Tornado XC Cylinder Head

[Ganbatte]

Does anyone here have either published data or personal experience with the new XC head for tornado? It's just out, and I've heard it flattens the infamous tornado power curve, at the cost of some power. From the name, I'm wondering if its fuel economy might be a little better too. Even links to hands on reviews would be welcome; I've found very little info on it.

[AndyB]

It lowers the compression ratio.

[Ganbatte]

And its effect on the power curve? 

[Bob27]

You can alter a power curve on a 2 stroke engine by changing the shape of a cylinder head. Basically a deeper cylinder head will provide more low end power and a flatter cylinder head will provide more top end power. Changes in compression will often change things differently in different engines, but in most cases with small 2 stroke engines, lower compression will give more top end power and high compression gives better bottom end power. There are a lot of little reasons for this and it will sound counter intuitive to many people out there, but its often how it works.

So my guess is that the tornado xc cylinder head has a more narrow and slightly taller combustion chamber with a higher compression ratio to increase the efficiency in the mid power range.

[Ganbatte]

ok, looking forward to published data, which seems to not be the custom in this industry. But I can hope.

[Bob27]

If only that could be the standard...

Maybe someone should make a way of scientifically testing everything from engine performance, wing performance, frame safety and performance and make it all uniform testing that it concreate so we can finally see through to what is truly the best and what is just trash.

[AndyB]

6 hours ago, Bob27 said:

So my guess is that the tornado xc cylinder head has a more narrow and slightly taller combustion chamber with a higher compression ratio to increase the efficiency in the mid power range.

Incorrect. I already said it has a lower compression ratio!

[Ganbatte]

So, a lower compression ratio will mean (perhaps slightly) lower efficiency, but nobody buys a tornado for fuel economy. Probably lower operating temps, which is generally happy news, but the big thing is its effect on the power curve, and that's not obvious or intuitive. I do wish AC would publish curves.

[Bob27]

Sorry, I am very experienced with 2 stroke engines and am more familiar with using standard profile wings than more modern and high performance paramotor wings. So maybe I should re-visit everything that I have said. 

Reflex wings are far less efficient and faster than standard profile wings, so for XC you need to hold medium to high power for long periods of time, not medium to low power like you would with the standard profile wings which are slower and more efficient.

So yes, a lower compression to increase the engines XC capabilities is completely reasonable.

[AndyB]

You say reflex wings are "far less efficient" than paraglider wings. Reflex wings typically achieve GR of 9:1 and paraglider 9.3:1. Competition paraglider wings can achieve over 11:1, but are quite different and it would be like comparing an apple and an orange.

My reflex wing flies level at 5400 rpm with trims in (best GR of 9:1). Trims fully out (GR 7:1) it needs 5750 rpm. The reason I say this is to show that between most efficient and least, the difference is not massive. A non-reflex wing will not be that much better than the reflex wing with trims in (9 compared to 9.3). Saying reflex wings need medium to high power and non -reflex need low to medium power, is just wrong.

Now if you fly a competition paraglider wing with an engine, then good luck, because you will likely need it!....they are just not designed for the much higher angle of attack when under power. 

[Bob27]

I am referring to the power difference required to flying with large amounts of speed bar in full reflex mode. In this mode some high speed 16 square meter reflex wings are hitting sometimes over 55mph, but they need close to full power to maintain elevation. On the other hand people with 16 square meter non-reflex wings are hitting maybe only 35-40mph, but with the right wing they can do that at nearly half throttle. It will also vary a lot with wings. Not all wings are created equal.

I have personally built many reflex winged rc airplanes because reflex airfoils do have there advantages, but efficiency is not one of them.

[Blackburn Mark]

17 hours ago, Bob27 said:

I have personally built many reflex winged rc airplanes because reflex airfoils do have there advantages, but efficiency is not one of them.

I always assumed that a reflex reduces a profiles pitch instability AND it unloads the rear of the wing giving the whole wing a *higher "aerodynamic" wing-loading (faster) and a higher "aerodynamic" aspect ratio (improved efficiency)
The speed dumps a lot of efficiency and the higher aspect ratio claws "some" of it back.
I am not sure it is sound to conclude that a "reflex" is inherently inefficient without balancing the gains and losses of the various regimes... But I am happy to be corrected, my grasp is a pretty rudimentary one    

Design two tailless RC models with the same projected aspect ratio (one reflexed and one not) and I suspect the advantage of a reflex would give the none reflex a run for its money (shallower sweep, less tip washout and all that associated jazz)

Edited October 11, 2020 by Blackburn Mark
Error correction

[Bob27]

Basically the entire reason we use a reflex airfoil on an tailless flying wing for it's stability. The disadvantages of it are that it produces more drat and less lift.

