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RE: Babcock Aeronca ready for maiden - 10/9/2009 8:10 PM   
billmod12


 

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Status: offline 		I came in a little late on this discussion but here are some comparisons ask for in one of the first post. So for information sake here are a couple from yester years and today. Lil Esquire 40", 1959 original fly weight 24 oz now 32 oz due to 3 channel and repairs over the years, balance point on plans 3 1/8" from leading edge, wing area 320". Jr. Skylark 37", 1960 original fly weight 18 oz now 22 oz, Balance pt on plans 2 5/8 back from leading edge, wing area 235". Super Cub, current model, original fly weight 26 oz now 29 oz. Balance point 2 3/8" form leading edge, wing area 346". All these models fly very well but the Lil Esquire is heavy. The super cub flew perfect right out of the box but the others from long ago took a lot of patience and many short flights to get them out of their single channel trim into 3 channel trim. They are all now a joy to fly. I have put in 15 flights so far today and have had a blast. Cheers Bill

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RE: Babcock Aeronca ready for maiden - 10/9/2009 8:15 PM   
billmod12


 

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Status: offline 		I forgot the pics!

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RE: Babcock Aeronca ready for maiden - 10/9/2009 9:28 PM   
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Status: offline 		Would you mind telling us what's the difference between single-channel trim and 3-channel trim?

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RE: Babcock Aeronca ready for maiden - 10/9/2009 11:18 PM   
Doc.316


 

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Status: offline 		Single channel planes typically have the incidence angle of the wing jacked up a bit and a bunch of downthrust. 3 channel planes have less incidence in the wing and less or no downthrust. Does the aeronca have a bunch of incidence in the wing?

Steve

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RE: Babcock Aeronca ready for maiden - 10/10/2009 2:54 AM   
billmod12


 

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Status: offline 		I guess what I should have said was multi channel not just 3 channel. I have 5 Old Timers from 1949 to 1955 that were originally flown single channel(rudder only) NO kick up elevator or throttle. You just fired them up and hand launched them because we had no fields suitable for ground rolls. They had a fairly aggressive climb and you flew them till they ran out of fuel and they glided down and you controlled decent by use of the rudder (which was usually small) and you tried to get it to land somewhere near you. The models were trimmed to land themselves at an attitude that would save the plane and hopefully roll a little. When you convert one of these to 3 channel or more, then add the extra power you need for ROG and flying in tight fields and wind you create a monster that will climb for the skies like a bat out of H#((. You have to change some things to get a mild mannered climb and an airplane you can control and actually fly. It usually involves changing some incidences, making it a tad nose heavy, adding elevator, enlarging the rudder, changing thrust directions down and side or sometimes doing away with them altogether. The way we trimmed them was to balance them by the CG on the plans then test glided them and shimmed till we got them to land them selves after a gentle running toss. You had no concern for flying around the field at 20 ft in a straight line at half throttle. Hope this explains it to some degree. Cheers Bill

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RE: Babcock Aeronca ready for maiden - 10/10/2009 4:06 AM   
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Status: offline 		Doc.316, the Aeronca has very close to a zero/zero setup, which is rather suprising for a rudder only airplane - perhaps 1 or 2 degrees incidence in the wing just by eyeballing (I haven't bothered to measure it.) There is maybe 2 degrees down thrust, and 3 or 4 right thrust. Check out the side profile picture in the beginning of the thread.

I have no issues with this airplane in pitch whatsoever; very stable and predictable. The excessive roll/yaw coupling is the hairy part about flying it. Even with minimal rudder throw it feels on the edge ALL the time. On landing, I set up for a long final because even power off rudder response can be unpredictable. And it's better with the added fin area - flying it now is just tense; before it was frightening. Russ Farris

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RE: Babcock Aeronca ready for maiden - 10/10/2009 4:25 AM   
Doc.316


 

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Status: offline 		Wow that description of flight made me smile...It is interesting that it doesn't have the typical positive incidence of the wing coming from the factory. I would expect more.

