|Jul 20, 2010, 07:48 PM|
Joined May 2010
ST Model Cessna 350 Review & Video
The Cessna Corvalis isn't your average Cessna single. It's low wing. It's composite. It features a glass cockpit standard, and its turbocharged '400' version is the fastest fixed-gear single-engined piston aircraft in production today. Originally a product of Lancair's FAA certified composite airframes - marketed under the Columbia brand - the Columbia 350 was directly competing with Cirrus for the high end GA market. In 2007, Columbia filed chapter 11 bankruptcy and Cessna acquired the company - and added a very different product to its lineup: The Cessna 350 Corvalis.
What follows is an account of my experience with my newest RC plane, the ST Model 'Cessna 350 Corvalis'. (If you're expecting an unbiased review, please see the bottom of this post)
I have to admit that I'm biased here - I love the look of the original aircraft, and any model that captures those curves is going to affect my judgement. I was looking for a second plane for parkflying, and something that would push my abilities a little, but not too much. Plus, I wanted something that would be constantly compelling me to go flying during the week. My research kept coming back to this plane. Still, I had a few concerns.
I've seen ST Model products on a couple of webstores before, but I'd never seen one in person. I could also find only a few videos on this particular aircraft, and while they looked okay, there was very little information available from people "living with the plane" so I couldn't be sure. A couple of private messages to owners of this plane, one in Europe, another in Dubai, and it seemed it would be okay - a step up from my current set of wings but I shouldn't expect too much. Given the value of the whole package, I felt it was worth trying.
I realised this quite late in the selection process, but the plane only has four servos. The flaps and ailerons share a servo each, which on a 1.4m plane means either leaving the wings fully assembled or performing quite a bit of fiddly retrimming every weekend. It also means I can't program differential or flaperons/spoilerons should I wish.
But then, I have an Exacto knife and I'm not afraid to use it. And all the evidence suggests it'll fly out of the box well enough.
The (very few) videos of the plane I could find on youtube indicated that it flew well, but it seemed to have a very high aspect ratio wing. I wasn't sure - is this representative of the real aircraft? And yet, this was the least of my concerns - I'd actually prefer a clean plane with an efficient high aspect ratio wing as it may translate directly to longer flight times. But still, what's the difference to scale?
A little research against the fullscale specs and I got the following figures: Model aspect ratio: 9.25, Fullscale aspect ratio 9.23. Difference .2%. Wingspan/Length ratio of model: 1.48, Wingspan/Length ratio of fullscale, 1.43. Difference 3.5%.
So there's a difference, but I'm not going to complain about 3 or 4%, especially when the difference is in favour of decreased wingloading.
Interested in what was available, I looked around for an RC model with much the same appearance. I found only two alternatives.
Nitroplanes markets a foam "Sky Trainer 400", which appears to be representative of a Cessna 400. From my research on various RC forums it appears that this kit has been available for some time and with mixed results.
Electrifly has just released a 1.2m wingspan balsa & fiberglass Cirrus SR22 model, sans flaps. It has a higher wingloading, so though it's very pretty, I felt it was likely to be a faster flyer and probably well beyond my abilities. I'll be watching this one with interest, though.
So, I decided to buy, and then sat around willing the mail to arrive faster.
I took my time assembling and had no real issues. This is the third foam ARF I've put together and as usual there isn't a great deal to do. Given I only have a little time free these days after the kids go to bed that's perfectly acceptable to me.
Connecting the wing servos took a while to get right, some adjustment was needed to get the servo throws where I wanted them, and to make ailerons and flaps symmetrical. The wing is a carbon reinforced, sealed two-piece affair with bell cranks driving the control surfaces, themselves driven by thin piano wire. This can mean that getting aileron throws even in both directions takes a little creative adjustment at the servo, but in the end I put most of my difficulties down to simply being new at the whole process.
