Robin Stevens
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Everything posted by Robin Stevens
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Yeah, the mass build for me will just be "the stuff I would have run out of time on this winter"
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I'm in a similar boat, got a couple of builds that have been on the shelves for a while that I'm taking the opportunity to work on. Might as well make the best of a bad situation. If doing an isolation build then something smaller and simpler would probably be more appropriate. Something like a limit EX or a mini tyro.
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Just to prove I am still working on this I'll show my progress. Things have just been a little slow, real life always gets in the way. Having a look at it I think Martin's suggestion of sectional anhedral is a good solution, but for the time being I'm concentrating on the fuselage. Most of the formers are about ready, I'm just planning out the stringers so there's a minimum level of fettling. The tail obviously needs to be planned out and the parts modelled. Given that this is taking a bit longer than I'd hoped I'm thinking of doing a simple PSS model of the XP-79 so I have something to take to events and the like.
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The Sabre jigs are very impressive, definitely a technique I'm willing to copy. The only thing I'm unsure about on the Frogfoot wing is whether to have the scale anhedral angle or to make it a flat wing, dihedral would look wrong so that's not an option
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Going for E374 with the wing centre section built into the wing as advised. So far I'm around half way through planning out the fuselage profiles, hopefully will have something ready to be cut in a couple of weeks. Thanks for the link Martin, interesting read with some things worth bearing in mind. Washout seems to be a key consideration, the Su-25 has a slight sweep to the wing so around 1 degree washout seems appropriate. The plan is to have the fuselage being self-jigging where possible, the key advantage of CNC cutting to me is that accurate interlocking surfaces can easily be produced.
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Will keep the pylons in mind, for the time being it looks like the fuselage should be draggy enough but like I said I can always change my mind later. The opportunity to have weapons all over it as variable drag/ballast is tempting though... 3d print of my CAD model is done (1:72 scale), I think I've got the shape and proportions right. The print is just as a test to make sure I'm happy with the shape before I start to take profiles from the model. Thanks for the offer Martin, there's someone in my club that's already offered the use of their CNC router but when I have the profiles and plan complete I can share the dxf files if 1.8m sounds about right for you. As far as wing section goes I'd been recommended Eppler 374, which looking at airfoiltools looks like it's comparable to Eppler 205. However 205 has a flatter base which would be more convenient for building. Had a look at different methods of wing detachment on the CAD model, I think having the port & stbd wings detach at the root is a better way to go than having a continuous detachable wing. The wings are very deep in the shoulder mount so there isn't much structure left if the entire wing pops off.
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Hi Phil, thanks for the info. I had seen the Steve Griffiths plan on Sarik but without an image on their website I didn't pay much attention to it, looks a little on the small size for what I'm thinking but it's good to know what's out there. As you say the Frogfoot isn't exactly a speed demon but it is pretty fast (around 850kph / 460kts). At the moment I'm thinking that the only concessions to scale I'll do is eliminating the weapon pylons to preserve the overall look of the plane, could always add them in later if needed. Nothing would be slimmed down for performance, the real thing can carry it's own weight in weapons and fuel so there should be plenty of overhead there. In terms of construction I'm currently leaning towards a balsa stringer and former construction with a planked and glass skin. Currently 3d printing the CAD model (scaled down) I made yesterday so I have a good indication of whether I have the right shape.
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Hi, I've been thinking of getting into PSS for a while and could never find a model for a subject I was really interested in, so recently I've started to take the plunge and start to draw my own plan for a 1:8 Su-25 Frogfoot (about 1.8m span) The Frogfoot is a Russian ground attack aircraft of similar (but not quite the same) role to the A-10. I quite like the Russian designs and the Su-25 seems like a good plane to start with for PSS. The fuselage is almost rectangular all the way through it's length and doesn't really taper significantly so construction should be pretty simple. Does anyone experienced with PSS have any recommendations on wing section to use? At the moment I'm thinking that the wing area should be sufficient with simply scaling down the design, no tweaking of the proportions. As far as I'm aware this doesn't get modelled often, if there's anyone out there with another I'd be keen to hear from them. Edited By Robin Stevens on 16/02/2020 18:17:23
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Thanks for the recommendations I think I'm going to go with the SC 0.40 two stroke glow that I have from another aircraft that I'm retiring. Looking forward to having the toot sweet finished, everything I've heard about it makes me think it'll be a fun flyer. My club isn't fussy about noise, we're fortunate in being in the middle of nowhere. A trusty glow 2-stroke will likely give me all the power I could need and be relatively practical.