Steve

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RE: Babcock Aeronca ready for maiden - 10/10/2009 5:10 AM   
billmod12


 

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Status: offline 		Russ, read this and visualize it several times. Not to say it is the answer but I know it has helped many a person including myself. http://www.modelaircraft.org/mag/FTGU/Part%2029/29main.html there is 4 pages. I think you are a LITTLE tail heavy. My Lil Esquire is so heavy that just 3 grams of weight will make it go from an enjoyable fun plane to a miserable flying machine. I even carry weights with velcro and if I change batteries I make sure I have the same weight going back in the plane. I had the same effects you are having and I never suspected how sensitive it was to balance. Work with no more than 3 grams at a time with weight and 1/32 at a time in changing incidences. Believe me that airplane is very capable of flying well but will land heavy you just have to be gentle bleeding off speed as you have been doing. I promise it will work. I know, I fought that lil esquire for a couple of months trying things. I refused to accept that so little weight would make so much difference then one day it dawned on me. That plane used to weigh 24oz and now it weighs 32oz. and then I visualized 1/2 of a pound of lead being put in my plane then it all made sense. Go for it! Cheers Bill

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RE: Babcock Aeronca ready for maiden - 10/10/2009 6:51 AM   
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Status: offline 		Hi Bill! How are things in Wilmington?

Actually, the Aeronca CG is almost 1/4 inch AHEAD of the plans CG, and has been from the first flight. UStik has suggested moving the CG aft a few times, which I am reticent to do - in my experience this will only lessen the effect of the small vertical tail/short moment arm and make things worse. But I think I'll try moving the cg a bit further forward; it can't hurt. At some point I may have to increase the wing incidence. And just to remind everyone, this model has full elevator control and pitch stability is a non issue. Full power climbs, cruise and power off glides are all perfect, with little or no pitch changes. The problem is directional stability/rudder/roll coupling. At the present CG the elevators are perfectly faired with the horizontal stab. Russ Farris

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RE: Babcock Aeronca ready for maiden - 10/10/2009 3:55 PM   
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quote:

ORIGINAL: maxpower1954

Doc.316, the Aeronca has very close to a zero/zero setup, which is rather suprising for a rudder only airplane - perhaps 1 or 2 degrees incidence in the wing just by eyeballing (I haven't bothered to measure it.) There is maybe 2 degrees down thrust, and 3 or 4 right thrust. Check out the side profile picture in the beginning of the thread.

I have no issues with this airplane in pitch whatsoever; very stable and predictable. The excessive roll/yaw coupling is the hairy part about flying it. Even with minimal rudder throw it feels on the edge ALL the time. On landing, I set up for a long final because even power off rudder response can be unpredictable. And it's better with the added fin area - flying it now is just tense; before it was frightening. Russ Farris

maxpower, I looked at the pictures of your model several times and couldn't make out both wing's and stab's incidence. Depending on the viewing angle it seems to be more or less. I think it could help if you bothered to measure it.

Doc and Bill pretty much gave a description how these models were set up initially and by test flights. That's the point we're missing again and again. Of course you observe slip-roll coupling issues (to be precise), but there's an interrelationship with pitch trim as far as flight speed goes. Remember the flat-bottom airfoil issue which makes for an unstable condition in the low AOA range.

Now setting up the flat bottom of such a wing level (parallel) to a slab stab is quite common. The usual flat-bottom airfoil has its chord line 1.8 degrees "above" of the bottom line, and that's where the "bottom stall" begins. (Zero lift is at even -2.5 AOA.) That 1.8 (or say 2) degrees decalage are enough even for a rudder-only model and simply mean it's not twitchy in pitch. That's what you want for a model having an elevator, and you reported to be very satisfied with the pitch behavior, so I assumed you'd want to leave the incidences alone.

Remember decalage and C/G position being "Siamese twins". Taking the incidences for granted, you have to set the C/G so that the model flies with the wing's flat bottom at least level, better inclined 2 degrees "up" (more AOA), to avoid the "bottom stall". That will give a certain lift coefficient greater than 0.5 (ideally 0.7) and a flight speed simply depending on weight.

If you want to increase directional stability by a more forward C/G then you have to increase the decalage correspondingly, for instance by shimming the wing's leading edge. As a consequence, you'd have more pitch stability and the model more sensitive to variations in flight speed / power. The latter would be made up for by more down thrust. But the elevator would likely have to produce negative lift what had to be made up for by the wing producing even more lift.

Maybe that's what Bill is observing: Trimming the model "a tad nose-heavy" gives a decent flight speed but at the same time a decent wing AOA putting it into the stable, higher lift coefficient range. So to speak, the forward C/G makes for better speed and more directional stability while the stab makes for the necessary high AOA. The wing is easily able to carry the model's weight and the stab's down force just because flight speed is high.

That's an unexpected and funny twist for me. Still I would do the obvious first, I mean leave all as is except the C/G and set it back first to get a higher ("stable" ) AOA. I wouldn't mind beginning with a more forward C/G either, but still leaving incidences alone. The least important of all is weight, so I'd stick to the drive, BUT I'd try a higher pitch prop. As I estimated in one of the first posts, I think more prop pitch is needed and if you trim for higher flight speed that is even more important.