The cabin is a real deficiency in this plane, I felt. I wasn't willing to tear the soft foam seats out in order to install radio gear in the available cabin space, but the limited space for radio gear beneath the seats - and above the wing - is tiny. I had an AR7000 that wouldn't fit, but the AR6200 fit fine. It seems any small parkflyer receiver will not be an issue, but the larger receivers will require surgery or creative use of tweezers. As it was I mounted the remote receiver on the sidewall of the cabin with some creative tweezer application to get it as far away from the other electronics as possible.
Having said all this negative stuff, I really was impressed with the build of this plane. The control rods and horns are all hidden away to give the plane very clean lines, the ailerons and flaps are hinged, the horizontal stab is carbon reinforced. Even irrelevant things like having a clean duct available for an FM antenna were nice to see, as was having detailed and reasonably translated build instructions, rather unlike my last plane.
I would have liked access to the interior of the plane - the molded fuselage halves are pre-glued together. As it was, when I added about 25g to the rear of the plane (just before the glider tow hook) to bring the CG to the recommended range I had to perform a little surgery.
A couple of notes on the video: The takeoff was done by applying power slowly, to gauge whether I'd have to abort, so the normal takeoff roll is undoubtably shorter. The landing was done without flaps as discussed below, was a little fast and there was a little float and bounce due to Yours Truly being all thumbs. The first half of the flight was at a high altitude while I tried to stall the plane, looking for risks before bringing it down to a reasonable altitude for circuits. Thanks to Mrs Ben-M for the video.
Total flight time on the log is 1 flight of 12 minutes, so observations limited to this time. First flight was clean with no surprises. Stalls were well behaved and there were no ugly wing drops - presumably thanks to the outboard leading edge droop - aileron control was positive during the stall. The flaps make a huge difference to flight speed - so much so that I became a little nervous about using them and chose to land without flaps (leading to a much faster landing). Some attention to flap programming, as well as a little more flight experience using them, and it looks like they'll result in very slow, predictable landings.
I'm no accomplished aerobat, but the plane was happy flying inverted, doing inverted loops, loops, immelmans, and rolls (all of which were missed in the couple of minutes the camera lost sight of the plane). The limited control throw and the high aspect ratio wing don't seem ready to deliver 3D performance, but then that's not what I bought the plane for.
Power seems more than adequate. The stock 1800mAh cell delivers 18 minutes at 50% throttle before the LVC cuts the motor; I flew for 12 minutes on the maiden at 50% so still had plenty of power in reserve.
Next week I will add half an ounce of lead to the nose or reposition the battery to bring the CG slightly forward. It is currently at the middle of the recommended range.
The plane is all-white and at distance it is very easy to get disoriented. I will probably paint the underside of the wing and horizontal stabiliser tips to aid in orientation.
The wheel spats were no issue on the flying field grass, something that had been of some concern to me following my previous plane (and its extensive wheel modifications)
I was not able to adequately test it at high speed. It performed well in some powered dives, however I can't conclude that there is no suffer from flutter, or that the cowl's battery housing isn't going to pop loose mid-flight. With flaps however, it looks like rapidly bleeding speed won't be much of a problem.
Living With It
I'm not sure I want to separate the wing halves and then have to reconfigure the servo linkages every flying session. As a result, the 1.4m wingspan - being wider than my car's interior - requires some care in transport. I've seen a video of someone assembling the wing halves at the field though, so perhaps I'm just being precious.
Batteries are reasonably inexpensive. The 20C 1800mAh battery that comes with the plane is the same dimensions as a 25C battery from my local hobby shop that'll set me back less than $50. I might get two.
The foam is better quality than the esky/packing-foam of my other plane, but it seems it will still show bumps a little. It'll take CA glue quite happily though, so repairs should be trouble free.
Despite the lack of 'room', there looks to be plenty of room for modification, if I develop the itch. The fullscale Corvalis has spoilers, which would be a fun (but possibly unnecessary) scale addition. In the spirit of fixing things that ain't broke, an additional aileron servo wouldn't go amiss either. And with a bit of surgery, there's a fair amount of space inside for an FPV camera or other goodies.
