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Member postings for Max Z

Here is a list of all the postings Max Z has made in our forums. Click on a thread name to jump to the thread.

Thread: Chris's ChtiCat Racer
19/12/2017 08:55:33

Looks great Chris! But Kamikaze-Gaston looks quite surprised you didn't put a cockpit in........


13/12/2017 21:58:10
Posted by McG 6969 on 13/12/2017 18:24:49:


Should that not be "DANGER / GASTON ON BOARD" (that's when he causes the most damage....and why not adding some taxicab checkered striping...)? wink


Thread: Why We board Planes From The left Hand Side.
01/12/2017 13:40:20
Posted by Geoff Sleath on 01/12/2017 12:49:25:

That's what I've always understood, too, Chris. I always use the terms port and starboard because they are absolute whereas left and right depend on which way you happen to facing.


There is an interesting take on this. I work with a 3D design software package. And as all of these kind of packages have in common, there is a top view window, a front or back view window, and a right or left view window. Additionally there is usually a perspective or isometric view window. Now once you have your 3D model of an aircraft oriented properly, the top and front views will show what you would expect, but the right view will show the left side of your aircraft model! This is very confusing at first, made worse in my case since the button-icons to switch between views have a picture of a motorcar on them, for which the same enigma applies. This confusion is caused by the fact that the convention for vehicles is to name the sides based on the perspective of the driver/pilot/helmsman INSIDE the vehicle, facing forward, but for an archtitect the right and left sides of a building are conventionally named based on the viewer facing the front elevation standing OUTSIDE the building.

Unfortunately for me, I am not an archtiect but a model aircraft designer..sad. But you do get used to it very soon.

Btw, the explanation in the linked article that the convention for passenger acces on the left/port side is based on the pilot overviewing the wing nearest to the terminal building begs the question why the pilot is sitting in the LH seat in the first place..........


Edit: Reading BEB's story again would explain the pilot's LH seating position to some extent, which would also makes the pilot's field of view explanation for the passenger door more plausible. smiley


Edited By Max Z on 01/12/2017 13:41:10

Edited By Max Z on 01/12/2017 13:53:18

Thread: The thread for your subscriber questions and queries **please do not start a new thread**
28/11/2017 15:22:47

Hurray, it comes through my mailslot this very moment.


28/11/2017 08:57:46

Unless it is later than normal I should have received the December issue by now, but I haven't (Netherlands). Any reasons why?


Thread: Vectorcraft
25/11/2017 16:11:14

Hi Chris,

I have to pay a fairly hefty entrance fee as a guest of the club that flies regularly in that facility, so I will not go there very often. Maybe you feel better now....


25/11/2017 10:39:43


Is it flying? I don't know, I believe it is, although at a very low altitude cheeky

Inspired by Chris / McG 6969 and his "Chticat" thread, I wanted to design my own little racing hovercraft. And when I found THIS nifty little unit I decided to construct it around that "Vector Unit Extreme".


Initial tests on the kitchen floor showed great promise, so I built a second one and went racing. Well, not really racing, but I did meet a young pilot who was very enthusiastic to be my co-tester. Have a look:

The small crafts are only about 170 mm long and weigh a mere 26 gram, collisions with objects and other craft seem to do them very little harm. The multiple collision you will see at the end of the video (two hovercrafts knocked over by a landing airplane) did them no harm at all smileysmiley


Edit: embedding the video does not seem to work, HERE is the link.

Edited By Max Z on 25/11/2017 10:56:46

Thread: Chris's ChtiCat Racer
24/11/2017 20:21:05

Hi Chris,

I recognise your "secret tool", but as a tool for a slightly different purpose than the one you mention. I checked with my wife, and she confirmed that it is a tool for copying sewing patterns onto plain paper (but a special kind), which is then cut along the imprinted line to create templates for cutting fabrics. In Dutch it is called a "radeerwieltje", in English a sewing tracing wheel (I believe).


Thread: The thread for your subscriber questions and queries **please do not start a new thread**
22/11/2017 17:45:40

Is it me or is the December issue late?


Thread: Chris's ChtiCat Racer
16/11/2017 20:38:38

Nice decoration! I am sure it will dazzle the competition......cheeky


05/11/2017 13:09:15
Posted by McG 6969 on 05/11/2017 12:33:30:

Aah... that looks really 'fun', Max.

Did you have a maiden 'glide' already?