Written for my own enjoyment, maybe also food for thought for the point man.

UStik1951

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RE: Babcock Aeronca ready for maiden - 10/10/2009 4:13 PM   
UStik


 

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quote:

ORIGINAL: Doc.316

Single channel planes typically have the incidence angle of the wing jacked up a bit and a bunch of downthrust. 3 channel planes have less incidence in the wing and less or no downthrust. Does the aeronca have a bunch of incidence in the wing?

Steve

Thanks Doc, but I'd like to hear especially what Bill means. (Thanks Bill as well.)

By the way, agreed on more incidence for rudder-only, but objection for the down thrust. Both together have to replace the missing elevator. I used even small down thrust on my rudder-and-throttle model, which had a symmetricallly airfoiled stab. The down thrust was just big enough to let the model climb without stalling. Idle engine would make the model descend rapidly due to its drag. That way I had very decent pitch control, even with only 2 degrees decalage, which made the model less gust sensitive. Of course, down thrust depends also on power, but I had low-powered models only.

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RE: Babcock Aeronca ready for maiden - 10/10/2009 5:10 PM   
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Status: offline 		For me I will say that the main enemy in my quest was the added horsepower. When I first flew them as long as I pulled the power back and let them lumber along as their design dictated they were fine but as soon as you tried to fly them in a controlled manner, not just interrupting it's direction with a blip here and a blip there, they became wishy washy and a trim battle. Now, just for info, the plans for the Esquire 40" .049/051, Live Wire Trainer 48" .09, had no right, left, or down thrust. As the same models got larger LW Senior 67", LW Cruiser 65", .19-.35, the plans started to call for right thrust. But none of them ever called for any down thrust. All of these planes were large 4412 flat bottom airfoils. Now, my small Carl Goldberg models under 40" semi-symmetrical airfoils had no left, or right thrust but as much as 4 degrees down built into the firewall and had higher stall speeds. Just rambling. Bill

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RE: Babcock Aeronca ready for maiden - 10/10/2009 6:21 PM   
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Status: offline 		Not to change the subject but something for Russ! Russ we discussed a DC-3 approach in one of my model slides about a year ago. I was finishing up all the model slides and ran across this. It was taken from a Stinson L-5 on final in Wilmington about 1954.

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RE: Babcock Aeronca ready for maiden - 10/10/2009 10:15 PM   
UStik


 

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Status: offline 		Please more of that rambling!

So it all makes sense, doesn't it? All you need to turn those optional free-flight or rudder-only models into 3-channel models is a suitable downthrust. You might reduce decalage but you don't have to. And maybe the small Goldberg models were meant only as R/C models and flown powered, but not throttled, most of the time. They had to fly quite fast and climb a bit, if altitude was used up in aerobatics. When they ran out of fuel that was the beginning of the landing approach, while the flat-bottom models glide and even thermal (at least today).

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RE: Babcock Aeronca ready for maiden - 10/10/2009 11:09 PM   
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Status: offline 		UStik, I have not had any luck with using down thrust in my flat bottom winged planes but have had to add right because of the increased torque/prop size. Down thrust just doesn't make them respond to my liking. However I have to use it in the Goldberg models but I am only using about 2-3 degrees instead of 4-4.5 degrees. The flat bottoms will thermal and so will the Goldberg @22oz but when it comes time to land the Goldberg needs more speed during the approach. Cheers Bill

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RE: Babcock Aeronca ready for maiden - 10/11/2009 4:14 AM   
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Status: offline 		Bill, when I saw your picture I initially assumed it was the Carolinas Aviation Museum's Piedmont DC-3 "clone" I used to fly for them. But it's a photo of an original, from a very cool perspective. Thanks for posting that. I wish I could make out the N-number. If you can send that picture as an e-mail attachment I can forward it to my buddies who still volunteer for the museum.

radiodaze@comporium.net

Do you remember National Airlines? They flew out of Wilmington untill around 1962. I'm sure you recall the infamous bombing of a National DC-6B enroute NYC to Miami over Bolivia, NC in 1960 - suicide by a lawyer so his family could collect his life insurance (it didn't work.) Russ Farris

< Message edited by maxpower1954 -- 10/11/2009 6:35 AM >

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RE: Babcock Aeronca ready for maiden - 10/11/2009 4:19 AM   
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Status: offline 		So UStik can sleep tonight (joking), I measured the Aeronca's force set-up with my trusty Robart incidence meter.

Wing = + 2 degrees

stab = 0 degrees

Downthrust = - 2 degrees

Russ Farris

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RE: Babcock Aeronca ready for maiden - 10/11/2009 8:03 AM   
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Status: offline 		Thanks a lot, so all is clear now and I can sleep tonight!

