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Too High

Old 08-07-2015, 06:27 PM
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Greetings All:

I've been flying a Norvel .061 diesel mounted on a 1/2A Junkers (slab fuse and slab wing). The engine runs like a charm and pulls the model around right smartly on 40-feet lines.

A question about a flight characteristic. When the plane comes around and is directly upwind, it suddenly gains a lot of altitude. Now I expect the lines to loosen a bit and can compensate, but I don't care for the altitude gain at the same time. Right now, I'm just struggling for level flight with this mini-beast so that I can move on from there. Is there anything I can do to remedy this?

I've cross-posted over in the diesel forum with a photo of the plane.

Davey Mo...
Old 08-09-2015, 04:26 AM
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Hi Davey, The tendency for the airplane to not only slow down each lap on the up wind side as well as rise is normal and there is not a lot you can do to prevent the rise beyond controlling it. by that I mean suppling sufficient down each time around.

One other thing I think you do that will help is to use shorter lines for windy days perhaps 35 footers.

John
Old 08-09-2015, 09:29 AM
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John:

Ah, very good advice. Lines at 40 feet are long, but this combination engine and plane is a bit fast and twitchy for my skill level. Will certainly go with your recommendation at 35 feet as conditions warrant. Perhaps I can master this beast yet.

As you can tell, I'm not completely pleased with the feel I'm getting from this. In hind sight, do you think a built-up wing might have been better for this model? I might try less power on shorter lines as well.

At any rate, thanks for taking the time to reply.

Davey Mo....
Old 08-09-2015, 10:04 AM
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You bet Davey and yes perhaps an .049 with shorter lines may very well increase your comfort level. Personally mentoring the folks I have helped I prefer a little different approach and that is to bypass the 1/2A route altogether but instead; Using larger airplanes that can be powered with .25 to say .40 and use RC engines.


There is a plethora of .25 to .40 engines out there that take only a rubber band to lock the throttle open for controlline use. They work fine. You will find that the larger airplanes will carry sixty foot line quite well and this will dramatically reduce your rotation rate. This is a big bonus for a new flyers. Something like a profile magician, sig Skyray and a number of others. Another plus is most of these type airplanes have a sufficiently long nose to allow the use of a conventional RC clunk tank eliminating the experimentation usually associated with properly plumbing a uniflow tank. Conventional clunk tanks work just fine and quite simple.

John

Last edited by JohnBuckner; 08-09-2015 at 11:44 AM.
Old 08-09-2015, 02:46 PM
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Your advice at this point feels mighty tempting! Perhaps a winter build project is in order. Thanks again!

Davey Mo...
Old 08-09-2015, 06:09 PM
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I have to agree with John about using larger engines to learn with. Way back in the late '50's my friends and I all learnt with .29 engines on a slab wing/fuselage plane and I continued with the same design to teach my son to fly except with a .40 up front.
Old 08-12-2015, 02:18 PM
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Does the Stuka have a flat bottom wing? That will always cause a lot of problems in C/L, except for relatively fast, heavy racers.

Phi C
Old 08-12-2015, 04:31 PM
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His photo shows a simple half A profile with balsa sheet wing no difference top or bottom side.

John
Old 08-13-2015, 09:52 AM
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Hello Gents:

You are correct about the sheet wing. I've speculated about cutting it out and replacing it with a built-up wing of some sort. Right now, I'm working on getting the center of gravity within the 11-18 percent range. Once that's done, I'll see how it does or does not perform.

Thanks for the oversight.

Davey Mo...
Old 08-13-2015, 11:26 AM
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DaveyMo and all the rest in here: There's already lot of good advice!<

Since I made a stupid-simple discovery, my small models aren't twitchy.

Use a larger bellcrank and matching horns!

Our handle movements are just about the same whatever the size the model. I don't understand why kit mfrs and other small model designers went to the 2" or smaller "1/2A bellcranks." Cost reasons? Or possibly they thought they looked "more appropriate" for smaller models..

Our "natural" "comfortable" amount of arm/wrist/handle input could drive a "1/2A bellcrank" to a much bigger angle than it drives a 3" or larger bellcrank system. Make it even worse? Use "1/2A control horns" too.

Apology: numbers and simple math follow:-
The example numbers are not precise, or even used, but give the idea.

