Author Topic: Aerobatic Capability (Read 7374 times)

Dennis Saydak · « **on:** December 18, 2014, 10:02:46 AM »

How aerobatic would a semi scale low wing model be that has a semi-symmetrical airfoil? Would it be capable of flying inverted and doing basic manoeuvers such as figure 8's? I'm talking about models like the old Royal scale kits (P-51, Spitfire etc.). Presume the wing incidence was set at zero and the model balanced properly. Does anyone have experience along this line?

Tim Wescott · « **Reply #1 on:** December 18, 2014, 10:09:06 AM »

It'd definitely fly inverted. Dunno about outsides, but I suspect so. You can always test by doing a half-loop to inverted, then trying an outside loop from level.

Fred Cronenwett · « **Reply #2 on:** December 18, 2014, 10:34:07 AM »

The big challenge is building the model light enough to perform aerobatics, most CL scale models are heavy enough they have a hard time doing aerobatics.

Fred

Tim Wescott · « **Reply #3 on:** December 18, 2014, 11:11:29 AM »

This is totally outside the scope of Dennis's question, but -- how much do you get dinged for having a non-scale airfoil? It seems that the airfoil is the first thing to fly out the window in a scale building effort, even when the plane is otherwise quite close to scale.

chuck snyder · « **Reply #4 on:** December 18, 2014, 11:34:12 AM »

The amount you get dinged for a non-scale airfoil is up to the judge. When I am judging I put a pretty hefty penalty on non-scale changes that are intended to make the model fly better. Includes over sized tail surfaces, dihedral, non-scale flaps. But I'm in a minority on this too.
Chuck

Allen Goff · « **Reply #5 on:** December 18, 2014, 04:24:24 PM »

I will go along with Chuck on this. If it ain't scale, it ain't scale. This is scale we are talking about, right?
It's not worth making changes that will cost you static point, they are to hard to make up with flying points.
The P-51 is a great scale subject, kept it "scale" and it will hold its own.
Blessings
Allen

Mike Keville · « **Reply #6 on:** December 18, 2014, 04:31:42 PM »

Agreed. Start changing things and it becomes what they call "Fun Scale"....another dumb'd-down event.

FLOYD CARTER · « **Reply #7 on:** December 18, 2014, 05:49:53 PM »

Many contests have an event called "Sport Scale". I guess this even includes profiles (and some actually call them 'scale'). I've won sport Scale events using full-body stunters which are mostly scale, but with "stunt numbers". Just as long as we make the distinction between Sport and Real AMA Scale, no harm done.

F.C.

Allen Goff · « **Reply #8 on:** December 18, 2014, 06:19:09 PM »

"Sport Scale" is the second highest scale event you can enter. If you want to compete at contests like Brodaks, StLouis, Dayton and the Nats, the stunter will not fair well. I have seen stunters with and with out throttle control and they all come up a little short on points. Stick with the scale version you'll be pleased in the end. Just trying to help out.
Blessings
Allen

Fred Cronenwett · « **Reply #9 on:** December 18, 2014, 06:50:07 PM »

The updated rules are written in such a way that throttle is almost mandatory. The rules say that the model shall be capable to sitting still with the engine (motor) at idle without a stooge or any help, and then take off.

I always warn people to check the outline of any plan or kit before you build against the 3-view you are going to show the judges, it better match the 3-view or you will see static point deductions. Always get the 3-view before you build and for that matter your complete documentation package. Remember you can't change the 3-view to match your model, the model is updated to match the 3-view.

As for the Airfoil, I don't think that most P-51 kits use the scale Airfoil and that feature is hard to judge. Wing thickness could be easily judged but the actual airfoil shape would be difficult to judge. There is also a wing thickness that can be judged. the F7F has an 18% thick root and a 12% thick wing tip, in other words you can't take the same airfoil and use it for the root and tip. If you shrink the root airfoil shape to match the chord of the tip it will be too thick.

Fred

Paul Smith · « **Reply #10 on:** December 18, 2014, 08:40:29 PM »

An aerobatic airplane like a Pitts Special or a Mustang or SPAD or any fighter that DID NOT at least do inside loops and inverted should be HEAVILY downgraded on realism of flight.

Real airplanes that could do outside loops are rare. And those that did generally had symmetrical airfoils.

Chris McMillin · « **Reply #11 on:** December 21, 2014, 08:08:12 PM »

Outside loops were performed by Jimmy Doolittle and others in the 20's and 30's with airplanes that did not have symetrical airfoils. Not until the 1960's were airplanes built with airfoils approaching symetrical, the Pitts Special, Yak 18, Zlin, and such were first built with standard airfoils and flew outside maneuvers with regularity, then they evolved.
My Pitts specials were both "flat bottomed" winged airplanes and I flew outside maneuvers regularly.
Chris...

Jonathan Chivers · « **Reply #12 on:** December 29, 2014, 08:57:12 AM »

Hi,
I have recently purchased from Al Rabe his excellent DVD on his builds. In part this covers some of his design philosophy and hard learnt experience with his Mustangs, Seafires and Bearcats.

