‘Grouchy’ Old Fogey getting you down?

Here's a way to get a more flexible flyer from the 'stock' Old Fogey

[17/08/16 UPDATE : The article 'end result' "Lazy Fogey" fuselage and a second sleeker "Bush Fogey" fuselage can be downloaded as scratch-build plans from the "Gaggle of Geese, Flight of Fogeys" article. (Link below)]

First off – the stock DTFB Old Fogey does exactly what it says on the box. As many will testify, it’s a fine light wind and indoor slow flyer. If you fly it within those limitations, you’ll have a very rewarding flying experience.

However, and I’ve watched plenty of YouTube videos to confirm this, a lot of pilots want to fly the Old Fogey in the wind conditions they experience most of the time (medium to strong, rather than light), and they want to fly it the way they want, which is usually a lot faster than intended! Plus, us heavier foam board builders often need to push our planes along a little faster, so that brings us closer to the 'wing-waggle zone'.

So, is it possible to achieve those goals of speed and stability in the wind?

Like many, when I took my Old Fogey out on windier days, or tried to fly it faster, I encountered the dreaded wing-waggle problem. Thinking (in error) that the plane was tail heavy, I relied on pushing the CG forward to ‘force’ the plane to fly level and true, but eventually I came up with a more drastic solution, which was to rebuild the tail and lift it higher;

You can read all about it in my Surgery on an Old Fogey article;

http://www.flitetest.com/articles/what-did-you-do-to-that-old-fogey

That modified Old Fogey went on to have an interesting life, appearing in classic videos like;

Blustery Old Fogey - http://www.flitetest.com/articles/blustery-old-fogey

and in Wing Envy as a biplane http://www.flitetest.com/articles/wing-envy-old-fogey-sesquiplane

Then I encountered the same Old Fogey ‘wing set’ being used in the Smash Drone, which I built in a modified form;

http://www.flitetest.com/articles/yes-it-s-a-smash-drone

From the start I was never happy with how MY Smash Drone flew, and found I had to add a pile of nose weight to get it to fly level and true (sound familiar?). Even after adjusting the thrust angle of the motor, which helped, the plane still needed that extra nose weight. I eventually concluded that the plane was developing too much lift! This led me to the radical decision to reduce the wing’s Angle of Incidence, which, wonder-of-wonders, transformed the plane’s performance!

http://www.flitetest.com/articles/soaring-with-a-smash-drone

Angle of Incidence is the angle between the wing chord and the plane’s longitudinal axis (also, in most cases, a line parallel to the chord of the horizontal stabilizer).

At this point I must sing the praises of the ‘Old Fogey’ wing set – as well as being super-simple and robust, I’ve consistently found that it’s capable of producing a humongous amount of lift.

As you can see from my experience with the Smash Drone and its later incarnation as a tractor plane...

http://www.flitetest.com/articles/frankenplane-2-the-fogee

...and from my proving and modification flights for the SE5 biplane...

http://www.flitetest.com/articles/ww1-se5-biplane-swappable

...I knew I could get a freer-flying model (and better performance) with a smaller Angle of Incidence, which could even, due to more efficient aerodynamics, produce BETTER slow flying performance and LONGER flight times.

This isn’t just me. If you follow this link, and go halfway down the page you’ll see the whole Angle of Incidence thing explained much better than I ever could;

https://dl.dropboxusercontent.com/u/66999462/AircraftDesign.jpg

(If the page above appears as a squished strip up the left hand side of the browser window, hover your mouse over it and a magnifying glass with a plus in it will appear - click, and the image will spread to fill the screen.)

And another source;

http://www.electricplanebygordon.com/wing-incidence-angle/

Basically, on planes with a higher Angle of Incidence, the faster you go, the more effective the main wing becomes relative to the horizontal stabiliser. In many circumstances this can be managed using elevator adjustment or a little 'downward' adjustment of the motor thrust angle. However, in extreme examples, these remedial measures are not enough and a lot of flyers mistake this continuing tendency to 'nose up' as an indication that the plane is 'tail heavy'. But it's not - just slow the plane down, the lift equalises, and the plane starts to fly level - no shift in CG required, just a slower passage through the air.

The other factor with a high Angle of Incidence is drag. Yes, it's fine to play off drag against lift, but if you've already got a large enough wing area to allow the plane to fly slowly, there's really nothing gained by making it harder for the plane to move through the air.

So that’s my initial logic for the Old Fogey; because the lift at higher speeds of the main wing is not proportionally matched by the lift from the horizontal stabiliser, the tail starts to droop, and as the tail droops it throws the plane into a ‘high alpha’ flight mode and the wing starts to behave like a leaf fluttering in the wind. (Probably not as simple as that, but it makes sense to me.)

Armed with this knowledge, I decided to prove my case for reducing the ‘stock’ Angle of Incidence of the Old Fogey by building a new, modified version.