So if you put 2 back to back the non-reflex would fall out of the sky. Now there are a few tailless aircraft that I have built where I haven't needed reflex wings due to an insane amount of sweep back and that probably my most efficient glider.

[Blackburn Mark]

2 hours ago, Bob27 said:

it produces more drag and less lift.

You seem to be excluding a subtlety:
Are we in agreement that a reflex increases the wing loading  (aerodynamically) and increases the aspect ratio (aerodynamically)..... ?
These things, if true, are not insignificant which may be the reason why we don't see a large difference between the two as Andy has pointed out.
 

[AndyB]

Why do you compare a tail-less rc plane to paramotor wing? They are completely different. The ppg wing maintains stability by virtue of the large not insignificant large weight dangling below it....like a pendulum, the weight always wants to stay below. It can wobble a little forwards and sideways, but naturally wants to hang down. 

I have over 100 RC planes and not one of them is even remotely comparable........except for my rc paramotor! All my flying wings have the CoG pretty much up in the centre of the wing.

Are you sure you are understanding what a reflex wing is when referring to a ppg wing?  Most people do not understand this.

[Bob27]

I believe I understand reflex wings perfectly well. Let's go through exactly how they work because it sounds like many people here don't fully understand.

First thing you need to understand is that a paraglider wing operates with a ram air intake which is strategically placed to take in air from the location where air pressure is highest. This means that the air pressure inside of a paraglider is higher than anywhere else on the wing. This allows for a paraglider wing to be more than a fancy bed sheet and it allows a paraglider wing to take almost any shape that the designer wants.

So what designers discovered is that the internal pressure in a well built wing is high enough that they could curve the rear of a wing upwards enough to to point where the trailing edge would create a slight down force. What this does is it makes it so that you can place the cg a farther forward. This makes it so that as your speed increases, the angle of attack increases and your speed decreases, the angle of attack decreases. It also allows reflex wings to maintain a proper angle of attack in relation to the wacky air currents in turbulence which is why they are more stable than non-reflex wings.

21 hours ago, AndyB said:

They are completely different. The ppg wing maintains stability by virtue of the large not insignificant large weight dangling below it

So this is true for non- reflex wings and wings not in reflex mode, but it is not true for reflex wings in reflex mode. Reflex wings in full reflex mode and with full speed bar, the A lines very tight with 50-75% of the load and the B lines fairly tight with the remaining load. All the remaining lines shouldn't have any load. If a reflex wing did rely on on those 2 unbalanced lines to maintain stability, everyone who has ever tried reflex would be dead. Also watch this video. It shows how reflex wings are not reliant on the wight distributed below the. It also proves my point that there are some pretty major changes the the airfoil shape to make a reflex wing do what it does.

22 hours ago, Blackburn Mark said:

You seem to be excluding a subtlety:
Are we in agreement that a reflex increases the wing loading  (aerodynamically) and increases the aspect ratio (aerodynamically)..... ?

So this is not completely true. If the entire purpose of the reflex wing was to unload the back half of a wing, you would die because of your lack of stability. If you don't believe me take a non reflex line and cut the c and d lines during flight. If I am right, you would fall out of the sky.(please don't actually do this as you would fall out of the sky.) So yes a reflex wing will increase the loading closer to the leading edge, but the back half of the wing is still regulating the angle of attack and regulating the angle of atack to make up for the C and D lines being slack. Also a reflex airfoil is still an airfoil just like a non reflex airfoil. So aerodynamically the aspect ratio doesn't really change.

 

[Blackburn Mark]

2 hours ago, Bob27 said:

If the entire purpose of the reflex wing was to unload the back half of a wing, you would die because of your lack of stability.

Did I say "entirely" ?
Are you being tactically uncharitable in your interpretations?
 

2 hours ago, Bob27 said:

So yes a reflex wing will increase the loading closer to the leading edge

So we do indeed agree....Yes?

 

2 hours ago, Bob27 said:

So aerodynamically the aspect ratio doesn't really change.

