Surgery on an Old Fogey!

Modifying an Old Fogey

[UPDATE - 31/08/2016 - Regarding these modifications in this article, I've been exploring the topic of Angle of Incidence, both from research and from experimenting with builds. The conclusion I've come to is that for most model planes, no more than 2 degrees Angle of Incidence is required for the vast majority of more modern designs. This actually led me to reduce the 'real life' Angle of Incidence on model plan versions of biplanes I designed - why? Because with the 'real life' Angle of Incidence, the wings produced too much lift, which needed to be countered by negative inputs like; adding lots of nose weight, excessive down elevator, or a steep downward thrust angle on the motor. Basically the plane is fighting itself - one part trying to lift the plane, the other part trying to keep it level - it is a waste of battery power that could be used to keep the plane flying longer. With this version of the Old Fogey I kept the 4 degrees Angle of Incidence of the original, and relied on a pile of nose weight to keep it flying level. If I had known at the time, I would have re-profiled the wing seat to reduce the A of I and flown it on the correct CG, which would have given me a freer-flying plane and much better slow-flying performance. I discuss this in my recent article 'Grouchy' Old Fogey getting you down?

NOTE - One of the solutions I suggest in this article, adding more nose weight, is actually counter-productive, making the plane very nose heavy and ruining its slow speed performance. The other suggestion, lifting the tail, is a perfectly valid way to eliminate wing-waggle. However, in the 'Grouchy' Old Fogey article I show a more benign way to modify the Old Fogey fuselage. Plus there's links to two alternate scratch build fuselage designs for the Old Fogey wingset, that have a wide flight envelope and will fly with zero wing-waggle. ]

When I first built the Old Fogey it flew great at slower speeds but as soon as I went faster, there was a bit of a wallowing problem. At the time I fell into the trap of thinking the plane was tail heavy and solved some of the issue by adding nose-weight, (that’s the pile of coins under the yellow tape) producing a final CG that was well forward from the one in the design.

However as the plane aged and became heavier, the wallowing gradually got worse and I just couldn’t get it to fly right. It had done it's job though, getting me through a lot of early flying. As soon as I moved-on to other planes I lost interest in the Old Fogey and put it aside. Then my son said he wanted to learn to fly...

I knew the Old Fogey had worked well for me - so would be a great plane for him to start with. I needed my Old Fogey to fly properly again, I needed it to be super-docile and very predictable.

To that end, I did some research on the Internet, looking to see if anyone else had come across this wallowing problem - specifically with the Old Fogey, and then more generally with other planes. From what I gathered, it seemed that a good way to combat the problem was to make the vertical stabiliser bigger to help dampen the oscillation.

I had a look at my Old Fogey and thought maybe there’s another way to do it… maybe if I could get a bit more airflow on the existing stabiliser that would help. After all, it is tucked-in behind a pretty big fuselage.

Now this solution is a bit drastic! Those of a sensitive nature should look away now.

Basically I shifted the tail up about 70mm. I was too quick to get a 'before' image, but you’ll recognise the outline of the original Old Fogey in this mock-up. The method I used involved shortening the fuselage by 20mm - which is why there's a gap there in the photograph.

Here’s the after. The tail has been shifted up and forward, and then reattached to the main fuselage.

I made the first vertical cut about 50mm back from the rear wing mounting skewers…

…I made a second cut parallel to the first and 20mm further back. Here's the cunning bit! I did NOT cut through the fuselage base. After removing the two side strips I worked forward on the fuselage, cutting through the glue join to free the next 120mm of fuselage base from the sides.

I then made two folding scores on the fuselage base – one score on the INSIDE of the fuselage at the end of the cuts I’d just made, and one on the OUTSIDE where the fuselage base projects from the tail. When these two bends are made at the same time, the tail ‘hinges’ up - rising and moving in to meet the main part of the fuselage.

Because the original cuts were straight, parallel and the same width apart - when the tail connects its alignment remains the same. Take care during the re-gluing to get it in the right place. Make this job easier by gluing one side at a time - as you glue the second side you can adjust up and down a little to get things just right.  

Following the new 'sporty' line of the fuselage base, trim away the excess sides. Now re-glue the sides to the base.

For added strength I put a plate on top of the tail. First I removed the curve, marking-on and making a straight cut from the tail to meet the old fuselage line just behind the rear skewers.

I then made-up a strengthening panel - making it long enough to overlap the tail, where I added a little slot in the centre to help keep the tail vertical…

…and long enough at the front to extend under the wing to give a strong connection to the main fuselage. The last part of the pad needs to step-in so that it fits between the sides.  I re-led the control rods, running them over the new panel.

My servos are on a higher mount (long story), yours will be ‘as original’ and you can poke/run the control rods over, through or under the new panel.

I checked my balance – purposely making the plane nose-heavy on the ‘plan’ CG. Neutral CG for me is about 10-15mm forward from the under-camber fold. [This, in retrospect, was a poor decision, a better answer is discussed in the UPDATE at the start of the article.]

After the flight I increased the motor power to a 14A motor (roughly 150W). This should give me a better climb rate and more consistent speed. It also allowed me to remove all my coin ballast.

I've limited the motor's output by setting the throttle maximum to 60% - this should contain any boy-racer urges my son has. As with the original Old Fogey, this plane does not need to go fast to fly well.

Onwards and upwards, Alibopo :)