Wing Loading: 44g/dm2
Wing Area: 22.3dm2
Battery: 1800mAh 3s1p
Requires: 5+ channel receiver
(you may find more info here and here)
Apart from the issues mentioned herein, I'm really impressed - it didn't break the bank, and I think I can live with it for quite some time to come. But time will tell what I really think of the plane. If I'm still flying it regularly in a year I'll call it a good addition to the hangar, if not, it's certainly been an economical upgrade from my last plane.
Price. At AUD$190 (~US$165) including battery, esc, motor and servos it was a steal.
Finish. For a foam plane, it looks pretty convincing.
Features. Flaps, steerable nosewheel, tow hook, decent flight times.
Aesthetics. It isn't your average Cessna.
Performance. Stable and well behaved in the air. Nice for scale flight.
Space. There's a big cabin with little way to get into it; the available space for installing a receiver is minimal, unless I get creative; there is a lot of empty space in the fuse that I can't get to without surgery - which will be required anyway if I need to add weight to the tail.
Foam. I suspect it's going to show its age, but only time will tell.
Decals. A little CA may be necessary to tack the decals down - the fuselage side decals tend to lift in the box (I've seen two or three examples, including mine, where this has happened). Removing the fuselage from its packing with care limited damage, and they were re-tacked down where required.
Finally, a shameless plug for any Aussie readers: I bought the kit from http://www.flyinmodels.com.au for AUD$190, which seems exceptional value given that it included everything except the receiver. It was my first purchase from Fly In Hobby Shop and I was really impressed with Alexis and Nathan, the guys I spoke to there: payment wasn't processed (or requested) until they'd actually put the item aside in their store, shipping price was unbeatable, and when they didn't have the exact receiver I was after in stock, they were willing to go the extra mile to find a reasonable alternative. While I don't think a demographic of one is sufficient to define a product or service, this was a really good purchasing experience.
Disclaimer: I've tried to fairly represent my own experience. I bought this with my own money, and it's entirely possible that this article has been biased - either way - by post purchase rationalisation or buyer's remorse. Your mileage may vary.
|Aug 28, 2012, 11:49 AM|
So, are you still flying it?
Have you performed any surgery? Mostly, I'm wondering if the battery can be moved back some, to fit a heavier one.
|Aug 29, 2012, 02:08 AM|
Joined Nov 2006
I'll go out and check mine for you tomorrow. I believe you can cut through into the cockpit without too much trouble, but I will give it a look to make sure.
|Aug 31, 2012, 02:49 AM|
Joined Nov 2006
Andy, you can cut into the bulkhead at the rear of the battery compartment. There is a ridge of foam there that you can rest the battery on. Trim away the lower part of the instrument panel and you should be able to get an additional couple of inches to slide a bigger battery aft. Any further back and you will have to cut through another partial bulkhead and your battery will end up where the seats are. How big a battery are you looking to put in there?
|Aug 31, 2012, 11:11 AM|
Probably a 2200mAh 3s 20C Loong Max, and a heavier motor, propped for about 20A. That's roughly what I have in my Parkzone Trojan - which has the stock Parkzone motor but less power than stock due to the choice of prop. It's definitely not over powered.
I have some 3000mAh 3s 25C Gens Ace lipos, but the weight might be too much.
|Aug 31, 2012, 11:08 PM|
Joined Nov 2006
I'm running 2200's with the stock motor, prop and ESC, the later rearranged for battery access and better cooling. It is a bit nose heavy and I don't like putting that extra weight over the nose strut, it getting regular abuse on our grass field. I'm pretty happy with the power characteristics as is, so i don't have any plans to up grade at this point. A nice new paint job is in the works, though.
|Sep 02, 2012, 03:53 PM|
Is there access to the bit with the foam seats, from underneath? I've heard it mentioned, but I don't think I've seen it in any of the pictures I've looked at, so I could probably live without that bit. It would be good to just cut it out neatly though.
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