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Swapping out a flat stab for an asymmetrical stab?? - 2/25/2011 4:03 AM   
rustyrivet


 

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Status: offline 		I wish to build a custom plane by enlarging the plans from an 80" Sig Kadet Senior to about a 105" or 110" wingspan plane. But, I really want a very slow and floating kind of plane that will more resemble the flying charachteristics of the Telemaster. The Kadet has a flat stab, while the Telemaster has an asymmetrical stab. It is clear to see in a Youtube Hobby Lobby video of the 96" Telemaster how the tail of the plane quickly lifts up during the take-off roll down the runway. The landing can also practically be made as a steady hover into a light wind.

Not being an aircraft designer, I was wondering if I'm over simplifying things a bit by assuming that I should merely just install an asymmetrical stab onto the Kadet to get the same easy flying/floating aspects. (??)
What I DON'T want to do is spend 9 months completing a custom plane...... only to find out during its maiden flight that I created a monster that flys crazy.





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RE: Swapping out a flat stab for an asymmetrical stab?? - 2/25/2011 5:55 AM   
BMatthews



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Status: offline 		First off it's not an assymetrical stab. It's a stab with a lifting airfoil.

Second, it's not the airfoil on the stabillizer that allows the ST to fly like it does. It's due to the light wing loading and the long tail and the big stabilizer area that allows the balance point to be located further back than on many other designs. The long tail and big stab area produces a higher value for a feature called the "Tail Volume Coefficient". And with the balance point being relatively far back compared to many other designs it means the stab is lifting up at all times. So the designers saw fit to give it a lifting airfoil to allow it to do its job more easily.

But even more than using a rearward balance point and lifting airfoil on the stabilizer the flyng charactaristics you described come from a low wing loading for the model's size range. By making the Kadet larger you will gain from the "scaleing effect" and assuming you can build the model to come out realtively light so that the wing loading is on the lighter side of the allowable range for the new size then it will fly slow and floaty. And since the Kadet Sr uses mostly built up structure instead of gobs of sheeting and lite ply if you build the big version the same way it's almost guaranteed that you'll end up with a light model. In fact it may be difficult to make it properly heavy enough to avoid a "calm air only" model. Although a model that floats a little as you describe wanting will not be a good model in blustery conditions anyway.

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RE: Swapping out a flat stab for an asymmetrical stab?? - 2/26/2011 12:56 AM   
rustyrivet


 

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Status: offline 		Wow.....you sir sound like you know something about aviation! Pardon my ignorance as I took the simple route and thought that the "asymmetrical" shape of the stab (ie; having the flat bottom and the rounded top) IS the substancial reason for the tail of the plane to lift. But from what you explained, I do now understand that the light and long tail of the Telemaster with the CoG located further back is an important part of the equation.


Anyway; today I had placed my 63" Sig Seniorita next to my 72" Telemaster. After carefully comparing the two styles, I think I have figured out what aspects of the two that I like, and will now try to combine these attributes into one plane. I like the visible stick construction of the Sig through the translucent red covering, but the long tail and gracefully endless wingspan of the Telemaster too. Sooooo....from the Telemaster plans, I now plan to enlarge the 95" Tel Senior another 15" or 20" to 110"-115". I will build this Telemaster with the stick construction, leaving out as much ply surfaces as possible. It will have a rounded nose, and the see-through red Monokote covering of the Sig Kadet. I'll finish the plane off with the traditional Sig kadet french-curve black patterns. I'll call my completed 110" plane a "Kadetmaster" . Hmmm..... but some how that conjurs up images of a macho-sadistical guy who abuses young men at the dorm. Ummmm......."TelleKadet"??


I appreciate your input, and anthing else you'd like to add is welcome. My main challenge is to build the plane structurally sound but yet light. With little flying experience, I have little knowledge of what is sturdy enough to withstand stress....and so have a tendency to build too heavy.

Here is a photo of my 89" AstroHog enlarged from the original 71" plans. It's a bit heavy at 19.5 lbs dry and 21 lbs with fuel, but flys very well any way. I removed half of the dyhadral from the wing. The wing breaks down with a Gator tube. Bending 1/4" piano wire into gear was quite a learning excperince too!




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RE: Swapping out a flat stab for an asymmetrical stab?? - 2/26/2011 4:50 PM   
Rodney



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Status: offline 		The biggest advantage to having a airodynamic shaped stab/elevator is that you can have a much thicker (stronger) main spar which can be important on larger models.

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RE: Swapping out a flat stab for an asymmetrical stab?? - 2/26/2011 7:06 PM   
BMatthews



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Status: offline 		It sounds to me like you want a model that flies slowly for calm days to let you enjoy seeing a "balsa overcast" flying overhead and to perhaps do some thermal soaring once the engine cuts. Additionally you enjoy building with lots of sticks to get that sort of look. From all this you just described yourself as a classic guy looking for an old timer model to put RC into. There's a huge number of really great looking designs from the old spark engine free flight days that folks have set up for RC using either just rudder-elevator-throttle or with a reduction in dihedral to more sensible amounts have added ailerons as well. And the designs are so full of character that you smile every time you look at the model. And they are already set up as stick built models so there's no need to try to fill in important design details.

To get some ideas on this alternative check out the four pages of plans and parts kits starting at http://www.bhplans.com/GMPg1.html . Links to the other three pages are in the upper right corner of the link to page 1. I understand that he can also supply enlarged versions of both the plans and parts if you wish. You'd need to email him for such arrangements if he doesn't list them that way.

For example a double sized 100 inch Brooklyn Dodger powered with a 1.20 four stroke would be amazing in the air. Don't worry too much about the very short looking nose. The final balance point on such designs is back around the 50 to 60% chord point. So the actual nose length is longer than you suspect upon first glance.

