Foamy power ??

[scubas00755511]

I have a Charger bi plane flat out with a Typhoon micro 15/10, 12v, 1500kv brushless, 11x3.8 size prop, 3cell 1500mah 12c cheap no brand lipo. The plane flew great in the warm desert, but now at 7000ft elivation, 40 degrees, it has little power, and I puffed 2 lipos in less than 5min flight time. Do I need a different prop size ?? Also what size lipo should I order and what brand is cheap and good quality? Please help ! Thank you... :dontknow

[skunkworx]

First, the current draw and therefore power input to the propeller, of a given motor/battery/prop combination is lower at higher altitudes, while the RPM of that combination increases. This makes sense because as the air gets thinner, the load presented to a given prop goes down. As the load goes down, the speed the motor turns goes up.

Second, static thrust drops as well for a given motor/battery/prop combination, though not very much, since the RPM's increase.

Third, you can recover the lost static thrust by either increasing prop diameter or prop pitch or both. But since the wing of the airplane needs to fly faster to generate the same lift as it would at sea level, adding pitch seems to be the right thing to do.

Flight testing supported this conclusion. I found that if I added pitch (using the same make of propeller) so that the current draw and therefore the input power were the same at the altitude where I was, as that which I saw with the same motor and battery at sea level, then the airplane flew very much like it did at lower altitudes. Of course, the airplane's landing speed was higher since it needed to fly faster to make the same amount of lift, but outside of that, takeoff performance and general flying ability, including aerobatics, were changed very little.

I don't have much of an explaination for the batts. Did you ckeck your voltages before/after flight? Could be the altitude change did something to them, although stuff usually pops after losing altitude (like a shaving cream can in your luggage at the airport...

You might be able to go with an 1800mah Thunder Power. They carry a little higher C rating so you have to make sure your cicuits or ESC won't overdraw your battery. Also make sure it'll fit and your airframe can fly well ubder the extra eight. I believe Thunder Power has 1300-1500Mah packs as well. prices will be around $30-$50 depending on sources.

Sorry it took me so long to respond. I got busy looking up a bunch of other stuff. Hope this helps :D

[scubas00755511]

Thank you so much :noteworthy I will go shopping for props and lipos today, send them to my little brother and post the results next weak. You the man !!

[skunkworx]

If you are at 7000ft, increase by 20%, 3000ft increase by 10% (roughly) Make sure he checks his voltages religiously also. That should keep him from smokin the batteries by overdischarging. Does it have a BEC? (battery eliminator circuit) This should make a 'cutoff' voltage and let you know when it's time to land. It should be integrated into the ESC. If it doesn't, I'd definately upgrade. Hopefully that should do it!

[scubas00755511]

No bec and cheap ESC, ill upgrade.Then Ill try a variaty of props, and I got 2 1350mah true 20c 3cell Full Max lipos. I will post results next weak. Thanks for info, I possted on Wattfligher, and RC groups forums, with no real help and here on Helifreaks you helped ALOT. :mrgreen:

[skunkworx]

Good deal! Always happy to help! It might take a little more tweaking, and messing with the numbers, but at least it's a good start! The upgraded ESC's have a BEC incorporated into them for not much more. Make sure you match up the right current ESC, if it's too low (amperage), your motor will overdraw it and cook the thing!
Sorry about the other guys not replying...this mostly is a heli site, so they don't really pay attention to planes, but they're the best bunch I've found! :glasses2:

[scubas00755511]

Thanks again skunk, I was refering to the lack of responses on RCGroups.com and Wattflyers.com they let me down, it took a weak to get any kind of response. :noteworthy Helifreks answered in a day. Heilifreaks rules all onlin forums.

[skunkworx]

Trust me, it's because I don't have anything better to do! :D I'm happy to hear things are going well for you. Spread the word bro!!!

[scubas00755511]

Smaller prop w more pitch worked great 9x6, 20c 1350 Fully Powered 3cell lipo, gave lots of power with no overheating. My little bro is back in the air ! :lolol Thanks again !! He just needs to learn how to land in thin air, takes alot of air speed, and drops hard when powered down. Maybe a single wing instead of a bi plane ?

[skunkworx]

Just what I like to hear!
Yeah that is true, the thin air (cold air aside) makes for faster landings, but I think the surface are of the wing is what will affect that. Also the drag is a lot different. The biplanes can usually fly slower because of the larger surface area of the wings and they have a little more frontal surface area which equals more drag which in turn slows them down as well (at least keeps them from being really fast). Bi-planes are better for handling though. As with helis, the bigger the better!
What size is he flying now?

