‘Grouchy’ Old Fogey getting you down?

by alibopo | July 20, 2016 | (0) Posted in Projects

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.

COMMENTS

ttprigg on July 29, 2016
Alibopo, Another great article- Thanks for taking the time to outline and share your "process". Not everything "works" the first time, but it all works together and may ultimatly expose the solution. I'm ready to build another! Tim
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alibopo on July 29, 2016
Thanks Tim, it was an interesting journey, but that Old Fogey 'thing' had been nagging away at the back of my head for some time. If you're thinking of a build from scratch, 've just added a link in the article for a modified fuselage plan, the "Lazy Fogey" (someone stole all the good names) and if you pop over to my website, I've also got a plan for a much sleeker shallow fuselage version which I've called the "Bush Fogey" (bottom of the page);

http://alipotter.co.uk/fogeyfix.htm

Cheers, Alistair.

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burt1166 on August 2, 2016
Thanks for the reply i will look at 'Gordon' .I understand the problems with scaling up i take most of my designs from full size planes and draw them out .I have had lots of planes that just do not fly but am now getting the hang of it .I have some nice wings i made up over the winter cutting my own ribs from balsa and film covered, very strong and light .I have stated to build a smash drone body from ply and tail and stab from depron .What is the dimension from the back edge of the wing to the front edge of the stab please .I have also had a lot of success using depron to make wing ribs 6mm it works really well using foam safe supper glue .The smash drone body is going to have a adjustable wing angle so i can try 3 or 4 different wings on it ( flat bottom and under camber ) i will add a pick when its done .Thanks burt
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alibopo on August 2, 2016
Hi Burt, you can get the Smash Drone plans here. It's a design by C.Stence;
http://www.flitetest.com/articles/now-you-can-crash-and-keep-flying
I hate to jump-on someone's design, but I didn't like the 'swoopy' nature of the Smash Drone - I feel it suffered some of the same limitations as the Old Fogey, in that it needed to be flown a 'just the right speed and no more' or it started to climb aggressively. It didn't suffer from 'wing-waggle', but it needed a lot of down-elevator input to keep it flying level at faster speeds. The design takes its Angle of Incidence from the Old Fogey. Once I'd reduced the Angle of Incidence on my build of the Smash Drone, the plane flew very level, rock steady, and the motor was doing a lot less work. It was a real smooth flyer. It's up to you, but I liked the way mine flew. You can compare them directly by looking at the flight demos of the original Smash Drone, starting with the article with the plans above, then these other ones;
http://www.flitetest.com/articles/sb-baby-tig-g-er-drone
http://www.flitetest.com/articles/the-zombie-hunter
http://www.flitetest.com/articles/smash-drone-pink-panther
...and the flight demos of my modified Smash Drone.
http://www.flitetest.com/articles/yes-it-s-a-smash-drone (second video after mod)
http://www.flitetest.com/articles/soaring-with-a-smash-drone
Cheers, Alistair.
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burt1166 on August 3, 2016
Ops submitted to soon ? I cut out sections to lighten it it stay strong and ridged but real light .
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alibopo on August 3, 2016
Hi Burt, maybe you can move this discussion to the FORUM section, it sounds ideal for the
Mad (Scratch) Builder's Corner. You can post some pictures and get a lot more varied input - I'll watch out for it there.
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ewlie on July 29, 2016
My son built a Old fogey but with the back end flipped over with the H stab at the top. We also reduced the angle of incidence. It didn't have the wing wobble, but because of the config it had to have tricycle undercarriage that made it really hard to land without tipping it over.
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alibopo on July 29, 2016
Hi Ewlie, I've no doubt his plane was pretty nice in the air though. If it's still flying, how about switching back to a tail dragger? I maybe need to clear up how I 'chopped' the back end of the 'cabin', but it's not that hard and you don't really need the curvy lines. A straight line from the H stab. to where the floor ends will work just as well. If you do that cut both sides, then you can slice and peel open the floor section that's surplus. I do think you need to slide the 'extra' bit of floor panel back into the fuselage to keep the fuselage stiff, but if it doesn't come off cleanly, a new rectangle of foam would do the job. Cheers, alibopo.
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jrvalentin62 on July 28, 2016
As always "Great Job." Thanks for posting and clearing up some things. Clear Skies, Calm Winds.
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alibopo on July 29, 2016
Thanks for the supportive comment.
Cheers, alibopo.
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jordy123 on July 29, 2016
