Aerodynamics Discuss the concepts of aerodynamics here

Mini-Telemaster aerodynamics

Old 07-25-2011, 01:30 AM
  #1  
JackM
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Question Mini-Telemaster aerodynamics

I started flying with one of the little micro Champs. No problems

Then I bought a 2nd hand 4 CH Mini-Telemaster (45" span) which had problems. I fixed most of the problems and am now flying it with the occasional crash and fixing it.

CG being was way back. Goop (epoxy?), lots of it, holding the tail on, was carefully removed and tail carefully re-attached helping a little. Weight was added to the nose (brass weights) because I couldn't move anything farther forward to make a difference. The plane now balances on the wing spar and is now about 1oz overweight which I don't think is a problem.

Although I can now fly it it still has issues.

In flight it seems to porpoise. Trimming is difficult. I feel like I am always fighting this in flight. I tried a smaller 7X5 prop with negetive effects so have remounted the 8X6 prop I was using. I am thinking of reducing the throw on the elevator.

In wind over about 5mph this plane gets bounced around something terrible. Up wind or down wind it isn't too bad but make a turn and watch out! Once, the plane literally tumbled. I am wondering if eliminating the wedge shaped wing tips might help steady the plane in the wind. I am also considering adding weight to increase wing loading

I am now building a replacement trainer plane. A 4 CH Herr Cloud Ranger. It is similar to the Mini-Telemaster. It has about half the dihedral, higher wing loading, smaller wedge at the wing tips. Shorter distance from CG to tail feathers. This one will eventually have floats.

I am wondering if anyone can offer some insight as to the porpoising and wind handling of the Mini-Telemaster and how the Clound Ranger should compare.

I am especially interested in why the wedge shaped wing tip on an aileron wing? This makes no sense to me since we have dihedral for self righting. I assume this wedge increases the dihedral effect and increases the dihedral effect a lot in a turn.

Thoughts?

Jack
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Old 07-25-2011, 01:42 AM
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xmech2k
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Someone more knowledgable is likely to come in with the more sure answer to this, but are you sure that is the right CG? I thought I read that Telemasters use their horiz stabs oppositte of most planes, where most planes H-stabs create an aerodynamic down force on the tail, Telemasters H-stabs are lifting surfaces, so that would mean the CG should be further back.
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Old 07-25-2011, 01:45 AM
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rcers
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Both are excellent fliers. I have had both.

The Telemaster is "lighter" in the air but suspect a decalage (Angle of attack of the wing and stab and their relationship) issue if you get the porpoising under control.

The Cloud ranger will handle more wind but is less docile. I just suspect the 2nd hand Telemaster might have been a bit misaligned from the get-go.

The Cloud Ranger was my first electric RC plane. Now I am 100% there.

Mike
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Old 07-25-2011, 02:25 AM
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JackM
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Mike,

Thanks for your reply! The decalage seems reasonable. I don't have plans and mounted the stab flat on the surface of the fuse. This puts the H stab at 0deg and the wing at about 2deg AOA. Given the problems I've had I may fly it a couple more times and salvage the parts for future use.

Your comments on the Cloud Ranger confirm my suspicions of it's flight characteristics. Building has been a breeze except for working out the fire wall to hold an outrunner motor which took a bit of thinking to work out just how to do it.

Jack
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Old 07-25-2011, 03:21 AM
  #5  
rcers
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Snap some pics for us....
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Old 07-25-2011, 04:01 AM
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Larry3215
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the teli-masters are designed to balance further back than most planes.

Balancing on the spar will make it nose heavy - which will cause porpoising.

Check the manual and balance it where its recommended. It will fly perfectly at that cg
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Old 07-25-2011, 04:02 AM
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Oh - you might also check to see if your up/down thrust angle is off. That can cause porpoising as well.
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Old 07-25-2011, 09:05 AM
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+1 on what Larry said.. A too far forward CG can cause porpoising. It's a mistake to assume that all planes should balance at 25 -30% MAC , or 'on the spar' or any other 'rule of thumb' (as is often advised).. The size of the tail and the length of the tail moment arm have a big influence on optimum CG location. Planes with larger tails on longer arms should balance further back. Balance as per the plan/instructions or failing that use one of the online calculators.
Porpoising can also very often be 'pilot induced'. Does it porpoise if you take your hands off the controls and let it fly itself? If not then it must be you that's causing it.

A too far forward CG could also exacerbate the poor handling in the wind though any very light wing loading model with high stability will get bounced around in the wind, it's pretty much unavoidable.

Forget the wing tips, they are not part of your problems. The upswept wedge wedge shaped design is intended to reduce drag by pushing the tip vortices outward. It probably has some minor 'dihedral like' effect but nothing significant.

Steve
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Old 07-25-2011, 11:57 AM
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JackM
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Since this telemaster was bought 2nd hand, was an arf, there weren't any plans. I looked at the manual on line and there wasn't anything about CG. The H stab is a flat plane so assume it is not lifting type. Spar is at about 30% MAC. Can't imagine further back after reading Andy Lennons book and others. Wish I had documentation on where CG should be. Thrust angle is as designed.

