RE: Babcock Aeronca ready for maiden

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RE: Babcock Aeronca ready for maiden - 9/21/2009 11:51 AM

UStik

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HighPlains, thanks a lot for the links, much appreciated. It's great to have the experts here. Now I know what you meant I think I experienced the effect as a pilot when taxiing in crosswind, but I never thought of it from a designer's perspective.

Doc, you don't have to wonder, of course the electric drive was (and is) way too strong compared to the original. But I think that's not the point as well as the prop.

Yesterday I was in a museum and saw several interesting models from the mid-1950 to 1960. The little Graupner Piper seems to have an enlarged vertical tail compared to the original. Note the rounded and curved fuselage and the little Cox engine. The second is a rubber-powered glider for youngster contests. Small vertical tail, boxy fuselage, quite big nose, huge propeller. Third model is one of the first kit models, rudder-only, .15 engine w/o throttle. Small vertical tail, short tail moment arm, big nose, very boxy fuselage, leightweight construction.

Goes to show that there were many different models back then. Yes maxpower, I agree we're not used to those models and they are weird and strange to us today. But for me, they are mysteries to unravel and that's part of the hobby for me. I'm a purist and can hardly stand seeing these strong drives and sub-fins and tailwheels. Just have to post here for a relief and you are annoyed with my nagging. Hope you don't mind.

Just for a joke, how about the flat-four Cox as a "scale" engine for the Aeronca? Of course kidding, particularly since it would be bad in this case. After reading your latest test flight report I have an idea what's the problem with the model. You didn't add that much lateral area but you added some sharp edges. The effectiveness of the existing tail is increased now, like the Piper in the picture needs a big tail. The big prop should be not the problem because its lateral area might decrease stability, but what you need is damping.

Dutch Roll needs not only small damping but also big moments of inertia. The third model has big lateral area, but not that far behind the c/g. The vertical tail is small and so is yaw stability (deliberately), but the tail and the boxy fuselage make for decent damping and the truss construction gives small inertia. Several old models showed bad habits after the boxy fuselage was replaced by a round f/g fuselage, and the old models had the tails built as light as possible. All three well-proven designs were optimized only by test-flying and modification, showing there were issues but the designers knew how to attain a goal.

Maybe the Aeronca was OK back then. In this case, you added a tail wheel and a heavy motor and thus boosted the moment of inertia. Now the damping was too little and you had to increase it by sharpening the aft fuselage edges (making the inertia even worse). No need for a tail wheel on a Tri-Pacer, so try the tiny motor on that one. And show a video, please!

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RE: Babcock Aeronca ready for maiden - 9/22/2009 5:23 AM

Doc.316

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Russ;
Well, Yes I do work for that company...used to work jets untill about 5 yrs ago. Now work props. I work as a flight test engineer and pretty much are responsible for the guys testing all the propeller planes. Good to hear you bought a good Cessna product.

The reason you won't hear me tell someone how to fix their model is there a bunch of uncertainty in aerodynamics. Very small changes can influence an airplane greatly. I might give them Ideas to try but the bottom line is in the flight testing of the ideas. This happens in both full scale and Model airplanes.

The last flight test of the model (where power reduction was tried) pretty much tells the story that the power didn't have an effect so the tail must have been small to begin with.

Oh, btw, one of the test pilots that departed the aircraft is an avid modeler. Mainly freeflight.

Steve

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RE: Babcock Aeronca ready for maiden - 9/26/2009 4:54 AM

maxpower1954

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Here's some inflight shots of the Babcock Aeronca at the Celebration of R/C at Muncie, by Terry Terrenoire - video soon to be on Youtube. Everyone really seemed to enjoy watching it, and the comment I heard most - it was the first one they had seen successfully fly! Russ Farris

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RE: Babcock Aeronca ready for maiden - 9/30/2009 7:28 AM

maxpower1954

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Hi UStik! Just a couple of clarifications - the E-flite Park 400 was 1.5 ounces LIGHTER than the original K&B Stallion .049, and I had to add deadweight to the firewall to keep the CG in limits. The battery can't move far enough to make up the difference. The aft CG you suggested would make the roll coupling/Dutch Roll worse, not better - any "stretched" full-sized airplane doesn't need a bigger tail, while a shorter version does (the 747SP comes to mind.) The flight times are about 20 minutes; I just land after about 8 to 10. And I didn't ADD a tailwheel; the original design had one - I just made it steerable. The changes I made to the Aeronca made it flyable - but it does feel like it's always on the edge of something I'm not completely in charge of. I'm actually more relaxed doing single-engine aerobatics with my Goldberg Twin Skylark 56, believe it or not! My limited experience with early R/C designs is certainly a factor here.