If I have understood Al correctly, he adds dihederal to low wing plans to balance out the handling to allow consistent line tension through the full stunt pattern.

Try asking Al!

Jonathan

Allen Goff · « **Reply #13 on:** December 29, 2014, 11:19:28 AM »

Chris, you are correct. People need to know what they are talking about before putting out incorrect information.

Blessing
Allen

Dennis Saydak · « **Reply #14 on:** December 29, 2014, 05:53:21 PM »

Gentlemen, thanks for your input & advice. The reason I asked this question is I have acquired a Royal Mustang Jr. kit that isn't true scale. It would make a great demo model especially if it is capable of flying basic aerobatics. I'm not hung up on either exact scale or contest calibre aerobatics in this case. A model that is easily recognizable as that of a real aircraft that can do more than just fly upright circles and inside loops is my goal. I believe according to your input my Royal kit would "fit the bill".

Tim Wescott · « **Reply #15 on:** December 30, 2014, 11:26:04 AM »

Quote from: Chris McMillin on December 21, 2014, 08:08:12 PM

Outside loops were performed by Jimmy Doolittle and others in the 20's and 30's with airplanes that did not have symetrical airfoils.

One of my favorite RC planes, that I had at the end of my first model airplane career, had a Clark-Y airfoil and no ailerons. It would do outside loops and sustained inverted flight. Sustained inverted because, if you have the right dihedral, the rudder will act as your ailerons. Outside loops because it had 210 square inches of area, and it weighed 14 ounces (and being RC, it had lots of room to maneuver).

Quote from: Chris McMillin on December 21, 2014, 08:08:12 PM

Not until the 1960's were airplanes built with airfoils approaching symetrical, the Pitts Special, Yak 18, Zlin, and such were first built with standard airfoils and flew outside maneuvers with regularity, then they evolved.
My Pitts specials were both "flat bottomed" winged airplanes and I flew outside maneuvers regularly.
Chris...

AFAIK, the B-17 had a 0018 root airfoil, and a 0009 tip airfoil. Please don't ask me why.

Jim Kraft · « **Reply #16 on:** January 06, 2015, 06:21:36 PM »

The Bucker Jungmeister has flat bottom wings and is very aerobatic. It also had 2 deg. negative in the top wing which probably helped.

Chris McMillin · « **Reply #17 on:** January 07, 2015, 01:26:58 AM »

Interesting, Jim. The Staggerwing has 1.5 degrees positive incidence on the bottom wing, which is forward. I used to perform aerobatics in the Beech and it was a great flying acro ship, if a little large and heavy.
Chris...

Jim Kraft · « **Reply #18 on:** January 07, 2015, 08:58:10 AM »

Hey Chris; That would make the decalage the same as on the Bucker. Kind of different though in respect that it would work out the same only when the Staggerwing is inverted which would also lead to its aerobatic capability.

Chris McMillin · « **Reply #19 on:** January 07, 2015, 07:48:46 PM »

I see what you mean, Jim. Never thought of it that way.
When at near stall, the Staggerwing will just descend and bob the nose up and down as the front wing stalls and the top wing unstalls. If you pull the column all the way back to the stop it'll stall both, though.
Chris...

Will Hinton · « **Reply #20 on:** January 08, 2015, 09:03:22 AM »

This has been a very interesting discussion, especially with Chris and others with knowledge and experience in full scale aircraft contributing.
However, please let me express this - an aerobatic manuevor done for c/l scale cannot earn one point more than other options that are available, so why worry about trying to build a ship that is capable? Is it worth the risk just for the satisfaction of doing it? A missed approach is worth all a loop is, and much safer. That is only one example, there are more, so if you're wondering what to build for as far as options, dig out the rules and read them carefully, then decide on your approach to the model you want to build.
Hey, this is a great event, so keep it enjoyable without the stress!

Fred Cronenwett · « **Reply #21 on:** January 08, 2015, 11:27:10 AM »

One option I really like is flaps, easy to perform and increase the realism score

The single engine model can perform these options when you have just throttle and flaps

engine control
flaps
Touch
Go
Taxi
45 degree or missed approach

Most scale models that I have seen are far too heavy to really perform the aerobatic options

Fred

Tim Wescott · « **Reply #22 on:** January 08, 2015, 12:37:53 PM »

Quote from: Will Hinton on January 08, 2015, 09:03:22 AM

This has been a very interesting discussion, especially with Chris and others with knowledge and experience in full scale aircraft contributing.
However, please let me express this - an aerobatic manuevor done for c/l scale cannot earn one point more than other options that are available, so why worry about trying to build a ship that is capable?

If you're not serious about winning it may be a fun way to fill a schedule -- build a ship that's simple and light and looks good from a long way off, put a throttle in it, and get your flight points from aerobatics rather than from flaps and retracts and all the whiz-wangs that you'd want to build into a "real" scale ship.

Chris McMillin · « **Reply #23 on:** January 08, 2015, 09:32:54 PM »

Most Scale models of acro airplanes have been built too heavy for loops and aerobatics, but if built to proper weight they would be pretty good for loops, eights and inverted flight. What is the weight limit for .018's now, 48 oz?
Chris...