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Nice colour scheme, looking good liking the eyes on the side rather than a cockpit. Looks so fish-like it could be Guppy Love I take your point on KISS, was worth asking though just in case.
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I might be best to just stick with glow then, throttle response will be critical on an aerobatic model like the Toot Sweet. I'll think about it again when I'm closer to finishing the model. I don't expect there to be any massive improvements in the small engine offerings but it could happen.
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Ok, thanks for the tip, I wasn't aware it was possible to do an engine conversion like that. I have an SC 0.40 two-stroke that was originally intended for the toot sweet that would be useful if I can convert.
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I am currently building a Toot Sweet (Peter Miller, RCM&E September 2002) and I'm thinking of putting a Petrol engine in the nose instead of the recommended glow. **LINK** This will be my first venture into Petrol, the relative cleanness and the cost and availability of fuel is attractive but I don't know what the best option for a plane of this size would be. I will admit that my knowledge on this type of engine is low, that's why I'm posting the thread. The plan suggests a 0.35 to 0.40 glow 2-stroke, or a 0.40 - 0.48 4-stroke. Does petrol suffer a performance penalty compared to glow or are they broadly equivalent, requiring a larger engine? Are petrol engines in this size available or should I just put a 9cc in and have almost unlimited performance? Currently the airframe is half built and is a winter project lined up. I would like to finish it for next year to give me something aerobatic to work with and flesh out the variety in my hangar.
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Soarcerer for Flat Field
Robin Stevens replied to Robin Stevens's topic in Build Blogs and Kit Reviews
Hi, been a while since I've logged in so apologies for the late reply. Having had the chance to fly the soarcerer on the flat and on the slope (calm days, with a big wing it's perfectly happy in a 5-10mph wind) a couple of times I can give this feedback. The Soarcerer is a timeless classic for a reason, I've never flown anything this stable and confident in the air. The only thing that I can fault it for is the stall can be rather severe but it is even and now I've got my eye in can be avoided. This is my first glider and the first time I've thrown a model off a cliff and expected it to come back and I can feel myself being a little bit hooked. As far as the aileron wing goes, I used a pair of servos. Unfortunately the wing isn't deep enough to fully enclose the servo so I went for the more rustic solution of mounting the servo hanging out of the lower surface. Don't make the same mistake that I did, the ailerons need to be nice and big for a positive response, I think I will be doubling the aileron chord when I make the standard size wing for more normal/aerobatic soaring. The size they are for the big wing is fine for a sedate soaring experience but I find myself using the rudder for turn more often that not. -
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Soarcerer for Flat Field
Robin Stevens replied to Robin Stevens's topic in Build Blogs and Kit Reviews
Soarcerette looks interesting, will have to give it a look if the big one keeps my attention I finished the wing, with sheeting on the top and bottom surface as suggested. Covered in nylon fabric. Glides well from what I can tell, haven't had it on the bungie yet but testing the CoG I managed 50m from a gentle hand launch. Looking forward to getting it on the bungie, just waiting for a ground anchor to arrive. -
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Soarcerer for Flat Field
Robin Stevens replied to Robin Stevens's topic in Build Blogs and Kit Reviews
The Soarcerer is just about ready for covering, at least the wings and tail feathers are. Going for nylon fabric covering, classic red fus and white wings. It's meant to be raining this Saturday, might start then. Also the bungee for the launcher arrived yesterday, going to be popping to the local fishing shop to pick up the bits and pieces. The more I work on the Soarcerer the more I want to make a mini one, about half - 60% scale with a pair of 9g servos. Soarcerer's Apprentice? -
