testing new wingtips

[Mark Goldberg]

Guys, Jonathan B and others have created some interest in trying some new style wingtips on the 4 place and Patrol. There are two styles of wingtips which Bob is interested in trying. The Hoerner style tips, and the Wittman style tips.

What Bob is hoping for is that someone has created some wingtips that he could perhaps make a mold out of to make a set and try them out. This would involve shipping them to Bob so he could work off of them to make another set for him to test. This would be the least labor/time path for Bob.

As I researched the Hoerner tips - it does seem like there are potential benefits. The Wittman style tips are much less researched. Maybe Bob will try them both to see how they compare with the rounded tips. If you think you might could help in this effort - please contact either me or Bob. Thanks. Mark

[spinningwrench]

What ever you do please make accommodations for easily mounting wing tip strobes/lights/position markers.

[Wyo Johnson]

Mark,

I have a contact that could machine a hard foam (30#) or MDF mold to any spec's that Bob wants. All they need is a CAD model which I could build. I have the B model wing rib already CAD modeled and would just need the width of the wingtip and what particulars on radiuses, etc. that Bob would want to try. I would provide Bob with that 3D model for free and work with the machine shop to cut the mold as they are in Hesston Kansas (Design Manufacturers Inc.). They have done a lot of work for me and are great to work with.

My suggestion is to try two types of molds:

1. Machine a foam wingtip and then build a one piece mold off the machined wingtip.

2. Machine an "OML" (outer mold line) tool out of Structural Foam or MDF, basically a block with upper and lower halves. The halves are painted with an epoxy paint (tool face) and then polished and treated with a release such as a PVA or just a good wax. The mold halves are clamped together and the fabric is placed into the block and vacuum bagged. Resin transfer molding would be easy for a part such as this and saves on epoxy waste.

My preference for speed, cost and accuracy is to use the clamp block mold, with resin transfer...happy to discuss/help at your and Bob's convenience.

Andy

[Bdflies]

Andy, is there any chance you’d share that CAD file? One of my buddies just got a gorgeous Bridgeport mill with a CNC driver. We don’t have a clue how to use it, but we’re trainable. And this would make a great project!
Personally, I'd go for your second option, but would leave it as top / bottom halves. Really easy to join the molded halves.

Bill

[svyolo]

Eventually I will make somekind of different wingtip. If someone offers them for sale first, you can put me down for a set.

[whee]

Mark,

I have a contact that could machine a hard foam (30#) or MDF mold to any spec's that Bob wants. All they need is a CAD model which I could build. I have the B model wing rib already CAD modeled and would just need the width of the wingtip and what particulars on radiuses, etc. that Bob would want to try. I would provide Bob with that 3D model for free and work with the machine shop to cut the mold as they are in Hesston Kansas (Design Manufacturers Inc.). They have done a lot of work for me and are great to work with.

My suggestion is to try two types of molds:

1. Machine a foam wingtip and then build a one piece mold off the machined wingtip.

2. Machine an "OML" (outer mold line) tool out of Structural Foam or MDF, basically a block with upper and lower halves. The halves are painted with an epoxy paint (tool face) and then polished and treated with a release such as a PVA or just a good wax. The mold halves are clamped together and the fabric is placed into the block and vacuum bagged. Resin transfer molding would be easy for a part such as this and saves on epoxy waste.

My preference for speed, cost and accuracy is to use the clamp block mold, with resin transfer...happy to discuss/help at your and Bob's convenience.

Andy

#2 Is the path we plan to take with the Hoerner tips we are building for the 4412 wing. This spring/summer we’ll hand carve some foam models to make the prototypes then if we determine the tips are worthwhile I’ll draw them up in SolidWorks and have a friend of mine tool-path them and cut out the mold half’s with his mill.

[svyolo]

I have never seen any kind of hard number claim for Wittman tips. There is a company that sells Hoerner tips for C150-210's. As a generic claim, it was 2-4 mph increase in cruise, 75-100 fpm ROC, and 4-5 mph reduction in stall speed. It didn't claim which model Cessna. KNOTS2U was the company.

[Wyo Johnson]

Bill,

Happy to walk you through the loft...I hesitate to kick you a CAD file as technically it's Bob's data and I would be reproducing it without permission.

Also you have to decide upfront if you are going to slide the wingtip over the end of the wing or attach it so that the wing skin is flush with the wingtip...this will change the loft.

The lofting is easy and if you have AutoCad or Solidworks it would take about an hour to convert your #4 airfoil drawing into a CAD shape if you are new to CAD.

PM me with your contact info and a good time to call and we can discuss.

Andy

[Patrol28]

Never have seen any real scientific data on Wittman's wing tip design. I read Steve Wittman's account on his seat of the pants test where he tried his design on one side and saw an advantage right away. Shortly after he incorporated it into his plans sets.
In regards to the Hoerner type tips I had a set on a C-180 in the '90's. I can't comment on the differences they make since the airplane had them when I bought it but a friend who flew my airplane bought a set for his 180 after flying mine. There is plenty to read about Hoerner's with test results.

[Archer39J]

A Hoerner wingtip would be a fun surfacing project. I imagine there's already models out there we could adapt to our wing, eyeballing it might not be optimal.

[svyolo]

I guess there are quite a few companies selling Hoerner tips for certified aircraft. They all make the exact same numbers claims. Hoerner was a bit vague, and said 1-2% increase in range, and increased ROC, but no numbers. But he wasn't trying to sell wingtips.

[Mark Goldberg]

There is a little movement with help from a couple of builders toward testing some new wing tips. Will post info when there is something to report of interest. Mark

[svyolo]

Searching for info, one of the hits I got was from another forum. I can't remember which one but one of the Supercub types. Maybe Husky. They did a tufts test before and after. Before the tip mod the tufts showed span wise flow for the outer portion of the aileron, and a bit forward of the aileron as well. After the new wingtips, the airflow over the aileron was fore to aft, like it should be.

[nichzimmerman]

Mark, this may be too early to ask, but if the flight tests are promising would you sell wingtips for both the original wing and B/Patrol wing or only the B/Patrol?

If redesigning the wingtip, also consider matching the trailing edge with the aileron, as it seems popular to rig the aileron trailing edge 1/2" above the flap and wingtip.

[Mark Goldberg]

We have not thought about the original BH wing's wingtips. Hopefully we can at least come up with a wingtip for the Model B & Patrol which will improve performance. Mark

[fairchild]

Mark----
There is a material that might be usefull for making wingtips--- both a one-off test set or equally in production.
The material is a fabric woven from polyethylene. Each fiber is constructed from two parts -- a core and a sheath. Both are PE- but the core is a higher melting point than the sheath.
It can be had as a cloth or a hard solid sheet form. When you heat it up to aparticular temp--- you melt the sheath which - when melted works like a pre-preg composite. The melted sheath
forms a resin-like liquid which encapsulated the cloth core. When it cools you have a composite structure which is worked like a thermoforming plastic. As an added befit--- the finished
product is VERY tough and strong. It is - in fact bulletproof. So possibly a single thin layer of the cloth might be enough for the tip-- except for any areas which might need backup for mounting hardware.
Here is a link to the material. They will send you some samples if you request them.

https://textiles.milliken.com/products/tegris

tim