Someone help me get this Stearman flying!!  
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All Forums >> RC Airplanes >> RC Scale Aircraft >> Someone help me get this Stearman flying!!
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Someone help me get this Stearman flying!! - 4/7/2002 8:39:47 PM   
wulf190



Posts: 1112
Joined: 3/31/2002
From: chicago, IL, USA
Status: offline 		I hope that someone might be of some advice regarding a troublesome Midwest Super Stearman. Here's the story with the plane; built per specs with a smoke system, 21st cent. fabric, robart gear, a 91FS up front w/ more than a pound of lead and this thing weighed in around 14 pounds. Ouch. First flight lasted about 50 feet....very tailheavy with CG on the plan location and way underpowered, recovered it in one piece and changed engine to a Homelite 30cc gasser w/ ignition. No question of enough power now, I changed the CG another inch forward. Results: CG seemed right and the plane lifted off correctly with adequate flying speed, seemed to bank left with acceleration, correcting right, I noticed the problem seemed amplified by acceleration, so I backed off the throttle to get it to correct, which it did, but with a lot of deflection, aileron and rudder. Now, losing altitude without much to burn, I don't have enough elevator throw and throttle to burn to pull the nose up quickly enough and the plane noses in a bit, ripping the firewall nearly cleanly off the front, mashing my nice cowl work and bending a strut a bit.

I discover upon inspection that one of the interplane strut connection on the lower wing is cracked, making me suspicious when I notice that the right top aileron will now stay in a locked down position due to the flex in the set-up. I do not know if this cracked on impact or in flight, resulting in my right correction. Either way, this is my first bipe and I need to check the wing incidence angles to be sure they are correct and the interplane struts don't change things or cause warps that might add to this tendency, right?? Also, I have ordered seperate servos to drive the top ailerons independently. Good idea? I also have suspicions that the elevator pushrod, with it's split into a y to drive both elevator halves is giving too much blow back, and am going to drive each with a seperate servo.....yet another servo.

I have some repair questions however. I can cut, or order a new firewall and probably make a pretty solid repair to the injured area. However, with all of this power and a TOTAL lack of access to tank, landing gear and battery access, I would not only like to reinforce the firewall area, but also make the firewall removable if possible. How might I make things strong enough in order to do this? I have a ton of time and dollars in this plane and I am going to fix all of this, try to get it right one more time and deal with it after this. Any other suggestions about the security of this bird would be appreciated. I can send pics of the plane, it's injury, etc. if needed. I have the feeling that if I can get this thing right, it will be one of my favorite planes. But my questions are, too much power? wing incidence? firewall fixing? control surface actuation? Am I on the right track?

Thanks for any suggestions.

Mike
       Post #: 1

Someone help me get this Stearman flying!! - 4/7/2002 11:23:20 PM   
MiL



Posts: 281
Joined: 1/22/2002
From: Bend, OR, USA
Status: offline 		just a guess... kinda sounds like maybe the thrust angle was incorrect. Might wanna double check the plans for those figures or ask others who have had this plane about that.

(in reply to wulf190)
       Post #: 2

Someone help me get this Stearman flying!! - 4/8/2002 2:00:54 AM   
wulf190



Posts: 1112
Joined: 3/31/2002
From: chicago, IL, USA
Status: offline 		I hard mounted the engine to blocks attached to the front of the firewall. Sanded to allow for the couple of degrees of right thrust, this is what the plans recommended for the 91FS power. Should I add more with the larger motor?