I'm trying to find out your 'motion principles', but not that easy without details... frown

Let's have a guess. I see a double bottom thickness, so it could be that the lowest one is just the contour edge creating a space for a air cushion. That is, if the prop is blowing into your quarter circular fuse right through the top bottom plate... also your high aft fuse & fin could indicate a hovering design...

All fine guesses, but I don't see a rudder? Don't tell me that your motor is mounted on a servo plate panning left or right to get some 'turning' thrust... surprise

I won't give any comment regarding your 'Dolle Mina'... cheeky

Hakuna matata


BRU - BE / CTR #5 Control

Yes Chris, i made some test drives in the house and at our clubhouse, and it goes very well and is fast. I did not dare to open the throttle fully, too many obstacles (tables and chairs).

It is a regular "Aéroglisseur", the prop blows into the inlet behind it, and creates an air cushion below. The lowest layer of depron is cut out in the middle for that purpose. I don't understand what you mean with "your high aft fuse & fin could indicate a hovering design..."

The motor indeed pivots on top of a servo/receiver/esc combination, THIS unit. Control is with a Graupner MZ-4 which was specially developed for this unit, but it can also be a regular HOTT transmitter.

My pilot feels offended, he feels he is definitely masculin. But you never know these days.....


05/11/2017 11:53:09

I am still out here Chris. You have inspired me to design and build this:


Carry on,


Edited By Max Z on 05/11/2017 11:53:49

28/10/2017 22:37:57
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.


(we could continue in Dutch if you like, but I don't think the moderator will like that cheeky)

28/10/2017 14:19:02

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.


Edited By Max Z on 28/10/2017 14:20:51

28/10/2017 11:03:27

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,


27/10/2017 10:22:20

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 cheeky)

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.


26/10/2017 12:59:45

Posted by McG 6969 on 26/10/2017 11:28:20:

It seems that you got yourself convinced than.

Not necessarily... thinking

Re upthrust: the propeller will create a downward moment. Whether that needs to be balanced will be dependent on the pressure distribution under the skirt and the position of the centre of gravity. Giving the prop some upthrust or downthrust may help to balance that, but I have no experience with hovercraft design so I don't know.

re matching the inlet piece to the side panels, here is a picture of my cad design:


Although the representation of the inlet is not accurate ( I kept it simple, with more effort it would have been possible to represent the folded sheet construction accurately), it is clear that you will need to add some near-triangular pieces at the top end corners.


26/10/2017 10:19:25

Hi Chris,

Just for fun, I am building a virtual 3D model of the Chticat in Rhinoceros, also to see the construction details and how I could simplify that when I leave all those tabs and slots off. Then I came across this: by copying the small size overview drawing and measuring it up, i noted that the top is slanted some 3.5 degrees backward. Looking at the unrolled shape of the motor fairing, the forward-bottom corner has an angle of 90.5 degrees. This would mean that the firewall is slanting 3 degrees backward, and the motor would be pointing upwards by that angle. However, when I look at the pictures on the internet, the firewall is vertical. Is there anything mentioned in Christophe's description about this? I can read and understand the French forum thread, but knowing what to search for is something else.


25/10/2017 21:08:41

Hi Chris,

Thanks for bringing this to our attention, I love it. I have the same problem as Andy and Stephen though, no immediate place to run it. I would have to join a club which has facilities for indoor flying and running these machines.

I am seriously thinking of building one myself, I do have some depron (imitation) laying around. I do not see the need to cut al these tabs and slots though, with a bit of careful assembly I think you can do without those.

I can see your problem with the front intake, and polyester overhead sheet may be a good alternative there. But 3 mm depron glued to the front-bottom part of the skirt would give that more rigidity, which you would need when bumping into things.

May be we'll meet on the track oneday....


Thread: Radio decisions, stick with 35mhz or go to 2.4Ghz??
22/10/2017 08:50:52
Posted by Percy Verance on 21/10/2017 20:32:12:

Both aerials remained in place, as did the 35mhz module, and a switch on the module meant you could revert to 35mhz simply and easily......

To explain this a bit further: MPX has for decades used a system whereby connecting two pins on the DIN-socket shuts down the HF part of the transmitter. The main use of this is Trainer-Student operation, the plug at the student end of the umbilical cord would have those two pins shorted. The Hfmx module employs this by using the on/off switch of the module at the same time to connect and disconnect these same two pins, i.e module on = transmitter HF off and vice versa.


Edited By Max Z on 22/10/2017 08:52:55

Edited By Max Z on 22/10/2017 08:53:54

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