Last night I could only sleep because I got some things off my chest by writing my last posts. Please don't mind.

By the way, seems to be a perfect setup on the Aeronca. C/G at 40% chord?

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RE: Babcock Aeronca ready for maiden - 10/11/2009 8:12 PM   
UStik


 

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Status: offline 		Think I know what you mean, Bill. What you said about trimming the models back then sounds very familiar, and I as well think you have to decide whether to fly them "vintage" or "modern". Still there are different ways.

My parkflyer shown above is balanced at 40% chord like in the old times. Initially it had a 7x500 NiCd battery, a 400 can motor, a 1:2.33 gear and a 7x6.25 prop. All per Multiplex recommendation and a real floater lumbering around. A fellow modeler in France had the Miss2, essentially the same model, balanced at 30% chord, with same battery and motor but 1:1.85 gear and 9x5 prop. (Both 28 oz weight, wing 54 in / 410 sqin.) The latter flies 50% faster with more down thrust (4 degrees instead of 2, and more thrust, of course) and can't be fully flared for minimum speed and three-point touch-down. Unfortunately, that fellow has removed his videos from the Web so you can't see yourself how it swung around. Maybe it's his flying style for maximum fun. Anyway, he was disappointed with my model's "extremely poor" flight behavior. For me it's just the other way around.

Still I'm thinking there must be something special on the Babcock Aeronca, and the sharp leading edge of the flat-bottom wing is my favorite. If that's the problem then it's independent of trim, be it floaty or fast or your way. Weight doesn't really matter as well, except that more weight reduces damping. All I suggested here was to check that theory and checking would be reasonably safe. Another way, even safer, would be trying aerodynamic tricks like a trip strip on the leading edge to make the bottom-stall, which presumably is very pronounced, noticeably smoother. That's why I can't sleep.

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RE: Babcock Aeronca ready for maiden - 10/11/2009 10:51 PM   
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Status: offline 		Bill is gonna ramble again! I feel that Russ' "Airknocker" is flying at it's weight limit. My Jr Skylark and Jr Falcon original single channel flyweight was around 18 oz. Now they are 22 oz with a 37" wing semi-symmetrical 235sq in. Russ has 26 oz and 240 sq in. Even in real planes the more you approach weight limits things tend to get touchy. I am assuming by trip strips you mean strips on the leading edge near the fuse to make the root of the wing stall first to help stop tip stalls?. I feel that Russ' plane will fly fine without the extra fin once we hit on the on the exact cause of the problem. From my experience here is what I would do: Take off the aux fin, set the throws to 3/8 ",balance it nose heavy, remove the down thrust, prop it at a static thrust of 52% of its weight, go strictly to hand launch until I resolve the problem. When I launch it if the nose begins to drop and I have to blip some up elevator if not excessive I would trim and fly it only as long as it took to observe it. I would remove some nose weight until it would rise instead of drop. At 1/2 throttle if the tail wanted to hang I would start by changing the incidence at the stab, if it is solid mount I would change the wing. On a normal weight model I would start with 1/16 shims but if it is a troubled model, known to be heavy, I would use 1/32 shims. I would start with the trailing edge of the wing up or the leading edge of the stab up. If that did not make it better I would do the opposite. If it made it better I would go to a 1/16 shim. I know I had no trouble with pitch with my "heavy one" but it was still wishy washy until I got the balance right. Still if I vary 3 grams either way especially towards tail heavy I will have some problems. Any more than 3 grams the plane starts to fly me and I am trying to save it all the time and dreading getting close approach speed. After you get it to fly like YOU want it then go back to ROG takeoffs. Enough rambling!!! NOW lets go to my modern day Super Cub. 29 oz flat bottom, narrow cord 47.5 in span 365 sq in area very same power set up as the lil esquire but 4 degrees right thrust and 4 degrees down thrust but is balanced about 2 1/4 " from leading edge It flew great right out of the box and still does. I went from 9.6V 165 gram NIMH batts 10x8 prop to 100gr 1300mah LIPOs 9x6 prop. The battery box is right at the CG so the plane just got lighter so I went from 2" to 2 3/4" wheels. I had to do a repair on the tail and had to add 2.66 times the weight added to the tail, to the nose to get it to balance but it still flies good. Cheers Bill Waiting for return ramble!

