Telemaster 40 Mod
10-30-2007, 11:03 PM
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Telemaster 40 Mod
I thought I'd build the Telemaster 40 I've had on the shelf for awhile but since I already have a Senior Telemaster I think I'll do some serious modding,,, starting with dumping the lifting tail.
Anyone know how to recalculate the CG once I change the tail to a conventional flat stab?
Anyone know how to recalculate the CG once I change the tail to a conventional flat stab?
10-31-2007, 04:42 PM
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RE: Telemaster 40 Mod
This is going to be a fun one!
First of all, the Telemasters tails DO NOT LIFT in the same direction as the wings. If this were true, the airplane would have an extremely aft c of g, and would fly very funny. Having had the 40 size, I know what I'm talking about. Let me give you some theory, before I actually answer your question.
It all has to do with the center of lift with relation to the center of gravity. Center of gravity is where the model actually balances. The center of lift is the point on the wing where the lifting force is averaged. By this, I mean that if you think of lift as the opposite of gravity, this is the point where the lift is balanced on the wing. Just replace gravity with lift, and balance the model again. Of course we can't actually do this, because there is no lift with no airflow. The other reason we can't do this is because the center of lift MOVES with the speed of the air, the angle of attack, and the position of the controls on the wing.
Now, think about landing a sport model or a trainer. The slower you fly, the more up elevator you need to hold the nose up. You are actually pulling the tail down, but the effect is the same. The reason for this is that the center of lift is aft of the center of gravity. Meaning that the model is wanting to drop the nose because the balance point is forward. The center of lift moves aft as the model slows and the angle of attack increases. Conversely, the center of lift moves forward as the model speeds up and the angle of attack is reduced. This arrangement is what gives the plane stability.
If you're familiar with 3D models, those guys move the cg aft as far as they can stand it and still be able to control the plane. In some cases, they move it aft of the center of lift and the plane becomes unstable. These planes are hard to land because the nose wants to rise as the speed bleeds off. This is because the balancing force of the tail actually has to hold the tail up, instead of holding the nose up.
Having said all that, we both know that the Telemasters are stable fliers with no bad tendencies, especially on landings. That's because it is balanced as the first paragraph describes. That being the case, the tail is actually installed upside down from the way it should be to provide the lift in the right direction. I know this, because the Telemaster I had would rotate much faster in the down stick direction than in the up stick direction. Why? Because the tail is more efficient in lifting that direction. The wing is flat bottomed, so it should, you would think, pitch up easier than down, but it doesn't.
Now that I have given you a crash course in aerodynamics, I would say that to make the Telemaster a better flying plane, use a slab type or symmetrical airfoil on the horizontal tail. Because of the type of airplane, and the speed envelope it flies in, there is no advantage to a symmetrical tail other than looks. Flat sided tails work just fine at these low reynolds numbers, and they react symmetrically to control inputs. To answer you question directly, the center of gravity should be at the same point no matter which type of airfoil you choose. The rule of thumb on a plane like this is around 30% chord of the wing. You can start there, and fine tune it to your liking.
First of all, the Telemasters tails DO NOT LIFT in the same direction as the wings. If this were true, the airplane would have an extremely aft c of g, and would fly very funny. Having had the 40 size, I know what I'm talking about. Let me give you some theory, before I actually answer your question.
It all has to do with the center of lift with relation to the center of gravity. Center of gravity is where the model actually balances. The center of lift is the point on the wing where the lifting force is averaged. By this, I mean that if you think of lift as the opposite of gravity, this is the point where the lift is balanced on the wing. Just replace gravity with lift, and balance the model again. Of course we can't actually do this, because there is no lift with no airflow. The other reason we can't do this is because the center of lift MOVES with the speed of the air, the angle of attack, and the position of the controls on the wing.
Now, think about landing a sport model or a trainer. The slower you fly, the more up elevator you need to hold the nose up. You are actually pulling the tail down, but the effect is the same. The reason for this is that the center of lift is aft of the center of gravity. Meaning that the model is wanting to drop the nose because the balance point is forward. The center of lift moves aft as the model slows and the angle of attack increases. Conversely, the center of lift moves forward as the model speeds up and the angle of attack is reduced. This arrangement is what gives the plane stability.