Thought the wing was waterproof foam!
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alibopo on July 29, 2016
No - just many, many layers of paint, hot glue and sticky tape! :)
cheers.
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burt1166 on August 3, 2016
Hi i am already working on the assumption that i will be reducing the angle as the wings i have made up are producing a lot of lift already .i managed to get some flying in at the week end with my own design glider 36" wings with a wing root of 7" and a Clark y profile it was the first time i bungee launched this in to 15mph wind the wing angle of incidence is quite steep .On half power it went on a near vertical clime ending in a giant loop.However it will fly into the wind very well and is very sensitive to control inputs .I will try these wings on the smash drone with my adjustable angle first .I looked at the plans and decided it seemed to have a very big body so i reduced it down to 70% and am going to cut it out to day from my thin ply.I see you used dowel for the boom i have a good boom design i have used 12mm square pine which i cut out sections with the scroll
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burt1166 on July 30, 2016
Hi I my self are only just getting my head round wing angle of incidence all my planes but 1 are scratch built after reading this i am now thinking i should some how make my wing supports adjustable so i can change the angle depending on the wind .Im 1/2 a mile away from the north Cornwall cliffs uk at 300ft above sea level and get wind from all points of the compass and mostly fly from a flat field with a small high start (to high and you carnt get back up wind to land in the same field) i have had to do a few blind landings the other side of hedges in other fields!!. Being able to change the angle of attack depending on the wind might get me better up wind performance, i make all my fuselage sides from 1.5mm birch ply with a scroll saw very light but supper strong when the inevitable nose into the ground happens.Your article has made me think thank you .
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alibopo on July 30, 2016
Hi Burt, I think if you are building established designs which are suited to outdoor flying, you won't need to mess with the Angle of Incidence. When I designed and built my SE5 foam board model, I went with the Angle of Incidence associated with the full scale version (or what it appeared to be in the 3-view drawings I found on the internet). But due to scaling problems this turned out to be too fierce an angle, requiring too much 'negative' input from the control surfaces and the engine thrust angle to combat the wing's lift. By negative I mean any of these solutions; A large down deflection on the elevator, just to make it fly level (which produces drag). Increased nose weight to 'hold the nose down' (which can mean adding to the flying weight, and definitely means flying nose-heavy, which makes it hard to slow down on landing approaches). Using an excessively steep motor thrust angle to combat the wing lift, (which just seems a nonsense, and a waste of battery power which could be better used to keep my plane in the air for longer). By scaling problems I mean I'm flying a 1/10 scale model at 10-20 mph - which means a scale speed of 100 - 200mph - on a design intended to fly at 50 - 120 mph? So at my scale speeds I'm going much faster than the full scale design requires. Solution - reduce the Angle of Incidence. The guide on Electric Planes by Gordon is very good, and his long experience of scratch building model planes makes him conclude that most models will fly with an angle of at the most 2 degrees. One issue that wasn't discussed in my article was Angle of Attack. On 'final approach', a well balanced plane can start to nose-up slightly, to increase the effectiveness of the wing. In a way it's the equivalent of adjusting the Angle of Incidence, and gives you the control you suggest. But you won't get this kind of responsiveness from an airframe if the plane is nose-heavy. The need to have higher Angles of Incidence than 2 degrees is well explained by 'Gordon', relating to models with designs based on the very earliest attempts at powered flight, and which fly VERY slow. Angle of Incidence does relate to the plane's flying speed, but that doesn't change depending on how fast the wind is blowing. You might appear to be flying slower going upwind on a windy day, but if you haven't changed the throttle the plane's speed through the airflow is the same as on a less windy day. Going downwind, it's the same. The plane is travelling through the air at the same speed, it's just that the 'air' is going in the same direction, making the plane appear to fly faster over the ground. People do fly faster on windy days to help keep the plane controllable, but if you think of the scale wind speeds, they are flying in the scale equivalent of a hurricane! I hope that helps. Cheers, alibopo.
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mutski on July 4, 2017
Excellent discussion of angle of incidence... thanks for the good info!
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‘Grouchy’ Old Fogey getting you down?