N1EDM

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Capriman, I have a couple of questions, if you guys have the answers....

Where is your other thread about the P-51 'diet'? I'd like to take a look at it. Thanks! Also, regarding your comments about the 91FX, I'm not sure if I have an older or newer OS 91. Can you tell me how to identify the 'old' engine and what parts (via TH, I presume) are needed to rehab it?

Thanks in advance,

Bob

Quikturn

My Feedback: (12)

Hi Bob,

The older engine has the metal remote needle housing cast as part of the backplate. The newer design has a separate black plastic remote needle valve assembly that is held on the backplate with a steel bracket and rear cover screw. My guess is that this is to provide better engine vibration isolation. The vibration is thought to introduce air bubbles from the remote needle valve to the carb on the older versions causing unreliable performance. This gave the 91 FX a bad rap in some circles but I think it's still a great engine. Not all people experienced this however. I think prop/spinner balance or engine mount choice may play a part in this.

Come me to think of it, I have a 46 FX I bought with a broken RNV. I JB welded it back in place and have no issues with it. I wonder now if it was broken deliberately?

Quikturn

My Feedback: (12)

Capriman, good idea to weigh all the balsa. With built up tail feathers it won't be hard to make it tail heavy. I won't buy new balsa but I will weigh what I have. Good tip!

Steve, sorry for your loss and I hear what you're saying. I've had good luck using one servo in the past and always go with new. Wonder if vibration plays a role in servo failure. My thought was to keep things more center mass. The P-51 is not a pattern ship so it won't need dual aileron digital servos IMO. I will add hatches to the aileron bellcrank area to make them serviceable if need be.

acdii

I agree on the single servo setup. I had one on a Deweyville, and though no warbird, and not very fast, it still managed to fail. The center ball link is what failed on mine, it cracked. My Stang, Corsair, and Super Chipmunk all have dual servos now at the ailerons because of that. It is also less draw on the pack since its a short throw right at the aileron and not pushing two ailerons, pushrods and bellcranks. It also gives you the ability to add weight to the wing if for some reason one is heavier than the other for lateral balancing. I had to do that to my 4*120, one wing needed 1/4 ounce to be perfect, and putting it on the servo hatch worked out perfectly. So going with dual servos over a single has benefits to it you dont get with a single servo.

On the P-51 it is easy to do, if you haven't built the wing yet, pay out your ribs so that you can make some holes from W2 to about W5(I would have to look at the plans to tell for sure) for running the servo lead through. Roll up some heavy paper into a tube and insert it in these holes and stiffen it with some CA. When you are ready to skin and have the bottom skin on, then where the plans call for the pushrod opening, this would be where you would put the hatch and servo. You would need 1/4 x 3/8 basswood for the hatch rails that go between the ribs. Make the opening just large enough for the servo to fit with about 1/16 gap on either side, then make the hatch to be 1/2" the width of the rail, (3/16), then make the hatch width from the bottom of the servo, to about 1/4" above the arm screw. This works for just about any setup, and only varies if you are using heavy duty arms that stick up higher than the supplied arms that come with the servos. I use Futaba 3004 and 3010 servos for this. Once the hatch is made, use it as a template to cut out the wing skin. I use plywood same thickness as the skin, then take 3/32" ply that fits in the opening and glue that to the inside of the hatch for strength. Place the hatch in the opening and I used button head #2 x 3/8 screws to secure it. Check to see if the curvature of the wing matches, if there is a noticeable difference take the piece of balsa you cut out and glue it to the outside of the hatch, then sand it to match the wing.

To attach the servo use 3/8" square bass or maple cut to the width of the servo, Line up the servo so the bottom of the servo is just a hair above the bottom of the hatch, and mark the position of the servo rails. Glue the blocks with medium or thick CA, and let them set naturally, dont use kicker since it can cause the CA to expand. Once set, then take 3/4" tri-stock cut to the width of the rail and clue it under it for bracing. Mount the servo as normal, then line up the servo arm on the servo and mark the opening for the slot. The slot varies on the throws, so that will have to be done during setup of the servos, and I usually leave that for final setup. I use a drill and drill out a hole at either end of the slot and then cut out the slot and file it smooth.

It takes about an hour for me to add them and find it well worth the effort.

This of my Corsair, the Mustang is the same.


