Simviation Forums

Hi there!

Hi Noel

That's a nice looking little aircraft. Microlights & homebuilds are very popular these days. They come in all shapes & sizes. Maybe I can answer a few of your questions.

The Rotax series of engines are commonly used for this type of aircraft. There are various types with a choice of 2 or 4-stroke. http://www.rotax-aircraft-engines.com/aircraft/aircraft.nsf/products?OpenPage

Many light aircraft have gull-wing doors on the canopy as you describe.

Methods of construction vary depending on the design. These range from a simple wood or metal frame covered with sailcloth (like a hang glider) or conventional doped fabric to the latest hi-tech materials. The world is your lobster.

I hope this is some help. These tiny aircraft fascinate me but I really don't know a great deal about them. I'm sure others will contribute their suggestions. Good luck.

I posted these in the Photos forum some time ago. My friend Dave Grint with his Streak Shadow at my local airport. Note the canopy is side-hinged. It's powered by a Rotax engine with a 3-bladed wooden prop. I think he told me that he updated the engine from the original specs. The pod is glass fibre & I believe the boom is adapted from a standard yacht mast.

Very quick replies, thanks guys. I was curious about my fold-up doors because in the case of an emergency and the pilot has no choice but to bail out, could these doors prove difficult to open in such a fashion due to the strenth of the wind?

Example

Drive your car or moterbike at 70mph and put your hand out the window.. the force of the wind is very strong, now if you try it at perhaps 500ft, it might prove even worse.

About engines.

Rotax engines appear to produce alot of power. I dont feel that the CMX requires such power, im aiming at around 15~30 Horse Power.

The CMX's primary purpose is to fly low and slow at speeds of only 50mph in cruise and an absolute maximum speed of 70mph with a prefered take off speed of 35mph. If one could get away with using a yet smaller engine than a rotax, one would, but only because of weight.

Moterbike / Chainsaw engines maybe?

About materials. I was watching a documentary about WWII planes and it said that the RAF was using Irish Linen to skin some of their earlier planes (early hurricane's perhaps) Maybe Irish linen might be an excellent material to choose. I would rather prefer aluminium or other such lightweight metals in the interest of safety and structural integrity.

Noel

Hi Noel

Aircraft doors usually have some sort of emergency feature. This is often a simple removable hinge pin. Once removed the doors fall off. Very important if the aircraft should overturn on the ground.

The ordinary air-cooled VW car engine as used in the VW Beetle was adapted for use in aircraft. This might suit you better than the Rotax. http://www.altimizer.com/

Fabric covering is still used on many light aircraft today. It's also used on the control surfaces of larger aircraft. This has changed a lot since the old days of Irish Linen although this is still used on vintage types if you can get hold of it. Do a search for Ceconite. This is a modern man-made fabric heat-shrink covering. It's lighter than Irish Linen & gives a far better finish.

PS. http://www.ceconite.com/

Brilliant reading thankyou

I dont know how if an old beetle engine will fit into the aerodynamic shell that I designed, it might be a bit too big. I imagined a motercycle engine would have worked well, as they do tend to accelerate rather quick. The below image depicts the engine shell and as you can see, there is a large air intake at the front. This was specifically intended for engines that create a lot of heat, such as motercycle engines. It would be a shame if such engines could not be used.

As this is your design you can fit whatever engine you wish.

Here's a few things to consider. From your shot it looks to me that it has 2 or more seats. I was thinking of an engine of sufficient power to cope with that sort of payload. I would have thought the 2-cylinder Rotax would be ideal as it was specifically designed for this purpose & complies with the airworthiness regulations. Chainsaw motors are commonly used on large-scale R/C models. I don't think they would have sufficient power for a full-sized aircraft + pilot. A motorcycle engine might be OK but it would need adapting to drive a propeller. The cowling would normally be designed to fit the engine rather than the other way round. Pusher engines are notorious for overheating so efficient cooling is vital.