If you're familiar with 3D models, those guys move the cg aft as far as they can stand it and still be able to control the plane. In some cases, they move it aft of the center of lift and the plane becomes unstable. These planes are hard to land because the nose wants to rise as the speed bleeds off. This is because the balancing force of the tail actually has to hold the tail up, instead of holding the nose up.
Having said all that, we both know that the Telemasters are stable fliers with no bad tendencies, especially on landings. That's because it is balanced as the first paragraph describes. That being the case, the tail is actually installed upside down from the way it should be to provide the lift in the right direction. I know this, because the Telemaster I had would rotate much faster in the down stick direction than in the up stick direction. Why? Because the tail is more efficient in lifting that direction. The wing is flat bottomed, so it should, you would think, pitch up easier than down, but it doesn't.
Now that I have given you a crash course in aerodynamics, I would say that to make the Telemaster a better flying plane, use a slab type or symmetrical airfoil on the horizontal tail. Because of the type of airplane, and the speed envelope it flies in, there is no advantage to a symmetrical tail other than looks. Flat sided tails work just fine at these low reynolds numbers, and they react symmetrically to control inputs. To answer you question directly, the center of gravity should be at the same point no matter which type of airfoil you choose. The rule of thumb on a plane like this is around 30% chord of the wing. You can start there, and fine tune it to your liking.
10-31-2007, 05:36 PM
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RE: Telemaster 40 Mod
Thanks for the in depth explanation Not24. I admit though that I'm still confused and it will take some serious thinking on my part to sort it out. In any event it seems that changing the stab will not cause problems.
When finished the plane will bear little physical resemblance to a stock Telemaster. The fuselage will still be there but it will be heavily disguised with curved surfaces. Those funky wing tips are going to bite the dust as well.
Should be a fun mod.
When finished the plane will bear little physical resemblance to a stock Telemaster. The fuselage will still be there but it will be heavily disguised with curved surfaces. Those funky wing tips are going to bite the dust as well.
Should be a fun mod.
10-31-2007, 10:33 PM
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RE: Telemaster 40 Mod
Don41
I know this is not much in the way of modifications, but it can and does make the old reliable TM40 a lot more responsive. I've had 2 now, both built from kits, one I sold in 1990 when I found I couldn't afford RC and full scale rentals at the same time, the other built in 2003 and died a painful death due to a woven wire fence jumping up in front of it !
Any way the first was powered with an Enya ringed 40, the second with a Thunder Tiger Pro 46, both were given the same subtle but effective mods.
1) All components were 0 degrees, it required approx. 1/2 inch of rise at the rear of the wing saddle to eliminate all incidence (a simple matter of a straight edge under the horizontal stab and building up the wing saddle until it's level.)
2) The engine was placed with a "smidge" of right thrust but 0 down thrust use the same method of finding this level For the engine as was used for the wing.
3) When building the wing take 2 of the 4 inch diehedral out, more would probably be ok.
Both had flaps and performed fantastically, especially the 2nd one which was powered by the Pro 46, wit these mods it loses a lot of the "trainer" features, it WON'T come of the ground by itself, it will run around on the ground at full throttle all day with the tail up if you don't give it up elevator, and once in the air, don't expect it to "recover" from ANYTHING it will just go where yo point it, and it's a blast.
Enjoy, Dan
I know this is not much in the way of modifications, but it can and does make the old reliable TM40 a lot more responsive. I've had 2 now, both built from kits, one I sold in 1990 when I found I couldn't afford RC and full scale rentals at the same time, the other built in 2003 and died a painful death due to a woven wire fence jumping up in front of it !
Any way the first was powered with an Enya ringed 40, the second with a Thunder Tiger Pro 46, both were given the same subtle but effective mods.
