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Author Topic: Profile Tail Fail  (Read 6666 times)

Offline Motorman

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Profile Tail Fail
« on: June 21, 2015, 10:52:12 PM »
Why do profile planes seem to have such a crappy empennage? They have a nice wing then a thin sheet stab/elev.

I see this on allot of designs. Maybe if you stiffen the fuselage with some CF or something and make a nice built up stab/elev then you can get performance approaching a built up model.

MM

Offline Igor Burger

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Re: Profile Tail Fail
« Reply #1 on: June 22, 2015, 05:13:50 AM »
Because those thin flat tails work better on small models? :- )))

Offline Motorman

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Re: Profile Tail Fail
« Reply #2 on: June 23, 2015, 06:11:27 AM »
I'm talking planes about 600 sq in.

Online Fred Underwood

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Re: Profile Tail Fail
« Reply #3 on: June 23, 2015, 10:39:10 AM »
I use a 5/8" stab on about 650 square inch profile model.  Seems to fly fine.  The problem is as you noted, stiffness and strength in a 3/4" profile fuse. Carbon fiber is one way, 1/64 ply is another.
Fred
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Offline MikeyPratt

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Re: Profile Tail Fail
« Reply #4 on: July 08, 2015, 09:35:47 PM »
I use a 5/8" stab on about 650 square inch profile model.  Seems to fly fine.  The problem is as you noted, stiffness and strength in a 3/4" profile fuse. Carbon fiber is one way, 1/64 ply is another.

I have a slightly different take on this.  Profile models are just that, a profile of the fuselage shape.  Building a built-up fuselage is better for sure.  I've seen many models with overly large tails (stab & elevators) at 25% of the wing which flies great when there is little to no wind.  When in wind or ruff air, and they get kind of loose.  The wind seems to rock the stab around because of the narrow fuselage,  I try to keep the area percentage around 25% also but make it a low aspect tail (this helps) at 3.5 to 4.5 max.

You can add a 1/16" balsa to the rear of the fuselage sides from the plywood doublers back to the rear of the stabilizer.  Make your fuselage by laminating two sheets of 1/4" balsa together with slow drying epoxy.  Cut out and finish shaping the fuselage then cover the fuselage using .2 carbon fiber matt and dope.  This is way lighter than 1/64" plywood, cheaper, and really strong. 

Later,
Mikey


Offline Target

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Re: Profile Tail Fail
« Reply #5 on: July 08, 2015, 10:17:09 PM »
Hey Mikey Pratt-

What would you think of adding a layer of glass, kevlar, or carbon, on a bias, between the two layers of balsa?
I would think that on a bias might help prevent twisting in rough air. I wonder if anyone has tried this.

R,
Chris
Regards,
Chris
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Offline Tim Wescott

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Re: Profile Tail Fail
« Reply #6 on: July 08, 2015, 10:38:15 PM »
Hey Chris:

Conventional wisdom says that if it'll do any good, it's better to put it on the very outside of the fuselage.  So, Mike's CF mat, or if you really feel motivated, CF tow or CF cloth put on a bias, should do better.

The only way to know for sure is to try both ways.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline MikeyPratt

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Re: Profile Tail Fail
« Reply #7 on: July 08, 2015, 11:44:09 PM »
Hey Mikey Pratt-

What would you think of adding a layer of glass, kevlar, or carbon, on a bias, between the two layers of balsa?
I would think that on a bias might help prevent twisting in rough air. I wonder if anyone has tried this.

R,
Chris

Hi Chris,
Using a heavier .5 carbon fiber matt between the balsa layers does help along with the .2 c/f Matt should make it really stiff.  I've done that in the past and it worked out really well.  The more you use this stuff (the more I like it) we find new and different way's to reinforce structures on our model aircraft.  Using the carbon fiber tow on angles along the fuselage my be a great idea and one that could be very useful when it is laminated between balsa sheets.

My typical finish is with the c/f matt is to cover the entire model including the cap strips on the wing.  At least 3 coats of nitrite dope under the c/f matt, with an additional 3 coats on the top of the c/f matt.  Sand the matt after every coat of dope until you see a slight shine on the matt.  Cover the open wing bay's with poly span with a 1" overlap over the c/f matt.  Again, apply three to four coats of Sig light coat dope to the poly span.  Do not sand the poly span until after three coats of dope (and then just lightly).  You can now switch to primer and shoot two coats DU 540 and let the primer cure.  You may need a third coat of primer if you have any imperfections.  After sanding off as much primer as possible, shoot a coat of Sig Light coat dope over the entire model to seal the primer.

