why not Enya?

Through 40 years of flying I've used a lot of Enya engines, but they never seemed to catch on in this country. They were certainly as well made, really better made then OS but I can't ever remember any name modeler winning the nats with an Enya. To be fair I didn't compete in this country with them but overseas that was all I used. What was it, were they too big, too heavy,
no 4-2-4 ? Dennis

1. The toughness has a down side; extensive and long breakin.

2. Enyas tended to be a little heavier than their rivals.

3. Yes, they didn't tend to 4-2-4 very well.

The "styling" is somewhat unusual, with their oft reliance on a removable front plate, rather than the standard backplate. Did this work unconsciously on modelers? Some of the earlier Enyas give the impression that there is not enough "ass end" to the crankcase. Look at the very early sandcasts, for example.

Over the years, they may not have had the best marketing, but some of their ads have been interesting. Weren't they the ones that had the RC plane lost in the frozen pond all Winter, and they find the plane in the Spring, oil up the Enya, and voila? Something like that.

I'd also have to say that the breakin period with a Fox is shorter. At least the philosophies of the respective companies vary widely. For Fox Stunts, they tell you that, essentially, the engine really doesn't need one! Enya has you doing one thing during the first hour of breakin, something else during the second hour, etc.

I didn't say that the front removable plate wasn't handy. I'm just saying that it is somewhat unusual, and funny looking on some of the Enyas, especially the early ones.

But solid citizens they are. Enya is Nissan to OS's Toyota, as I see it.

It was very heavy for the small plane--I wrote about my exploits with the Frankenstein plane alot on Isky's forum.

It would run quite a nice 4-2 break with a 9-4 clipped to 8.5.

I never really did get enough weight on the tail to get the CG where it should have been.

I later built a Akromaster and chose to use a Fox .15 instead of the Enya. And I kind of felt that the .19 was too heavy for the Akro as well. (the .15 loop engine has plenty of power for the Akro)

But I wanted to build something for the .19 so I'm scaling up the Akromaster about 1.25X for the Enya .19. THe wing, as kitted can be built easily with an extra panel on each end. Even if you left all else as stock, I think it would be a good match for the .19

I'm making several other scale-up changes as well since I'm scratch building it--I'll let everyone know how it turns out.

Your observations are right on the money and I have heard others in the technical analysis ranks mention the same things. Balance of the model around the pitch axis is a static thing--the measure of its ability to make appropriate changes in attitude is affected much more by dynamic forces working against its inherent moments of inertia. For a given weight, the shortest couples will result in the best capability to rapidly change pitch and recover.

Anyway, my friend and I are playing with modal/vibration analysis as well as a way for anyone with a string and a stopwatch to arrive at actual moments of inertia values for plane to plane comparisons.

It is one reason why we build light--especially the ends. And as you pointed out, why the short noses work better. It would be interesting to be able to quantify this effect on successful designs like we do the planform area ratios, etc. since I suspect that there is an optimum range of rotational moments for our purposes. One could overdo the short couple design--a la Voodoo or similar.

Simply my thoughts and opinion,

I've done a fair bit of analysis on this sort of thing. The detailed analysis involves discussion the "radius of gyration". It has to do with the distribution of mass throughout the object. The radius of gyration is defined as the distance from the rotational axis (in the case of free-moving bodies, the CG) at which you can assume the mass is concentrated in a point that gives the body the same moment of inertia. A barbell has a larger inertia that a constant-diameter rod of the same weight and length, because the mass is concentrated at the ends instead of spread out. This mean the radius of gyration is longer. The applicable equation is

I = mr^2
where I is the moment of inertia
m = mass of object
r = radius of gyration

It takes calculus to figure out what it is from a given shape, but sometimes you can adequately approximate it if you have massive items connected by reasonably light structures.

Since balance is a proportional to the distance, and inertia goes as the square of the distance, making the nose shorter and adding more mass to balance can result in the moment of inertia being smaller. Of course, the overall weight goes up, which is where the compromise comes in.

Qualitatively, reducing the inertia and changing nothing else always improves the damping, and increases the response natural frequency. This means the turns are easier to start and stop. It's not a free ride, because you can't make the inertia smaller and maintain balance without giving something up. If you keep the same engine mass, for instance, and shorten the nose, you have to shorten the tail, which does reduce the inertia, but also reduces the restoring force proportionally. This changes the relationship of lift to pitch rate. It also raises the max rate which may at first seem like a good thing but may lead to too much rotational rate for the amount of lift.