(in reply to wulf190)
       Post #: 3

Someone help me get this Stearman flying!! - 4/8/2002 12:37:36 PM   
MiL



Posts: 281
Joined: 1/22/2002
From: Bend, OR, USA
Status: offline 		I don't know if you should add more, like i said, it's just a guess and i thought it would be worth checking. Maybe you would realize you had made a mistake, or parts were of the wrong dimensions or something. If everything looked correct according to plans then i don't know. I'm not really that knowledgeable about this stuff... prolly shoulda kept my mouth shut in the first place

(in reply to wulf190)
       Post #: 4

Someone help me get this Stearman flying!! - 4/8/2002 7:26:20 PM   
Tmoth4



Posts: 1358
Joined: 3/14/2002
From: Brecksville, OH, USA
Status: offline 		wulf190,
A couple of degrees right thrust should be enough for the homelite.
If you're getting radical trim changes under power, check for twisted wing or loose flying wires that allow a wing to twist. Also, you might be a little too nose heavy if you're dropping the nose a lot when landing.
You'd have to add a lot of hardwood, brackets, screws and stuff for a removable firewall, which would add even more weight.
Check for slop in control surfaces and flexing of pushrods under load.
These are just some ideas based on your description above.

(in reply to wulf190)
       Post #: 5

Someone help me get this Stearman flying!! - 4/8/2002 8:13:14 PM   
wulf190



Posts: 1112
Joined: 3/31/2002
From: chicago, IL, USA
Status: offline 		Considering I added a bunch of lead to the front, and with mounting of the ignition unit to the front of the firewall as well, it was all ready pretty crowded up front. In fact, I hope that I can get it all back in the space of the cowl. What was voluminous with the 91FS got really crowded with the ignition, switch, lead and the motor itself in there. I could ease up the space required if I could get that ignition system in the tank compartment somehow. Problem also with the existing setup is that the four machine screws holding the gear to the l/g mounts are completely within the airframe, with no access to periodic tightening of these screws, let alone access to fix a possible cracked gear mount in case of hard landing. I am not married to having access to this area as my guess is that it would be a non-issue if I could get the thing in the air all ready.

Are the Dave Brown fiberglass pushrods w/ the 2/56 rods strong enough to avoid flex or blow back? Also, I obviously need to reinforce the strut hold downs. What material is best for this? I still have the die cut pattern for the rib and could cut one of different materials, my guess is that doubling up the 1/8 ply w/ a little carbon fiber is a good idea. Also, I am guessing that I need an incidence meter to check the wing alignment right?? One thing to add in this regard is that, although the struts were built to match the plans, a little flexing is necessary to get all of the line-ups correct for the hold down screws. This is probably not right as it doesn't feel like something I should have to do. I can't notice too much by sight, but it wouldn't take much with the wing off a bit to make it crazy. Anyone with experience in this dept.?

(in reply to wulf190)
       Post #: 6

Someone help me get this Stearman flying!! - 4/9/2002 1:20:33 AM   
Tmoth4



Posts: 1358
Joined: 3/14/2002
From: Brecksville, OH, USA
Status: offline 		Try supporting your pushrods with one or two 1/4 balsa guides inside the fuse, if you see a lot of flexing. That should stiffen things up considerably. It'll probably be tough, with the fuse all stringered and covered, but you might have to do a little necessary surgery. Biplanes are tricky to align. I always put the plane on a big flat surface and prop the tail up and put a small level on the stab. I measure distances from the table to the wings at various points, and distances between the wings, making sure both sides are equal. I also measure distances from a point on each wing tip to a center point on the fin or tail post to make sure of alignment from the top view.
A lot of it is standing back and eyeballing, too.

(in reply to wulf190)
       Post #: 7

Someone help me get this Stearman flying!! - 4/9/2002 5:37:07 AM   
wulf190



Posts: 1112
Joined: 3/31/2002
From: chicago, IL, USA
Status: offline 		Seems like the alignment from wingtips to tail is the same per side. My concern lies in the interplane struts which run at kind of an awkward angle like the real plane. It is difficult to sand the strut (1/4x1/2 basswood) to get a nice tight joint angle, as a notch has to be sanded out at the approximate angle of the strut itself. I am wondering if another material might be easier to construct, if in fact the struts cause some problem. Would an incidence meter be helpful?