The Aeronca will fly again at my club's Fall electric meet this Saturday. Russ Farris

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RE: Babcock Aeronca ready for maiden - 9/30/2009 10:35 AM

UStik

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Thanks maxpower, seems I've mistaken several of your specifications and things were not that bad (e.g. the 20+ minutes flight time). I was, and still am, just bothered by the added fins, even though you found a very tolerable solution. Another nuisance for me is a powerful drive, but that's me and I was just grumbling.

With the museum models I tried to show that many, if not all, of those vintage rudder-only models had Dutch Roll issues, solved by different and sometimes strange modifications. You never know in advance what will help. So the Aeronca seems to be no exception but rather regular. Indeed it seems to be short-coupled but for Dutch roll, damping and moment of inertia are important.

Of course the modern electric motors are lighter than the old glow engines, but the whole modern drive and R/C equipment still (often) weighs at least as much as the whole old glow drive and R/C. I know that it's hard to place the battery for correct C/G. (See other thread where I showed a very small motor and the battery in front of the main bulkhead, just turned out well in that case.) Actually I was teasing when I proposed to "simply" do that. I apologize for not conveying the nuances.

And just to be pedantic, I didn't mean an especially aft C/G but to avoid a forward C/G because the vintage models had the forward limit of C/G (if any) given in the plan for a start and were balanced more aft in test flights to have a minimum sink-rate glide. At least that's what I learned back then, when decalage and C/G were characterized as "Siamese twins". Given the fixed decalage, a more aft C/G would reduce flight speed and thus the Dutch roll problem as well (as would do less weight).

My experience with vintage R/C models is at least as limited as yours. I had just three rudder-only models and only dreamt of the Twin Skylark when I was a teenager. (Still have the old worn-out catalog.) I followed your thread from the beginning and I'm quite hooked. Back then I had only four-channel reeds and a very limited influence on the models. I knew how to balance a free-flighter for automatic flight and the rudder-only models were not different. But I didn't even think of doing vertical eights and had no idea what real flying is and what benefits even an elevator would have. So I well believe you and admire your Twin Skylark flying as well as today's rudder-only flying. Thanks for sharing all this great stuff!

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RE: Babcock Aeronca ready for maiden - 10/1/2009 6:49 AM

maxpower1954

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Thanks UStik, I do appreciate your ideas because I need all the help I can get!

By the way, your command of the English language is excellent - Russ Farris

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RE: Babcock Aeronca ready for maiden - 10/1/2009 7:16 PM

UStik

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quote:

ORIGINAL: maxpower1954
The changes I made to the Aeronca made it flyable - but it does feel like it's always on the edge of something I'm not completely in charge of.

Thanks again, maxpower! So may I express another weird idea? I didn't think I was so right when saying those models are like mysteries to unravel. The Aeronca is an especially interesting example and a tough nut to crack. It just stayed on my mind, and when staring at the pictures you posted above and thinking about the sentence above, that weird idea bubbled up.

If you still feel uncomfortable with the model, maybe the fins did indeed help but did not solve the actual problem. Question arises what the actual problem is. If we take for granted that the strange behavior of the model is Dutch Roll, then we have to search for slip-roll coupling. That's what decreases (Dutch) roll damping, and damping is what is needed to avoid or stop Dutch roll. It's not yaw-roll coupling and not stability what matters most. Just re-checked that on Denker's website here (from figure 10.9 on).