Now you can shoot the colors.

Later,
Mikey
 

Offline Serge_Krauss

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Re: Profile Tail Fail
« Reply #8 on: July 14, 2015, 01:48:07 AM »
As I have posted and illustrated a couple times elsewhere, .5-oz fiberglass with 45-degree bias really stiffens a profile fuselage and makes it quite resistant to twisting. Just opening up and trussing the aft fuselage with balsa trusses, before laminating with 1/16" balsa both lightens and stiffens the fuselage over that of a solid 1/2" piece. Here you then have a profile-legal 5/8" thick fuselage.

Phil C. uses foam and laminates for an even lighter fuselage, but I find that 1/2" balsa core (or 2 x 1/4") plus 1/16" balsa laminations, with the truss work and biased fiberglass is very stiff and torque resistant. The (biased) .56-oz fiberglass with epoxy is as light or lighter than CF veil, due to thickness and amount of epoxy necessary to fill and attach it. I weighed a couple nearly identical tails to verify that the one with CF was no lighter than the FG one. Unless you have woven CF, the glass should be noticeably better as a surface stiffener. I think that you'd achieve a reasponable result by laminating the glass under the surface laminations, with a significant loss in work and mess.

SK

SK

Offline Chris Wilson

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Re: Profile Tail Fail
« Reply #9 on: July 14, 2015, 02:39:30 AM »
Why do profile planes seem to have such a crappy empennage? They have a nice wing then a thin sheet stab/elev.

I see this on allot of designs. Maybe if you stiffen the fuselage with some CF or something and make a nice built up stab/elev then you can get performance approaching a built up model.

MM

Maybe the mind set of building a simplified 'profile' extends to the whole model?

In other words why bother with the tail when you have skimped on the body?
MAAA AUS 73427

You have enemies? Good. That means you've stood up for something, sometime in your life.
 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

Offline Tim Wescott

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Re: Profile Tail Fail
« Reply #10 on: July 14, 2015, 08:55:08 AM »
Maybe the mind set of building a simplified 'profile' extends to the whole model?

In other words why bother with the tail when you have skimped on the body?

That works until you start competing in a profile class.  Then you start thinking in terms of making the Best Profile-Legal Model Ever.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Online Gerald Arana

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Re: Profile Tail Fail
« Reply #11 on: July 14, 2015, 10:07:11 AM »
As I have posted and illustrated a couple times elsewhere, .5-oz fiberglass with 45-degree bias really stiffens a profile fuselage and makes it quite resistant to twisting. Just opening up and trussing the aft fuselage with balsa trusses, before laminating with 1/16" balsa both lightens and stiffens the fuselage over that of a solid 1/2" piece. Here you then have a profile-legal 5/8" thick fuselage.

Phil C. uses foam and laminates for an even lighter fuselage, but I find that 1/2" balsa core (or 2 x 1/4") plus 1/16" balsa laminations, with the truss work and biased fiberglass is very stiff and torque resistant. The (biased) .56-oz fiberglass with epoxy is as light or lighter than CF veil, due to thickness and amount of epoxy necessary to fill and attach it. I weighed a couple nearly identical tails to verify that the one with CF was no lighter than the FG one. Unless you have woven CF, the glass should be noticeably better as a surface stiffener. I think that you'd achieve a reasponable result by laminating the glass under the surface laminations, with a significant loss in work and mess.

SK

SK


A curved surface is also much stiffer than a flat sided one. Especially if one puts FG/CF on both surfaces.

Cheers, Jerry

Offline Chris Wilson

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Re: Profile Tail Fail
« Reply #12 on: July 14, 2015, 07:00:56 PM »
That works until you start competing in a profile class.  Then you start thinking in terms of making the Best Profile-Legal Model Ever.
I am under the impression that the original post was not considering the 'best' of anything. (?!)
MAAA AUS 73427

You have enemies? Good. That means you've stood up for something, sometime in your life.
 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

Offline Tim Wescott

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Re: Profile Tail Fail
« Reply #13 on: July 14, 2015, 07:03:17 PM »
I am under the impression that the original post was not considering the 'best' of anything. (?!)

