Spoilers For BOT

[Carl]

I wannt to put spoilers on my BOT ARF but have a question on size. I have read the artical about putting spoilers on using 1/16 balsa sheet and carbon fiber mat and these are 1 1/2 inches wide, but he only raises them about 1/2 inch when landing. If yoiu were to use aileron material for the spoiler would 1 inch wide be ok or should you use some wider material to get it up to 1 1/2 inches.

This is my first glider though I have been flying electric for 4 years. It is hard to get the BOT to settle in for a landing and thus the need for spoilers.

Thanks for the help.

Carl

[ISoar]

You can make the blades 2 bays wide and have them go 90° up, but it is easier to make the blades larger (3-4 bays) with a smaller throw and blade height (chordwise).

The disadvantage of wider (spanwise) blades is that there is more of the wing airflow disturbed when the spoilers are closed, as no spoiler closes perfectly, or is seamless.

[Ollie]

As ISoar says, imperfections in spoiler fit disturb the air flow over the wing even when the spoilers are closed. There are two thing that you can do to minimize the disruption. First, build, fit and adjust the spoilers as perfectly as you can. (This is very important.) The second thing is to locate the spoilers about half way between the spar and trailing edge. The boundary layer is thicker back there than at the usual just-behind-the-spar location. The thicker boundary layer will tolerate very minor bumps and gaps better than with the more forward spoiler location.

[Soar_dude]

My question is about your statement about having the spoilers further aft. Will they be as effective as ones that are just aft of the spar?????? Correct me if I am wrong but your strongest lift force is centered on the spar (thickest part of the wing) and get weaker as the flow moves aft.

Soar Dude

[Ollie]

Hi Soar Dude,

Aft located spoilers work very well. The extreme case is spoilerons.

You might find some reading about how lift is produced interesting. See:
http://www.av8n.com/how/htm/airfoils.html

Lift production involves flow ahead of, around and behind the wing. Spoilers disrupt the process and their location is not critical in their deployed state.

[Trobin]

I just purchased the Dynaflite BOT and because of the threads describing the wing failures I'm going to strip the covering off the center section and add strength via carbon fiber ribbon. As long as the covering is off I'd like to add spoilers. I've got moderate building skills and I have not added spoilers before. What do you use for the spoiler itself? A flat piece of thick balsa? trailing edge material? some type of hardwood? balsa/glass combo? I've read several threads on the matter but would like any additional input on any aspect of adding the spoikers to the BOT.

[Ollie]

A piece of unwarped trailing edge or aileron stock makes a good spoiler blade. For the spoiler blade to remain unwarped both sides have to be treated exactly the same. Same glassing (if used), same film covering, etc. The spoiler should be fitted very carefully so that the gaps around it are no more than a couple of thousandths of an inch. Fitting and adjusting spoilers properly is one of the most difficult tasks that the beginner faces.

[SaltyOne]

The slickest set of spoilers I've seen actually sit on top of the original wing skin. They are made of fiberglass and epoxy. They were constructed by laying wax paper on top of the wing in the area of the spoiler and then laid-up onto the waxed paper. That way they conform to the contour of the wing top. They are about 3/32 inch thick, about 1.5" wide and about 12" long. They are attached to the wing using clear tape on the leading edge of the spoiler. The only penetration of the wing surface is for the actuating arm which sticks down into the wing at a 90 degree angle to the spoiler. They are actuated with micro servos mounted inside each wing panel. It's extra work, but if top performance is important (i.e. little disturbance of airflow over the wing) it's the way to go. Hope this helps.

George

[Carl]

Thank you very much for all of your information. I think that I will go with the spoilers that were demostrated on the web site.


Carl

[schrederman]

I believe it was Mark Drela that said surface-mounted spoilers was not a good way to go. I have to agree that the disruption in the airflow by another surface sitting on top of it is not a good thing. The boundary layer trips and the flow goes turbulent at the leading edge of the spoiler. It's a lot more work to recess the spoilers and fit them correctly, but in the long run, better.

Regards

Jack Womack