Remember the Sine function? Okay, well, see it this way...in a triangle with a right angle at one end and a 30 angle opposite the 'base,' the 'base' is half as long as the hypotenuse. If you have a 2" bellcrank, each arm is 1". If the bellcrank is turned 30 from neutral, it only took 1/2" of line movement to get it there.

If your handle has a 4" line spacing, the lines are 2" above and below neutral, agreed? Rotate the handle 30 and each line moves ; (2" x Sin 30; 2" x times 0.5 =) 1" from neutral.

If you're using a 2" "1/2A bellcrank," that much line movement pulls the bellcrank to 90 away from neutral!

With a traditional 3" bellcrank and 4" line separation handle, the bellcrank in the model will turn more than 30 , but not 90.

With a 4" bellcrank and handle, obviously, the bellcrank turns the same angle as the handle. We don't need to match our hand angles to the control surface angles, this is just an example.

Even if the control horns are "scaled" to match the small "1/2A bellcranks," a human sized handle will turn that system too far, too quickly = too twitchy!

It may not be easy to fit a 3"- or-so, bellcrank into or onto a 1/2A size model, but it makes a huge difference!

Otherwise, you could bring the lines out from the handle closer together... But, that makes finding a comfortable neutral much more critical, and you may feel that you need to move the handle further to make control inputs. Wrong, but a natural tendency...

If you want any model to feel right, use the same proportions at the handle, the bellcrank and the control horns as for models you are most comfortable with! And using the same size pieces is the simplest way to do that. Remember, you can make up bellcranks and horns that weigh less, but still have the "right" dimensions.

(edited - phrasing)

Last edited by Lou Crane; 08-13-2015 at 11:30 AM.
Old 08-13-2015, 02:28 PM
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Line spacing at the handle results in total throw of the control surface in exactly the same way that servo arm length at the servo results in total throw at the control surface of an RC airplane.

If the model is too sensitive you can simply adjust to closer spacing at the handle. Even the old iconic handle included with just about every Cox airplane ever sold I just measured 3.5 inchs widest (most sensitive) and 1.5 inchs closet (least sensitive). I also just checked an old Carl Goldberg Half A handle and it too is 3.5 inchs at its widest but only three quarter inch at its least sensitive adjustment.

I believe half A bellcranks in most cases do just fine when a half A handle is used and set up or adjusted properly. A four inch only handle is of course going to be perhaps overly twitchy.

John

Last edited by JohnBuckner; 08-13-2015 at 02:31 PM.
Old 08-14-2015, 10:52 AM
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John and Lou:

Nice discussion here! Thanks, Lou, for the clear explanation of the trig involved. I barely passed my upper level math classes; but the beauty of a well-described application is undeniable! Very good of you, John, to look into the specs on 1/2A setups.

Now before I give you the stats on my setup, I've got one question concerning line space on the control handle. All other things being equal, does a very small spacing (e.g., John's 3/4" Goldberg) still allow for a full elevator range of motion, or does it cut it short in any way?

Here's what I now have:
- Line length 42'
- Handle spacing 2-1/4 inches (can go down to 1 inch)
- Bellcrank 2-1/8 inches (hole to hole)
- Connecting rod at control horn in the hole farthest from the elevator.

Davey Mo....
Old 08-14-2015, 02:48 PM
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DaveyMo, thanks for the measurements! Did you measure the elevator horn arm from its hingeline, too?

John, I agree that commercial 1/2A goodies have performed well over the years, and still do. I'm a bit concerned that a newish CL flier might not get them set up close enough to allow a good flying neutral range where it should be. If it is far enough off, the first flight could too easily be the last. There may not be range enough, not to say time enough, to find a neutral before the ground rises up to smite thy aircraft.

Ideally, for me at least, the handle should be relaxed and comfortable to set level flight when your arm/hand/wrist aim at the model. Then, raising that combo causes a climb, and lowering it causes a descent. Gradual position changes cause gradual changes of height.

I'll play with these numbers, just for my own satisfaction.

Threat? I'll probably be back with more <grin>
Old 08-14-2015, 03:37 PM
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In my opinion This is being way over thought. Its real simple and absolutely zero math involved. A simple board wing 1/2a airplane with a half A bellcrank (2 inch or thereabouts) and it seems a bit twitchy to the user drop down from that to about two inch at the handle, problem solved.

Davey I do feel that your forty two foot of line is a bit much line for a board wing half A trainer There is absolutely no reason to put a humongous 3.5 inch bellcrank on that little wing heck what is the wing cord?