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RE: Babcock Aeronca ready for maiden - 10/11/2009 10:55 PM   
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Status: offline 		Russ, here are a couple of pics for you!!! and anyone else!! Yes I do remember the National crash in Bolivia. My dad was there for 2 solid days picking up body parts and searching for bodys with the L-5. The bomber was the last one found and was about 4 miles back from where the plane rained down. Hall Watters a fish spotter using a super cub found him and it was his hanger at the airport that the FAA or CAA used to put it back together. Hall took about 400 pictures of the scene that were later donated to the Library. Hall was a major aviation contributor to the area and when he died a year or so ago his family went to the library and took everything out that he had contributed including the 400 pictures of the crash and about 2000 more of his aviation pictures and contributions.

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RE: Babcock Aeronca ready for maiden - 10/12/2009 3:30 AM   
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Status: offline 		Nice pictures, Bill! When I started flying for Piedmont in 1986, we were still using that 1950s-era terminal. My interest in National is because they were the only airline in my hometown of Ft. Myers, Fla. and contributed to my early fascination with aviation. Russ Farris

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RE: Babcock Aeronca ready for maiden - 10/14/2009 11:00 AM   
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Status: offline 		Return ramble, well, I'm a bit short of time and ideas right now. Our modern parkfliers are rather similar, yours having even a bit more wing loading. They are trimmed nearly the same, yours a bit more nose heavy. It seems to have less dihedral, too. I try to understand what's different with your vintage models, except the weight I mean.

I re-tried my parkflyer with the camera. It adds 6 oz to the 28 oz, wing loading is 12 oz/sqft instead of 10. Still not that much but the C/G is rather low because the camera is under the fuselage. Now the model feels a bit touchy on the rudder, but nothing else. Actually, it feels more stable in straight flight and in the pitch axis. With more weight I even like to balance the plane a tad more tail heavy. Anyway, I have to be careful with rudder with the camera under the fuse.

My explanation is that more mass makes for more slip (due to inertia) and thus more roll. The low C/G adds to that, and much more weight would give even more slip-roll. Maybe it would really help the Aeronca to reduce the dihedral, but I still think there must be something special and it might be the sharp wing leading edge. My parkflyer has a blunt leading edge and the "bottom stall" is quite smooth. But there is an increase in drag and therefore an unstable condition at low AOA. That's why I fly it at high AOA only, what it's balanced for. "Positive" stall is very smooth with that airfoil, and it has a big down-pitching moment helping as well.

The Aeronca with the sharp leading edge might have a more pronounced "bottom stall" and has a high wing loading what might give that devilish swinging. In this case, it would help to reduce weight as well as dihedral, but still I would check that theory first by trying a more rearward, high-AOA balance. Besides, I still think more prop pitch is necessary for the high wing loading / high flight speed, though I don't know which type of Park 400 (which kv) is used.

By the way, wasn't there a flight video announced?

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RE: Babcock Aeronca ready for maiden - 10/15/2009 1:15 AM   
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Status: offline 		About downthrust on those old designs...the ones that don't look like they have any actually do. This is easy to see in a diagram, but a little hard to explain. Please bear with me...

Picture a DeBolt Champ, for instance. The firewall is at a right angle to the fuselage. It doesn't look like there is any downthrust. But the wing and stab are both positive to the fuselage (the wing more than the stab). If you left all the aerodynamic pieces the same ... the thrust line, wing incidence and stab incidence, and then rotated the fuselage to tip it up at the nose so that the stab or the wing was parallel to the fuselage, it would now be obvious that the engine was pointing down. We would see that as downthrust. But aerodynamically, nothing changed (except the fuselage would fly at a higher angle and probably be a bit draggier).

It's a nice way to have downthrust without hanging the motor at an unsightly angle. But it also means that the common practice of shimming up the trailing edge of the wing on old timers is actually reducing downthrust.

Jim

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RE: Babcock Aeronca ready for maiden - 10/15/2009 1:45 PM   
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From: Augsburg, GERMANY
Status: offline
quote:

ORIGINAL: buzzard bait
It's a nice way to have downthrust without hanging the motor at an unsightly angle. But it also means that the common practice of shimming up the trailing edge of the wing on old timers is actually reducing downthrust.

That's why I would increase downthrust in this case. When I add an elevator, I want the reduced stability given by less decalage and would set the C/G back to maintain the balance. Actually, I would picture the wing keeps its AOA but the fuselage is shimmed tail-down/nose-up. I want less steep climb than without an elevator, hence even more downthrust. Did I miss your point?

And is shimming the trailing edge really common practice? That would be an information for me, and I'm still thinking I'd have different reasons to do it. So why is it commonly done?

I can't help but think of two-way models, used as free-flight or rudder-only (maybe throttle). All might be different if Class I aerobatics is at issue, but I have a blind spot there.

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(in reply to buzzard bait)
       Post #: 75

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