Following some links there, I came across the explanation of other forms of slip-roll coupling - other than dihedral, the obvious. The first two interference effects are interesting in our case - redirection and turbulence, especially the latter (figure 9.7). Denker is talking of a large, messy wake reducing lift on the leeward wing of an airplane moving sideways (side slip). Quote: "The magnitude of the effect of the wake is very difficult to predict. It will depend not only on the general shape of the fuselage, but also on the details of the surface finish. It will also depend very nonlinearly on the airspeed and slip angle." Propwash is mentioned in addition.

Now look at the Aeronca's fuselage. The engine cowl is pretty round but the part from the firewall to the wing's leading edge, although shaped round, has the protruding joint or seam of the two fuselage halves. For any airflow not parallel to the centerline it acts as a break-away edge and probably makes the wake even messier. That might explain the unpredictable behavior of the model. My vintage-style parkflyer, which is rock-steady, has a nicely rounded fuselage upper front cover. Maybe the designer had reasons other than look.

Unfortunately, one would need a wind tunnel to research this problem. Aside from that only a dumb test comes to mind. You could put transparent tape over the whole upper fuselage in front of the wing to cover the break-away edge and render it harmless. No need to remove the fins because you should just feel more comfortable if that measure helps. As I said, a weird idea and pure fun for me, but not to urge you to really try it since it would be no fun but stress for you after all.

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RE: Babcock Aeronca ready for maiden - 10/3/2009 11:14 AM

UStik

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Think I should amend my last post. Actually, I was surprised that nearly all old models had a boxy fuselage but a round top front part. I remember building models with my friends in the 1960s when the fuselages were built-up and simple to build, but we always had to struggle carving and sanding the nose and top blocks. Maybe not only for look? Just a puzzling observation.

More important: I re-read your flight reports and found BobHH's comment that he once flew one that flew great. Your Aeronca just has to be different and you have to find the relevant differences. Seems your copy flies especially unpredictable. Denker's term "nonlinearly" struck my mind, and a Dutch roll is a bad but still kind of smooth and round motion. Your reports sounds as if the Aeronca gets out of control all of a sudden.

I stick to my suspicion expressed in the last post and even add another, similar one. You mentioned the sharp leading edge of the wing. It seems to have a flat-bottom airfoil, which is actually well-proven but has one nasty trait as well. The lower side kind of stalls even at 3 to 4 degrees positive AOA and 0.4 to 0.5 lift coefficient. Lift is not really affected but drag increases tremendously. That is normal behavior of the usual flat-bottom airfoils and is of course exacerbated by a sharp leading edge.

Now if you have balanced the model for a bit higher speed than done back then, it might fly only a bit above the 4 degrees AOA and 0.5 lift coefficient. A small rudder input or gust makes for a slip (intentionally in case of rudder) and thus less AOA on the downwind wing, which lets the lower wing side "stall" and produce huge drag. That would make the model swing around in the direction of the initial yaw and might lead to 60 or even 90 degrees bank, as observed by you. The added fins just dampen that swinging motion, so your impression is it's better but still there.

In this scenario, the simple remedy would be balancing the model for more AOA and lower speed. What I failed to do so far was to discern weight and balance. The C/G position is roughly independent of weight inasmuch it makes for a certain cruise or glide AOA. The flight speed, on the other hand, depends on weight given a certain AOA.

You mentioned you had set the C/G a bit forward of the plan position and you reported a 30 ft automatic take-off. Both seems to indicate a slightly too high, non-vintage balanced flight speed, regardless of weight. If you have the battery behind the main bulkhead, could it be slipped a bit aft?

That's the way my parkflyer was balanced with the old brushed drive. And I remember it swinging around like crazy when balanced more forward as erroneously recommended in the plan. I checked with Multiplex and they said they didn't know either how the forward C/G sneaked into the plan. Of course, it were nonsense and they had especially built another copy of the model and tried. I should balance on a new, aft position and would be enthused by the docile flight behavior. Indeed I was.

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RE: Babcock Aeronca ready for maiden - 10/4/2009 7:21 AM

maxpower1954

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You might be on to something here, UStik...

I flew the Aeronca today at my clubs fall electric fly-in. The wind was light and variable at launch, but picked up to about 15 mph soon after - yikes! In turbulence, it required a very delicate touch; one of my flying buddies who is a tech for my airline remarked on the dutch-roll (his words.) Your idea of the inside wing stalling makes more sense than anything I've come up with. I do think the wing loading makes
things considerably worse. If the Aeronca weighed 16 ounces instead of 26 it would be quite different. As is, the flight envelope is very limited.