Thankfully I noticed the roll rate on the dewey was not quite up to par, and inspected the servo before it became a kit. I replaced it with a swivel joint ball link one. I got a few flights on it before I learned how to fold the wing for storage on a take off where a cross wind flipped it over just as the tail came off the ground. Since I have to rebuild the wing, I will probably bash it and make it a bi-plane and move to dual servos on that one as well.

capriman

This is a good subject to bant around, but my decision will be based on total weight of the servo system including all related hardware. I can build a bullet proof linkage using the current available hardware on the market, but where I argue with myself is this: A single servo might fail in flight and it WILL bring the plane down.....2. servos would seem to provide redundancy, but where will that one servo be in it's range of travel when it fails ?? will it return to center and then not move any more, or will it just fail at it's deflection point leaving you to try and fight it with the other servo ?? A failed servo on the elevator with 2 servos might be a different story as you might get one elevator stuck in a position, but that can be fought with the other elevator and opposite aileron and rudder to counter act any roll that it would produce. I have seen more nitro planes crash on takeoff due to the after run oil fouling the glow plug than I have seen due to equipment failure like this topic. My opinion on the number one reason these 60 size Mustangs crash is simply being over weight and failure to build in the proper washout at the wing tips. let me get some more info on the needle valve for you....

capriman

Needle valve parts... http://www3.towerhobbies.com/cgi-bin...?&I=LXANA7&P=V http://www3.towerhobbies.com/cgi-bin...?&I=LXCM87&P=V http://www3.towerhobbies.com/cgi-bin...?&I=LXGBG0&P=V
http://www3.towerhobbies.com/cgi-bin...?&I=LXMW56&P=V

I think the reason these parts were used in later 91 engines was to isolate the NV from heat of the back plate. If you increase the moment length of a moving arm, the deflection of the moving part will also increase, (most of the time)...
If you are going to weigh the 1/16th balsa and have a gram scale, here is the formula: 1/16th by 3 by 36 inch sheet will weigh one point seven seven grams per cubic foot density ( 1.77 gms / Cu/Ft. ) so if your sheet weighs 15 grams it would be classed as 8.5 pound density. If your sheet is 4 inches wide OR 48 inches long, the factor is 2.36 grams per cu/ft. ( you have 1/3 MORE balsa to weigh ) If you have 1/8th by 3 by 36 your number is 3.54 and if it is 4 inch wide or 48 inchs long, the number is 4.72 ..... start weighing your wood and keep records. I am sittimg on almost 1800 sheets of hand selected and hand weighed contest wood that I have collected over 40 years so I can choose what to use. I did need 4 sheets of 1/8th by 3 by 48 long, "C" grain, 6 lb density ( 28 to 30 grams) and called Sig, and they cut it for me...waiting on shipment now.

stevegauth30

To each his own. It really is up to the builder how they wish to set up a plane. I was only sharing my experiences. I have also seen a plane with dual servos go in ( only once, and it wasn't mine.) another thing to look at is the quality of servos. Obviously, if using the cheapest you can find, there is that much more risk of having one fail. That's not to say that one shouldn't use the single servo setup, because people do it all the time with good results. Just think about what servos you use. I used to get the lower quality servos and had a few fail, but since spending a little more on servos, I haven't had one fail yet. Just my two cents. Steve.

acdii

Wheel doors done and working, just need to fine tune the air system now.

http://www.youtube.com/watch?v=GxvjLShtD6o

N1EDM

My Feedback: (2)

Capriman,

Thanks for all of that information. I just missed out on a NIB 91FX on eBay this afternoon.... I have another one already and would like a second one....

Thanks again,

Bob

rotodoc

I have 2 del 20's. One on a H9 P-47D 60 and the other on a CMP F-6F 60. Both have seen hundreds of flights and are still flying missions. Never had the first problem with either.

capriman

My P-51 "on a diet" thread is here.... http://www.rcgroups.com/forums/showt...5#post27173936

N1EDM

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Thanks. Just subscribed...

Bob

raptureboy

The single servo operation for ailerons has been in use for years and there are many of these planes flying just fine with this setup. I changed my snap on ball link to a bolt on version from Dubro and also used golden rods to the bellcranks as I also changed the wheel location on my P-47 to the scale position. When you think about it, how much stress is there on an aileron at any particular moment? Now an elevator fighting against the force of pulling out of a loop is another thing altogether. This duel servo arrangement for ailerons is only a recent thing, and in my opinion brought on by the arf manufacturers to save time and $ not having to set up aileron bellcranks and pushrods. All my single servo aileron planes from trainer to warbird work just fine and no wye is needed also. Giant scale is the only place where I would see a real need to go with separate servos. But as it has been said here, you have to go with what makes you comfortable in the end. You can ck out my arrangement here. http://www.rcuniverse.com/forum/kit-...7-build-3.html

FlyerInOKC

My Feedback: (6)

OLD FOGGY ALERT! - An antique speaks out!

Back in the bad old days when the earth was cooling and dinosaurs still roamed the earth and I was a young lad starting out in RC in the 70s. One servo was used for the ailerons because servos were so expensive. They competition builders with sponsors would use two but for the rest of us at $50 a pop it was way too expensive. The old KPS-9 were great for ailerons because they had one rotating arm and two straight line connections moving in opposite directions. They were also about the size of 2 Futaba 3004s glued end to end and taller. Kraft really shrank servo size when the KSP-10 came out. Now go look at the price of a good servo today and compare it to $50 in 1970s dollars and you can see why 2 servos became so popular and one servo with bellcranks began to disappear.