No, but the thread kind of diverged off into a discussion of rear fuselage stiffness, so I went with it.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Dennis Saydak

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Re: Profile Tail Fail
« Reply #14 on: July 15, 2015, 07:32:03 AM »
I like Mikey's recommendations. My Rayette has a 1/4" laminated balsa fuselage epoxied together with commercial epoxy (Fullers Resiweld), which many homebuilt guys use. I applied veil to the aft end and replaced the 3/16" stabilizer with 1/4" sheet.
Just when you think you're getting ahead in the rat race.....you find the rats just get faster! MAAC 13120L

Offline Target

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Re: Profile Tail Fail
« Reply #15 on: July 15, 2015, 08:14:13 AM »
An I beam profile, you don't see that too often!
Looks good to me.

R,
Chris
Regards,
Chris
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Offline Motorman

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Re: Profile Tail Fail
« Reply #16 on: March 22, 2016, 08:29:56 AM »
I am under the impression that the original post was not considering the 'best' of anything. (?!)

Except the best way to make a tail on a profile plane.

MM

Offline frank mccune

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Re: Profile Tail Fail
« Reply #17 on: March 22, 2016, 10:46:25 AM »
    WOW!!!!

    What I was attempting to determine in my original post was a question regarding increasing tail by increasing the weight of the tail components.  Nose heavy profiles were the driving force prompting my post.  Perhaps by adding all of the other additional laminates etc,, one will increase the ability to balance a profile without stick on weights etc.  I was thinking of thicker balsa or heavier wood to be used for this purpose.  A simple way to add tail weight.

                                                                                                       Thanks for all of the replies,
                                                               
                                                                                                       Frank McCune

   

Offline Brett Buck

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Re: Profile Tail Fail
« Reply #18 on: March 22, 2016, 10:51:14 AM »
I am under the impression that the original post was not considering the 'best' of anything. (?!)

   Thread drift is a feature, not a bug.

     Brett

Offline Brett Buck

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Re: Profile Tail Fail
« Reply #19 on: March 22, 2016, 11:00:54 AM »
    WOW!!!!

    What I was attempting to determine in my original post was a question regarding increasing tail by increasing the weight of the tail components.  Nose heavy profiles were the driving force prompting my post.  Perhaps by adding all of the other additional laminates etc,, one will increase the ability to balance a profile without stick on weights etc.  I was thinking of thicker balsa or heavier wood to be used for this purpose.  A simple way to add tail weight.
   

      Just using heavier wood will accomplish the purpose but in the least effective way possible. Increasing the cross-section is a better way. That's why people seek out light wood and try to beef it up on the outside.  Wood in the middle of a profile fuselage is just dead weight - you would do better using the light stuff and adding dense weight at the tail (like lead) because it will end up lighter overall and be just about as stiff.

   In this thread, the question was how to use the weight most effectively. I don't design/build for minimum weight, but I do care about using the extra weight to improve something.

    As a counterpoint, I can beat just about anyone in profile with 25-year-old kit that has been crashed at least 40 times and undergone major rebuilds on 3 separate occasions, so treat the above as a thought experiment.

     Brett

Online Trostle

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Re: Profile Tail Fail
« Reply #20 on: March 22, 2016, 11:30:21 AM »
An I beam profile, you don't see that too often!
Looks good to me.

R,
Chris

The Lancer was a Berkeley kit.  It was for Combat.  Profile fuselage and an I-Beamer.  Good looking airplane for a profile.  The kit shows up from time to time on e-bay.

Keith

Offline Target

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Re: Profile Tail Fail
« Reply #21 on: March 22, 2016, 02:25:27 PM »
Roger that, Keith, I'll keep an eye open.
I can completely confirm with Brett that making a heavier horizontal is likely to result in a heavier plane than a lighter tail with stick on lead. The leading edge of the stab isn't as far forward, so it needs to be heavier than anything added further back.
I learned this eventually the hard way on sailplanes. A bigger receiver battery some like to add isn't as effective as a smaller battery and good old lead in the front for lowest all up weight.
Something to consider.
R,
Chris
Regards,
Chris
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Offline Chris Wilson

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Re: Profile Tail Fail
« Reply #22 on: March 22, 2016, 06:14:55 PM »
Except the best way to make a tail on a profile plane.

MM

Nope, the original post only held one question, that of "Why do profile planes seem to have such a crappy empennage? "
Occams razor tells us the simple answer to the 'why' is that its themed. Sheet body, sheet wing.
MAAA AUS 73427

You have enemies? Good. That means you've stood up for something, sometime in your life.
 Nothing in life is so exhilarating as to be shot at without result.  It's not enough that we do our best; sometimes we have to do what's required

Offline Motorman

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Re: Profile Tail Fail
« Reply #23 on: March 23, 2016, 08:46:39 PM »
I use a #11 blade.


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