ahicks

My Feedback: (2)

On the 4 Star, I would suggest that a 6" pitch prop would give increased take off and vertical performance without allowing as big a speed increase on any down lines. It also slows the airframe down easier on final approach. An 18x6 prop works pretty good with the RCGF 26 I've been flying... FWIW

rcmodelflyer2010

thanks your advice,i will try the 16x6 prop tomorrow and post later how it went.does this mean that the bigger the prop the lower the rpm and more torque and the smaller the prop the more rpm but less torque?
does this mean that im more likely to climb inverted with a smaller prop with more rpm.

best regards,rcmodelflyer2010<br type="_moz" />

sdherington

Here is the scenario. Larger diameter prop with lower pitch is higher rpm and more thrust. Smaller prop with higher pitch is higher airspeed in flat flight but less thrust. I agree with ahicks on the 18-6 or even an 18-4. I fly this engine in a Wildhare Edge with a XOAR 18-6 and it has unlimited vertical. Like I told you I am running a MA 16-8 3-blade on my Pawnee with good scale results. It is best to experiment with your engine, your airframe and several different props. Every engine and airframe is different, even 2 of the exact same setup will act somewhat different.

ahicks

My Feedback: (2)

You mentioned you were running OK with a 17x8. An 18x6, with larger diameter but less pitch, would load the engine similarly/turn about the same rpm on top as the 17x8 - but with the differences noted as above. Sport fliers may prefer that kind of performance. Somebody looking for higher speeds, willing to sacrifice a little vertical and take off performance, might want to go with 8" of pitch...

A 16x6 might not load the engine enough, allowing it to over rev., but could be worth playing with to see?

rcmodelflyer2010

should i get an 18x4 prop then as this should give me good rpm and not lose so much torque.its a good job there are guys like you's about to give a helping hand or i would be stuck lol my last engine which was a glow engine was a sc 46 with a 11x6 prop and it ran great for the size of the engine but the engine ive got now is like 3 x bigger i do much rather have petrol now tho instead of glow as i do think they are reliable engines and easy to start oh and most of all cheaper to run lol

regards

ahicks

My Feedback: (2)

The 4" pitch props are kinda crazy. The guys using those are generally flying 3D. Huge amounts of torque, but very little speed potential. Just right for that kind of flying, but from a sport flyer's perspective, they may be a bit too much of a good thing....

rcmodelflyer2010

think i will go with the 18x6 then.

thanks for your help,looks like another nice day for it anyway.

regards<br type="_moz" />

rcmodelflyer2010

hi.yesturday i smashed my sig four star 120 up to bits from about 70ft up,i had been flying for bout 30 mins with perfect weather conditions and the plane was flying really well.
i landed and then took off again got to bout 70ft made an easy left turn then with no warning the nose dropped 45 degree and mashed hard into the ground i had no control at all :-(

the plane is a total right off and the engine was damaged but can be salvaged.
when i got home i was thinking that the only thing that could of gone wrong was the receiver battery had died but when i tested it and connected the servo's to receiver and battery it was all working perfect with no battery loss???

my cdi unit was installed behind the engine firewall and was at least 22'' away from the receiver.

the only thing i can think of that went wrong is that im flying on 65mhz fm futaba ff6 radio system which the radio signal got lost for a few seconds although this has never happend before and ive had this radio for about 2 yrs and never had a signal loss.

was just wondering if i could get some thoughts on this matter and for me to avoid any issuse that may cause this to happen in the future and like i said in my recent posts this was my first petrol/gas engine and maybe ive made a mistake somewhere.

best regards<br type="_moz" />

sdherington

So sorry to hear that. I hate to say it but they all have an expiration date and we don't know what it is. As sheilded as all the modern ignition systems are I doubt that was the cause but you never know. I use an Opto Switch from 42% Products tied into a channel on all my gassers (now required by the IMAA). If you were flying 2.4, I would have been able to offer some advice. Did you have a failsafe setup on your radio? Have you been able to check the engine and ignition?

rcmodelflyer2010

hi

i never had a failsafe and ive tried the engine and ignition and they are fine.i can say one thing tho that has just come to mind my throttle servo was at the front of the plane and the servo control rod past between the cdi spark plug cable and thought it strange that the servos were hunting now and then and wonder now if that was the problem.