Checking my paper plans for the Old Fogey I found that, taken across the front and back edges of the wing, it had an the Angle of Incidence of 4 degrees.

Here’s a mock-up of what I wanted to achieve. It doesn’t look too different, until you notice the ‘break’ in the cabin line at the back where I swung the wing up. I also added a new curve to tidy up the fuselage line that trails off to the tail assembly.

Next stage was to alter the actual plans. But how much to change it? I simplified my choices; in one degree steps from the standard four degrees right through to zero degrees.

A lot of flat-bottomed wing foam board planes fly with a zero Angle of Incidence, so I was tempted to go for the zero degree option...

...but I ‘bottled out’ and decided to go with one degree, which, at the back of the wing seat, handily coincides with a vertical measurement of 13mm above the original position (a tiny bit less than ½”). After marking on the new profile, I sketched-in a modified curve on the fuselage.

I used this little template to mark the wing apex and rear points. The front (with the arrow) stays put and the template swings -about the front to get the little ‘vee’ at the back to cross the correct line I’d already marked on the paper. The wing apex was then marked by pushing a pin through the template.

I repeated the same exercise on the ‘other’ side of the plan by flipping the template over – this time I included another little ‘vee’ nick to help locate the wing apex. After that it was the familiar process for us paper plan-to-foam board builders. I usually mark through the paper plan with a pin and then follow a dot-to-dot path to re-draw the cutting lines onto the board.

Fast forward and here it is, the ‘new’ Old Fogey, and yes... that IS the dodgy, moth-eaten 3 year old wing from my very first Old Fogey.

Hard to spot the difference in the fuselage, but it’s there.

Now, the question you all want answered - did it make any difference? See for yourself;

OK, it’s a maiden, I start out too strong on the throttle and straight away the wing-waggle kicks in. But then I get the hang of it, ease off the throttle and it all settles down. Sadly, I haven’t managed to eliminate the wing-waggle, so I suppose I should hang my head in shame and admit defeat. But I am able to fly faster than I could previously, and I am flying on the correct CG instead of the super nose-heavy one adopted by many. It’s definitely a couple of small pluses, but it's also very disappointing.

I’ve flown these Old Fogey wing sets on three other planes; my original modified Old Fogey, the smash drone, and the Frankenplane I built from the Smash Drone. All of those flew very nicely, and the last two with a significantly reduced Angle  of Incidence (and correct CG), and all with no bad tendencies. So what’s the deal, why didn’t it work this time? I could probably baffle myself and everyone else with a hodgepodge of aeronautical half truths and speculation, but maybe it's easier to look at what I know from previous experience.

I had already ‘fixed’ wing-waggle on my first Old Fogey using the solution of lifting the tail assembly...

...which got rid of most of the problem, so I had a clue about what to try next. I will admit I had less understanding of the differential lift problem at the time, and didn't think to reduce the angle of incidence as well. Meaning - I fell into the trap of thinking the plane was still tail heavy, and continued to fly it with a nose heavy CG. (That's the pile of coins under the yellow tape at the front!) Which also means I unwittingly lost the slow flying performance, which meant if I slowed down the plane tended to nose dive! Which again I assumed was because my plane was built from heavier foam board. Plus carrying extra nose weight meant carrying extra total weight... 860 grams / 30.4 ozs eventually. I'm amazed the plane flew, but it did, and pretty well, all things considered! I digress... but it does show how that first error in thinking produced a whole pile of negative effects.

Anyway, to continue my investigation I decided to repeat that same fix on my ‘new’ low Angle of Incidence version of the plane. This time I did it without shortening the fuselage.

To start, I disconnected my rudder and elevator linkages and cut-off the whole tail along the line of the fold at the back of the wing. I marked the vertical cutting lines using a set-square pressed onto the bottom of the plane. That makes fixing the tail back on much easier, but if you get it slightly wrong it’s easy enough to sand a little off to get the tail sitting square. I also cut-off most of the curving portions from the side panels. The cut to remove the curved sections is parallel to the bottom of the box section and 40mm or 1 37/64″ up from that bottom edge (sorry about the horrible imperial equivalent).

Of course at this stage you need to remember my plane already has a modified wing seating. To reduce the Angle of Incidence you need to modify the standard wing seating, and it's best to do it now.

You can use this handy little template, which you can print out on A4 or Letter size paper. Old Fogey Wing Seat modifier

Transferred to foam board, this template will fill-in the space marked in blue. modifying the wing seat to the new one degree Angle of Incidence.

To work out what to remove, the template has the existing profile marked on it and this needs to be aligned with the existing wing seating to allow you to mark-on the cutting line. The piece that's going to be removed is the red hatched area shown above.