To give you some idea this is a flexwing, probably the smallest & lightest type of microlight possible. It's basically a powered 2-seater hang-glider fitted with a Rotax 912ULS engine.

[quote]Hi there!

[quote]Noel - are you designing/building this "for real" or are you building a flightsim model?

If you're building "for real" there are other programs better suited to simulating the aerodynamics of your design (X-plane, for instance).

At this present time, the CMX will remain as nothing more and nothing less than a 3D model. Its likely to stay that way for a long time. There is a group of enthusiasts around the globe that have some interest in the design, one of which is making scaled down model versions of the aircraft and has asked can he represent his university using my design in an all-country science exibition.

Basically, Im just harvesting usable information at the moment.

I cant get used to X-Planes utterly ridicolous modelling system. and I dont think you can import files from proper modelling systems like Autocad / Max / Lightwave and Maya. I might attempt it again at some point though!

At this present time, the CMX will remain as nothing more and nothing less than a 3D model. Its likely to stay that way for a long time. There is a group of enthusiasts around the globe that have some interest in the design, one of which is making scaled down model versions of the aircraft and has asked can he represent his university using my design in an all-country science exibition.

Basically, Im just harvesting usable information at the moment.

I cant get used to X-Planes utterly ridicolous modelling system. and I dont think you can import files from proper modelling systems like Autocad / Max / Lightwave and Maya. I might attempt it again at some point though!

OK.  Compared to modelling for flightsim, *I* have found X-plane's modelling unmanageable.  gmax is comparatively easy.  However, X-plane does use the modelled geometry to calculate the flight dynamics.

Having said that, with the flight dynamics utilities available, having the correct basic numbers for the different components will help tweak the final dynamics of your flightsim model.

Good luck!

Oh Hagar! I almost forgot to mention. The CMX is actually a single-seat ultra light. The pilot position is central to the frontal part of the cockpit to make full use of those oddly shaped windows of mine. In this fashion, the pilot should have good upward, downward, frontal, sideward and to an extent, rear visability. There was an idea to make a trainer version that would incorperate duel seats that would sacrifice some rear visability and also lightness.

I didnt have high hopes for chainsaw engines by the way  ;D but chainsaw engines arnt always small, you can get bigger 200cc chainsaw engines that provide good power. I might examine the shape of the smaller Rotax engines and re-think the design work for its aerodynamic shell.

The reason Im being so fussy about that, is because I feel it imperative to make absolutly sure that the aircraft produces as little drag as possible. The CMX in itself is not the most aerodynamic of platforms and although it might easy to just slap an engine on the roof and fly the thing, that becomes stupidious because drag causes fall in speed, fall in speed equals more thrust required and more thrust required equals more fuel required.

So with such things in mind, I think the benifits of cutting drag to the maximum of ones capacity is important.

Hope that explains the fussy attitude anyways  

After looking at those Rotax engines I figured if I re-designed the engine shell like this:



Then engines like the Rotax 447 UL that provides ruffly 40 HP and 35 Torque at 6800 RPM's should fit neatly, I cant imagine the design causing too much drag or anything like that.

OK. I obviously got the wrong end of the stick. I assumed this was for an FS model. This is way out of my league.

I almost forgot to mention. The CMX is actually a single-seat ultra light.

The shape of the fuselage pod & divided windscreen led me to think this was a 2-seater. That central windscreen pillar seems to be just in the wrong place to me & would interfere with the pilot's forward vision. Unless it's part of the airframe structure it might be better to have a one-piece moulded windscreen. This could be hinged at the front (or the rear) as on many modern light aircraft. IMHO

Given the speeds, probably not, but for cooling purposes, you might want to have the rear of the engine enclosure open (or maybe it's just the modelling stage).  After all, you have an opening for the air to come in, but where does it come out?  Also, a suggestion - unless it's a design element you really want, why not make the front of the engine enclosure as a nice grilled fairing?  That way you don't have a (relatively) small tube"sticking out" in front, and you end up with more inlet air area.