In the case of a heavier engine and shorter nose on the same airplane, the moment of inertia goes down, the wing loading goes up, and the other aerodynamic parameters stay the same. This improves the damping ratio, but also reduces the acceleration:pitch rate ratio. This would potentially detrimental if it had been perfect before, and then it would be a matter of trading off better damping for worse anti-hop characteristcs. Assuming that we are talking about the Patternmaster-type designs, however, it's my personal opinion that they have always looked a little "flappy" to me for the weight. I would have probably cut down on the flap size or added ballast anyway. So the extra motor weight may have actually improved the situation in two ways!

Note that Scott Reise found something similar with his Cardinal and flies it with a lot of ballast on the CG

For completeness, the inertia is not just a scalar number, but actually a 3x3 matrix. The diagonal terms define the scalar inertia around each of the three rotational axes. The off-diagonal terms describe how movement around one axis couples into another. In our situation of very light, violently maneuvering airplanes, the off-axis terms are very important to the motion of the airplane, and need to be minimized, just like dynamically balancing a car tire. Redefining the 3 axes by rotating them relative to the airplane results in different off-axis terms. There is a point where you can rotate the axes to make the off-axis terms disappear. These axes are called the "principal axes" around which rotation is not coupled in to the other axes. It also another reason not have have much yaw angle, since you end up trying to rotate around axes that aren't the principle axes, thus causing one version the familiar wallowing through corners.

More secrets for my buddies - I have in the past fiddled with adding equal amounts of weight to the inboard TE and the outboard LE of the wings to try to move the principal axes around to fit particular yaw angles. This was moderately sucessful in that it did more-or-less what I expected. But while it helped the kinematics, other factors indicated that trying to fly with significant yaw angles had detrimental aerodynamic effects, and so I eventually came to the conclusion that tangent was best overall. Some airplanes with minimal aerodynamic yaw restoring force (notably Brian Eather's "Firecracker") don't carry as much penalty, so it may be a useful technique.

Great overview of the inertia topic Mr. Buck!!

You pretty much described the reason for my interest in a way to quantify a complete model in a few minutes. Prediction of these numbers requires a rather powerful software model or alot of hand work--but an experimentally obtained number can be generated.

For many years I have been a Yacht measurer for US SAiling. In the latest versions of yacht handicapping through the use of a velocity prediction program (VPP) we are able to generate boatspeed predictions for a variety of conditions and use this data to handicap non-similar designs racing against one another. THe system was developed out of MIT in the seventies and has been highly refined as the model performance metrics have been more accurately described. One of these is the pitching gyradius. It was well known that boats with the weight concentrated around the center of gravity, with light ends (all carbon composite and titanium stuff) were significantly faster in waves. THe problem was the input data to the VPP is all measured data--no design or planned shape or weight information is used. WE now actually do a data acquisition of the full scale hull shape and produce computer wireframe. Acutal displacements are then done as well as aerodynamic sizes and shapes. We incline the hull with known weight to measue righting moments. It is a very thorough and complex process but works suprisingly well--results corrected to seconds over races of days.

One of the things we can now experimentally determine is the pitch gyradius--we do this by timing a damped pitch oscillation and feeding that data into the model.

We think we could do the same for a model plane using a support wire and cycle timer.

Brett, (Or anyone?), in your opinion, having knowledge of this area and what these factors imply, would we gain anything by being able to benchmark known-good performers in this way? Or is it just another thing that pretty much takes care of itself?

Thanks

>I'm going to make a suggestion.
>You can fly a much
>larger airplane then you think.
>The key word is weight
>reduction and a subtle change
>of the aircrafts flying habits.
>
> Take the lowly ringmaster
>and go on a weight
>reduction program. use a 3/8
>fuselage and really taper sand
>it ,
> Gut the wings weight as
>much as you can pick
>soft wood for everything.

I have two of the same model Enya .19 and the engines are, as mentioned previously, more powerful than the typical loop scavenged .19. My best-flying, full sized, stock, kit-built Ringmaster was powered by each of these engines during its career. I've forgotten which prop I used, but I believe that it was a nylon Top Flite 9-6, although it could have been a 9-4. I flew the combo on .012" X 60' lines.

It did everything well and was a joy to fly.

You now have an answer from some one with experience, rather than theory to impart.

>Kelvin,
>
>I have two of the same
>model Enya .19 and the
>engines are, as mentioned previously,
>more powerful than the typical
>loop scavenged .19. My
>best-flying, full sized, stock, kit-built
>Ringmaster was powered by each
>of these engines during its
>career. I've forgotten which
>prop I used, but I
>believe that it was a
>nylon Top Flite 9-6, although
>it could have been a
>9-4. I flew the
>combo on .012" X 60'
>lines.
>
>It did everything well and was
>a joy to fly.
>
>You now have an answer from
>some one with experience, rather
>than theory to impart.
>
>OS