1) All components were 0 degrees, it required approx. 1/2 inch of rise at the rear of the wing saddle to eliminate all incidence (a simple matter of a straight edge under the horizontal stab and building up the wing saddle until it's level.)
2) The engine was placed with a "smidge" of right thrust but 0 down thrust use the same method of finding this level For the engine as was used for the wing.
3) When building the wing take 2 of the 4 inch diehedral out, more would probably be ok.
Both had flaps and performed fantastically, especially the 2nd one which was powered by the Pro 46, wit these mods it loses a lot of the "trainer" features, it WON'T come of the ground by itself, it will run around on the ground at full throttle all day with the tail up if you don't give it up elevator, and once in the air, don't expect it to "recover" from ANYTHING it will just go where yo point it, and it's a blast.
Enjoy, Dan
10-31-2007, 11:17 PM
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RE: Telemaster 40 Mod
Thanks DIR. I was pondering going to 0.5 degrees of dihedral and 0.5 incidence. Glad to see others have done that sort of tinkering already. I cut the dihedral in half on my Senior but I wish I had taken out even more. Do you recall how much throw you put into the flaps of your 40s?
I'm fitting my OS 52 four stroke in the plane but had planned on using right and down thrust. I guess I can leave out the down thrust for the maiden flight.
Like you I'm trying to dump the trainer aspects of this one but I'm also going to give the fuselage a complete make over. Basically I want to build another plane without ending up with two Telemasters. Since I already own the kit I thought this would be a fun build. Actually I guess it's called kit bashing??
Regards
I'm fitting my OS 52 four stroke in the plane but had planned on using right and down thrust. I guess I can leave out the down thrust for the maiden flight.
Like you I'm trying to dump the trainer aspects of this one but I'm also going to give the fuselage a complete make over. Basically I want to build another plane without ending up with two Telemasters. Since I already own the kit I thought this would be a fun build. Actually I guess it's called kit bashing??
Regards
11-01-2007, 09:17 AM
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RE: Telemaster 40 Mod
As I recall they were 45 degrees+, can't have too much unless they're deflected too far on take off is my opinion. Got a question for you, I've already posed this somewhere else and was answered by MikeFreas (don't ask me WHERE or how to get there cause I don't know, I'm not big on computer stuff !!! ) fortunately I had the good fortune of requesting reply by email so I got returns by him and you.
My question, after cartwheeling my senior telemaster a couple days ago and busting the fuse just ahead of the stab, I have this thing in my head that says shorten the fuse (I think 12 inches would be about right) what do you think ? Mikes only comment was a concern of balance, but I THINK the balance point or CG location at the wing doesn't change, right? I know weight will have to be added to the tail and it will be far more than was lost by reducing the tail moment due to the "leverage" factor. That's no big deal, I'm guessing 10 or 12 ozs. will be removed and if I had to add 5lbs. it wouldn't matter, but where on the wing lies the the center of gravity??????? Same as it was, or different ?????
Regards, Dan
My question, after cartwheeling my senior telemaster a couple days ago and busting the fuse just ahead of the stab, I have this thing in my head that says shorten the fuse (I think 12 inches would be about right) what do you think ? Mikes only comment was a concern of balance, but I THINK the balance point or CG location at the wing doesn't change, right? I know weight will have to be added to the tail and it will be far more than was lost by reducing the tail moment due to the "leverage" factor. That's no big deal, I'm guessing 10 or 12 ozs. will be removed and if I had to add 5lbs. it wouldn't matter, but where on the wing lies the the center of gravity??????? Same as it was, or different ?????
Regards, Dan
11-01-2007, 11:07 AM
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RE: Telemaster 40 Mod
Rather than give you one of my gut feeling responses (I say it would work) I suggest you go to this site and crunch the numbers.
http://www.geistware.com/rcmodeling/model_calc.htm
http://www.geistware.com/rcmodeling/model_calc.htm
11-01-2007, 05:30 PM
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RE: Telemaster 40 Mod
ORIGINAL: D.L.R.
but where on the wing lies the the center of gravity??????? Same as it was, or different ?????
