wulf190

My Feedback: (19)

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

MiL

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.

wulf190

My Feedback: (19)

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?

MiL

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

Tmoth4

My Feedback: (1)

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.

wulf190

My Feedback: (19)

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.?

Tmoth4

My Feedback: (1)

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.

wulf190

My Feedback: (19)

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?

Tmoth4

My Feedback: (1)

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?

wulf190

My Feedback: (19)

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.

Tmoth4

My Feedback: (1)

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.

Edwin

My Feedback: (2)

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

wulf190

My Feedback: (19)

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.

Edwin

My Feedback: (2)

I had a similar problem with a mustang. Except I was the builder. I had to add so much weight to the firewall that its broken off twice now, and its only had 2 flights. Bummer. My problem is landing gear and its short coupled. A real big problem on ground handling. I plan on glassing the firewall to the fuse using some heavy cloth. By that I mean 6" or so from one side of the fuse, across the firewall, and 6" or so on the other side of the fuse. All sides. That should do it. Take out the retracts, move the tail wheel from the scale position to the rudder and that ought to take care of the ground handling.
Edwin

jhess

My Feedback: (28)

Your problem my friend is not enough positive incidence in the
stabilizer. You need to jack up the front of the stab about 3/8
of an inch to get the tail up in the air. All of the old sterling stearmans were that way from the manufacturer . We all added lots of weight untill we figured that one out

wulf190

My Feedback: (19)

This sounds on par. I can also tell you that I would be remarkably disappointed to have to rebuild the tail of this thing, something that I would sell the plane over, if the buyer were willing of course to do such surgery himself! Built according to plans, and quite well, I think, it might be worthwhile to go ahead and buy that incidence meter and check this out. Are the symptoms of this problem such that I have described? What are the symptoms? I have never had a plane not fly out of the box before, so this is a particularly frustrating experience for me. It's also tying up my nice TME smoke pump.

EASYTIGER

My Feedback: (119)

A porposing bipe is an incidence issue. Just "uncomfortable" to fly, and everything changes with different power settings. You need to get an incidence meter.

jhess

My Feedback: (28)

yeah ,You are right those cabanes are tricky to set up .
The stearmans I have messed with all called for two deg. positive in the stab and one degree in the top wing. this keeps the tail in the air and compensates fro the drag produced by the top wing

EASYTIGER

My Feedback: (119)

Sounds just right. Top wing either slightly positive, or zero. Tail depends on the model.
But boy, can a bipe be a headache with the wrong incidence...

wulf190

My Feedback: (19)

Thanks fellas. The tail has a little positive incidence all ready built in, a 1/8" sheet sanded to virtually nothing at the back of the stab and the full 1/8" at the front end. The stab is mounted on this plate, must give it a degree or two. I don't know about the top wing yet, but will check it with the meter and post the results here after I check it. It sounds as if I need to add a degree to the top wing for good measure. I am learning a lot here from this advice, and really appreciate this. I would like to build the Don Smith HE51 at some point, and this advice will really help me out. I had discounted how important these aspects are in a biplane, thinking I would be fine with my pattern and warbird experience....wrong. The porpoising describes it's flight characteristics perfectly, take off goes great but, the second its up, watch out. I'm feeling a bit more confident now about figuring it out. At least if I don't I can value the lessons learned during the process and hey, it will certainly make the end of the journey more enjoyable when I really do get one of these two wing jobs to fly!

MinnFlyer

My Feedback: (4)

Don't forget to check your lateral balance! And about the incidence meter.... Get one! That's one of those things I hate to buy. You spend 30 bucks or so, and you only use it for about 2 minutes on each plane. BUT THOSE 2 MINUTES ARE WORTH THEIR WEIGHT IN GOLD!

MAJSteve

My Feedback: (-1)

I agree with the incidence meter. I build bipes almost exclusively, and theres nothing more frustrating that setting the roots of the wing exactly right and having the tips a couple of degrees off. Heat gun usually takes care of it with some gentle persuasion.

I've got one Sterling Stearman finished now, but like the previous posts, it seems to want a LOT of nose weight. So I'm going to cut it loose and add some positive to the stab. I generally set the wings to 0 but I'm going to add some positive to my small Ziroli to see if that keeps it more online at speed. As it is now, it requires constant attention to keep it straight and level.

Once I get the wings straight and level, I make the interplane struts out of 2/56 rod stock and solder on threaded ends. I put ball joint sockets on it and put the balls on the rib tabs. THEN I readjust again and again till the whole thing is tight and the sockets align with the balls without tension on the wings. Then I cover them with medium balsa - two pieces front and back about 1/8 in thick. I do the sides with one wide strip. Once this is glued, its very easy to sand an airfoil on it. HOWEVER, the Stearman's I've seen up close have something a lot closer to a 2 x 4 with radius'ed corners. The fancy ones have airfoil interplanes and cabanes.


At the field, it takes about 2 minutes to put the interplane struts in place. Better than screws in my opinion.

Also, regarding Sterlings - I just built a hog bipe and boy do I like the way the screws go in from the top. Should be easy to modify the Sterling to do the same. The way they are now they're a pain to put in and take out.

johnnyo

My Feedback: (7)

If you haven't done anything with the firewall yet, here is an idea that will work. I had the same concerns when building my 72" Waco. Make two new firewalls from 1/4" ac ply. Trim and fit one, do not glue in yet, when satisfied with fit, determin the amount of acess you need for the tank, ignition etc.. Cut the second fire wall about 3/8" smaller all around. Also determine from the plans or what ever if there are any other attachment points to the firewall other than the outer points. Know cut roughly a 4" square hole in the middle of fire wall that you trimmed and fit, if the hole can be bigger that is fine. (leave enough area around the firewall to attach fire wall number 2.) When satisfied with the fit, acess and the amount of area to attach number2, epoxy in the original position, if possible reinforce with epoxy/fiber mix around the inside of the fire wall to fusealauge junction. Know center the second fire wall and drill 6 mounting holes through both fire walls, drill large enough for 8/32 fasteners. Drill the epoxied firewall large enough for 8/32 blind nuts. (Depending on access, you may want to do this pryor to epoxying it in.) You can now boult your engine to the 1/4" plate you have made and attach it to the firewall ring in 6 places. plenty stong. Use washers to set your throust lines, I would recommed 2 degrees right thrust. you will have to mount your engine slightly to the left of the the firewall center line, so with the right thrust the prop hub will be centered.
Deffinitly get a incedence meter or make a good one.
good luck
John

wulf190

My Feedback: (19)

Thanks JohnnyO, I haven't gotten to fixing it yet. This sounds like a good way to go about the issue. My only concern would be if vibration of the homelite would get to it. The plate on the front should help solve this problem I would guess, stiffening the assembly. The firewall is large enough in diameter that I should be able to make this work. It's going to take some pretty accurate cutting to get a good fitting firewall, testing my jig-saw and circular sanding skills here, but I think I can get it done. The tower that mounts one of the Robart struts cracked as well. These are always a bear to reach. And, if built according to plan, you better hope the lock nuts that attach them to the towers never come loose, because no one is going to reach any of these four socket screws anytime soon! Although seemingly a sturdy mount, who in the world would negotiate an arrangement like this?? Cutting an access hatch for the area would involve cutting right into the main ply fuse crutch. Even then, you could only get access to two of the screws thru this hatch, leaving the forward two to chance. This is a plane that will like SOFT landings if not modified when using the Robart gear, although the gear is really a nice addition.

wulf190

My Feedback: (19)

After all of this, it would be fair to post a pic at least...