rlaw

I am building my first airplane in twenty years. I am building a gillows spitfire . 17in w.s., fixed flaps, custom 5.5" four blade prop, emax 2822 brushless motor, 30amp esc and 1300 mah 11.1v 15c li-poly. I am using a futaba 2.4 fasst 6ch system. So far the the frame has been reinforced and covered in 3/32 balsa. I plan to cover the plane with lite weight carbon fiber. I am looking at a finished flight weight of 400-450 grams. I balanced the CG at the center of wing that is called for on the plans for free flight (rubber powered version) as it sits it is .25oz tail heavy. The motor is rated for 300-600 gram plane. Before the carbon fiber goes on I want to get som feed back on the setup. I originally had functioning flaps, but was informed that with the weight to wing area ratio that as soon as I throttled down the plane would fall out of the sky. I have never flown a rc plane. I had an itch, started scratching, now here i am..... It is amazing How much you can pack into one of these planes with a little planning.

thanks

Ryan
Cincinnati, ohio

MJD

My Feedback: (1)

Hi Ryan,

Remember we're all slimers over here, but some of us do both, and very badly too. Just kidding, there are a lot of knowledgable folks here on small aircraft, and most of the advice is relavant no matter what the powerplant.

Here's my two bits -

- You have a very, very high wing loading airplane there:

At 17" span, the MAC (the mean average chord) of a Spit wing would be 3.03" according to my scale data. At 17" span, the wing area works out to 51.5 sq in.

(51.5 sq/in)/(144 sq in per square foot) = 0.358 square ft

Wing loading = weight / wing area

= 1 pound/0.358 square feet = 47 ounces per square foot[X(] ! Egads!

And.. don't forget that the effective wing area is likely a bit less due to scale effects and whatever else.

In my opinion this would require a catapult launcher and parachute recovery if you really are going to hit a finished weight of one pound. That's simply a ton of weight for this little aircraft to carry IMHO. Do you know of someone that has done a conversion with these kinds of specs? I don't.

Assuming it can fly at that wing loading, I had rattled off a few other things before I did the wing loading calcs:

- This is a 1 lb built-up 17" w.s. Spit, with a fully tapered wing planform that has a propensity for tip stalling in small scale models if the tips etc. aren't sprinkled with the right kind of magic powder. While elliptical wings are the most efficient due to the ideal lift distribution, remember that doesn't allow for our attempts to sand a nice airfoil into a tiny chord wing section. Under a microscope, the tip cross-section of balsa or balsa/tissue wings on these small models we build probably resemble a roughly sawn 2X4. So that combined with good old Reynolds numbers issues can sometimes play havoc. To reduce surprises due to tip stalls, make absolutely sure you do not have wash-in [a twist in the wing where the TE is lowered, increasing the angle of attack at that section] anywhere, and preferably a touch of wash-out [the opposite, TE up a hair reducing the local angle of attack] progressing towards the tips, and equally on both panels.

- I don't know what scale the stab on that Guillows kit is relative to the aircraft scale. The stab was likely scaled up for stability as a rubber FF, and if so then good. The full-scale Spit had a very small stab area (wasn't it somewhere around 10-12%?) which does not scale down well at all. Again due to reynolds numbers and moments and all that stuff, small models generally require larger stabs as a percentage of wing area, than do the same design in a larger scale - if the same level of pitch stability is desired that is. So I would be extra cautious, & ensure the CG is not anywhere the rear of the allowable range according to Guillows.

- If you have not flown RC before and try to fly anything like this yourself, you will break it despite all the CF in the world. That's just the reality, this is not close to a good first model for anyone. I'm not talking about building skills or setup, any of that. It just is not the type of airplane a low time RC pilot can handle. It will not be a floater, it will fly like a tiny overloaded fighter which may be cool, but is too advanced for a low-timer. Get a hot shot small electric pilot to take it up for you, and listen to every piece of advice he/she has on the aircraft if there are changes in the set-up they might want to see. (Including wing loading concerns!)

- How are you covering this aircraft with CF? Are you applying CF mat to the structure like tissue, or layered with tissue? Curious. [EDIT: sorry, my dumb-dumb - I missed the sentence about the 3/32" sheeting. If I had read that, an alarm would have instantly sounded.]

No discouragement intended, just trying to paint a picture of what may be.

MJD

p.s. oh yeah, and ditch the flaps. More weight is not what you need. Bring it in fast and clean.

windy city

rlaw,
Please STOP right now!
MJD is right on all points.

