Aeroovee to Rotax mount conversion???

[Brett]

Is that some sort if muffler or just a large collector? Will be interested to see how loud it is. I manged to fit my muffler in but am glad to be honest.

[xeriotti]

Is that some sort if muffler or just a large collector? Will be interested to see how loud it is. I manged to fit my muffler in but am glad to be honest.

Its a BFC... Big Fat Collector XD

Collector diameter, has to do with headers diameter and lenght... There are calculations to make it perform best. When putting together an exhaust system for an aircraft sometimes theres no room or the optimal solution just cant be fitted.... This gets pretty close to that. I have great expectations for this setup :)

It sounds amazing.!! Pretty much like a sportbike (My neighbour complained about that last night)... like a 929 i used to have... Its loud but sounds fat.... Havnt heard it outside yet, but i bet a 180mph flyby with that engine screaming almost 6k rpm will be nice to hear... its raining now, but im taking it to the airfield to fit the wings as soon as it dries :)

[xeriotti]

A 5kms ride to the hangar... I may fit the wings tomorrow :)

Anyone flown their plane with no cowling? i want to make sure it flies straight before i make my cowling...

[Bryan Cotton]

Anyone flown their plane with no cowling? i want to make sure it flies straight before i make my cowling...

That seems like a bad idea. For those of us with aircooled engines it's not an option at all, as the cowling forces the air through the heads rather than letting it go around. It would be very draggy though.

[Kai]

Bryan,

Yes- agreed.

If my experience is anything to go by, I would not be too concerned about cooling. Initially my engine was doing just fine without the cowling on the ground at full tilt, but overheated badly with the thing installed.

Aerodynamics is as you say another matter altogether. When I did my builders course in Osh back in 2004, I recall John telling us that the cowling was an essential part of the flying qualities- and no one had ever test flown without one. We were also told that the front of the plane below the straight line from the back of the prop to the point where the canopy started to curvature was a mini lifting body: don´t impose too many deviations.

If his engine is straight in all axis, he won´t have any great surprises- apart from the fact that on the ground it pulls to the left like there is no tomorrow: right pedal! There must be enough free space under his cowling and the engine to put in a few aluminium spacers for alignment should they be needed.

[xeriotti]

Bryan,

Yes- agreed.

If my experience is anything to go by, I would not be too concerned about cooling. Initially my engine was doing just fine without the cowling on the ground at full tilt, but overheated badly with the thing installed.

Aerodynamics is as you say another matter altogether. When I did my builders course in Osh back in 2004, I recall John telling us that the cowling was an essential part of the flying qualities- and no one had ever test flown without one. We were also told that the front of the plane below the straight line from the back of the prop to the point where the canopy started to curvature was a mini lifting body: don´t impose too many deviations.

If his engine is straight in all axis, he won´t have any great surprises- apart from the fact that on the ground it pulls to the left like there is no tomorrow: right pedal! There must be enough free space under his cowling and the engine to put in a few aluminium spacers for alignment should they be needed.

No one ever flown one with no cowling? :S

The engines alignement is mentioned anywhere on the plans? My engine is flat with the aerovee mount.... so its like factory supplied it. But really would want to test fly it before making a cowling from scartch

[xeriotti]

Looks like it would fly without a cowling to me...

[builderflyer]

Looks like it would fly without a cowling to me...

Similar to what Kai recalls, I remember John Monnett explaining to us that the fuselage (which would obviously include the cowling) of the Sonex was designed in the shape of an airfoil and that it supplied a percentage (maybe 15 %) of the total lift of the aircraft. So, given that, one would have to assume that flying without a cowling would have a noticeable effect on the performance. You may want to pass this question by John Monnett before attempting a flight.

Art,,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,Jabiru 3300 #261

[rizzz]

It would be good if someone like Joe could chime on this topic.

My opinion about attempting to fly without a cowling? Really, really, really bad idea! Seriously!
I urge you to rethink this or at least have a chat with the people at Sonex before you go ahead with this.

As many have stated, the shape of the fuselage of a Sonex/Waiex provides a significant amount of additional lift.
You say, "Looks like it would fly without a cowling to me..." !
Well! It looks like it would fly without a canopy as well but there are a few people who have actually inadvertently done so and as they will tell you, it really doesn't!
Here's one example: /viewtopic.php?f=25&t=6646&hilit=canopy

If not having smooth air flow over the top of the plane makes that much difference, what to you think not having smooth airflow over the nose of your plane will do?

And in the end, what are you trying to gain by attempting this? Get some idea of how straight it flies before designing your cowling?
I doubt that if it flies at all, it will be flying well enough for you to make any sort of judgement about how straight & level it’s flying.

What about just making your cowling such that you can still make small adjustments to the position of the engine later on if necessary? That’s what we all did.
And finally, what about putting a trim tab on your rudder if it does not fly straight? We all have one, for exactly that reason, the Jabiru people have if on the opposite side of the VW people since the prop turns the other way.
BTW, like most planes a Sonex flies straight at one speed/engine setting only, we set the trim tab to get the aircraft to fly straight at cruise speed/power, but climbing out significant rudder is required one way and on descent significant power is required the other way. It’s quite a significant amount of rudder that’s required compared to most aircraft I’ve flown and I only have a normal aspirated VW engine.

Sorry to have to be so direct but I fear this has a high probability of ending in disaster.
On a brighter note, I really admire your Rotax engine project so far and I've been following it very closely as I dream of one day replacing my VW with a Rotax.

[Kai]

So we all agree that a cardiac arrest up there during the first test flight is something that should be avoided.

Having established this and in addition decided not to mess up the front end of the fuselage and stick to the contours suggested in the plans- do you recall that for a while there was something called a Todd´s canopy? I am not absolutely sure why some people went for them, but I speculate that one of the reasons was less prone to cracking during installation and much better resistance of the windshield to mogas. Whatever the reason: it made the front end of the Legacy look like a dolphin- and totally deviated from the plans.

What´s more- I´ve flown one. It also had the smaller flaps. Upstairs there was not much difference. And it was not particularily difficuilt to land either. But you had to keep very strict control of the airspeed during the flare- a tad too slow and the famous Legacy float was gone: whammo! and you were careening down the strip much faster than originally intended.

Better stick to the plans. Aerodynamic prototype development work is only for those paricularily interested.