can you recommend a transmitter and receiver that would work well with ignition systems? im in the prosess of building a p51 mustang 85'' and going to put a dle 100cc in her and would like not to smash it up if i can help it lol

you mensioned failsafe? does this stop the plane from crashing? or is it some kind of fixed setting like lowering the throttle or resetting the servo's? sounds like something that i need to be doing anyway

regards

sdherington

You are correct on the the failsafe.
I have no special recomendation for a Radio.
I do isolate the engine compartment as best I can. I use ny-rod push rods for my throttle linkage and try to keep the servo as far back in the fuse as practical. I also use a ball snap link on the carb to keep it from vibrating.
How were the engine mounting bolts? Were they loose after the crash? Did you use blue Loctite when they were installed? I had two standoffs break on one of my planes and it did strange things to the aircraft. Now I run bolts all the way through. The good thing was I was about 2 feet off the ground when this happened. I flipped my ignition switch on the TX and killed the engine. Landing wasn't pretty and damage was fairly easy to repair.

sdherington

By the way failsafe will not stop you from crashing.

rcmodelflyer2010

yes everything seemed ok with the engine bolts and i did use locktite on all screwable nuts and bolts just to be safe and they were still locked after the crash.think i will use ny rods on my throttle linkage next time just to be safe and i will defo use a fail safe as i think my plane would of still been flying if i had it in force.

its funny how attached you can get to a plane,specialy when you have built it form a pack of wood and all ive been doing this last 24hrs is running through what happend and what i could of done to avoid the crash haha
oh well never mind learn by mistakes,re build a re fly is what i say :-)

sdherington

I know how you feel. I lost three planes on 2.4. All three did exactly the same thing. A Giant Aeromaster with a G-45, A Hanger9 Pawnee, and a Rascal 110. THe Pawnee wa the first to go and it had never been on anything but 2.4. The Aeromaster and Rascal had dozens of flights on 72 before I switched to 2.4. I switched back to 72 and am now considering going back to 2.4 since they have made some improvements. I will go with the JR X9503 since it is just like my 9303. Easy to program with lots of bells and whistles.
Another thing I have done is stated using a Power Buss between my RX and servos. It is just a PC board the has leads coming in and header coming out. My battery(s) hook to it and I have heavy wire feeding the power section so I don't get voltage drops. The traces in a RX aren't really heavy enough for large scale servos.

rcmodelflyer2010

its funny isnt it that planes do this signal thing with petrol/gas.when i was on glow engines i could fly as far as the eye could see and no signal loss what so ever.when i was reading up about gas engines before i bought one,one of the major cons was signal loss between the receiver and cdi.do you get the same signal loss on heli too?
i was reading something the other day that you can change your spark plug to another type to lower signal interferiance .

i was looking on youtube this morning about some guy who had just built a huge jet with twin turbine engines which totaled around $7000 and he lost signal and boom that was the end of it!
i know these big jet are real good fun and some day i think i would like to purchase one but due to the fact that signal loss is still playing a big part in the aircraft world i think i will stick to props and keep the cost down to under $700.

this new project im on at the minute which is a giant scale p51 mustang, i bought it from tower hobbies think it cos me around $250 as a kit which i thought was quite good as they are well over $500 if you buy it (arf)
once i get to the stage of engine and throttle installation im going to take a couple of steps back and double make sure that everything is as good as it can be.also think im going to try a good 2.4ghz transmitter and receiver too as no expence can be spared for a good tx and rx

regards<br type="_moz" />

ahicks

My Feedback: (2)

Are you running bigger or possibly digital servos? Are you doing that with a 4 cell 4.8v battery pack? This combination can lead to a brownout condition for your receiver, especially during a maneuver that's stressing a servo - like knife edge flight. Easier yet for this to happen as the battery wears down, during an extended flight, or perhaps the second or third flight after charging. Afterward, during your post mortem inspection, everything will check out just fine.... or you might find a stalled servo? Whatever, after I lost a plane last year (probable bad switch) I've taken steps to minimize or eliminate the possibilty of voltage loss to the receiver. Going to 5 cell packs was one of them.

