Millers Twin

[Leo Mehl]

This is John Millers new Pathfinder twin, It flys good just like John.

[john e. holliday]

That is awesome.  Have fun,  DOC Holliday

[John Miller]

Thanks guys, it's a lot of fun to fly. Best of all, it handles well. I'm beginning to believe that a pair of .15's to .25's are the optimum for a twin.

[proparc]

Plane looks cool baby!!!

[Mike Foley]

    After seeing this model at Pasco last week I decided I had to have one. I will start on this project as soon as I receive the short kit from John. I will be doing a photo sequence of the build and writing a non biased opinion on the quality and construction.  My goal is to build the model within two months max not counting finish. Stay tuned, it is a very good looking model.

[Richard Grogan]

Fine looking bird John! How did you reinforce the aft fuse from tail twists? Looks mighty sharp, congrats!

[John Miller]

Fine looking bird John! How did you reinforce the aft fuse from tail twists? Looks mighty sharp, congrats!

Thanks Richard. An interesting question, with what I hope to be an equally interesting answer.

I've become convinced that the "Profile fuselage twist" or PFT is caused by the circular propwash over the tail section.

So, based on that belief, I figured that there were several methods to deal with it. Strengthening the fuse adds weight, and complication, usually without a lot of success.  The profile fuse, at a normal 1/2 inch width, is difficult to adequately stiffen up.

I looked at possible solutions using the design. I started out with a single engine profile, and I wound up with what I consider an interesting solution for a single engined profile.

I tilt the stab about 3 degrees towards the inboard side. In flight, the PFT will set the stab level. Also, I believe that the slight tilt helps a bit, even if it's not all removed by the PFT.

An example, when giving up elevator, the tilted stab adds a slight nose in motion, opposite of what the spinning prop does. Of course, the opposite happens with down elevator, again fighting the effect from the prop.

It seems to have worked fine on the several profiles I've used it on, but, the twin turned out to be another issue completely.

Since the engines are on opposite sides of the stab, they, for all intents and purposes, cancell the twisting effect on the tail section. I tilted the stab on the blue one, and it's still slightly tilted in flight, unlike the single engined profiles I've done this to. This leads me to conclude that one can set the stab level with a twin profile.

An edit added because I forgot to include this information.

Another design element is using the built up fuse construction itself to add some anti twist, by the way the built up profile fuse is constructed. Simply put, aft of the wing trailing edge, the top and bottom fuse formers, are narrower than the center, forming curved sides with the sheeting. This helps add resistance to twisting without adding weight.

You might be able to see the slight tilt when comparing my blue one, with Gordan's red one.

[Willis Swindell]

I noticed this problem while building my twin with twin rudders. I used 1/64 in. plywood down the sides of the fuselage with balsa caps top and bottom. I shaped the fuselage first then applied the plywood up to the high point of the wing . worked great.
Willis 

[Mike Foley]

   John,

How about making the fuse out of two pieces of 1/4" laminated with carbon fiber for the fuselage. This is what Mike Pratt uses on his Primary Force and makes for a very stiff fuselage.

[John Miller]

Mike and Willis,

Thanks Willis for shareing your solution, and those pics of a very neat looking twin. If it flies as well as it looks, you've got something going there bud.

I am an advocate of 1/64" ply over foam for profile fuselages. strong, and light.

Mike, there are so many ways that have been used to address the problem of PFT. almost all have worked to some degree, but often leave us wishing for more. In the case of the Pathfinder twin, we chose to use a built up profile to save some weight. The solution, curved sheeting aft of the wing, seems to work quite well. It also appears that the propwash from the seperated engines cancel out the circular effect, thus not contributing as much twisting force to the stab. I believe further efforts, with this  plane would only add complication, and possibly weight.

As it stands, both of the prototypes currently flying have needed no balance weight to set the CG where we want it.