[scubas00755511]

He has a 35" wingspan, Im going to order the Great planes Flattaina foamy for him 36" single wing. What do you think or recomend, he should try, changing over his motor and exc. ??

[skunkworx]

They should work if you swap them, but you might have to upsize your prop a little (less frontal drag) The single wing might be a little faster too. They have a 40" foamy bi-plane that looks like it could fly really slow and it's really maneuverable. Sorry don't know the name. I think they have them over at Discount Hobby if you want to see a built one.
Sorry about the slow response, I've been feverishly working on my heli to get it in the air and haven't had the time to be on here much.

[scubas00755511]

Wher you flyen at in SD? I fly almost every day in PB, or at Sea world (silent flyers).

[skunkworx]

Umm, Garage right now! I went to the SEFSD meeting last month, but I'm not a member yet. I found another guy on here and we were planning on flying @ Admiral Baker park by Qualcomm Stadium (as long as we don't get kicked out!). I live in Golden Hill right now though. Any other good flying sites around?

[scubas00755511]

I fly at schools after 2 and a park on the bay is always avalible. Do you think a flat out or a shaped wind foamy would fly best in 7000ft elivation?

[skunkworx]

I think it depends on what your bro is going for. If I'm reading this right, shaped wing* foamy? If so are you talking about a scale plane or ??? The flat outs are lighter so I would assume that would be better (and way cheaper!). Let me know if I got this wrong...

Flatouts are pretty good because they are really light. Like I said before, I'm biased to the Yak 54 design because they have a little more wing surface area (from what I have seen) which allows slower speeds if need be, but the big control surfaces really toss it around nicely! I don't think who you get it from matters as much as specs do.

Looks have kinda been the biggest part that I look at, but was suprised to find the Yak 54, Cap 232 and the Extra 300s designs to be really good for hard 3D stuff. The Cap and the Extra are a little quicker if speed is on the menu.

In order my favorites; Yak 54, Extra 300, and Cap 232.

There's an Edge 540 that looks really nice on Tower Hobbies. Only $30! Same 35.5" span on it, 80% deflection on control surfaces! Cool 'RED Bull' grapics. Could be a good candidate maybe...

[scubas00755511]

I ment flat out verses standerd shaped wing and plane. I just got the mini yak54 arf wooden plane, but thats for me. I just was thinking he might have smoother landings and flight performance with a foam arf that is'nt flat out.

[skunkworx]

Oh, (you can use either monokote or foam coverings) It could be possible. Is he into aerobatics or just buzzing the bystanders? I would try a trainer type setup because they are a little more forgiving, maybe a used plane will work (make sure it flies, NO EBAY JUNK!). He should go visit a local field and see what they fly. It's easier to copy-cat because he'll know it will work (best place to buy used!), if he's feeling frisky, he can go out on a limb and try something new.
I'm a little out of the loop on the airlanes right now as I'm pouring everything into my heli right now. Typically you have to find out how much wingload the frame can bear. There is a way to "guestimate" the variables; operation elevation, prop size, power supply (gas or Electric)and motor size. I'll see if I can find it for you, otherwise it's a hunt-and-peck situation...His LHS should be able to help out with this also.
I think most of it comes down to preference tho :D

[scubas00755511]

He is into aerobatics, and learning hovering and other 3D manovers. Im looking to get him somethig w less drag than a biplane, yet still foam. What kind of Heli are you flying?

[skunkworx]

Trex SE silver, U? The foamies are really good for aerobatics but they are really angular when turning (they react quickly to inputs) the regular planes are more 'groovy' (they take a little longer to react), I would definately get someting single wing with large control surfaces. He should be able to do a 1:1 transfer of all electronics even if he gets a larger foam plane (verify the manufacturer's recommended parts list).

[scubas00755511]

Im flyen a Trex SE and a Trex600 CF, Im putting together a Flattaina foamy. My little bro is in Flagstaff, AZ, who is having the proplems.

[skunkworx]

I finally got mine in the right direction, but still have to fine tune it. I'm from AZ myself. I might be moving back at the end of the month. Maybe I'll come fly over in PB sometime before I go. I have to be over here periodically, so even if I leave, I'll still be here from time-to time. I'll let you know if I get mine in the air anytime soon. -Tim

[scubas00755511]

Ill help you dial your bird in any time. I know alot about Trexes, And I can fly 3D pretty good for flying just a year. Im from Yuma, AZ. Hell Hole !! PM :lolol me and ill give you my phone #.

[skunkworx]

Even more funny, So am I!!! My parents live out on county 17!