Hanger 9 1/5th scale Mustang.

[Txmustangflyer]

The primary concern should be to use a 100% of the servo’s motion. Maybe 80% if really boxed into a corner! This means a shorter servo arm, period. A shorter servo arm will allow your flap to get closer to 80° before reaching the 3 point lock up.

If need be flip the servo so the output is closer to the LE. Move the servo up or down in the wing. Place the control horn pivot aft of the hinge line (with the flap in the profile setting [up]). And the simple fix is lengthen the slot to clear the push rod. But whatever you do, please follow good solid mechanics! Flaps do put a load on servos, so give them a fighting chance.

Did some more thinking on this one, Konrad. None of the servos will be at 100 percent travel with exception of throttle, choke. Even the inner gear door servos won't. Thats even before changing the arms. The deflection needed for the control surfaces is too low. Below are measurements at the TE given on high rates. The only ones that come close are the elevators.

 

[Konrad]

...The deflection needed for the control surfaces is too low. Below are measurements at the TE given on high rates. The only ones that come close are the elevators.

Why does the low motion of the control surface dictate servo resolution? It is the ratio of the control horn and servo arm that dictates this.

 

[Txmustangflyer]

Why does the low motion of the control surface dictate servo resolution? It is the ratio of the control horn and servo arm that dictates this.

True, but even if you use the supplied servo horns with the kit, they only travel about 50 percent of their range at those deflections. Its kinda wierd. To fix would mean gutting the wing, moving the servo mounts closer to the surfaces, etc. The rods and control horns have to be seriously altered. Its thos kind of stuff that we warbird guys deal with in the arf world. We do what we can. The rest we live with. Its probably why the servos specified were some of the highest torque spektrum makes. Even flipping the servos wouldn't fully correct. Its also part of the reason my next plane, is a kit build. Another part of it is being clise to scale. They have limited space for servos, they kinda have to go where they fit. For F3A your aircraft are designed for maximum speed, tightest turns possible. You use every bit of travel you can get and, at times, probably wish you had more. In scale warbirds we're after making it fly like the full scale plane, only wanting extra power in reserve if we get in a jam. Its not about speed and turning on a dime with 9 cents change, so arf designs don't worry so much about max traveling the servos. Look at the aileron deflection in the screenshot. The mustang's aileron, to max travel the servo, would need a travel amounting to twice the 22 mm measured at the TE. No matter the position of the servo. At 22 mm, that amounts to a snap roll, for the mustang, at that deflection, the roll rate would send you to a chiropractor in a real aircraft. You'd definately see red as all the blood rushed to your head. Elevator maxed out would induce GLoC. The upward pitch of the plane would overstress a real P51, possibly causing structural failure..if the pilot had the upper body strength to move the stick far enough and the room in the cockpit to do it. They still "bent the bird" quite often. For the subject of the servos, the geometry just isn't there. In some ways, they are using the servo position, arms, and rod length to limit the amount of deflection we can achieve, so we don't overstress the design.
In a full build kit, if I know, from the start that I want more deflection, in the case of the ailerons, for neck snapping roll rates, for instance, I can reinforce the wing during the structural part of the build, beef up the spar, double ribs at key points, etc so I don't tear a wing off in a snap roll. With an ARF, to do that, would, again, mean gutting the wing. Instead, they compensate using higher torque servos, but placing them so that the aileron (or flap in this case) would hit it max long before the servo does. The result, if you mess up and set everything to 100 percent travel, is a. The aileron rips off its hinges, or b. The trailing edge of the wing twists and snaps. Neither is a good scenario. As it is, since you focused on the flap, is the area between the flap leading edge and the trailing edge of the wing I have to rework, as it is, just to get the flap to even come clise to the suggested deflection, an error in manufacture. I thought, initially, it was just ultrakote being kind of loose and bunching up. Trimmed that away and found out sand paper is gonna be involved. Its not a straight cut, but looks more like something Doc cut after two bottles of Sake. I can only hope to kinda fix it..it will never be perfect.
I figure I'm going to have the same issue with the ailerons, elevators. I addressed it on the rudder when I recovered it.
The blade in the cutting process has become wavy feom long term use. Be different if the factory were to stack, clamp, and laser cut multiple sheets, instead they press cut individual sheets. The result is a pretty substantial variation from blue print to production just from the wear of the die in terms of final product. Going back through early build threads of this kit, there were no inyerference issues, but lots if comments on the servos using maybe half the possible travel. It is what it is.

 

[Txmustangflyer]

Ok. The mustang exhaust.

I need to vent some, because this has turned from a minor irritation to the point it nearly shelved the build. 4 months ago, yesterday, I ordered a Bisson wrap around pitts for the mustang. Needed some tweaks from standard, but not huge tweaks. Nip here, tuck there. Was told then it would be a couple of months as they were waiting on material. Ok.
At the end of that 2 months, the owner calks me and basically gives me a shine job, stating he had material to work with but, it was still going to be 2-3 weeks.
Now, I'm typically a nice guy. I got something on order and its delayed, just keep me in the loop and I'm good. I wait another month. Nothing. Send a polite email asking for an eta update...crickets.
I wait a week, figuring his 8 to 5 has him busy..still no response. Attempt to call...machine, again, leave a polite message, not mad, just an inquiry. No return call, no email after 4 more days. I send an email with a link to a US metal supplier that has aluminum, brass, copper, and steel down to a .035 thickness, in stock. Even offered to buy and ship direct to him whatever material needed to make the exhaust...crickets.
Last attempt, another phone xall and email. No response.
So, I've gone to seeking alternate methods. A. Working towards having the individual parts machined to make the exhaust myself...waiting on that quote.
B. Found another US manufacturer of exhausts, J&A. They haven't made a zenoah exhaust in a while, but checking to see if they still have one. Found them thanks to another RCer. They don't sell direct, only to dealers but were nice enough at the request of a dealer, direct to me.
C. Another RCer has stepped up and said he would make it, if J&A fell through.

Last night, I got an call from J&A. I'm in luck. Under a bunch of dust, cobwebs, and a few other boxes, lurked, in the shop, a lonely, untouched for many years, G62 wrap around pitts. Now, guys, what I'm about to say sums up old school rc. Upon telling me he had it, of course, I asked what he was asking for it. Response: free plus shipping.
(Jaw drop)
He also said, "You'll probably need to modify it, the outlet pipes may be too small"
Ok. I can do that.

 

[Txmustangflyer]

Apparently, a little bird told Lance @ Bisson I was getting nervous. He also, finally, reached out this week. He's shipping his exhaust this week as well.

Go figger.

 

[Txmustangflyer]

The wiring has begun.

 

[Txmustangflyer]

Photo moment for encouragement

 

[Txmustangflyer]

A big piece is now on. Drilled for the anti rotation pins, painted and awaiting a touch of some 1200 grit to make it perfect smooth.

Its still a face any pilot could love

 

[Txmustangflyer]

All the cowl needed to clear the engine and get some good air flow over the top of the cylinder. At the back of the opening there is a goid 3/8s spacing between the cowl and cylinder so should keep it happy. The only parts that actually touched were the plug, and the front two corners of the engine...the zenoah nestles in nice. The bit of extra is so I can space the engine forward a touch at the standoffs. Made sure I had the room without having to trim on the cowl more. Other than some file work to smooth the edges thats the cowl cut. Just gotta drill and mount now. Only other thing i have to cut is the openings for the exhaust outlets and, if necessary (I hope it isn't) clearance for the exhaust header.