I suspect you are being uncharitable again.
Within the context of paramotoring, I doubt very much that the amount of "reflex" we use does a great deal more than "unload" a portion of the rear of the wing so it is hardly lifting in the negative or positive in stable flight.
The video shows an "unloaded" wing, a wholly different animal to a loaded wing.
As Andy stated "The ppg wing maintains stability by virtue of the large not insignificant weight dangling below it"... this remains true on either style of wing!
Any additional stability we gain is in the context of remaining open during moments of unloaded lines.

Try to imagine how much "pitch up" that trailing edge could impart into the pilot-wing relative positions through "reflex" alone..... Not much if its measurable at all.
So it would seem the trailing edge becomes neutral or very close to it in reflex mode, not adding nor removing lift ergo not adding induced drag as it would when in high lift mode... The "active" portion of the wing is, it would seem, higher in its "aspect ratio", yes?  

I think you may be conflating paramotor wing levels of reflex with more traditional reflex implementations on hard bodied aircraft that can and do make use of much larger pitch moments.


 
 

[AndyB]

5 hours ago, Bob27 said:

I believe I understand reflex wings perfectly well. Let's go through exactly how they work because it sounds like many people here don't fully understand.

This makes it so that as your speed increases, the angle of attack increases and your speed decreases, the angle of attack decreases. It also allows reflex wings to maintain a proper angle of attack in relation to the wacky air currents in turbulence which is why they are more stable than non-reflex wings.

This is not a good explanation of reflex. Your air-speed on a paraglider is fixed by the weight that is dangling from it.  Your speed is only altered by letting out the trims (lengthening the rear lines) and thus reducing the angle of attack, so the wing goes faster. Pushing speedbar pulls down the front A's, again reducing the angle of attack and hence increasing speed. Both of these are the exact opposite of what you say above. 

You have not explained at all how reflex works. That is why I asked if you really know. 

I also asked why you compared a reflex glider to a flying RC wing, when they are not in the slightest bit similar.  

[Ganbatte]

This discussion of reflex wing principles is all very interesting, but... I'm hoping someone knows something about the thrust curve produced by this new cylinder head?

[Blackburn Mark]

5 hours ago, Ganbatte said:

I'm hoping someone knows something about the thrust curve produced by this new cylinder head?

What exactly are you looking for in the thrust curve? (I assume you mean "power curve")
If its dubbed to have "flattened the curve" then its reasonably safe to assume that the aim has been to make the machine less "peaky"... More pilot // trigger-finger friendly at the expense of some top end.
If the compression is lower then maybe some loss in efficiency at wide open throttle BUT that might be offset with a slightly better cruise efficiency.... but we cant read that in a power curve.

Are you going to be able to read any more than that from a power curve?
 

[Ganbatte]

Yes, ok, "power curve". Tornado has a reputation of "breathe on the throttle, get face planted"; my practical interest is "does the new head flatten out that curve enough to be considered a bit more civilized/comfortable? To that end, it'd be nice to see how much those curves differ. A few percent, meh, forget it. If the new curve is something an honest person would call "reasonably linear", then that's a horse of a different color, as they say.

[Blackburn Mark]

1 minute ago, Ganbatte said:

my practical interest is "does the new head flatten out that curve enough to be considered a bit more civilized/comfortable?

Why else would they bother?
The response hysteresis may be gone but I doubt it... Cant see it being worse though... Id put money on it that its an "improvement".

Do you have the "old" curve?
Wouldn't mind a look at that  

[Ganbatte]

I'd like a look at both, justaposed. Barring that, detailed review by someone, here, 'tube, wherever, would still be something. If we were discussing a $5 item, the answer would be "buy one, try it out, see what you think". Not as cheap/easy w one of these machines, so due dilligence is appropriate.

[Blackburn Mark]

2 minutes ago, Ganbatte said:

I'd like a look at both

Ah, so you have no access to the old one either... ?
The new one would only give you a clue as to where in the RPM range the hysteresis would be at its worst.
Quantifying that would be quite the trick  
Like I said, it is a "safe assumption" that it is an improvement if that is what the designer professes to be the point.

Besides that, it would seem plenty of people have many happy hours on such machines (even "peaky" ones) so it is also safe to assume the issue is not insurmountable with a touch of trigger finesse  

[AndyB]

I fly Tornado and have not had a problem with the throttle response. The only problem I ever had was applying power the same way I do it on my Nitro ie zero to full in a split second. Face plant time! It is so punchy the legs can't keep up.

I do lots of beach flying at an altitude of around 1'. Again, I have no problem with throttle response.

I was told the change to the head was to improve fuel usage for XC flying. Since I only usually fly 1 hour it does not affect me.