I can move the battery back easily to the plans CG, and will test fly on the next calm day and report back. One thing I forgot to mention is I have slightly more dihedral than called for - 2.25 inches per panel, versus 2.0 on the plans. Could that be part of the problem, do you think? Russ Farris

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RE: Babcock Aeronca ready for maiden - 10/4/2009 8:12 AM

UStik

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That small bit more dihedral (6.93 degrees instead of 6.17) may contribute to the problem as well as a bit more weight or a bit forward C/G, but I wouldn't mind (my parkflyer has 8 degrees dihedral). Low wing loading would relax (actually occult) all such problems, but I think a bit more aft C/G for more cruise/glide AOA would be the ultimate check, at least in the first place. The (now not even that high) wing loading makes for more speed and inertia, and especially the latter makes the strange behavior clearer. When you've identified the problem you may still try the smaller drive.

It's an act of daring to fly that model in strong wind, hats off!

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RE: Babcock Aeronca ready for maiden - 10/4/2009 5:27 PM

otrcman

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quote:

ORIGINAL: maxpower1954
One thing I forgot to mention is I have slightly more dihedral than called for - 2.25 inches per panel, versus 2.0 on the plans. Could that be part of the problem, do you think? Russ Farris

Hi Russ,

I've been following your Babcock saga but hung back without posting because I wasn't quite sure what your "dutch roll" characteristics were. I'm still not positive whether your airplane is oscillatory or simply way too rudder sensitive. Either way, I couldn't help commenting on the increased dihedral.

Let's try to break this dutch roll thing into component parts. First, we have an airplane that rolls quickly when it is sideslipped. As you know, an airplane with a lot of dihedral rolls quickly when you apply rudder input. So half of the equation is how much "roll-due-to-sideslip" the airplane exhibits. When you added dihedral, you made the airplane so it rolled more for any given amount of sideslip.

The other half of the equation is how easily the airplane sideslips, either due to rudder input or due to turbulence. Common things that make an airplane sideslip (yaw) easily are: (1) lots of rudder area or travel, (2) very small total vertical tail area, (3) a short tail moment arm, or (4) lots of lateral area forward of the CG. Oh, and (5) could be a large prop and powerful motor, as doc.316 mentioned.

If you build in lots of roll-due-to-sideslip and ease-of-sideslip, you have a nightmare scenario. A gentle nudge of rudder and you are off to the races. And every time you make another input to quiet things down, away you go again.

How to fix the problem? There are several fixes, and you intuitively picked a good one by increasing the vertical area. You essentially made the airplane more resistant to sideslip by adding vertical stabilizer area. Notice that it didn't take much, either. Here are some other potential fixes: Reduce your wing dihedral. This works on the other half of the equation by reducing the amount of roll that you get from a given amount of sideslip. A good example of this fix is the B-25. Early B-25's had straight dihedral, which caused the airplane to roll too much with an engine out. Later B-25's had the outer wing panels "flattened out" to reduce roll-due-to-yaw. Made it a much more easily controlled airplane with one engine out.

The other fix is to move the CG forward a bit (sorry UStik, we disagree on this one). Moving the CG forward has the effect of increasing directional stability more resistance to sideslipping, or yawing. Moving the CG forward effectively lengthens the tail moment arm and reduces the lateral area forward of the CG. As a bonus, if shortens the moment arm from the CG to the prop, thereby reducing the destabilizing effect of the prop. Of course you may have to fiddle a bit with elevator or wing incidence to get the pitch trim back where you want it.

Doc316 is right on the money when he says that flight test is an essential ingredient for dealing with this sort of problem The interaction of directional stability and dihedral effect is a very complex subject and doesn't lend itself to pat answers.

Dick

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RE: Babcock Aeronca ready for maiden - 10/4/2009 7:44 PM

UStik

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No Dick, I don't disagree.

Your point on directional stability is quite clear and was discussed in several posts here, as well as your other points. Actually, the whole thread is about flight test, and maxpower has gotten quite far in it.

