Don Still's Stuka questions

A Don Still's Stuka is now under construction from scratch using Pat Johnston's plans. All is going well using 5.3 to 6.4 lb balsa throughout, thinking that lighter balsa may be too soft for durability or too pourous to fill with dope hence little, if any savings on weight and loss of strength. (Question: is this logic correct?) 1/64th plywood doublers going aft of wing TE some distance to construct a removable wing for transport in a Lancair 360. I expect the weight penalty for this addition will be about 1-1.4 oz. max. An OSLA25 will be used with a tongue muffler and to move the CG aft, a 3/4 inch shaft extension will be used. Moment calculations from the aft side of the aft fuel bay bulkhead established as FS-0 revealed a zero delta on weight differential when you add the weight of the shaft extension but a minor aft CG movement which is beneficial. The replacement of the metal 3 oz fuel tank for a bladder or pacifier fuel bladder could save 3/4 to 1 oz weight saving plus a further aft movement of the CG. What is a source for a pacifier bladder and balloon for secondary protection and how would exit the fuel line for pinching access while starting?

I would assume that a wood prop would be lighter than graphite or plastic prop. (Is this a realistic assumption?) The motor mounts are hogged out between the two hard bulkheads leaving 1/16 inch on the top, outside edge, bottom leaving a 1/16 inch channel web. The 3/8th inch channel is filled with soft balsa in a crutch construction format between the two mounts.

Any other ideas to lighten the nose of this bird will be appreciated. Dee Rice stated that one can remove about 1/2 oz from the OSLA25 by milling metal off the head and body of the motor. Has anyone done this and if so could you give us further light and knowledge on how to do this without any detrimental effects. An ST needle valve replaces the removed original needle valve assy.

I assume that a soft balsa thin shell can be carved out of 4 lbs balsa or perhaps multiple laminations 4 lb balsa thinned to about 1/16 inch covered inside and outside with carbon veil or fiberglass. What do you prefer? The nose cowling, underside of the fuel tank bay and wing will be removeable with the removal of four screws 4-40 screws. One aft of the wing, two forward for the wing and landing gear, one for the nose cowling.

What effort should be made to lock, interlock the wing into the fuselage to transfer loads and vibration? This is my first time at this venture and shared experiences would be appreciated. I am assuming that a 1/64th ply pocket on the fuselage mating the top side of the wing is an appropriate idea with additional width for wing fairing. Can this be hogged out with lightning holes or is this getting too finicky at suffering loss of strength? Appreciate a response on this and any other ideas to accomplish the goal.

Most built up fuselage models have the elevator horn buried in the fuselage. I opted to bring the pushrod outside the left fuselage side just under the Horizontal Stab to allow for an adjustable elevator horn.

Regarding wood preparation and covering. I plan to use Brodak dope throughout. (Hint), I have found that Brodak dope will coverand Randolphs clear dope. I am using Randolphs thinner with no problems with Brodak Dope. A lot cheaper by the gallon. Also, I have mixed Brodak Dope with PPG Durycryl DDL Acrylic lacquer metallic additive with good results.

Covering and paint preparation begins with raw wood. I am wondering if you can add too much weight in wood preparation and still have to prep the silkspan for that great smooth final finish. Is it possible to do too much work on wood prep that could have been accomplished after covering. I am one of those persons who tend to sand, sand, sand, sand some more and do a lot of redo work and fear I may be counterproductive and consequently work too hard and may even add more weight than necessary at each stage. So the question is; what is the minimum and lightest amount of wood preparation needed to get that contest finish before covering with medium silkspan? I have been told that you can eliminate a couple coats of dope by lightly spraying all wood surfaces to be covered with water. The wood fibers stand up. Sand lightly with 200, spray with water again, repeat the sanding then start applying dope. An old free flight trick. Saves two coats of dope. Any other tricks?

I have been told that the difference in weight for a contest finish between medium and heavy silkspan is minimal. Does anyone have any knowledge of this and is it preferable to go with heavy silkspan for added strength or is the weight penalty too great?

This should be enough questions to stimulate some responses. I appreciate any applied experience to this posting.

Warbirds are typically dull finished, yet stunt planes strive for that plastic look. Appearance points often are judged on gloss and not necessarily realism, etc. What would you do if you were building a Stuka Stunt and what would your weight budget be on finish for glitz and polish or realism?

Thanks to all in advance.

Bob Smiley
A Lancair 360 builder/flyer trying to be a modeler.

Just one point about your milling question: a 1/4 oz at the nose can most likely be handled by an 1/8 oz piece of tail weight. I think light is great, but sometimes we pursue that goal a littl beyond what is reasonable (IMHO)

LAST EDITED ON Jul-04-03 AT 09:56 PM (CDT)
 
>Just one point about your milling question: a 1/4 oz at the
>nose can most likely be handled by an 1/8 oz piece of tail
>weight. I think light is great, but sometimes we pursue that
>goal a little beyond what is reasonable (IMHO)
>
>Alan

I just build and and fly the stuff as best I can in both areas. I note that GMA once wrote me that his best flying Nobler (I think this was the "black ship" that he won the '57 NATs and the Walker with) was probably the heaviest one he had built. I forget what he said the weight was in ounces now (have the letter here somewhere I think) but it sure wasn't a featherweight-as Noblers go- by any means.

Alan,

You may be right. I however, offer the following. Wing area 479 sq in which is 3.33 sq feet. If you are alloted 11 oz per square foot wing loading for a competitive stunt ship that means your outside weight is 36.6 oz. total weight. Very achievable I do believe.
However;

Don McClave is building a Stuka Stund and he said we should shoot for 30 oz total weight. Hmmmm that is an 18 percent reduction in weight!!!!! or a wing loading of 9 oz per square foot.

I have no prior experience with this plane and do not know what standard to reasonably strive for. At this point, I am inclined to take Don's goal and advice.

Bob Smiley
A Lancair 360 builder/pilot trying to be a modeler