Rubber Band Power

[Texman]

Excited to see how this flies..

[mbauer]

A couple of photos showing the rubber band and propeller installed.

Went with 2-each 1/4" Super Tan Rubber Bands.

They might be too much:
1) Got a distinct Roar to the propeller
2) Tried to let it hover the fuselage, the fuselage went crazy unwinding just as fast as the prop was, only it looked like in the opposite direction. Did this crazy dance for about 1-1/2secs before turning on its side and crashing to the floor

Rubber band and prop installed, Once wing spar dries (bottom of photo), will install it and the wings before adding the canopy skin on top of fuselage.




Mike

[Don Boose]

It is to be hoped that once they are installed, the wings will help to counteract the torque!

If you still have torque problems, wingtip washout (starboard wingtip for a right-rotating prop) or a thin cardboard trim tab might help.

Does the prop have a little down thrust? That is also useful with powerful rubber engines to prevent stalling.

Don

[mbauer]

Worked more on the P51 today. Only items left are the landing gear and weight & Balance.

Tailfeathers glue drying:


Bottom View:


With 6" Prop:


Model weighs 2.2oz at this stage. Wingspan is 22". Paper tube appears to be handling the 2 rubber bands really well, cranked it three time till prop was hard to move, then let it rip while holding plane. Man it goes fast, not much reserve, you can hear the prop roar.....Tube is 14" long, no adverse issues yet.

Was able to work on the model today, just checked the race status off and on.

My son-in-law had several bad crashes last night getting to Unakleet. Managed to detach his cartridge from several ribs. His partners machine is bent up, not able to continue without new tub, both decided to get ready for next year.

Race should finish tomorrow at Big Lake, Alaska. Will be going up for the activities. While he was racing, did not get far from the computer. But now, he is waiting for a plane ride out, weather is so bad no planes are flying.

Able to get some things done around the house.

Mike

[mbauer]

Originally Posted by Don Boose

It is to be hoped that once they are installed, the wings will help to counteract the torque!

If you still have torque problems, wingtip washout (starboard wingtip for a right-rotating prop) or a thin cardboard trim tab might help.

Does the prop have a little down thrust? That is also useful with powerful rubber engines to prevent stalling.

Don

Hi Don,

No, won't be doing washout. Internal wing structure does not have any ribs, just a spar. The shape of the cardstock is what ends up being the airfoil. To do washout would mean and equal /opposite effect somewhere else. I've got the wing skin glued to the main spars, just that any changes to the shape now cause it to "Oil Can" somewhere else.

Tested a model trying to create a natural little tip washout when gluing but created more issues than worth, so this model did not do it.

Now down thrust is where its at with these. Hoping to test fly on Monday when I get back to work from a week of vacation to help with race week.

Might glue on some trim tabs, originally was thinking to warp a control surface as needed, but the mentioned oil can effect might cause the use of some glued on tabs. To fly with any control it will need something. Not exactly a straight build like tissue and balsa. Warped in several places along fuselage etc..

Adding Landing gear now.

Mike

[mbauer]

Finished the P51 build. Have a few graphic changes, the parts fit is good.


A couple of lessons learned:
1) Won't be gluing the wing skin to the spar anymore. This is the first tried that on, what happened? Wing no longer has its airfoil shape, created a triangle shape airfoil instead. Used a 1/16" thick spar.

Thinking that if glue the skin to the spar it would give added strength to both. The other model the airfoil shape is good, it was not glued, but has 1/8" thick wing spar.

2) P51 is mostly to scale, did shrink the tailfeathers some to help balance the model easier with less weight needed. This works, but now it soon will be time to see if they still work. Total balance weight needed? 5/8oz.

Model weighs 2.4 oz with landing gear installed. After weight & Balance model flight ready weighs 3.1oz

Thinking of doing a P40 Warhawk next, but, also looking at other options.

Mike

[mbauer]

When ordering parts from FAI, decided to purchase one of the newer designed props, it only came in 8" and was fairly expensive compared to the other props.

Since the rubber bands spin the 6" so fast it makes a roaring sound, thinking might setup the 8" prop to see what it can do. Do have standard 8" props too.

Lots of clearance for the 6" prop, might be able to fit much bigger prop in place.

Flight testing on Monday....

Mike

[Don Boose]

The larger prop should help. I'll be interested in the results of smallifying the tail surfaces. I understand your reasoning (less weight required in the nose) and I am certainly no expert, but when I was active in the DC Maxecuters and Flying Aces Club, the experienced designers always increased the size of the tail surfaces of small rubber powered flying models for better flight characteristics. Of course, with these paper models and the construction techniques you have invented, different aerodynamic rules may well apply.

I understand why your wing construction doesn't led itself to wash-in/wash-out. A trim tab will provide the same effect of lowering the wing against the torque.

I am enjoying the saga.

Don

[mbauer]

Don,

Yes, all the above from the tried and true. Know what works, trying to find out if there are areas to "cheat" at.

The fuselage sides are just that, no round or aerodynamic shapes added.

Not sure if a rudder will overcome this effect or not, so why not make smaller and find out? Total experiment...Rudder itself will be the "tab" to bend. Something you can't do with tissue and balsa, would need hinges.

Like you mention, this is a learning experience. All of my other models, the cardstock could carry the flight loads. This is not the case with rubber power.

The main load is carried by the internal rolled paper tube. The flight loads are now transmitted through the balsa wood box for the wing spar.

Tried using paper to reduce weight since the loads are carried by other than paper. That didn't work so well.

Now using the lightest weight cardstock I have available, 90# Index, to maintain the fuselage shape without internal bracing like was needed for the paper version.

You can see in the photos, that on the left side of fuselage, it is bowed in at the star and bar. Heavier cardstock would not do this, but the weight penalty is too much. This compromise may stop the model from flying, or need big trim to correct...

Folded paper airplanes are very forgiving in their design. Hopefully this very useful paper property will help overcome the weight issue when using paper as a design medium.

Will this work, yes, but not very effectively. (hoping that is for the yes part) Learning some valuable lessons for future builds. What flying they do will be short once power is off, lots of drag and weight.

My joy will be in watching them take-off if they can. To me that means they are actually capable of flight.

It has been fun to design and build these, having fun even if they don't fly. Got the bug to build a small balsa and tissue version have in storage.

Thank you for watching, and commenting: sounds like you're an experienced hand at building free-flight models! Please keep the comments heading this way.

Mike

[mbauer]

Oh boy, whole new picture and direction to go.

Instead of doing another airplane reproduction. Deciding to just do a stick and wing version like you used could buy for cheap. Plastic landing gear, a balsa stick, balsa wing and tail.

Why not a paper version using the tube?

Design computer is cranking up....

Mike