What still seems to be not clear though is what we mean about C/G. In another attempt, let me point out that all I meant is leaving the given (decent) decalage as is and balancing the model as intended back then (at the given point and maybe even back, found out by flight test). All other things unchanged (decalage, weight, drive, dihedral, fins), that would be the flight test at issue right now. After all the model is controllable now.

If I got you right, you mean increasing directional stability by forward C/G, but at the same time increasing decalage so flight speed would not increase. Again, no disagreement. All I was after is lower flight speed because I think that would relax the Dutch roll issue or whatever it is (apart from the possible airfoil issue). What do you think?

And may I repeat that we're not talking about a "real" airplane but a (former) rudder-only model. Those intentionally had big slip-roll coupling as the means of controlling them, and small directional stability to have better spiral stability. The decalage had to be chosen so that the model speeds up a bit in a turn what replaced up elevator, and the C/G set for good glide speed. Obviously, all was a compromise and found out only by flight testing. I'd be very hesitant to interfere with this delicate balance of parameters. In fact I'd try to restore that balance, at least as a starting point for further experiments.

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RE: Babcock Aeronca ready for maiden - 10/5/2009 5:01 AM

maxpower1954

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I'm enjoying the debate about what is wrong with the Babcock Aeronca far more than being the point man of my "flight test" program!

I even considered building a conventional sheet balsa wing in an effort to reduce the AUW, but what's the point? It is what it is - an overweight, marginal early attempt at an R/C ARF model.

Remember the Cox RTF control-line models of the 1960s? As a kid, I had many of them. With the exception of the PT-19 (which could actually loop) they were overweight, marginal early attempts at U-control
RTF models. When I built my first balsa control line, the Goldberg Wizard, I couldn't believe how much better it was. "Balsa Flies Better", as the slogan said on many kits then.

In my opinion, the Aeronca was always iffy as an R/C model. I forgot to mention that it and the Tri-Pacer were three way kits; R/C, U-control and free-flight (that's why the elevator was incorporated into the design, they even came with a metal bellcrank.) Guess they were trying to sell to the widest possible market. The biggest issue is the high wing loading, which exaggerates the problems and I believe roll-coupling/dutch roll combined with a very sharp leading edge is causing airflow seperation on the down going wing, as UStik suggested...perhaps. With the high wing loading, it has a very narrow speed range to fly under some sembalance of control. It certainly has more going on than just an undersized vertical tail...

UStik, Doc.316 and Dick, I appreciate all the great ideas - keep 'em coming boys! But I don't think it's possible to turn this sow's ear into a silk purse. It's flyable, (more or less) as an example how far ARFs have come in 50 years. Russ Farris

< Message edited by maxpower1954 -- 10/5/2009 7:32 AM >

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RE: Babcock Aeronca ready for maiden - 10/5/2009 4:30 PM

UStik

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It's amazing how many new words I'm learning here. I'm aware how you must feel as a point man, but isn't pondering and experimenting what modeling is about? Probably many of the old rudder-only designs were iffy (look at the third picture in my post above), at least that dawned on me when I was in the museum. But wouldn't we have been more than happy to get one flying at all, 50 years ago?

I wouldn't build another wing but try to make the model as similar as possible to the 1950s original to reproduce the old feel - even if iffy (purely nostalgic). The smaller and lighter drive would be an obvious way but not absolutely needed. After building it similar to the original, you had to set up (C/G) and fly it appropriately.

Maybe the best would be trimming it like a free-flight and letting it climb with power but without touching rudder. You might trim in a wide turn. At some altitude cut power and use tiny rudder deflections to control the model. I think that's all what was done with the model back then, and I think it should fly decently.

I'd love to find out the guys who designed and sold models in those days. I wouldn't be surprised if these early ARFs aimed at the rank beginner who's on it's own, figuring he wouldn't successfully fly it anyway. The manufacturer had an expert who could demonstrate it and impress the innocent. They bought the model because it obviously flew great and because it looked so nice - must have. They would crash any model, even better flying ones, so why bother. Cynical, but impossible?