(in reply to wulf190)
       Post #: 8

Someone help me get this Stearman flying!! - 4/9/2002 7:37:08 AM   
Tmoth4



Posts: 1358
Joined: 3/14/2002
From: Brecksville, OH, USA
Status: offline 		It's hard to picture without seeing it. I think basswood is pretty good to work with. Have you tried permagrit files? They're my most used tools besides x-actos.
I've never used an incidence meter.
Maybe you've got a heavy wing on one side?

(in reply to wulf190)
       Post #: 9

Someone help me get this Stearman flying!! - 4/9/2002 7:56:07 AM   
wulf190



Posts: 1112
Joined: 3/31/2002
From: chicago, IL, USA
Status: offline 		Tmoth; there is a thought. I have not balanced the plane laterally, but will do so along with the other mods. I think the elevator pushrod set up is garbage. There is just too much flex in the set up for my liking, and I know I'm not going to go diving into the guts of this thing any further than to swap out a pushrod or two. I am confident my elevator concerns will be solved. How much torque is there upon accelleration? The stearman is definitely overpowered with the homelite up front...more so than any other plane I probably have flown, but I usually power with recommended engine sizes...in this case it was just out of the question. This said, I was pretty carefull about accelleration and throttle management and such. I feel like my good flying and building skills have been reduced with this plane, and the stearman may as well be my Sig Kadet of 20 years ago! I appreciate the feedback.

(in reply to wulf190)
       Post #: 10

Someone help me get this Stearman flying!! - 4/9/2002 8:08:12 AM   
Tmoth4



Posts: 1358
Joined: 3/14/2002
From: Brecksville, OH, USA
Status: offline 		I have a 1/5 scale Waco with a 25cc homelite in it, weighing about 14.5-15 lbs. It's probably a similar size and weight to what you have. I haven't noticed much torque effect. I just have to maybe hold a little right rudder during takeoff and climbout.

(in reply to wulf190)
       Post #: 11

Someone help me get this Stearman flying!! - 4/9/2002 5:23:04 PM   
Edwin


 

Posts: 3421
Joined: 2/8/2002
From: Leander, TX, USA
Status: offline 		Interesting thread here. I'm real interested in hearing what the final outcome is. About incedence meters, I'm a firm believer in them. You can build one for about $5 pretty easy. I have a jpg file that would explain it much quicker than telling you. But in a nutshell, it uses a cheap compass with a quick link in the center hole and 1/16" scrap wire hanging down mounted on telescoping brass or alum. tubes. Contact me back channel and I'll send it to you if your interested.
Edwin

(in reply to wulf190)
       Post #: 12

Someone help me get this Stearman flying!! - 4/9/2002 8:36:50 PM   
wulf190



Posts: 1112
Joined: 3/31/2002
From: chicago, IL, USA
Status: offline 		Thanks Edwin, will do. For good measure I am going to fix anywhere I think that there could be a problem. The firewall is a bit of a struggle for me however. Nearly a clean sweep of the 2 piece firewall from the airplane, it shouldn't take much to put a new one on the front. It looks kind of tough, however, to get anything removable on the front. The round front end is all balsa sheeting with 1/4x1/8 stringers. Exposed now, I can add some basswood gussets to the glue joint, which wasn't done by the builder of the fuse (I purchased the plane with the fuse built). I just dont think I can get anything in between the stringers to add enough strength to the stringers/sheeting to make the front end solid enough to mount a vibrating firewall to. I could glue on the new firewall and mount something removable to the front of that firewall but it still wouldn't give me access to the tank area, or the l/g mounts unless I cut a big hole in the middle and I am just not confident I can get the front end solid enough to withstand vibration over the life of the plane. Who designed this thing like this? Is the Ziroli version similar? Am I wrong in thinking that mounting sort of a "firewall ring" behind the firewall, mounting the wall to the ring with blind nuts and machine screws won't add enough strength? The only way I would know is to rebuild the plane this way and find out the hard way that it wouldn't be tough enough. Experience tells me that vibration might get the best of the area.

(in reply to wulf190)
       Post #: 13