rcmodelflyer2010

i am using a 4 cell 4.8 yes and the sero's im using are as follow:

elevator digital 13kg torque

rudder digital 13kg torque

throttle standard 6kg torque

2 aileron servos digital 6kg and 2 flap servos at 6kg also standard.

do you think this was all to much for my 4 cell battery? and its funny that you mention this but just before i crashed i was using full throttle elevator and aileron servos then it went into a steep dive and there was no control what so ever?

regards

ps im just going to re check all my servos battery and receiver for possible damage!<br type="_moz" />

rcmodelflyer2010

one more thing that i mite add i was having a little engine trouble also at the time as it kept on wanting to quit so when i landed i opened the low end needle as the engine seemed to be a little lean once done i did a test and the engine seemed to rev higher than normal well this is what it seemed like so im also wondering if maybe there was a sudden almost like an impulse coming from the ingine which knocked my signal out?

regards<br type="_moz" />

sdherington

I fly 5 cell packs on all my planes on both the servos and ignition. Minimum 2000 ma. You have to watch which pack you use also on large servo planes. Make sure it will deliver the amount of current you need in a spike. A snap roll uses all the servo's at once and really puts a demand on the pack. If it will handle that then you should never see a brown out condition. You could have a cell going bad in the pack also. Do you have a smart charger that you can hook to a computer?

You might want to check the board in your RX and see if you have a cold solder joint. If one heats up under a current load you have have a power drop. This is another reason I use the external power strip. They aren't that expensive and it really takes a load off the RX.

rcmodelflyer2010

both my tx battery and rx battery are 2000 mah and are both the same make of battery.you said you use a 5 cell battery,does this put more voltage into the receiver?or is it a 4.8 5 cell battery?
ive not got anything to hook up to my computer although i have a buddy cable which allows me to hook my tx to the computer for rc simulators.
you have given me a few things to consider anyway mate and i thank you for that and to be safe im going to get new tx &amp; rx and also use 5 cell batterys as you have mentioned.

once again i thank you for your time in helping me out.

best regards :-)

ahicks

My Feedback: (2)

A snap maneuver could cause a strain as well. I'm sure there are dozens of other maneuvers as well? Another thought, a throttle servo at wide open, if not adjusted properly, could be stalled and maybe causing this as the 4 cell pack is run down a little?

FWIW, I run 2 - 5 cell packs that run through 2 switches to power my receiver. One switch plugs in to the reciever normally, the other to a Y in the rudder servo, supplying power to the receiver's buss (and boosting available power to the largish rudder servo). To minimize weight and capitalize on all the power now available on the receiver's buss, I run the ignition off an IBEC, also powered from the receiver buss, at a Y used to power the throttle servo. 20 ga minimum wire used everywhere.

This gives me the redundancy and amperage available from 2 batteries, the redundancy supplied by 2 switches, and using the IBEC, very little or no penalty from additional weight on board. This lets me use this system on 26-30 cc planes with no strain.

sdherington

5 cell packs are 6 volts. They should charge to 7.2 or close to it. If you only have 4.8 then there is a real problem. I cycle or form all my packs before I use them whether they be nicd or nimh. I recommend buying good smart charger that will charge/ discharge your packs. You can get one for under $75 US. I run mine through three cycles of discharge then charge before I ever use them. Mine hooks to my computer and I get a graph that I can store and check against later charge cycles to see how the pack is doing.

rcmodelflyer2010

wow that sounds good think i will have to look into that.ive just been looking on tower bobby website and they have an rc aircraft verion of an alternator that charges your pack plus you can run lights and strobes off it and once your engine goes down to idle then your receiver pack takes over.go above idle and the power comes from the alternator.have you heard or seen this before?cant imagine it doing your battery much good tho as it will be charging at different points of the flight which would give memory loss
it is a must tho for me to get kitted out with some good stuff for testing my gear etc as i really dont want to crash this warbird lol

regards<br type="_moz" />

sdherington

Yes I have seen those. I have heard mixed views on them.
FYI my charger is a Thunder AC6 Dual Power. It only charges one battery at a time but it will charge anything from pb to lipo.

MercerAUST

Did you have a metal push rod between the throttle server and the engine throttle? I did this once, not knowing anything about ignition engines, ignored the odd server twitching and crashed due to a brown out when the ignition spike jumped along the pushrod into the server/Rx circuit.