of seconds of operation, no matter where the gear position is), which necessitated some dismantling and sewing machine oil. The resistance/torque of the setup also started to exceed the capacity of the BEC leading to a ~0.2V drop (to ~4.8V) when retracting the gear upwards, which isn't a nice thing to do to his Spektrum receiver! :shock:

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#5) 
 Post subject: Re: Durafly Spitfire EP
PostPosted: 19 Nov 2010 21:38 
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This is why I haven't fooled with retracts. Take the gear off and throw it in the air. Retracts are cool, but I am not ready for the pain.

Dave F


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#6) 
 Post subject: Re: Durafly Spitfire EP
PostPosted: 29 Nov 2010 12:51 
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Well it took awhile before both weather and schedules permitted a maiden, but I finally got her up! :) Gave me a chance to test/fix a couple more things anyhow....

So short report as follows:
Details
This is a big scale EPO foam Spitfire that is a larger and heavier than, say, Parkzone warbird models. In size, weight and details I would say it is more akin to the large FMS models. It has a 1.4 m wingspan with a very generous chord and wing area, however. The control surfaces are similarly very generous.

Quality-wise, the foam and finish are very good, although the paint doesn't adhere to the foam too well and comes up very easily, so I've had to come up with some padding when transporting/storing. It isn't a completely "scale" representation of the Spitfire, but you would be hard to pick it. The largest deviation is that the undercarriage is fairly widely spaced compared to a full-sized Spit but I'm not complaining about that one! :) The servos are not the best though, with all control surfaces hooked up to budget micro servos which is asking for trouble.

The retract mechanism uses regular servos with a sliding pin arrangement that locks positively at both ends (and hence transmits all the forces into the undercarriage rather than the servos). It's a good setup and seems a lot better than the servoless setup on the FMS models which can be troublesome. However, it is still a little on the spindly side and I wouldn't trust it to take bruising landings. I ended up fitting my own skids on the wings and belly for such a situation

There are lots of protuberances sticking out including 2 wing scoops and a chin scoop, but for me that is asking for trouble on landing. Luckily they are on sliding mounting plates and so easily attachable/detachable.

Flying Characteristics
The motor is a torquey and on take-off or slow speed it really swings the model to the left. Learning to use a fair bit of right rudder to compensate is the order of the day. Take-off runs are relatively short, however.

Apart from having to watch the motor torque a little, this is a viceless aircraft once flying. Whilst I would say it does not have a spectacular performance, and is relatively slow-flying for its scale, it is nonetheless a real sweetie in the air. This will be most likely from its very ample wing-area. It has enough power, good climb, very responsive elevator, light and accurate ailerons and the rudder will even allow somewhat of a knife edge. Scale aerobatics and low and easy passes are the order of the day. Some have commented that the elevators are very sensitive, but for someone who has progressed from smaller and lighter scale warbirds (including ultra-micros) I had no issue with this at all and enjoyed the control crispness.

I'm afraid I've only done the single flight and landing (see below), and I opted to fly her all the way down with a shallow angle and some speed on. No problems there, I could maybe go a bit slower next time. I didn't hit the sprung gear that hard but had a small bounce. The undercarriage did survive OK, but the plastic split a little around one of the mounting screws to the wing so I can see gear-down landings are probably going to need to be very gentle. I'm thinking now how I might re-inforce the plastic mounting plates here.

As I get more experience I'll expand a little bit more, however the 2nd flight ended ingloriously and illustrated the importance of adherence to RC model flightline protocols! :x I was flying with my Dad and, unfortunately he sub-consciously walks towards his models as they are flying without realising it. Now I saw him doing this and should have said something before I throttled up, but there was only the 2 of us on the oval so I figured "should be right" as I lined up away from him. I also didn't say "taking off" so you can guess what was coming. Just as she lifted off (although swung quite a bit to the left) unfortunately the wayward pilot veered right towards his plane at the same time. :roll: It was either the plane or my Dad getting a back-full of propeller, so I chopped throttle and swung hard right and cartwheeled in. Crash-wise, the airframe sustained no damage which is testament to solid construction, but the nylon screws used to secure the wings to the fuselage both popped like a circuit-breaker (I guess better they broke than something else, at least was clean screw break and no threads got stripped) so no more flying was done.

