Steven S Posted October 26, 2017 Share Posted October 26, 2017 Yes Chris, the Vicomte is still in the queue. I took 3 sets of (pdf) plans to "Staples" for full size sets of prints, Peter's Grumpy Tiger Cub, his Werewolf, and The Vicomte 1915 from Outerzone. There are so many that I would like to build and every month a new one comes along, like this months Weekender motor glider. I have to make a decision soon as it started snowing here today so building season is upon us. The snow won't stay, but... Right now I am leaning towards starting with the Grumpy Tiger Cub and have started an album with a picture of a De Havilland Hornet prot0ype ( yellow underside) that I plan to finish it as even though the Grumand Tiger Cat paint scheme would be more appropriate. Quote Link to comment Share on other sites More sharing options...
AndyD Posted October 26, 2017 Share Posted October 26, 2017 ive got the pdf but ive promised my self I wont start it until at least the 1st of dec as ive got two or three planes nearing compleation and I must get them done first.hopefully it will give me time to follow the blog and pick up any hints and tips. Quote Link to comment Share on other sites More sharing options...
John Robertson 3 Posted October 27, 2017 Share Posted October 27, 2017 McG 6969: "@ John Robertson 3 > personally, I wouldn't want to start a 'war' with Iris. During a former career,The LotH was a teacher way back in Texas (*). She used to have and 'drill' a majority of tex-mex teenagers in her classrooms (*). In future Texan history books even Genghis Khan might be described as a 'mild' conqueror (*). (*) = a 'full stop'... ". A war? I wouldn't dream of it. I've had my say. End of. Besides, I've got better things to do - my much-repaired UMX Radian had a lovely flight this evening in a brisk westerly, over the beach, with the hills of the Isle of Mull in the background and Texas somewhere beyond that. I edited a little 20 second video from my HatCam specifically for this post but I'll be damned if I can figure out how to post it here. A "still" will have to suffice. To console myself over my inadequacies I'll just go and drool over my DX9 Tx, which arrived this morning. Life can be good, sometimes. Quote Link to comment Share on other sites More sharing options...
Max Z Posted October 27, 2017 Share Posted October 27, 2017 Two more things Chris, first I had a look at the rear end, and was surprised to see that it was largely open. I have always thought that the skirt needs to be closed on all sides to build up the pressure needed to support the vehicle. On top of that there is a baffle that directs most of the escaping air upwards, creating a downward force where the supporting air cushion would be weakest due to the pressure being lowest near the escape. The other thing is forget my comment on the extra bits for the front intake, I made a more accurate representation (spending quite some time, you can tell 3D cad is my second hobby), and it convinced me that the gaps can be closed with a little persuasion. (hey, I know I am showing off, but what's new in our modelling hobby ) I have read that often the inlet fairing gets damaged by the prop on a collision, caused by the flexing of the front end. So it is important that the whole front end is as stiff as possible to minimise the chance of that happening. I have a gut feeling that your use of polyester sheet for the fairing will make it more resistant to prop damage, but on the other hand will make the front end less stiff. Time will tell.... I have looked at some more pictures on the motor angle thing, and I think most of them do indeed have upthrust. Max. