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Old Jun 24, 2008, 10:34 AM
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United States, CO, Delta
Joined Oct 2005
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Ventus 6Mtr LET

Can any of you guys out there shot me any pictures of your Elevator install.I was hopefully going to use a standard size Servo.Plus if possible i did not want to cut to much on the tail.If i have to so be it.Anyway as scale as possible. Thanks Guys. As Always Paul
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Old Jun 24, 2008, 06:08 PM
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United States, MN, Minneapolis
Joined Dec 2002
266 Posts
elevator tail

No pictures but I sure would use a highest quality digital full sized servo in there. there should be plenty of room to mount it horizontally in the fin post.
elevators don't take that much travel so keep the servo arm pretty short.
If possible use ball links rather than clevis with 4-40 rod and hopefully a hollow carbon fiber tube over that.
strive for zero slop, that last thing you want this baby do is flutter in a high speed pass or something.
IMHO the elevator is much more important than most of the other flying surfaces.
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Old Jun 24, 2008, 11:35 PM
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Joined Oct 2005
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Elevator

Kevin! Thank you for the info.I was thinking of ball link.You just confirmed what i was thinking,i also like the idea of the Carbon Rod.Thank You Paul
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Old Jun 25, 2008, 12:03 AM
scalebldr
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Long Beach, Ca
Joined Nov 2005
170 Posts
Quote:
Originally Posted by paul dufek
Kevin! Thank you for the info.I was thinking of ball link.You just confirmed what i was thinking,i also like the idea of the Carbon Rod.Thank You Paul
HI have a look here http://www.soaringissa.org/Reference...udElevator.htm

Easy to do, another idea works just as well

Rick
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Old Jun 25, 2008, 12:23 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
Paul, the advise from Kevin is sound. I have the LET 6m Ventus and I use a carbon pushrod to actuate the elevator just like Rick has on his ASH26 in his link. However, I have a slightly different opinion than Kevin regarding servo size. I think you might find it tight to get a std size servo in the fin of the Ventus. I know I wasn't able to especially with the pre-installed rudder post in my Ventus.

From a DATA perspective, consider the following:

If you analyze the torque requirements of that elevator, I can guarantee you will see no more than 50inoz at 100 mph assuming your deflections are around +/-30 degrees! That Ventus won't fly at 100 mph unless it's in a vertical dive. Given the clevis at the servo end of the elevator control rod is likely to be only about 1/2" to 3/4" from the pivot point, the force you apply to the elevator control horn will likely be greater than the rated force of the servo (since the servo is rated at 1" from the pivot point). You will notice in Rick's pictures that the clevis is much closer to the servo arm pivot point than 1", increasing the forces applied to the elevator.

In my opinion, a mini dgital is ample for a 1:3 scale Ventus - something like the HS5245 or similar. These are rated around 76inoz at 6V. That means that if you placed a control linkage at 1" from the center pivot point of the servo arm and then attached the other end of the linkage to a control horn 1" from the hinge line, that servo could exert 4.75lbs of force on that elevator before stalling. As you shorten either the length of the servo arm clevis attachment point OR you shorten the control horn linkage attachment point, that force increases proportionally.

My 6m Ventus stab has an elevator that is 30" long and has an average chord of about 1.6".

If you go to this link: http://www.csd.net/~cgadd/eflight/calcs_servo.htm

and enter your data you will see the torque needed for such a small surface is very small. For my stab at 60mph with 30 degree deflection, it calculates out to 19 inoz. Not very much. In order to get a torque value equal to 76 in oz, the rating for a HS5245 at 1" servo arm/control horn length, I have to fly at 120mph AND deflect my elevator at 30 degrees ASSUMING that I have the control rod 1" from the servo arm pivot point and the elevator control horn is 1" from the hinge line!! I wouldn't have any wings left if I deflected the elevator 30 degrees at that speed!

At 100mph the torque needed is only 50 in oz giving you 40% margin. I personally feel that a standard digital on an elevator of a 1:3 scale sailplane is overkill. Some may argue that if you have the room then you should go as large as you can. I personally believe that mini digitals are perfectly adequate for the job. I have used them on MOST of my scale sailplanes without issue. Actually, on my 10.6m SB-10, I used analog minis - again without issue!

If you consider the worst case scenario of a plane in a dive and your need to recover it, it is unlikely that you would pull full up elevator (30 degrees) to recover the plane from a dive. You are more likely to gradually pull it out using a lower elevator deflection. Let's say you used 20 degrees deflection to pull the plane out of the dive. On my Ventus, I would have to be flying at 145mph before I would stall the elevator servo using a HS5245. For a really gradual pull-out with 10 degrees deflection, that speed would be approximately 290mph!!!!!

(NOTE that in the above, I have assumed that the servo rotates the same number of degrees as the control surface which may or may not be the case depending on how you created the servo linkage system).

Anyway, some food for thought as you progress with your build and note that these are my own opinions based on personal experince over the years!! Do what you feel comfortable with!

Tony
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Last edited by SoarScale2; Jun 25, 2008 at 12:37 AM.
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Old Jun 25, 2008, 07:54 AM
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United States, MN, Minneapolis
Joined Dec 2002
266 Posts
Even Better Advice

Paul, Take Tony's and Rick's advise over mine, they both have far more experience and especially on your specific airframe questions.
I only wanted to urge you not to put a punny analog servo in there and have it flutter on you. Linkage probably even more important than all out strength.

I love having such good info for just a question asked.
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Old Jun 25, 2008, 10:54 AM
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United States, CO, Delta
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Ventus

Dennis,Rick,Kevin. Thank you guys,this is great!Dennis i can fit a standard in the fin,but the clearence is so small,i just wanted to avoid hogging out holes for the linkage.LET did such a nice job.But if i have to i will cut and chop.Rick thank you for the info,iam gonna look at that one to.I gotta get this thing ready for Monroe,plus the weather has" FINALLY"started turning nice.Dennis you gonna make it up here to Monroe this year?Gotta go to work now so i can pay for this hobby, i mean diease. Rick,Kevin,Dennis Thank you again. Paul
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Old Jun 25, 2008, 11:18 AM
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United States, CO, Delta
Joined Oct 2005
495 Posts
Let

OOPS Tony i for got you.I thought i could rememberhow you did your linkage at Yaki!! But forgot! My wife had the camera,so i didn't bring it.DUH!I should have asked you or Steve to take a photo.I really like the way you did it.No hurry but curious,have you done anymore thinking on the "Reiher".6Mtrs of course!! Tony fast question,cause iam lazy you dont have the cable for the MC24 to transfer data do you? If you come up here you can maiden mine!Are you coming up this year?I know at $5.00 a gallon it aint cheap.Also we have our Aero Tow in August,we are about 6 hrs closer than the Monroe Boys.OK now i really Gotta go to work. Thank You Tony for the info!! Paul
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