John
Old 08-14-2015, 06:50 PM
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Gents:

Thanks for your continued interest. I just finished with the work of reducing the center of gravity MWC from 31% down to 17%. Will give it a test flight by mid next week. Yes, 42 feet is a lot of line, so will likely shave it down to 35 feet. By the way, no deadly crashes yet after three full flights (over grass w/ a paved takeoff strip) though a few close calls.

Now for the business at hand:
Average wing cord = 6"
Bellcrank offset = 7/16"
Elevator horn at hinge line standoff = 3/4"
Elevator = 1"

Davey Mo...
Old 08-16-2015, 03:55 PM
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DaveyMo,

Great! ...and keep it going!

I live above 4900' above sea level, and that affects both engine output and aerodynamic performance noticeably. I occasionally fly a 30+ year old plank 1/2A on a TeeDee and whatever 15 or higher % nitro fuel I have. Lines are 0.010 solid wire about 42' long, and no problem. Wing is 1/8" sheet about 200 sq in - you wanna see flexing dihedral? Weight is just over 4 oz, dry. It's an original, but generally inspired by Dick Sarpolus' similar models, many of which appeared as articles in the old Flying Models magazine.

All-flying stabilator tail - which, btw, Sarpolus never used. VERY maneuverable, yet comfortable steady level flight and stable return from maneuver turns. I use either a Sullivan multi-hole handle at wide spacing or a handle I carved to match the model. Perfect (brand) aluminum 2" bellcrank, 1" stabilator horn radius. The proportion from bellcrank-to-pushrod radius to stabilator horn radius 'tames' response to comfortable.

For heavier models, the altitude is a more serious problem. A Classic-eligible ENVOY (by Alan Aldridge, from a magazine article plan ) flies very well at 10.5 oz dry, but consistent power from a TeeDee is hard to assure up here. Re-dimensioned the control linkages when I built it. With reliable power, it feels as solid as my .35 and .40 stunters, just doesn't pull as hard. ENVOY is about 225 sq in.. Same line length and material - it isn't line length that's the problem. I'm tempted to chop the model up to put a NorVel or AP into it. A bunch of work - it would also need a larger tank. If I get really motivated, I might build a similar, but own-design, 1/2A stunter for "modern" power and Spiderwire-type lines. I've found that my own designs fly at least as well as - often better than - comparable models in the same categories...

John, I'm sorry that my trying to understand things troubles you. It's part of what I enjoy in the hobby. If I tend to see math that applies to our situation, that might just help another flier understand a bit better, why not? Just doing a thing the way it has worked before can become boringly repetitive, to me anyway, and not solve some typical quirks. Some low intensity studies I've done over the last 50+ years work beautifully for me, and adapted well for flying buddies over the years. That adds to my own enjoyment and confidence.

We share, after all, a hobby, each in our own most enjoyable ways... no?
Old 08-19-2015, 11:20 AM
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One thing I didn't see mentioned is when you are trying different size bellcranks and control horns move the bellcrank to maximum deflection each way and make sure the force is not being transmitted to the stab/elevator.

George
Old 08-20-2015, 09:59 PM
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I don't really agree that the lines need to be shorter - after all, this is a Norvel 061 with about 3 times the power of a traditional 1/2a trainer. Even in a decent breeze, 42' lines should be fine.

Theres lots of good advice here, but I suspect the 31% CG might've been a major part of the problem. I certainly wouldn't shorten the lines without first trying it with a more forward CG.
Old 08-22-2015, 01:51 PM
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Much obliged, Steve and George. I'll leave the bellcrank and the lines as they are so that the only variable on my next test flight will be the shifting of he COG forward to 17%. Now if we could just get some decent weather.

Davey...
Old 08-26-2015, 04:06 AM
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Originally Posted by DaveyMo
Much obliged, Steve and George. I'll leave the bellcrank and the lines as they are so that the only variable on my next test flight will be the shifting of he COG forward to 17%. Now if we could just get some decent weather.

Davey...
While you are moving the CG you might want to take the time to ensure that everything else is lined up correctly.

Yes, 31% seems a bit tail heavy and would make it twitchy (for me at least). Good luck.

