Jim Armour Tutor

[Clay Schmidt]

I'm just beginnig to build a modified Tutor as described by Jim Armour in an 1986 Model Aviation Ted Fancher column.  I plan to use a LA.40.  What size of tank would you all recommend I use?

[Ralph Wenzel (d)]

There are too many unspecified variables to give a single answer. Plane weight? Prop? Fuel? Altitude? What flight regime do you prefer - slow or fast?

I'd say that if you start with a 5 oz. tank, you can always suck out however much you don't need. If you install a 4 oz. tank, it'll be real tough to get that extra ¼ oz. into it when if you need to add nitro for higher-altitude fields.

[Clay Schmidt]

Weight should be round 40OZ.  Prop,,I'll probably start with a 10.5x4.5 APC.  My home field is at 1900ft and I like 5.25 to 5.5 laps.

I don't have any experience with the LA .40 and this is a practice plane so a little extra fuel would be nice.  I was guessing around 4 oz. and was curious what others were using.

Clay

[Bill Hodges]

Clay:

I am currently flying a Fancerized Twister with a B-40 on it.  It is a great flying plane.  I have a 5 1/2 oz. tank on mine, but only put in 4 3/4 to feed the B-40.  I hope you are as happy with your F-Twister as I am with mine.

Okay, my brain just kicked in.  You are talking Tutor and I was seeing "Fancher" and reading in Twister. 

Bill Hodges

[Bob Kruger]

Clay;

Are you starting off with an original kit or from scratch?

V/r

Bob

[Jerry Bohn]

Where do you get 5.5 and 5 oz tanks?

[Bill Little]

Hi Jerry,

I usually get them from the hobby shop about 40 miles from here, who inturn gets them from Brodak.

Or, Randy Smith or Tom Dixon at the local contests.  Both do mail order and would be happy to tell you what they have and suggest for different engines.

Bill <><

[Clay Schmidt]

Bob,

I sent you a private email.

I'm building mine from scratch.  I have a set of plans for the original Tutor. I used them and Jim Armour's dialog to draw my plans  using ModelCad.

I used compufoil to copy the wing airfoil.  I found that a NACA 0018 after the trailing edge was clipped and the airfoil resized to the correct chord dimension matches the root rib on the Tutor plans perfectly.  There is no tip template on the plans so I used the 0018 and the same procedure for the tip also.  I  took these two templates and lofted all the ribs for the wing.
I then sent the file to my brother  so he could prepare the Compufoil file for laser cutting using AutoCad.  After he was done we proofed the patterns and then sent the file to Eric Rule at RSM for laser cutting.  Eric does a fantastic job with his laser.  I had two sets of perfect ribs the following week.

I am not using the same construction method on the wing as the original Tutor. My wing will be a C tube wing constructed almost exactly like a stock Trivial Pursuit wing.  On the outside the airplane should look very close to Jim's.

Bill,

Everyone that has a Fancherized Twister is telling how much they like the airplane.  When I saw and read about Jim's stretched Tutor I couldn't resist.

Clay

[L0U CRANE]

Hope your home 'air', altitude, etc., work this way...

A decade or so back, I'd designed my own sharply tapered-wing stunter, using the same percentage airfoil at root and tip. The model was very susceptible to choppy and cross wind in roll. A few other models developed soon after gained from splitting the difference - much less roll  problem in adverse wind conditions...

What this means, is this: If an 18% section means a 1.8" root thickness (10" chord), then a 6" tip chord would need a chord of 1.08" to be 18%. That's a 0.72" change of thickness.

Splitting the difference - half the 0.72" - is 0.36" change. The tip section % would derive from a tip thickness of 1.08 + .36 = 1.44". For the notional 6" tip chord, that works out to a 24% rib section. (Tip thickness same as root - 1.8" -  would give a 30% section!) The deeper section from splitting the difference helps offset the change in Reynolds' Number, without getting ridiculous.

These are pretty extreme numeric examples, and a less flagrantly visible application to more typical stunters should do well. Has for me for quite a while...

[Clay Schmidt]

Lou,

Thanks for the info and advise.  I really wasn't very clear about  the airfoils I am using so I'll try and explain what I did.

I did use a NACA 0018 as the base airfoil for the wing at the root and tip.  The Tutor has a 8.75" root chord and a 6.75" tip chord less the flap.  The wing on the plan is 1/2" thick at the flap hinge line.

I used Compufoil to alter the the 0018 for a 1/2" trailing edge.  All Compufoil does to the rib template is find 1/2 thick in the airfoil and tells you how long to make the airfoil so you can clip the trailing edge for 1/2" thick and a 8.75" chord. Compufoil does not alter the shape of the airfoil. Compufoil puts the clip mark right where it need to be.  Obviously when you lengthen the airfoil the thickness increases.  A 18% airfoil 8.75" long unaltered is 1.575 " thick.  After the alteration my airfoil is now 1.805" or 20.63% thick at the root.

I used the same procedure for the tip.  A 18% 6.75" airfoil is thinner so Compufoil will have to move further forward on the airfoil to find the 1/2 thick trailing edge I need.  After Compufoil did the alterations I ended up with a tip thickness of 1.445 inches or 21.41% on a 6.75" tip. 

My thickness difference is .36"

So what do you think,,, am I in the ball park?

Clay

[Allen Brickhaus]

I have been told that the Dubro 4 ounce tank actually holds more fuel, perhaps even up to 4 1/2 ounces.  That might help.

Allen Brickhaus

[rustler]

Anyone done an Armourised Tutor II yet? Could be a labour of love since the wing's already built.