Faults/Upgrades
There are quite a few quirks that an owner will need to attend to first before going flying. Without too much detail I would suggest the following short-list:

1. Reversing one of the landing gear servos so that they both go up and down together! :shock: (or plugging the 2 gear servos into separate RX channels and say, mixing on the TX to one toggle switch)
2. Rather than the min 40A ESC recommended, from some owners current draw tests and how hot mine got I think 60A minimum is a lot safer
Rather than the recommended 2200-2600 mAh 3S battery, a heavier 3000-3200 mAh battery works better for CG. I used the heavier batts and was just right, so lighter will tend towards tail-heaviness
3. Replace all the micro servos with good quality 9gs (I used Hextronic HXT-900s)
4. Hinge tape the elevator hinge lines. There have been failures of the elevator hinges
5. You may need to balance the spinner and/or motor. Quite a few have reported severe vibration (not me luckily! :o )
6. Having a spare standard servo for the undercarriage or so may be a good idea as one of mine failed straight out of the box
7. Fit belly skids for longer grass field landings? I think the paint will get hammered otherwise :cry:

Conclusion
Very nice plane. Not a fly-out-of-the-box proposition with some care and attention needed first, but it looks great, crisp controls, scale aerobatics and a playful pussycat in the air. Not a heck of a lot of straight-line speed for her size, but that isn't my thing anyway with the parks I tend to fly in.

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#7) 
 Post subject: Re: Durafly Spitfire EP
PostPosted: 29 Nov 2010 14:59 
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maccuham wrote:
good looking Spit ..where is the Me-109 her enemy?

Uwe

:lol: :lol: Weeeellll, that's another story Uwe. The Parkzone Bf109 was there for sure (with flaps fitted this time), however Dad had a bad, bad lesson with the rechargeable AA's that Spektrum supply with the DX6i. He did charge them up, but I don't know, I reckon one of them must have been faulty because the TX voltage went from 5.4V to 4.8V in about 40 minutes.

The TX low voltage warning went off.....normally not a problem right? :!: Well, I've never seen ANYTHING like what happened next. Within about 10 seconds of the TX low voltage alarm going off, the TX conked out completely, and the Messerschmitt just plowed straight into the ground. I've just never seen AA battery die like that before! Looked at the TX readout again, and within a few more seconds had dropped to 4.1V! :shock: He got off lightly, no damage apart from a ripped off right landing gear.

I think I'm going to similarly give my 4xAA TX rechargeables a miss and stick with Lithium batteries. They have given stellar performance in my DX5e.

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#8) 
 Post subject: Re: Durafly Spitfire EP
PostPosted: 30 Nov 2010 10:53 
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Excellent write-up Ben as always :). I think you're this forum's official test pilot ;)
How rough a surface (or grass length) do you think those retracts can handle for a take off?

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#9) 
 Post subject: Re: Durafly Spitfire EP
PostPosted: 30 Nov 2010 12:03 
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Pete wrote:
Excellent write-up Ben as always :). I think you're this forum's official test pilot ;)
How rough a surface (or grass length) do you think those retracts can handle for a take off?


Thanks Pete! :) The retracts I think could maybe do up to about 1'' of grass OK. The tailplane gets flying very early in the take-off run and there is plenty of elevator authority there to keep the nose from going over. Landings she can be a bit nose tippy on long grass like several tail-draggers, but that doesn't hurt anything.

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#10) 
 Post subject: Re: Durafly Spitfire EP
PostPosted: 06 Feb 2011 15:51 
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Just started assembly on my Spit yesterday and discovered the retract problem! Using a reversing "Y" harness cured the problem, but-- I hate those things and removed it and then programmed my old PCM10X transmitter to mix the retracts with the flap channel-- Now, the retract switch operates both gear in the proper direction -- :D
The only other problem I found was that the wing trailing edge is a little too big for the fit to the fuselage. That's the project for today before I watch the big game! :P
I already determined that a 4S 3000Mah battery and a 60 amp speed control would fit and be a better choice for fuel!
I'm a fair weather flyer and we ain't had much of that here in Houston, lately, so when the WX is decent I'll go fly!


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