Another alternative would be to have the rank beginner build the model strictly per instructions and make it a fool-proof build. That way he would at least have a chance to successfully build the model and fly it in the very limited way described above. So the purpose of the model was to attract the beginner to buy it in the first place, and after that provide for successful first flights. I like this scenario more.

By the way, aren't there setup/trimming and flying instructions?

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RE: Babcock Aeronca ready for maiden - 10/5/2009 5:54 PM

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Hello Russ and All! I have been out of touch for about 5 months but am back with a bunch of crazy experiences with converting old single channel planes to electric. I am currently flying a Live Wire Trainer, Little EsQuire, and Skylark Junior all converted in the last 2 months and ALL of them have been a trimming nightmare especially the Lil EsQuire. I have learned a bunch about going from single channel hand launch trim to more power, ROG, and straight line flight trim. I am flying my lil EsQ very heavy, original single chanel weight 24 oz. now it is 32 oz. They all fly great now but for awhile there it was tail hanging,cart wheels on takeoffs, out of control banks, fast landings, you name it! But I was a bad hard headed student! I learned the hard way! Russ, Your plane is beautiful!! and a great example of the past. Fly it and have fun. Cheers! Bill

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RE: Babcock Aeronca ready for maiden - 10/6/2009 5:10 AM

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Well if it is dutch roll (the airplane basically swims through the air with an oval shape being drawn out by the wingtip) you have a couple of options. You can put on dual yaw dampers and split the rudder (I am joking about this but that is what they would do on a full sized plane) or cut the wing in two and rejoin it with less dihedral (ouch!). Or you can add fin area low (which is what you did...good job).

Last year I was flying one of the planes for the local college and they had a flying wing with small ruddervators (rudders on the ends of the wing) unloaded it flew fine with just a bit of dutch roll, then we loaded it up with a 8 lb water bottle and WOW did it oscillate! It was interesting because if you slowed it down the dutch roll would slow down. So I know weight is definately a factor. Balancing it a bit farther forward helped a little bit. But when we added a bigger fin low (actually below the wing since there was no fuselage) it helped a lot. The wing was interesting since it was developing all of it's dutch roll tendency's from having a swept wing ...it didn't have any dihedral.

So, all in all I think you did good with the fin...you might try slowly moving the C.G. forward.

How sensitive is the elevator? Does it take a bunch of throw to get the plane flared for landing?

Actually, this is pretty interesting to learn everyone's ideas on this subject....it would be cool to build a variable stability plane with a wing that the dihedral could be easily changed and different fins plugged in....if you aren't learning you aren't living.

Steve

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RE: Babcock Aeronca ready for maiden - 10/6/2009 6:56 AM

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Well, guys I think it might be possible to reduce the dihedral to what the plans showed, by using CA debonder and careful surgery with an X-acto knife. That way, we know the force set-up will be original, except for the added fin area. I'll test fly that change first, then move the CG slightly forward. If that doesn't work. I'll move it back to the plans CG. I've reduced rudder throw a little more, and increased the elevator up travel some...the landings have been controlled crashes basically. Little or no elevator power in the landing flare. As long as I make the changes one at a time, under calm conditions we can experiment with the "yellow peril" safely, I believe. I'm not willing to reduce the size of the power system, as the margin over stall seems quite "marginal". I wish you guys had you own Aeroncas to experiment and learn with; the different ideas each of you try might make a decent flying model! But I still think it's like taking a Cox P-40 RTF UC and making it into something it can never be, because of the heavy weight. Russ Farris

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RE: Babcock Aeronca ready for maiden - 10/6/2009 7:22 AM

UStik

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I know what you mean and wish you good luck (and wish as well I had an Aeronca, too). It's hard to adventure such a nice model, but at least some of the ideas mentioned here are meant to make it safer.

The weight is upper limit but not that heavy, it's 13 oz/sqft wing loading and for instance the Twin Junior Skylark is rated for up to 14 and hasn't even a flat-bottom airfoil. You may feel the drive is marginal (you specified 0.6 static thrust/weight ratio) but it's not ideal for the model. The smaller (300) motor with the right prop would give the same T/W ratio at lower weight.

Precondition is of course the lower weight but also slower flight speed, which might cure the downwind-wing-stalling problem as well. Little elevator power in flare indicates a too far forward C/G, so that is cured as well when trimming for lower flight speed. Why chase 12.5% too much dihedral when tinkering with C/G is so easy and way more effective?

