Lil Sister (oz16425)

About this Plan

Lil Sister. Free flight Embryo Sport sport model for rubber power. Wingspan 16.9 in.

Vector format plan.

Note this plan is freely available as a download from the publishers at: http://aero-modeller.com/bonus-coverage-from-issue-5-923/

Update 2/12/2025: Added article, thanks to RFJ.

Quote: "I must whole-heatedly confess, I have a real hard time designing model aeroplanes that don't look like, what I think, aeroplanes should look like. The graphic artist in me tells me to think it out, make it fit the formula, balance the proportions and make it look good. Perhaps one of the hardest things to accomplish is keeping it simple AND making it look good. And - the next hardest thing to do is make it light enough to keep the wing loading down so it will fly great but make it strong enough to survive the knocks that everyday flying can force on a model. Remember the golden rule: As mass increases, force of impact increases exponentially.

The Lil Sister hits right on the money with most of these points and it is very simple to build and the wood sizes are reasonable for anyone who can work there way around peanuts, walnuts, Bostonians, etc. etc. My Lil Sister weighs in right around 16 grams as pictured here with a Peck silver plastic prop and no rubber. I am going to fit it with a carved balsa propellor from Zephyr Model Motors that will trim off another gram and a half. This will get me down close to my goal of 14 grams to meet the minimum weigh limit of 14 grams imposed by many competitions.

Construction of the Lil' Sister is very straightforward and throws no punches as she goes together. As always, wood selection is of prime importance with these smallish airframes, so go as light and strong as you can keeping in mind the type of flying you intend to do. For the prototype, I did not go for ultimate weight savings and I typically want to get a new design up an flying well before I go for broke (maybe a bad choice of words) and set my sights on competition.

Fuselage The bulk of this design is strip wood. For the fuselage, I chose some good and springy 10-12 pound 'A' grain stock for my longerons and cut my own strips so the consistency was as close as possible. I used this same strip stock up front and wherever strength was needed. For uprights and cross-members behind the wing, I selected some 5-7 pound stock. My general rule of thumb is to put the weight where it is generally needed so as not to add gobs of clay to make it right for flight.

All of the cross-members from the wing T.E. forward are of the same length. This feature makes mass production a snap (again, maybe a bad choice of words) as all can be ganged together and cut/sanded to the same exact length. This also promotes a nice, square fuselage structure. Build the fuselage sides one on top of the other in the standard fashion. Be aware to build the right side nose upright 1/16 aft of the left side to build in the proper 2° of right thrust.

Once you have the side built and all the glue gobs sanded smooth, block the sides perpendicular to the building surface and over the top view of the plan. I use a pair of 2 in sq steel machinists angles for the task. They are dead on square and weigh a lot so they don't move around easily. I find that flat magnets like the ones that fall off of decorative refrigerator magnets work great for keeping the fuselage side pinned to the steel angles..."

Supplementary file notes

Article.

Corrections?

Did we get something wrong with these details about this plan (especially the datafile)? That happens sometimes. You can help us fix it.
Add a correction