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted October 27, 2017 Author Share Posted October 27, 2017 Hi gents, @ Don > great to have an ‘insider’ from France visiting. Please feel free to suggest/correct anything about the ChtiCar on here. Do you have a carbon fiber strip up front? @ Steven > perhaps when I start my Vicomte build, yours is going to get ‘up-queue’d… @ Andy > no worries, young man. Just start the build of the beast when you feel like it, leaving you some time to correct my ‘mishaps’ anyway. @ John R3 > absolutely, “Life can be good, sometimes”. But, in this case, I only have an ol’ DX6i to drool over… Hakuna matata Chris BRU - BE / CTR Drool Control Edited By McG 6969 on 27/10/2017 18:39:27 Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted October 27, 2017 Author Share Posted October 27, 2017 Hallo Max, Some time ago when visiting your profile’s albums, I realized that CAD designing had to be somewhere on top of your hobby’s row. So, please, keep on “showing up”. The explanation you are giving regarding “closed skirts”, “pressure needed” and “air cushion” is perfectly true… if the ChtiCat were a common hovercraft… but it is not, it’s an ‘aeroglider’ - or ‘aéroglisseur’ in French. So, what we are looking for is a ‘suction to the ground’ not a ‘cushion to lift it'. Hence my earlier comparison to Chapman’s Lotus 79 and its ‘ground effect’. Hovercraft’s problem is their reluctance to turn which results in an enormous glide when at speed and they really need skilled operators. This concept, when optimised, can really ‘glue’ the craft to the ground. You are right concerning the fact that the ’spoiler’ at the back exit creates a ‘downward’ effect which is just what we need there to keep it controllable. Now we could experiment with the incidence of that device… The front ‘thrust fairing’ creates a downward suction by accelerating the flow into the venturi. Think about it as an inverted Clark Y… The main problem is to balance the nearly central ‘suction’ with the back-end flow to keep the beast out of yaw troubles at high speed, which speed is very much needed to give enough flow to the rudder… Anyway, after building several prototypes before making it public, I think the designer got the incidence right to compromise the for & aft ground effect… … ppfff… heavy stuff, just got a slight feeling to be in aero class again… in need of an apéro, me thinks… By the way, should we expect a Depron RBC kit soon? Hakuna matata Chris BRU - BE / CTR Stanford Control note > apologies, but I had to edit the post as I really forgot to add some emoticons... Edited By McG 6969 on 27/10/2017 19:45:55 Quote Link to comment Share on other sites More sharing options...
Iris Vlieghe Posted October 27, 2017 Share Posted October 27, 2017 Dear Chris, After reading all of this - a couple of times - I started questioning myself about whether it is my English skills or my lack of 'technical' knowledge that made all the above seem like some kind of Chinese to me. I decided I could handle some 'booze' too, me thinks... Makuna hatata - Iris BRU - BE / CTR Booze Control Quote Link to comment Share on other sites More sharing options...
AndyD Posted October 27, 2017 Share Posted October 27, 2017 I can see this is going to be a great build blog cheers. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted October 27, 2017 Author Share Posted October 27, 2017 ... well, let's just hope it could become "a great build", Andy. Only time will tell, but keep on visiting/ commenting. As The Loth already quoted... "Makuna hatata" (keeping an eye on here, anyhow ) Chris BRU - BE / CTR Quote Control Quote Link to comment Share on other sites More sharing options...
Mark Elen Posted October 27, 2017 Share Posted October 27, 2017 Hi Chris, I'm watching this with great interest. Not got much to input as foam/Depron is all new to me. Looking forward to seeing the Baron/Vimicote come to life too.👍 All the best Mark Quote Link to comment Share on other sites More sharing options...