Only once you are totally happy with what needs to come off and what needs to go back on, then you can cut off the old profiles and graft on the new bits. 

Once that's done, the 'box' element of the tail assembly is glued back onto the fuselage, making sure it is square and level, and flush with the back edge of the new wing seat. I flipped and refitted the off-cut curving portions to the underside of the box, using them as fillets to help strengthen the tail. There was a little ‘fettling’ to fit them around the horizontal stabiliser, but nothing demanding.

At that stage, I had a flat ‘cabin’ bottom running all the way back to the join. I’m sure it wouldn’t have mattered much, but it did look a bit ‘industrial’ (and kept the tail off the ground)...

...so I decided to modify the shape to what you see above. First I sketched-on a nice pair of linked curves on one side of the fuselage.

Then I slit the floor-to-side join, to free the floor up to the edge of my new curvy line. I then encouraged the floor to bend up enough to keep it out of the way for the first ‘curvy’ cut. Once I had that first curvy profile cut, I used the off-cut as a template to mark out the cutting line for the other side of the fuselage. After cutting the second side I glued the floor section in place to stiffen the rear of the ‘cabin’.

With my new ‘high tail’ I toyed with the idea of converting to a tricycle landing gear, but for simplicity I stuck with the tail-dragger setup. After a little pondering I decided the plane would look a lot better with the wheels a little further back. I did this by moving the front skewer only and punching two new holes.

Control rods are led from exactly the same servo positions as before, but are fed through the fuselage at the back. I stuck a little length of tube (cotton bud stick) in the slit there to help control play in the wire.

I did the same on the rudder side.

Inside, a couple of little tubes help direct the wire towards the servos, and stop excessive movement.

Without the wing, you can see how neat the top profile is, and how nicely the curves work...

...and here’s how the plane looks with the wing on.

So - new day, new plane, new video.

To make a fair comparison, I went with the ‘stock’ CG, just behind the wing apex fold. This is correct for the plans, and also agrees with the CG calculations I made using the calculator on this page;

http://chrusion.com/BJ7/SuperCalc7.html

In my calculations I fudged some of the measurements, to allow for the wing curve, but it still produced the same result as the ‘official’ CG.

My All-Up-Weight with a 3S 1000mah LiPo is 650 grams / 23 ozs. This is heavier than a DTFB Old Fogey because I only have access to one of the heavier foam boards, but I’m still flying on a Blue Wonder 1200KV motor with a 9 x 3.8 prop. The motor runs a teeny bit hot with this prop - ideally I should use a slightly smaller prop, but I didn’t want an ‘anaemic’ power setup for the maiden.

Ignore the 'wobbles' in the first clip - I was trying to show how slowly I could fly. It all makes sense once you see how easily the plane goes out from the hand launch. By the end, I hope you'll agree, the plane flies much, much better all round. Winds were about 4-5 mph, rising steadily as the day progressed. This is the result I was after. I’m flying on the correct CG, and I can fly ‘flat-out’ or slow with only slight changes to the elevator trim, and no bad habits. I managed flight times of 10 minutes on a 1000mah LiPo, making the plane dramatically more flight efficient than my original Old Fogey.

When comparing slow speed performance, I feel it does very well considering its ‘heavy’ foam board construction. Without battery it weighs-in at 554 grams / 19.5 ozs. A ‘stock’ Old Fogey weighs-in at 377 grams / 13.3 ozs. Or with my 96 gram battery load; 650 grams v 475 grams. My version is about 25% heavier than the DTFB version! Someone would need to confirm it, but I'm pretty sure a modified DTFB version would fly almost as slowly as the original.

As far as I'm concerned, the new setup is a complete success.

This next video is another outing with wind speeds of 10-12 mph (which rose to about 15 mph by the end of the session). Definitely not Old Fogey weather, unless you hammer-on a whole pile of extra nose weight. My only compromise to the flying conditions was a small forward shift of the CG to the wing apex.

Even in these stronger winds, I managed flight times of around 8 ½ minutes on a 1000mah battery.

CONCLUSION

So - when is an Old Fogey not an Old Fogey? This version has the same fuselage length and wing set, but the tail assembly is lifted to bring it closer to the plane’s longitudinal axis. In addition, the Angle of Incidence of the wing is reduced from 4 to 1 degree. Taking all that into account, I suppose the answer is; it isn’t really an Old Fogey any more.

But if you have a donor Old Fogey sitting around, and you want to open-up its flying envelope, or are struggling to get it to ‘fly right’ for you, then I suggest that for a competent builder this is a fairly quick and easy modification of the existing airframe. One that will produce a more versatile and forgiving plane.

If you do go with the complete ‘mod’ package, make sure you use the ‘stock’ CG. Keeping this new plane super nose-heavy will just make it harder to slow down when landing, and deprive you of some great slow-flying performance.

Cheers, alibopo.