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RE: Babcock Aeronca ready for maiden - 10/6/2009 7:22 AM

maxpower1954

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UStik, there were minimal set up instructions on the Champ, no rudder travel or kick up elevator limits. Just check the CG, launch and don't attempt the first turn below 75 feet. That was it. Did you Google point man? (a military term.)

The gamble to make the ARF Tri-Pacer and Champ was a bold one, and expensive. It may have even farmed out to another company like StromBecker, which had experience wth vaccum-formed flying rubber models. I know they were designed by Chuck Hollinger, a well-respected modeler. But who knows how much was changed from design to execution? Did he take into account the effect of the fuselage joining flanges increasing the frontal area? Sadly, he passed away a few years back - I would love to have five minutes with him about this model. I know they weren't successful commercialy, they were only available from 1958 to 1960.

I've put out this plea before, with only Bob Harris responding. Does ANYONE have any experience flying these models back when they were new? I know BobAeros told me at Muncie, a few years ago at his club in Ontario, someone tried to fly an Aeronca - it flew straight out, then snapped-rolled into the ground destroying it. It had an .049 not sure of the radio gear. Russ Farris

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RE: Babcock Aeronca ready for maiden - 10/6/2009 7:30 AM

maxpower1954

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And the new wing loading is now 16.3, on re-weighing the model and recalculating the area (230 sq inches, 26 ounces) Russ Farris

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Post #: 45

RE: Babcock Aeronca ready for maiden - 10/6/2009 7:42 AM

maxpower1954

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And UStik a Park 300 isn't heavy enough to balance the model, without another ounce of dead weight! It was my first choice as well, but adding deadweight for a less powerful motor didn't make any sense to me, since the AUW of the airplane would remain the same, with less thrust. Russ Farris

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RE: Babcock Aeronca ready for maiden - 10/6/2009 8:10 AM

UStik

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Well, 16.3 oz/sqin is much but probably the flat-bottom airfoil can carry it (like my parkflyer carries a camera) provided the drive is strong enough, what it is now. Can't believe the model flies near stall, seems to me it's trimmed for a moderate AOA (too moderate for the aifoil bottom-stalling at 3 degrees), and with the heavy weight it has to be rather fast and the prop doesn't seem to "grip" (maybe needs even more pitch for that airspeed).

The smaller drive would be possible only if the battery could be used for balance, for instance by putting it vertically in front of the main bulkhead or by cutting a hole in the bulkhead to slide the battery in. I brought up the smaller drive just to show an alternative.

Sorry, it's all speculation. Did you try making the model slower by pulling elevator? I mean what happens then, would it calm down, does it come near stall?

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RE: Babcock Aeronca ready for maiden - 10/6/2009 4:46 PM

otrcman

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You know, Russ, it's just possible that you are the most successful flier of a Babcock Aeronca in the history of the model ! As you say, we'll never know for sure unless some folks with "back then" actual experience can be found.

Here are some random thoughts in no particular order:

1. Maybe your model flies as well as any Babcock Aeronca ever did and the guys from 1958 would be truly impressed if they could see your model fly.

2. Or, maybe the successful rudder-only fliers of the old days were very good at trimming and flying such models.

3. Maybe Mr. Hollinger's balsa prototype (I'm assuming that's how he did it) flew fine at a lighter weight and he too was appalled at the way the plastic plane turned out.

4. Maybe nobody ever got under 26 ounces back in the old days either. I was initially surprised that your model came out heavier that the original's claimed weight, given today's much lighter radios. But reading through your posts, it sounds like the model needs quite a bit of weight in the nose to achieve the desired CG. That would have been true in 1958 also.

5. This is just a general observation from my experience with Babcock radios back in the late 1950's. If Babcock put the same amount of field testing and development into the Aeronca that they did into their radios, then you probably have more flight time than Babcock ever did. I was consistently unsuccessful with my Babcock radio equipment, and numerous trips back to the factory didn't help much. My first really successful R/C flights came only after abandoning Babcock as a lost cause and buying an Orbit single channel receiver and transmitter. In fairness, I should say that I made many successful flights with a Babcock compound escapement.