Max Z Posted October 28, 2017 Share Posted October 28, 2017 Hi Chris. I looked up the definition of "Aéroglisseur" in Wikipedia. To me, that means it is the same as a Hovercraft, being dependant on the existence of an air cushion to lift the vehicle off the floor. I have difficulties with understanding your explanation of the "road-hugging" (tracking) capabilities of the ChtiCat. The front ‘thrust fairing’ creates a downward suction by accelerating the flow into the venturi. The venturi principle is indeed based on Bernouilli's law, accelerating the air will lower the pressure. But as soon as the air leaves the venturi, the air decelarates again and the pressure returns more or less to what it was before entering (minus friction losses). So the rear compartment will not see a decreased pressure. The only way to tap into the vacuum generated by a venturi is to make a hole in the throat and connect that to some form of closed chamber. It is true that the front and rear spoilers create a downforce since they are at negative incidence to the airflow. But how does this relates to tracking the vehicle going around the corners? Suppose the downforce will overcome the lift force of the air cushion and pushes the runners against the floor, because only then will it have an effect on the behaviour of the vehicle. You are making the comparison with a racing car, but that comparison goes limp since a car has wheels and the ChtiCat does not. The most important quality of a wheel is that it has much less friction in the rolling direction than it has in a sideway direction (which is why it was invented in the first place...), and this makes it track more or less straight. In a curve at speed, the centrifugal force will try to derail the vehicle and slide it sideways, but this is countered by the sideways friction. Here it makes sense to increase the downforce, and hence the friction, to improve the tracking and prevent losing the grip on the road. Now, if you were to brake hard in the curve, the wheels would stop spinning (assuming there is no electronic system to prevent that), and the vehicle starts slithering and spinning all over the place. This is the analogy to your ChtiCat with it's wheel-less underside pressed to the floor, and the same friction force equally opposing the track of the vehicle in every direction. There is no denying that the ChtiCat shows great curve-holding performance, but I believe this should be attributed to a happy combination of side area distribution, centre of mass position and rudder authority. It acts like a (very short) wing put on it's side. Operating the rudder will make it yaw, putting it at an angle to the airflow, which then creates a "lift" force in the horizontal opposing the centrifugal force. My 2 cents, Max. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted October 28, 2017 Author Share Posted October 28, 2017 Hi Mark, You should try some Depron while the glue dries on your EDF project... I'm really looking forward to the Vicomte build as well. Hi Max, Unfortunately, I didn’t made up the French name of ‘aéroglisseur’, but it doesn’t reflect the idea of ‘hovering’ ie sustaining at the same spot. Definitely the ChtiCat, if we can believe those vids, isn’t hovering at all. If you don’t mind, let’s have a look at the ‘external’ aero package first. At the front, the ‘thrust fairing’ has a (small) negative incidence up to the semi-circular venturi opening. At the back, the ‘diffuser’ has a larger angle of extraction, giving ,as you wrote, a certain amount of downforce. This primary downforce will be largely increased by the internal accelerated flow. Indeed the venturi creates a higher airspeed hence a lower pressure. But that acceleration doesn’t stop brutally when it leaves the restrictor, it decreases gradually towards the diffuser increasing the downforce at that spot. You must compare that flow of ‘low air pressure’ inside the whole ‘box’ to the barometric pressure applied on top of the deck. The difference of pressure will give you what I called ‘suction’ earlier. Now regarding “tracking around the corners”. Remember what Don wrote a few posts ago. “No power, no control”. If you cut the throttle too much before cornering (by applying rudder), you loose your thrust and ‘suction’ hence the downforce and road-holding, but ALSO your rudder becomes less operational. No control anymore. If you have a correct amount of thrust, the rudder will respond and the suction will be strong enough to fight the centrifugal force of the cornering. Concerning the “no wheels” on the ChtiCat, well yes & no. Not literally of course, but don’t forget there are ‘gliding roundels’ at each corner. It doesn’t help the cornering but simply avoids the creation of an air cushion underneath the beastie. Well, that makes 4 cents together… Hakuna matata Chris BRU - BE / CTR Cents Control Quote Link to comment Share on other sites More sharing options...
Max Z Posted October 28, 2017 Share Posted October 28, 2017 Hi Chris, I cannot see how suction counters the centrifugal force, but the fact is that the ChtiCat performs phenomally going round the corner. We both made our points, I suggest we leave it at that and enjoy your building blog and further adventures with it. Max. Edited By Max Z on 28/10/2017 14:20:51 Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted October 28, 2017 Author Share Posted October 28, 2017 Hi Max, No worries, I can enjoy sharing different approaches for a particular 'phenomenon'. The only regret I could have is that English is only my third language, so I guess I experience some difficulties to express myself in the right terms somehow. Especially when it gets quite 'technical'. Verbal communication could make it a lot easier. If you allow me, concerning 'suction vs centrifugal'. Imagine a vacuum cleaner with the tube extension end positioned vertically. Place a piece of cardboard horizontally on top and you'll need no force to slide it sideways. Now switch it on and try the same. You'll need a lot more 'traction' to the piece of board to move it sideways. If the obtained vac has for example -0,3 bar, you'll need more than (let's say) 300gr of thrust to move the paper sideways. That's why the ChtiCat keeps 'on track' in cornering when there is enough suction/downforce. Enjoy your weekend, young man. Hakuna matata Chris BRU - BE / CTR Vacuum Control Edited By McG 6969 on 28/10/2017 21:35:33 Quote Link to comment Share on other sites More sharing options...
