AMA Chartered Club #340

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 The 495th R/C Squadron, Inc.


495 R/C Squadron - Projects

Rupert Kosmala's Ephinay

Power:  Homelite 25cc Gas
Span: About 98"
Length: Don't know yet
Weight: Probably too much
Wing spar consists of two 1/4 X 3/8 Spruce with carbon fiber with double 1/16 balsa shear webs. Secondary spar 1/8 X 1" balsa. Leading edge 1/4 balsa. All the rest of the construction is 1/16 balsa, apart from the supports for the wing joiner tube.


Wing slots in the making. Framed wing panel less trailing edge. Wing panels and wing joiner, a 1" dia AL tube. Wing panel with leading edge sheeting and trailing edge.

Wing Tip - Phase 1

Wing Tip - Phase 3

Wing Tip - Phase 4

Wing Tip - Phase 5


Completed Wing Panel
Each panel is 43.75 in, for a total span of 96.5 in.

Beginnings of the Stabilizer

Framed up Stabilizer

Vertical Stabilizer taking shape


Tail Feathers almost complete!

Tail assembly mounted on Fuselage

Ingredients for the Fuselage

Fuselage Payload Bay Shaping Up

Tying in the tail boom, the wing joiner tube and the payload box

Finding out where the engine should go to get the right CG position

Engine mount tacked together

Engine mounting plate


Engine mounted into position

Soon, it will be time to get dressed Where it all comes together

Forward of the firewall



Dressed enough for the first flight

The Third Try!



Before completing the cosmetic work like cowls and covers, I wanted to find out if this thing would fly. Although I forgot to weigh it while I had it assembled I know that it was somewhat overweight at around 16lbs, with more than a third of that being the engine!  The CG had ended up further forward than I wanted it, but flying it would indicate how serious a problem that might be.  My biggest concern was the possibility of a difference in the rigging of the two wing panels, even half a degree difference in incidence would give a pronounced roll at lift off.

Attempt Number One

Taxi trials showed that it was not overpowered and a long roll was required before it started to rotate.  I was mightily relieved on its first lift off when the wings remained absolutely level requiring no aileron input.  However, nearly full up elevator, and there's plenty of it, was needed to get it to break ground.       Adjusting the decalage by giving the stabilizer some negative incidence did shorten the take off run slightly but it was quite clear that the CG needs major movement.  A few, short, straight line flights were enough to convince me that the Ephinay will be a good flyer, but not before it gets more power and a new CG - anybody got a G38 for sale?

Attempt Number Two

The consensus was that the plane did not achieve a high enough speed at take off and that the elevator was having to do too much work because the decalage (the angle between the stabilizer and the wing) was not right.  We decided that the CG position was not at fault, though we had some reservations about the possible effect of turbulence over the tail surfaces created by the open box of the fuselage.   So, we decided that more power and a changed decalage would probably solve the problem. Careful recalculations produced a stabilizer/wing set up and a CG position which was moved slightly forward.

Art Alfano kindly loaned me a Quadra 40 which, as well as having more power was more than a pound lighter than the converted Homelite 25.  This meant constructing a new engine mount as the new engine had to be moved forward 4 inches. Careful measurements of the existing decalage showed it to be already exactly where it should be, which cast a little doubt on our theory that it needed to be changed.

Modifications made, it was time for the rubber to hit the road. A sprightly take off run and she lifted off the deck into a healthy climb, apart from a lot of up elevator she was flying straight and true without needing any trim adjustments.  What a great feeling that was!!  A 180 deg turn was made very easily but after leveling off she started to nose down slightly, a bit more "up" should have leveled her out but it didn't. She started to nose down more and more and I continued to apply more and more  "up" until it ran out.  She was still nosing down and I was bending the stick when the ground rose up in greeting and ended the flight.  I just stood there in disbelief - I thought we had it licked.

The tubular steel engine mount was totally demolished as it absorbed nearly all of the impact, it must have have hit at about 45 deg. Otherwise damage to the rest of the plane was minimal.  A couple of servos stripped their gears, the aft fuselage tube collected a slight bend and there was minor stress damage to a wing panel.  Detailed examination may reveal more damage but it won't be enough to prevent a third try!

The experience gained so far suggests very strongly that the problem is indeed turbulence from the open box end of the fuselage plus that caused by the unfaired center section.  The tail surfaces are working in very turbulent air which severely reduces their effectiveness.  Our guess is that at take off the stabilizer and elevator were only just effective (hence the large amount of up elevator needed to make it lift off) and as the plane leveled off from the climb its speed increased and therefore so did the turbulence, making the tail surfaces even less effective,  resulting in the conversion of my pride and joy into a lawn dart.

For attempt number three I will reduce the turbulence over tail by fairing over the center section to smooth out the airflow over the radio gear and by constructing a cone over the open box end of the fuselage - as well as a new engine mount of course.

Attempt Number Three

The  Quadra 40 was returned to Art as he found he had a plane for it and I was left wondering what to replace it with.  Both my G38's have been doing a great job in the Cub and the Marquardt Charger for the last dozen or years and it seemed a pity to break up those friendships.  The Homelite had proven itself not up to the task so rather than go out and buy a new engine for a plane that has shown some reluctance to fly, I bit the bullet and installed the G62.  This engine had been gathering dust since the HA-1 "Iron Maiden"  died.  At two and a half times the size of the Homelite power should not be an issue!  Unfortunately the weight goes up with the power and the Ephinay now stands at about 20lbs - but with 26lbs of thrust.

The picture shows the fairings added at the back of the box and over the center section, hopefully they will do the trick.  Creating a cowl is out of the question until the Ephinay proves itself a satisfactory flier.


With the new fairings in place, everything checked out and the G62 eager to go, the Ephinay taxied out to the end of the runway, and to my delight and that of the audience she lifted into the air after a modest ground run and climbed out very smoothly and under full control.  
After few circuits at a safe altitude it became clear that she was very responsive to all the controls.  Unlike the previous attempts I had plenty of elevator control which seemed to prove that the turbulence generated by the open box and center section did seriously interfere with effectiveness of the tail feathers.  Apart from a few clicks of elevator trim the plane flew straight and true without surprises, which is what one would expect from a commercial model, but which cannot be taken for granted for the first flight of a new design. There is no substitute for that thrill.
Now that I know that it flies, and flies well, the next phase will be to do a lot more flying to learn its characteristics and get it to handle the way I want it.   Designing a throttle linkage to operate precisely and reliably across a fully flexible motor mount is a bit of a challenge and I was a little unsure of the arrangement I had devised for the G62. I had checked the response before taking off but my doubts were justified when for the second landing the idle would not come down low enough and the plane kept on flying. A couple of clicks on the trim resulted in the engine quitting on approach. I was surprised by how comfortably the plane just floated in for a greaser.
After a couple of false starts I am very happy with the way she flies and look forward to further developing it!

The experience of creating a brand new design and then flying it without any prior knowledge of what will happen when it leaves the ground for the first time is fascinating and exhilarating.  It is unique and gives a measure of satisfaction not available from any other type of flying.

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