If you like the idea of an old timer like this but nothing at Bob's site really stirs you don't despair. There's heaps of other classic designs of this sort that could be converted to RC and scaled up to 100 inch span. And they would all come with built in gentle flying manners and the ability to thermal soar once the engine cuts out or if you can set up the engine to tick over reliably at idle for long times and still throttle up at the end of a "gliding" session.

At 100 inch span a good target weight that would still allow for some thermalling ability would be around the 8 to 9 lb mark. And given that there's not a lot of wood and a lot of air in the models even a heavy builder should be able to meet that target. Going heavier will reduce the ability to thermal soar but the good manners for such a model would not go away until the high side of 34 to 14 lbs was reached. And even then it mostly just would not be a slow flying model anymore. It wouldn't get truly ugly to fly until you neared 17 to 20 lbs. But you'd have to go totally over the top on beefing up the construction to get anywhere near that weight.

Mostly the big mods you'd want to do for RC'ing an old timer design are simple and basic. Wing spars and the main longerons in the fuselage would be swapped for spruce or at least basswood to strengthen up these key parts. In some cases I'd look at redesigning the wing spars to make the wings more durable to flight loads caused by hard pullouts. But hopefully you avoid such things since these are gentle flying designs and not really intended for hard aerobatics. Although the odd gentle loop or barrel roll are certainly OK. I'd also look at slightly beefing up and triagulating the fuselage around the wing joints just to make the model more durable. But again this is mostly about adding a few diagonal sticks and won't add much weight. And in some desigsn you would not need even that much.

So check out some of the old timer models and see what you think and if anything strikes your fancy.

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RE: Swapping out a flat stab for an asymmetrical stab?? - 2/26/2011 7:58 PM   
BMatthews



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Status: offline 		And I just found a thread on another site for a guy doing a 108 inch Dallaire. Reading down through the whole thread may tell you if you like the old timer idea.

http://www.rcgroups.com/forums/showthread.php?t=1387923

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RE: Swapping out a flat stab for an asymmetrical stab?? - 2/27/2011 8:14 PM   
rustyrivet


 

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quote:

ORIGINAL: BMatthews

A) ......It sounds to me like you want a model that flies slowly for calm days to let you enjoy seeing a ''balsa overcast'' flying overhead and to perhaps do some thermal soaring once the engine cuts.......


B) Additionally you enjoy building with lots of sticks to get that sort of look....

c) From all this you just described yourself as a classic guy looking for an old timer model to put RC into.......







BM,

In reply to your input:

A) Yes, I want a sloooooww flying plane. Mainly because I've never been able to master flying them. Guess I'm just a slow learner, and my hands shake from fear if I'm not on a buddy box. I'm in this hobby for the building aspect of it.....which is stange to 90% of enthusiasts today.

B) Yes, but also the stick construction is light weight as well as interesting to see through the translucent Monokote covering.

C) Not really; Just happens that the first R/C plane that I ever built was a Seniorita.....20 years ago. (-flown once, and I still have it) The 60's -70's look is about as "old-timer" as I want to get. I guess each generation has his preference favorites. Im 57 years of age. Perhaps if I was 77 and listened to big-band music, I'd like some of those Ben Buckle and Cleveland Company style planes you are suggesting. LOL

Thanks for your help. I admire your knowledge in aeronautics.

......................











On the topic of the Sig....here's a 7 year old photo of the Seniorita wing that I opened up to install ailerons 13 years after I built it. I also applied a block to convert the wing from rubber-band to a bolt on. Not knowing better as a beginner at the time, I had originally built it as a 3 channel as Sig suggested;



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RE: Swapping out a flat stab for an asymmetrical stab?? - 2/27/2011 8:38 PM   
BMatthews



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Status: offline 		Fair enough, we all build what we find looks right to our own eyes.

As for learning to fly well it sounds like you may not be approaching each flight with the right mental attitude. Learning to fly is more than just watching and reacting. If you only react to what the model does then you're not really in control and you'll always be behind the model. You need to plan ahead to know you want to turn "there" at a given bank angle and then make the model follow your mental image of how you want the model to turn and what heading you want it to have as it comes out of the turn. Setting yourself goals for each flight from takeoff to touchdown is quite important if you're finding that you feel lost when flying. For most of us we're OK with planning no more than a few seconds and each maneuver ahead. For others, perhaps such as yourself, a more complete and longer term flight plan may help in mastering the model. Try planning how you'll take off, what angle and power setting you want to climb at, what altitude you'll level off at and then what sort of pattern you'll fly for that flight. A great exercise is to do turns that form a figure 8 just out in front of you. By turning alternately right and left at consistent size circles and correcting as needed to achieve this you set yourself goals and you become the master over the model instead of the other way around. Work out a mental image before the flight of how you want the model to look during the climb and when doing the figure 8 turns and then control the model to achieve that image. And work at avoiding tunnel vision focused on just the model. You need to be aware of the world around you out of your peripheral vision as well so you know where over the field you're flying and can work the controls to put the model where you want it to be instead of allowing it to wander. Along the way you'll learn to adjust for wind and other factors. The landing approach circuit is another place where you need to have a strong mental image of what the model is supposed to do and it pays to plan that aspect ahead of time and base your turn locations on the field obstructions and wind strength to set how high you want and what sort of glide slope you come in at. At some point from this pre-flight visuallizing you'll gain more confidence and you won't need to plan each maneuver so far in advance. But without this pre-planned image of what the model should do it won't matter how slow a model you build. It'll still be the model that is the master and you that is the servant instead of the other way around until you learn to take control.

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All Forums >> RC Airplanes >> Scratch Building, Aircraft Design, 3D/CAD >> Swapping out a flat stab for an asymmetrical stab??
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