Max Z Posted October 28, 2017 Share Posted October 28, 2017 Posted by McG 6969 on 28/10/2017 19:02:27: Now switch it on and try the same. You'll need a lot more 'traction' to the piece of board to move it sideways. Hi Chris, That is just my point, you will need a lot of force to move it in any direction, not just sideways. By the same token, when the suction under your ChtiCat is high enough to avoid it slipping sideways, it will equally avoid it "slipping" forward, i.e. brake the vehicle to full stop. Max (we could continue in Dutch if you like, but I don't think the moderator will like that ) Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted October 29, 2017 Author Share Posted October 29, 2017 Posted by Max Z on 28/10/2017 22:37:57: ... when the suction under your ChtiCat is high enough to avoid it slipping sideways, it will equally avoid it "slipping" forward, i.e. brake the vehicle to full stop. I must admit that my example with the vacuum cleaner was a bit simplistic, Max... You are right to say that in that case the motion 'hold' should be omni-directional. But, then you forget that the suction/downforce is obtained by (say) only 1/3rd off the prop thrust available and that the major part of it goes on top of the 'box' and goes on taking care of the forward motion of the ChtiCat. I'm pretty convinced the mods wouldn't appreciate your 'Dutch' suggestion as they don't want the forum to become a Tower of Babbel (pun intended)... Hakuna matata Chris BRU - BE / CTR Babbel Control Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted October 29, 2017 Author Share Posted October 29, 2017 Hi to all interested, A few days ago, I asked for some info regarding the ChtiCat on a French forum, hoping for some light in the tunnel. Well, I got some answers from Christophe, the designer himself. Concerning the motor mount, they all seem to use the 3° up thrust. He did some testing with less - down to 0° - but the beast was loosing some efficiency at the entry of a corner (some kind of ‘understeer’, apparently). He tends to adjust his models to obtain the least possible ‘corrections’ needed at high speed (well, yeah). Quite a lot of rudder throw though & expo to suit the preferences of the ‘driver’… For the ‘sliding roundels’ - or skates, skids, … ? - at the four corners, his suggestions were: > for indoors: felt, Velcro (the soft side), nylon or Teflon furniture leg skids around 20 to 25mm Ø are fine. > for outdoors: carbon fiber strips or, a lot cheaper - aka free - some plastic packaging bands. Longer strips needed, up to 1/3 length but at the corners, for plastic bands. Hope this helps a little. Hakuna matata Chris BRU - BE / CTR Skids Control Edited By McG 6969 on 29/10/2017 18:26:19 Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted October 30, 2017 Author Share Posted October 30, 2017 Hello again, After a lazy weekend of shopping, watching F1 and pondering about aero forces, I finally managed to prepare some bits for the beastie. Before starting to score the fuse deck to help with the fold, it’s safer protect the outside with a thin foil of adhesive vinyl. I used some cheap ali-like vinyl from Brico - I guess somehow the BE the equivalent of Halfords in UK - and just unpacking the roll gives already a lot of scratches, but I guess it’s sufficient to be ‘crashed’ soon enough… The ‘diffuser’ at the back end must have a bevel starting at 12mm of the edge opposite to the tab. Next will be to get all those bits together… Hakuna matata Chris BRU - BE / CTR Vinyl Control Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted October 31, 2017 Author Share Posted October 31, 2017 Hi to all, I finally got the Por out of the drawer again since my Bella build. I realize it isn’t the fastest way to assemble Depron but if allowed an honest opinion, I hate hot glue and don’t really like foamsafe CA. Just me… So, not that much done, but the two fuse sides and bottom side plates came together with the good old Duplo blocks getting it square. While those bits were drying, I prepared a 6x1mm carbon strip to protect the front thrust fairing. Not related to modelling, but I always use a wet Scotch Brite pad to remove the gloss of carbon parts. Then glued with slow epoxy and held in place with a strip of Cellotape, hence the shiny bubbles. Just before leaving La Grotte, I had the opportunity to get a first dry-fit of the bits already prepared. I noticed a slight mishap with some tabs sticking out of the pod sides. I must remember to take care of that before the final assembly. More to come… Hakuna matata Chris BRU - BE / CTR Tabs Control Quote Link to comment Share on other sites More sharing options...
