1/5 Scale Grumman Tigercat flies

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Built for Al's Hobbies owner Ali Machinchy, this Tigercat is much modified from the 3W Modellmotoren kit to accept two 150cc Moki radials. It was briefly mentioned in the WIP thread, but now it has flown, I thought I'd post a few pics in a thread of its own. Here's the story so far on a build started in October '08, but that has only taken about 11 weeks of actual building time, being done on Fridays, weekends and evenings.

The first taxi trials were done at Longhorsley in Northumberland on the Friday of the Bank Holiday weekend. Cowls off first while adjusting the needles to try and get identical top and bottom ends plus an even pick up on both engines.

So with the engines running pretty well, the props came off, cowls went on and the props back on again! Into the start up box and off we go. Things seemed ok for the first few minutes, but then the engines stopped coming back to their 800rpm idle that they previously had been settling to, then one stopped.

Props off, cowls came back off, props on and, oh yes, the Transmitter was flat, OH! and so was the 12v charging battery!! After a quick as around, charging facilities were found for the Tx and the charge battery, but it delayed things somewhat, and Ali couldn't even go and fly something else for a while!

Later in the afternoon, with the engines cool and life back in the Tx, we had another go, and after much fiddling with the mixtures, all seemed to be well. In all, I think there were about three separate taxi sessions with both cowls on and off.

So..........anfter much needle twiddling and charging, Ali was finally happy to go for a flight. Fuelled up, started up; those huge prop arcs so frighteningly close to the cockpit. Life for a pilot of a real Tiger must have been none too dull!!

then taxi out and line up.........

and power on......

Speed was increasing rapidly, and the model became light on its wheels, and can be seen below with daylight under the starboard wheel........

With three quarters of the runway used up, Ali pulled back on the stick, and..................

Original post

The model rotated and began climbing away. Ali must have hit the landing gear switch pretty sharp as in the following picture, you can see the nose gear doors have opened to start the retraction cycle.

The gear door sequence is quite complex and took ages to see up because the nose gear doors have to open, then all the gear retracts, then the nose and main doors shut. For gear down, the nose gear doors open first, all the gear drops, the main doors stay open and the nose doors close again!

A climbing left turn was started, but Ali immediately commented that the model was nose heavy. Now it was set up nose heavy deliberately as a) we know Ali likes his models nose heavy, but b) with the landing gear in the scale position it needed to be a long way forwards so the model didn't fall on its tail on the ground. With the tanks full and the landing gear retracting backwards, we knew it would move rearwards once in the air. The sound was fantastic, and amongst the people assembled around the pilots box, you could hear the comments confirming the obvious.

A minute after the wheels left the ground, the Tiger was at a safe altitude and turning back into wind. Although some distance down wind, I got this picture which has been cropped leaving only about 30% of the frame. Unfortunately my 70-300mm zoom isn't the best in the world and isn't image stabilised, so this distance shot is the best I could do at that range.

The next few pictures are a sequence during a fly by. Little else needs to be said......

We were a little surprised and relieved that the nose gear had retracted. During tests in the workshop, the rams didn't have enough strength to get the nose leg past its worst geometric position, although with a nudge, it went all the way and once up, stayed firm.

Gear down it dropped freely under its own weight and locked into place. We hoped the airflow on the nose gear door would assist the retraction and not prevent it from fully deploying. It did however, all work as it should, including the gear door sequencing.

Just after this picture was taken, while the plane was in a left hand bank turning cross wind to return up the runway, the starboard engine suddenly lost power, flicking the Tiger rapidly to the right.

The Tiger had pounced, but Ali fought back, righted the plane stuck the nose down, selected gear down, and headed for the runway, the starboard engine still not happy. As spare altitude started to run low, Al eased up, reducing the rate of decent. As the speed bled off, the forward C of G which had possibly reduced the harshness of the flick, was now hindering holding the nose up as the Tiger made for the runway.

Elevator authority was now running out, the big props were acting like air brakes. The Tiger looked like it wasn't going to make the runway and would hit the out field. Ali increased power to help the elevator, but the starboard engine still didn't want to pick up. Without speed, power and height, it wasn't looking good as the model rollied and yawed to the right on final approach.

With speed, altitude and options run out, gravity took over. The long nose leg hit the ground first, snapping the strut just below the drag link. A fraction of a second later, the remains of the nose leg dug into the ground, ripping off the nose of the model, immediately behind the nose gear former. A virtually clean break, and probably saving the rest of the airframe from any damage!

Other than a bent main axle, a couple of slight wrinkles in the lower fuselage skin under the wing, and a small puncture hole in the lower wing skin from a prop blade, the nose was the only severe damage. I was annoyed but relieved, as at the moment the model flicked hard right, I thought it was game over.

Ali said from the start of the project it would either work off the board or die big style. It didn't work off the building board, but neither had it died like it really should have done in that flick. It it had gone left in the flick, chances are there would have been no recovery.

The engine problems we believe is down to some of the warm air from the engine, escaping back around the firewall rather than exiting the cooling holes. This in turn is heating up the air in the nacelle where the carb is pulling its air from. As the carb pulls hotter air, that is screwing the mixture leading to the engine problems. More on the engine remedies in post to come, but a I'm taking this opportunity to make a few small changes here and there that should improve the handling and operation of the model next time out.

Two days work has seen the nose go back on, cracks filled and glassed over, and it is now ready for panel lines, rivet detail and final painting again. Getting the new props and repaired nose gear back from the USA is what is likely to hold up further flights.

Steve

Member for

15 years 1 month

Posts: 17

Amazing model Steve, commiserations on the outcome of the first flight. Top marks to the pilot for containing the situation, she could easily be matchwood otherwise! Here's to a swift return to the skies!

Ali is an excellent and very experienced pilot, but he said if it had been the port engine that lost power, the flick would have put the model into a spin straight away with little chance of recovery. While it was annoying, it could have been game over, so hopefully next time out, Ali will tame the Tiger!

Steve