Sal Taibi's
Power House
By Golden Age kits

Written for 'RCM&E' March 1984.

Picture of 'Power House

The kit - Fuselage - Wing - Tail surfaces - Tank installation - Radio installation - CG position - Flying - Conclusion

The 'Power House' was designed in the mid 1930's by Sal Taibi and the design was published somewhere between 1936 and 1938 (I have a copy of the original article, but it is undated).

Sal is still flying and winning contests today and is credited with many designs; most of them probably better looking than the 'Power House' However: it does have a certain charm and when the Golden Era kit appeared and was featured in the October 1981 RCM&E 'Counterpoint' column, I decided I must build one.

Before going any further I must apologise to Bill Daniels of Golden Era for taking some two and a quarter years to complete the project. There are many reasons for this, the main one being my original intention to make the model as 'Vintage' as possible and then having to bow to the inevitable compromises needed to produce a practical flying model in a finite time.

Many hours were spent on trying to find some way of controlling the model without adding very obvious non~original rudder and elevators. Eventually, the tail was built as per kit.

In the interest of saving construction time, it was decided to try the, then new, 'Micafilm' out on the tail surfaces ('RCM&E' April 1983). I was immediately converted to this material and used it for the entire model - a decision I have not regretted.

Having already compromised the vintage aspect of the model it seemed fairly logical to use my Cotswold UHF radio to control the beast. I continue to be amazed at the fairly low numbers of this reliable, practical, British made equipment which are to be seen about the flying fields. Incidentally, 459 MHz R/C equipment was used in the early days of R/C in the USA.

Finally, there remained the problem of a vintage powerplant. Somehow, I could not quite bring myself to use a modern four stroke engine. Yes, I know there were model four stroke engines in existence before 1950, but they were about as common as model Turbo-Jets and electric powered aeroplanes. The nearest thing that I possessed to a vintage motor of a suitable size was a Merco 61 with twin plug head so it was pressed into service. As an aside, I personally find the exhaust note of model four strokes in the form usually used (i.e. without a silencer) to be flat, wet and thoroughly unpleasant!

Having, I hope, explained the reasons taking so long to produce a modern film-covered glow motor powered, UHF radio equipped, 'vintage' model; back to standard kit review format.

The kit

With the exception of one piece of 3/8"sheet balsa which is used for the cowl pieces and bottom and various gussets, plus a small piece of 1/16in. sheet used for the cowl top, all wood in the kit was ready shaped. This is no mean achievement if you consider size of the model and the modest price.

The one small criticism I have relates to the wing ribs, which appear to have been produced on a bandsaw. Most of the ribs are intended to be identical but there was a considerable variation in the size and shape of those in the review kit. This could easily be corrected after construction by the use of a sanding block, but I chose to find the smallest and trim all the others to match before construction.

All the wire is supplied unshaped but this is relatively small in section and easily shaped to the patterns given on the plan.

The plan itself consists of two large sheets which are supplied rolled, and includes details of an alternative wing construction to ease transportation problems. More of this later.

Fuselage

Anyone who has built the traditional small rubber model will have no problems with the fuselage. The original design used 5/16" square balsa, but in the interest of price and availability, this has been changed to 3/8". I would advise the use of a mitre block or disc sander if available, otherwise, like me, you may use up lots of time trimming the ends of crosspieces, etc.

A hefty ply plate is used to anchor the undercarriage, whereas the original simply had the wire bound to the lower crosspieces. Nylon saddles are supplied to attach the wire to the ply. You could, of course, mount these on the outside but I chose to mount them inside as per plan. Here you have a choice in that you can take the u/c wire straight out through the side of the fuselage which leaves a considerable length of unsupported wire outside the saddles, or take the wire down through the ply and longerons to emerge at the bottom corners of the fuselage. The plan shows the latter, while the u/c sizes given will produce the formerl

Engine bearers are incorporated into the basic sides with the engine secured to further pieces of hardwood bolted inside the main bearers. This makes for very simple engine changes.