AndyD Posted October 31, 2017 Share Posted October 31, 2017 looking good,im getting itchy fingers. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted November 1, 2017 Author Share Posted November 1, 2017 Thanks Andy, but too early to get "itchy fingers" already. I'm wondering if you will be able to keep your 'first of December' word... Precisely one month to go for you and two weeks for me to finish the ChtiCat as I would like to start the Vicomte around mid november. I guess I will have to ask Gaston to push up his performance. Hakuna matata Chris BRU - BE / CTR Job Control Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted November 1, 2017 Author Share Posted November 1, 2017 Hello to those still out there, I finally came to the point of having a small reward with the bits slowly getting together. The basic structure is assembled as seen from the top of it... … and from the bottom. The base went back to the building board for a last square checking and the gluing in of the front bottom plate. As Gaston saw some intensified ‘movements’ in La Grotte, he managed to get out of his ‘summer lethargy’… Unfortunately - not being totally awake - he didn’t warn me that I forgot to adjust the tabs’ lengths on one of the sides of the pod. A bit of ‘bodging’ needed later, I guess. Hakuna matata Chris BRU - BE / CTR Tabs Absence of Control Quote Link to comment Share on other sites More sharing options...
Mark Elen Posted November 1, 2017 Share Posted November 1, 2017 Hi Chris, Many thanks for the PM yesterday, this is looking good👍 Are you sure Gaston is awake? Looks a little bleary eyed to me😂 Regards Mark Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted November 2, 2017 Author Share Posted November 2, 2017 You're very much welcome regarding the files, Mark. With Gaston, in fact you never really know if he's 'awake' as his top-ranked and well known hobby is... sleeping. So, his eyes are barely a barometer for his intellectual readiness... Still his presence remains invaluable for this lonely apprentice. Hakuna matata Chris BRU - BE / CTR Hobby Control Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted November 2, 2017 Author Share Posted November 2, 2017 Hi to all, As yesterday was a national holiday here in BE, there isn’t much building progress to notify. But I went on crawling the web in my quest to find more details about how to install the ‘electronic’ bits in that quite restricted fuselage area. Unfortunately, at the end of the trip, I found nothing at all. Nihil. Nada… It must be a well kept secret by the Frenchies. What I found, between loads of pictures, is this one: Complete with blue flashing light et all, I decided to dedicate it to an earlier visitor living in France and named Don. The ‘Police Nationale’ builder seems to have ‘rigidity’ problems as well as he decided to double the thickness of the pod sides! Probably an anti-terrorists version… Without any doubt, the ChtiCat is a successful concept for indoor fun and if they do it this way all the time, I guess there will be some ‘rebuilding’ needed… Having a closer look at the picture, it reveals that there are a lot of ‘personal adaptations’ regarding the fin & rudder but also the powertrain. The one at the right of the pic carries an Emax 28xx and the third one - white with the ‘witch on a broom’ - has a XXD 2212 as I intend to use. Now I also noticed an amazing ‘Evo’ or ‘MkX’ version in the row. The sixth from the right > brown-ish with a tractor/pusher powertrain (?) and double fin/rudder… But still no positioning info for the electronics. Hakuna matata Chris BRU - BE / CTR Row Control Quote Link to comment Share on other sites More sharing options...
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