Dick Fischer

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RE: Babcock Aeronca ready for maiden - 10/9/2009 5:28 AM

maxpower1954

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I think you may be on to something, Dick. Certainly, the ARF technology of 1958 (the year the Boeing 707 went into service, wow) wasn't up to the job. Balsa was safe for many years to come.

For starters, the empty weight of my Aeronca minus battery, radio, motor and prop but with light-weight modern wheels is 19.7 ounces! The original S/C gear was 5 ounces from what I understand, and an .049 like the K & B Stallion shown on the plans was probably around 3.5 as a guess. The AUW would have been pushing 30 with the heavy original tires. Holy smokes! That's 19 ounces/sq. foot for a rudder-only model with questionable directional stability.

I had the same thought you did about the prototype Chuck Hollinger probably built; it would have been balsa. It's barely possible that it was designed straight to the molds, I suppose - but even today the major companies do "test shots" of new designs so they can make any required tweaks prior to production. Chuck may have indeed been horrified by the final result...with the expense of tooling, this was a major loser for Babcock.

The Tri-Pacer and Champ were only in production about a year, but they seem to have showed up in every hobby shop in America - most of the guys at Muncie knew exactly what it was, and a few had seen attempts to fly them - unsucessfully. One flyer from Canada related how only a few years ago someone tried a Champ with an .049. It went straight out then snapped into the ground during the first turn, totaling it. I just may be the world's highest time Babcock Aeronca pilot since I have about 45 minutes on mine. 45 intense minutes, I might add.

And to prove I'm a glutton for punishment, if I can score a Tri-Pacer I'll give that a whirl, too. At Muncie, John Castronova was displaying his Champ and Tri-Pacer kits, and after seeing mine fly (?) decided to get his Tri-Pacer into the blue (I had lots of free advice for him...) Russ Farris PS - Calling all Babcock RTF flyers!!! I know you're out there; I've seen one post recently where a Champ flew 30 secs then cratered, back in it's heyday.

< Message edited by maxpower1954 -- 10/9/2009 8:05 AM >

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Post #: 49

RE: Babcock Aeronca ready for maiden - 10/9/2009 7:03 PM

UStik

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quote:

ORIGINAL: maxpower1954
For starters, the empty weight of my Aeronca minus battery, radio, motor and prop but with light-weight modern wheels is 19.7 ounces! The original S/C gear was 5 ounces from what I understand, and an .049 like the K & B Stallion shown on the plans was probably around 3.5 as a guess. The AUW would have been pushing 30 with the heavy original tires. Holy smokes! That's 19 ounces/sq. foot for a rudder-only model with questionable directional stability.

Thanks again for the new words and terms! By the way, I'm using an online dictionary with forum where all terms and phrases are asked and answered at least once.

But don't fret!

Not poking fun at you, just funny to remember my own rudder-only attempts in the late 1960s. I had rubber-powered models and free-flight gliders before and was used to their low wing loading. Now came Topsy, a popular R/C beginners model back then. As a free-flight it weighed 7 oz and had a 6.5 oz/sqft wing loading. With 32.3 in wing span and 195 sqin total (wing and stab) area, it's smaller than the Babcock Aeronca. Assuming the stab as conservative 20% of the wing area, the wing had only 163 sqin.

The picture below is borrowed from don't-know-where. It shows exactly the same equipment I had (and 6.8 oz empty weight). Now the model weighed whopping 17 oz, meaning 15 oz/sqft wing loading. I was appalled and didn't believe such a lead sled could fly. But after all others had successfully flown the model and I absolutely trusted Graupner, so one day I screwed up my courage and just launched the model. You guess, it flew great. It still did after some crash repairs adding to the weight.

So don't fret the weight. Such models could bear even more weight. If something is wrong with the Aeronca, it's not weight. Flight reports about the model snapping into the ground don't mean much. Even the most docile glider would snap in high-start if set up improperly. I'd rather look at the airfoiled stab of Topsy and the Aeronca's huge stab, meaning they should be flown in the best-glide or slowest-sink-rate flight regime where the stab often contributes to lift instead of detracting from it.

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