Quikturn

My Feedback: (12)

I think there are good points on both sides of the single vs dual aileron servo debate. Personally, I've never had a servo fail on me so I haven't really considered that when deciding which way to go. I've had many airplanes with a single servo, control horn, strip aileron setup without a problem. The pros to a single servo would be less cost, less weight, less current draw on the Rx pack. Cons would be no redundancy in case of failure, more slop in the setup (debatable). The pros to a dual setup would be redundancy in case of a servo failure, more precise control, new Tx functions such as aileron differential and reflex. Cons would be more cost, weight, current draw. Anything I'm forgetting?

Capriman, I'll be watching your build.

stevegauth30

The thing I like the most about dual set up is that you can adjust each aileron independently in your tx rather than having to mess around adjusting everything mechanically. As for redundancy, like I said earlier, if you spring for descent servos, they more than likely won't ever fail. I personally, and this is only my opinion, only use hitec servos, and not the cheapest ones either. Like I said, that just what makes ME comfortable.

FlyerInOKC

My Feedback: (6)

I can relate Steve all my servos say Futaba on them.

Quikturn

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My early models had Futaba S148's but recently I've had good luck with JR's value series ST47/ST47BB's.

Whats interesting is the TF kit uses a single servo for ailerons and dual servos for flaps. Why not reverse that and use the single servo, bell crank setup for flaps instead?

FlyerInOKC

My Feedback: (6)

Quickturn, I use the Futaba 3004s mostly I build in 1/5th scale almost exclusively with a wingspan usually no greater than 86 inches.

acdii

Futaba, JR and Hitec here too. I dont trust other brands(maybe Airtronics are OK).

I believe that the current draw would cancel out between the two. When you have one servo driving two ailerons, and having to push those long links and bellcranks, it takes more effort to do so. When you have a servo with a short throw to the aileron, it should be half the current draw, so two servos using half the current of the one, would be a wash. Anyone have a current meter to check into this?

I prefer the dual because it is so much easier to setup, and if you make a mistake with the internal links for the single servo, you have a hard time correcting it once the wing is skinned and finished. the hardest part with dual servo is fishing the lead through the wing, but if you account for that during the build, it becomes a piece of cake. The added weight towards the tips may diminish performance a bit, but its a scale plane, and should fly in a scale manner, so it wouldn't matter much at that point.

I agree about the flaps, why two flap servos and one aileron servo? The ailerons are used a lot more than the flaps. Of course they are huge flaps, and the plane was designed way back when servos were light on torque, you needed much larger servos back then to have high torque. Maybe the kit is due for an update for newer tech, like EP, lighter servos, and better positioning of components.

stevegauth30

One thing I do now on all of my builds is to make my own servo extensions. This enables me to run all my wires as built and then at the end I install the connectors. I grew tired of trying to fish extensions through a wing and cussing the whole time. Also, if you buy wire and connectors in bulk,( I buy wire 100' at a time) it works out to be like half cost. If you build a lot then it's justify able.

Quikturn

My Feedback: (12)

Acdii, you may have hit the nail on the head about the flaps. They're pretty big and would take a lot of torque to move them down with one servo depending on how they're used. If you use them to slow down (not the proper use) by lowering them at high speed then you may strain or stall the servo. But if you slow the airplane first, then lower flaps it should be easier.

I wouldn't think a long link would ad resistance but the bellcrank I think would. Of course you use nyrods and make a gentile bend to each aileron. That would eliminate the potential for slop as well.

The neat thing about the 2 aileron servo setup is you can adjust for differential. If the nose of your airplane spirals during rolls you can adjust the amount of up vs down aileron on each wing to eliminate that. Another thing (I don't know if anyone does this) is that you can make both ailerons deflect up a touch during landing configuration to provide more tip stall protection.

FlyerInOKC

My Feedback: (6)

I'm in the middle of a Top Flite Cessna 182 build and it specifies 2 servos for ailerons and Flaps. I have a partially finish TF Corsair and it has the same 2 servo setup for both. I traded for the Corsair not for the airplane but because it had Robart retracts, struts, tank, etc along with 4 new Futaba 3004 servos already installed. I wasn't crazy about the build quality but the incidentals made it a great trade. The owner couldn't sell the Corsair but the kit and engine I gave him sold within a couple of weeks so we were both happy.

capriman

Quickturn makes a good point about lowering the flaps at higher speed. I used to fly Piper Tri-pacers and you had to operate the flaps with a handle. You really got to feel the force needed to lower them at speed ( 80 mph ), and it was severly frowned upon to use more than one notch abouve that speed. We should use the flaps on the Mustang the same way...slow it down some and then add flaps.

stevegauth30

Exactly. Flaps are used for lowering stall speed. Not lowering flying speed.