George
Old 08-27-2015, 06:44 PM
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Hello All:

Success with a brace of flights today on 42' of line! Correcting the COG gave me much better handling and far fewer hair-raising approaches to the ground! The first flight seemed nose heavy so I had to adjust the lines for slight up elevator on the second flight. Worked like a charm. Perhaps I need to shave a little weight off the front end.

Engine: Since I moved the engine forward on this tail dragger, fuel draw seemed weaker at startup. I'll probably raise the tank 1/8" or so.

By the way, Lou mentioned Dick Sarpolus above. This is one of Dick's designs. I'll keep a copy of your discussion on component proportions in mind in future projects.

Thanks all for the great discussion - this is truly a "happening place"!

Davey Mo...
Old 09-04-2015, 06:51 PM
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wondering, does the outside wing have any weight in it to offset the weight of the lines? Did I miss you mentioning this before?
Old 09-04-2015, 09:06 PM
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I'm also interested to hear...

Tipweight might not be necessary - the upper cylinder and tank are outboard of the model's centerline, no? Spiderwire lines are nearly weightless, too.

Tipweight may be another thing I've overthought (?) (Much of my Army career was in places where opportunities to fly weren't frequent. I could think about and try to understand things. I got more benefit in the infrequent flying opportunities ...And I could to test ideas. Many didn't work, or were more effort than they were worth. What I offer is what did work well.)

You can 'pre-set' tipweight to balance line weight without numbers. This works best for larger models, tho, as you are likely to have a spare empty reel around, and an idea of your flying lines length and diameter (An empty spare reel is used to balance the weight of the reel with the lines on it.)

So, turn the model upside down on a level surface so it can rock on the fuse top and rudder. Put the reel with lines centered halfway from the fuse center to the leadout guides. Center the spare, identical empty reel the same distance from the fuselage center on the outboard wing. Match any line clips or connectors side-to-side too.

If the inboard wingtip sinks to the table surface, add weight at the outboard wingtip until it is close to balanced, or very slightly outboard heavy.

The principle - As the model flies fairly low and level, we carry half the line weight at the handle. The inboard wing's line guides support the other half. It's the big kid-small kid seesaw situation.

Half the line weight at full distance matches full line weight at half distance. If the model balances on its centerline in flight, it will not tend to roll inward due to line weight.

CL models usually need tipweight weight to balance the half of line weight carried at the leadout guides. But, I did have a very light, small .15 profile where the engine and tank overbalanced line weight. A small amount of weight in the inboard tip balanced the model - it flew great. This is rare, though.

This works best for fairly low level flight. Our stunt maneuvers change the strength and directions of many forces in very brief time. CL models fly and maneuver upright and inverted - "insides" and "outsides" - equally. Balancing line weight as above sets your model at the center of the range of those changing forces.They vary equally both ways from neutral level flight.

(Again, this is not precisely accurate, but very close for practical purposes. It does work well, dependably.)
Old 10-18-2015, 11:05 AM
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Hello All:

I tried a few more flights of the diesel Junkers and am convinced I can get better handling (still a bit too twitchy, though much improved by the advice here). I've ruled out neurological disease on my part, so that means the airplane needs further attention!

While thumbing through an old Brodak catalog recently, I ran into a discussion of a phenomenon called "hunting." What the term basically means is that the aircraft is searching for a level flight but can't find it due to over control or a design factor. The writer suggested three solutions.

1) A larger bell crank. In this thread above, Lou's argument in favor of a larger bellcrank is compelling, so I placed one of those (3") on order.

2) A slightly larger hole in the control horn. This would introduce some elevator sloppiness and reduce any inadvertent control inputs (shaking hand, etc.) on the part of the flier.

3) Misalignment of flight surfaces. The article writer thought this problem could be difficult to detect and the hardest modification to make. But I tried to evaluate my plane for alignment with simple tools, and it seemed to be OK, at least by eyesight.

So, I'll take the easy advice in the first two and fly with it. Will let you know how it goes.

Davey Mo....
Old 10-18-2015, 05:34 PM
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Amazing you are going to ignore the very simple and probable solution of just one test flight with the lines just a bit closer together at the handle before you start rebuilding whole linkages. That only takes minutes at the field.

Just one more personal thought and opinion. This is a forum after all and forums are indeed all about opinions. The idea of deliberately adding slop to a control system in an attempt to prevent huntin or PIO is a mistake.

Just one short flight with the lines a little closer at the handle is all its gonna take to convince you

John

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