Neutrino (oz7762)

About this Plan

Neutrino. Radio control sport model. Wingspan 60 in.

Quote: "Not a delta or just an unusual design, it is a thoroughly engineered ultra performance airplane. Neutrino, by Dave Youngblood.

It takes a trained eye to tell the difference between the 'new' designs and the old ones we've been flying for years. Most of the planes at the local field look alike to me and, let's face it, they all fly about the same. The standard low-wing multi is popular because it's a darn good flying machine. But let's consider some alternate layouts. What about shoulder wings (or high wings)? Ever have the wind get under a wing on take-off? What about a pusher and/or a canard? Well, there may be hope for these but it seems like flying back-wards, and besides, how does one keep the engine cool while taxiing? Or a flying wing?

One version, the delta, is quite flyable but in general is known as a flighty, semi stable, speed whiz. However, it can be tamed and turned into a machine as nice to fly as most standard ships and better than quite a few. This taming results in a delta, but with important differences. So I'm going to describe an airplane that doesn't look like the others, although it does much the way they do.

Hours were spent discussing these things during the daily meetings of the Houston RC Bull Thrower Society (five or six of us ate lunch together every working day). For experimentation I obtained a ready-to-fly Midwest Hustler (oz2873). The first step was installation of a full-house proportional rig, including steerable nose wheel and throttle. This alone tamed the landings considerably, and allowed for flying at reduced power to evaluate performance. Many flights later (with Veco 45) a few conclusions were drawn. The configuration proved convenient, serviceable, and it was different. Few people fly full-house, stunt deltas.

However, several drawbacks were apparent in its flying qualities. Most serious was the matter of pitch control (you know: elevator). Balanced according to the plans the thing would hardly remain in the air almost full up was required and the conventional elevator was completely ineffective - this at about 70 mph. When the engine died the glide resembled that of a dead pigeon. As the balance point was moved back the delta became more responsive and a place was reached where nicely flared landings could be made even dead stick (but at a rather high airspeed). The thing was surely responsive under power. All the maneuvers of a conventional ship could be performed reasonably well, but it was almost unstable.

These are not criticisms of the Hustler, really - just of the Hustler when flown the way I wanted to fly it, two pounds overweight and a .45 up front. The pitch control problems became much less severe when you cut out 2 lbs, but I had to carry a quad prop rig with four servos to get full-house per-formance.

The Hustler has as much total area as most low wings (including stab) so why does it behave that way? There are several reasons. The most important is that short tail-moment. To fly the airplane, a torque about the CG must be produced which will at least cancel the nose down torque inherent in a stable lifting configuration. To do this, we push down on the tail of the airplane, ie: we carry a little up elevator (or negative incidence in the stab on a conventional ship), but on a delta the tail moment is less than half that of a conventional ship, so that, to obtain the same torque, we have to push down on the tail more than twice as hard.

But the object is to go up, and now a fair portion of our wing isn't helping to lift the 5 lbs of dead weight, but only to counteract the force with which the tail is pushing down. In fact we are also using part of the wing to push down as well, since there is no separate stab. The obvious solution to this problem is to put a conventional tail and fuselage on the delta, which Howard Lincoln did and produced a very nice flying machine that won a contest or two. But it was for the station wagon crowd only. Try fitting an airplane 4 ft long, 4 ft wide and 1 ft high in an ordinary car.

The fellow responsible for my quad propo gear, Udo Birnbaum of Dallas, suggested using elevons instead of the standard elevator aileron hook up. By doing so we wouldn't be spoiling the lift of that big center portion of the wing by trying to use it for elevator. On the Hustler the elevator in back spoils a portion of the lift from the center section of the wing, which contains most of the lifting area of the wing. The elevons, on the other hand, act only on the small area of the tips, so by having the center section for lifting alone a large increase in performance was expected. He built a delta slightly larger than the Hustler, put elevons where the ordinary ailerons would have been and it did have much nicer characteristics. Getting rid of that big wide board (the elevators) from behind that nice thick high-lift center section had done wonders for the flying qualities.

To further improve the delta, I decided to add a stab. There are several places for it. A fuselage is too bulky. Mounting it on the rudder is a structural nightmare. So I added one on each tip. This leaves the fall delta configuration free for lifting and provides a more or less conventional stab airfoil. The effective elevator action is now further back (a longer tail-moment) and the rolling moment is also longer, which should smooth out the delta's sharp roll response at high speeds. And it is different.

Conventional 45-degree slope and a con-figuration of about 900 sq in was chosen to give roughly the performance capability of a standard multi. The symmetrical airfoil (what else for a stunt ship?) has no reflex; a well placed CG and a tiny bit of up elevator does the job without affecting the inverted characteristics. It tapers from 15% thickness in the center to 18% at the tips, because a thicker section does stall at a higher angle of attack and we do not want the tips stalling first. Besides, 15% in the center makes a nice radio compartment and I had an 18% rib pattern which was just right for the tips.

A large conventional fin and rudder (remember the short tail moment - to keep torque the same, the force, and hence the area, most be greater) was installed, The rudder is nice for landings - hold the wings level with elevons and steer with rudder. Powerwise, a rebuilt K&B 45 seemed the logical choice. It's light, which helps the chronic noseheaviness of these delta's, and besides, why spend money on a new engine. You want a .60? At 5 lbs you'll shake the airplane and radio apart - it'll climb almost vertically with the K&B 45 anyway.

Construction is conventional, if you ignore the 45-degree sweep. The wing construction (and that's all there is) is the familiar Live Wire (oz5554) type with a solid 3/8 x 3/8 leading edge, two 3/4 square spars running almost parallel about 3 in back, and 3/32 leading edge sheeting. A couple of extra 1/4 in spars top and bottom run straight across for about 1/3 the span. These hold the thing together, so use hard balsa and don't cut through the one that runs across the radio compartment hatch..."

Update 26/6/2025: Replaced this plan with a clearer copy, scanned from fullsize at 300 dpi, thanks to dfritzke.

Direct submission to Outerzone.

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