Regards, Dan
but where on the wing lies the the center of gravity??????? Same as it was, or different ?????
Regards, Dan
The long tail moment adds stability, so that means if you shorten it, you should probably move the cg forward just a little to compensate. You may find that it flies the best in the same location, but I'd start nose heavy, just as you would with any new model.
I matched my incidences on mine by changing the tail, not the wing. That way I didn't affect the thrust line or the angle of the fuselage with relation to the ground on takeoffs and landings.
11-02-2007, 04:21 PM
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RE: Telemaster 40 Mod
It's actually level. If you do what the other guy said, the tail would be lower than it would be with the wing incidence left alone. It makes it so that the tail can be way off the ground with the mains still stuck. I really don't remember which way the tail incidence was. I think it would have been positive, and I moved it to negative. The plane flew fine, but would have been better with a flat tail. Build the wing with no dihedral at all. It's not needed for someone who knows how to fly. Flaps were nice, but the plane didn't need them. It would have been better to put spoilers on the wings to help it land.
11-02-2007, 05:07 PM
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RE: Telemaster 40 Mod
Not24
I agree about the flaps but I have some experimenting to do so in they go.
I checked the incidence shown on the plans,,, it's four degrees on the wing and one degree positive on the stab. This is slightly different than the Senior so I emailed Hobby Lobby and they confirmed the 4 degree, 1 degree measurements.
At the moment I am considering a one half to one degree difference between the flat stab and wing. Probably zero before it's all said and done.
I have 1.0 degree dihedral planned but you may have a point, I may just zero that out.
BTW: I have checked a few of these design scenarios out in RealFlight 3.5 Telemaster. It's remarkable how much the characteristics change when these design changes are implemented. It'll be interesting to see how accurate the sim is when all is said and done.
D.L.R.
You proposed shortening your fuselage,,, did you try crunching some numbers in that calculator I mentioned?
I agree about the flaps but I have some experimenting to do so in they go.
I checked the incidence shown on the plans,,, it's four degrees on the wing and one degree positive on the stab. This is slightly different than the Senior so I emailed Hobby Lobby and they confirmed the 4 degree, 1 degree measurements.
At the moment I am considering a one half to one degree difference between the flat stab and wing. Probably zero before it's all said and done.
I have 1.0 degree dihedral planned but you may have a point, I may just zero that out.
BTW: I have checked a few of these design scenarios out in RealFlight 3.5 Telemaster. It's remarkable how much the characteristics change when these design changes are implemented. It'll be interesting to see how accurate the sim is when all is said and done.
D.L.R.
You proposed shortening your fuselage,,, did you try crunching some numbers in that calculator I mentioned?
11-02-2007, 10:41 PM
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RE: Telemaster 40 Mod
Don41, no but I will ,and thanks by the way. Got some stuff going on at the American Legion right now that requires my attention, we're being armed to the gills, we have the only M1 Abrams Main Battle Tank on display at ANY veterans orginization, and now we're in possession of a 4.2 inch mortar that has to be firmly attached to mother earth so it can't walk away.
I'll keep you posted when I get back to it, I've got a Lazy Tiger Cub on order and when it gets here getting it built will be my 1st priority since I think our local flying site which is city property is going to go away next year. Got to assure I have something I can fly (hopefully) out of my lawn.
Regards and again thanks for the calculator location.
I'll keep you posted when I get back to it, I've got a Lazy Tiger Cub on order and when it gets here getting it built will be my 1st priority since I think our local flying site which is city property is going to go away next year. Got to assure I have something I can fly (hopefully) out of my lawn.
Regards and again thanks for the calculator location.
12-12-2007, 05:23 PM
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RE: Telemaster 40 Mod
Why dump the lifting stab? Think about what the stabilizer does--it keeps the nose from rising (or, in other words, it holds the tail down). The idea behind the lifting stab is to get you a plane that won't go nose-up when you add power. Most models want to climb when you give them throttle. If you have a lifting stab, the additional speed will generate lift at the back (really, less down), so if it's done right, your trim won't change with different throttle settings. That's a good thing.