Wing

In the original design this was a very simple, light, one-piece all balsa structure. My own feeling is that this would be quite satisfactory for an R/C version provided that the model was flown in a sensible manner.

However, to cope with the sort of treatment it might be subjected to, the structure has been 'beefed up' with hardwood spars and ply dihedral braces. This is a vicious circle since the provision of either requires the use of the other The result is that the wing weighs roughly twice as much as the fuselage and u/c together.

To cater for those who have difficulty transporting an 84 inch one piece wing, details are given for producing a three piece wing with the dihedral braces being sawn through in two places to produce boxes to accommodate 1/4" ply wing joiners. The logic of this escaped me since it meant that the wing joints would coincide with the wing retaining bands. Fortunately, there is a simpler answer; make the wing in one piece, saw it through the middle, and you have a two piece wing.

Modified wing

Tail surfaces

These are built up as flat structures with the tailplane being sanded to a thin lifting section after assembly. This is somewhat hampered by the fact that the spar material has, very sensibly, been changed to hardwood. Some preshaping of the spar is advisable.

As a concession to 'vintageism' the control surfaces were hinged by sewing with Terylene thread. If you can't find this material use some other method. Other types of thread are unsuitable.

Tank installation

Just how much of a problem this poses depends on the size of the tank you intend to use. A four ounce size can be fitted easily by cutting away the instrument panel bulkhead but is a little on the low side for satisfactory operation. If you use a vintage engine with integral tank, the problem does not exist.

Radio installation

There is almost too much room for this. Any type of gear could be easily accommodated. The only real restriction is in obtaining the correct CG position and this makes it advisable to keep everything well forward.

The battery pack was mounted under the tank (it could, if necessary, be installed below the motor), with the receiver immediately behind it. Three servos were mounted on hardwood rails which were, in turn, mounted below the lower cabin longerons.

Pushrods were of 3/8" square balsa with the threaded wire ends supplied. Rudder and elevator horns were as supplied, with the rudder horn mounted on the base of the rudder post which passes through the tailplane. This arrangement works well but it is necessary to cut away a large slice of the top longeron in order to easily install the tail.

One benefit of the Cotswold UHF gear was that it was possible to install the vertical dipole receiver aerial inside the fuselage.

CG position

Two centre of gravity locations are shown on the plan. For F/F purposes, it is recommended that the model be balanced on the rear spar as per the original design. For R/C purpose, the front spar is indicated as the balance point (these locations falling at roughly two thirds and one third of the wing chord).

My radio installation, in fact, produced a balance point mid-way between the spars which seemed like a fair compromise to begin with! All-up weight was exactly 5 lb.

Flying

Since the model was obviously going to be overpowered, a long exhaust extension was added to take all unburnt lubricant away from the model. This, together with a 13 x 5in. Topllfte propeller gave a flat-out speed of rather less than 8,000 rpm.

The first take-off, in flat calm conditions, took less than five yards and after reducing power to half throttle, the model climbed away at a good 30 degrees with a natural left turn.

With the possible exception of the 'Windbag' inflatable wing model, the 'Power House' is the most vice-free model I have ever flown. For instance, it is necessary to hold on the rudder to maintain a turn; releasing it produces an instant return to a straight glide or gentle left climb. A complete flight can be made without ever touching the elevator control. However, in anything above a very light breeze, the model suffers badly from wind shear and tends to drop the last three or four feet before landing. As originally set-up, there was insufficient elevator travel to prevent this, so some differential was introduced by offsetting the servo arm to give more up than down. There is virtually no stall, holding on full up elevator merely produces a slow, nose high, descent.

I am still unsure about the CG position. To get the best performance it is necessary I add down trim for powered flight (it will maintain height on just one 'click' of the throttle ratchet above tick-over) and remove this for the glide. This suggests that the CG could probably be moved back to the free flight position on the rear spar and complete the whole flight on one trim setting.

Conclusion

Having flown the model, my only regret I that I did not finish it sooner. Need I say more?

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