Jack
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Old 07-25-2011, 01:27 PM
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JetPlaneFlyer
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Jack,

Instructions say

The CG is located at 2-1/4 back from the leading edge
of the wing
More info on the 'porpoising' might help.. 'hands off the sticks' does the model fly in a series of stall - dive -climb -stall - dive - climb? Or does it gently 'porpoise' (phuegoid oscillation) without ever pitching sharply up or stalling?

Assuming CG looks ok....If it's flying in a series of stalls then it either just needs some down trim or it needs some downthrust on the motor. If it only does it when you have power on then it's downthrust thats needed. if it stalls even when gliding then it's down trim that's needed.

If 'hands off' it gently porpoises without stalling then that's dynamic stability issue which is a little bit more complex to solve but tweaking the CG may help... this would be quite unusual on this type of model, it's more common in high performance sailplanes.

Steve
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Old 07-25-2011, 01:40 PM
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rcers
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And remember the Telemaster lifting tail allows a rearward CG. The mini and the micro versions both have a flat surface and thus a more common CG.

My Sr. Telemaster is 6+ inches back - freakishly rearward. Floats like a feather

Mike

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Old 07-25-2011, 02:01 PM
  #12  
JackM
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Steve,

Thanks for the CG location! That is the location of the wing spar and the current CG.

I think this is a trim issue based on what you say. I now need to fly the plane on a clam day which has not been offered by the wind gods for a while. Being a beginner it is tough to trim a plane in windy conditions while trying to keep from crashing! In calm conditions I will be able to observe the flight better. The one time I flew this plane at dusk in calm conditions it ran out of electrons and glided beautifully and was very controlable.

I am looking forward to the Cloud Ranger and hope it has a bit more wind penetration.

Thanks!

Jack
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Old 07-25-2011, 02:03 PM
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JackM
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Steve,

The instructions you linked are different than what I had previously found. Interesting and very helpful!

Thanks!

Jack
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Old 07-25-2011, 02:15 PM
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Originally Posted by JackM View Post
I am looking forward to the Cloud Ranger and hope it has a bit more wind penetration.

Jack
O yes - it is much happier in the wind. It is much more aerobatic too.

You have me now wanting to build one again and stick floats on it.... You going with the Herr floats?

Hmmmmmmmmmmmm

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Old 07-25-2011, 02:34 PM
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JackM
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Yes, I built the Herr floats in about 3hrs. Very easy build but could have been made easier/faster/better if the nose block was designed a bit shorter and another station added to the hull. I was planning to use monokote on the floats as per Herr's instructions but am considering a liquid finish. I also need to make a much better rudder(s?) than came in the kit.

I am very interested in sea planes and my favorite planes are the DHC-2 and Canadair CL-215 CL-415which I hope to build some day. I live near some easy places to land on water and the nearest field is about 35min drive so I plan on flying off water as soon as I feel confident enough to do so. First scale plane on floats will be a Super Cub.

Regards,

Jack
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Old 07-25-2011, 02:42 PM
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Cool - and you have me thinking. We have a large pond in our neighborhood with surrounding area with no homes. Would be fun....

I need a good build anyway. I could have both of them framed up on a Saturday.

Could do lights as well. Hmmmmmmm
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Old 07-25-2011, 02:58 PM
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JackM
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I built my Cloud Ranger w/o the hatch in the belly. I have a flat deck inside the fuse that will hold both the ESC-BEC as well as the battery allowing for positioning to CG.

I will try to post pictures tonight after I join the wing halves.

Jack
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Old 07-25-2011, 03:00 PM
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Great pics rock!

I would do the same on the hatch. The top is a much better spot for the battery especially with floats.
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Old 07-25-2011, 03:10 PM
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Tail airfoil shape makes no almost no difference to the required CG location.. A flat plate tail can lift just like a flat plate wing can.

Anyway.. Jack, i think you are right to wait for a calm day to sort the trim. on the face of it the most likely cause based on what you have said so far is that the motor needs some downthrust.

Steve
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Old 07-25-2011, 03:25 PM
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JackM
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By a flat air foil lifting, is that just or mostly due to AOA? When I think lifting or falling H stab I think in terms of semi-symetrical or flat on one side airfoil which some planes appear to have.

The motor does have some down thrust (haven't measured) and about 3deg side thrust. One crash ended up with broken firewall and when I fixed it I was very careful to get the motor back where it was originally. I am a machinist/modelmaker so am used to working close tollerances and measuring.

I have a couple of books on aerodynamics but they are very limited in scope.

Jack
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Old 07-25-2011, 03:27 PM
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Originally Posted by JetPlaneFlyer View Post
Tail airfoil shape makes no almost no difference to the required CG location.. A flat plate tail can lift just like a flat plate wing can.
You are right - I should have said the tail setup impacts the neutral stability point and this allows a more rearward CG.

For those bored a good discussion here:
http://www.rcgroups.com/forums/showthread.php?t=1440260

What I know is my 45% MAC CG on my Sr. Telemaster would be challenging on the Mini Telemaster.

Cunards are a good example of this.

Mike
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Old 07-25-2011, 03:28 PM
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Originally Posted by JackM View Post
By a flat air foil lifting, is that just or mostly due to AOA?

Jack
Yes - just like sticking your hand outside the car window and changing angles.

This is also how the flat foamies fly.
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Old 07-25-2011, 03:35 PM
  #23  
JackM
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Mike,

Thanks, I like learning!

Jack
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