Do yourself a favor and look up a few different Gullow conversions to see what power systems they used.
You will see your power system is way too big.

We just want you to have a fighting chance!
windy city

Andrew

Hello Ryan

I'm pretty sure the advice you'll get here is not what you want to hear. While Guillows kits can be quite detailed, they are notorius for being overdesigned and heavy - OK for a static model, but really not a very good flyer. MJD has pretty well covered all the points.

Small plane modelers live and die by wing loading. 12 to 14 oz/sq. ft. is considered to be pretty heavy and a 10 to 11 oz. loading is better. MJD's estimate of 47 oz./ft based on the available parameters is unflyable. Guillows models, even when flown by someone with a lot of small plane experience, can be a handful with careful weight savings.

You cannot build a plane strong enough to survive a hard impact, so we generally say build to fly, not to crash. Essentially, that means as light as possible - strange as it may sound, adding re-enforcement may be more detrimental than helpful.

There are a lot of good first planes available that will improve your chances for success. IMHO, the 17" Spit is not one of them.

rlaw

Ok, Any links Would be Great. I am scared and lost, but at least I have direction know. I have created a powerful lawn dart that resembles a warbird... keep the info coming. my learning curve is greater than I thought. My Background In building any rc is in Gas powered lg. offshore style boats... That said I am tired of swimming and would like to fly.. I think as usual I took on a larger task than my knowledge will allow. I have to laugh.... I started this build with the assumption that weight should be no more than 2/3 max thrust of the power system. I have read any thing I could find To understand brushless power systems and proper battery selection. I have a 5000 kv motor and a 900mah 11.1 I could use Which would drop 30 grams of weight. I will try a search engine again for similar builds. I am begining to think I should have bought a ARF for my first plane..
Thanks to all. This is very helpful (MJD and Windy City)

Ryan

TFF

Sounds like you have equipment for a 25-30 in wingspan model if kept light. The people who fly these Guillows planes like that use the super tiny radios with the magnetic actuators or the cottage industry super small servos. They would call a 3 oz plane heavy. Sounds like you have some nice equipment that needs to be in a little bigger plane. Once you know how to fly you might be able to double the size of that Spit and make it work. I have built many of Guillow's planes and the kits may seem priced "right" but are the hardest way to try to get a flying plane.

longdan

The ARF would be my recommendation. They are pretty cheap and when you stick it into the dirt, you haven't lost hours and hours of painstaking work.
At the top of the 1/2A forum is thread about building a small trainer which would be much better suited to the power system you have (not that I know much about lipos and brushless motors).
Thes later on, once you have mastered this, look at doing the small spit. And I would ditch the CF. It won't help in any way except to weigh the plane down. Small models don't need anywhere near the reinforcement that larger ones do.

rlaw

Recently notified by my four year old daughter my plane waaasssss awesome........ I may be starting a new project.... no word on current condition

eroc144

My Feedback: (1)

Lots of info here [link=http://www.rcuniverse.com/forum/searchpro.asp?phrase=guillows&fuzzyMatch=on&author=&forumid=70&topicreply=combined&message=subject&timeframe=%3E&timefilter=0&language=single&top=500&criteria=AND&minRank=0&sortMethod=d&submitbutton=+OK+]If you search the 1/2a Forum for Guillows[/link]

lildiesel

The 24" Aeronca Champ kit might work. A high wing cabin job like that would be better as a first plane.

Of course, I've never done anything besides putting a baby Adams, light weight RX, and 110 mah pack with a restricted .020 in any Guillow kit and had only limited success at that.

combatpigg

My Feedback: (3)

I think Big Al and Matchlessaero built .010 powered planes in this size that weighed about 5 ozs RTF. I've never built anything this small, but the equipment has to match the application almost exactly, the smaller you go.

planebuilder66

My Feedback: (8)

Strap some C or D model rocket engines to it and it will fly for sure, and the wieght per an engine isn't too bad either,..... Alright, just get yourself a copy of the LST plans and build that first, then step into a classic design like a falcon jr., then try a mid sized gullows kit if you dare, something in the 30" range. I've had luck once with converting a gullows cessna to fly R/C, but you had to be on the sticks all the time to ensure it's existance.

windy city

rlaw,
Depending on the "KV" ver of your emax 2822 you should be fine with the LST Trainer or the Jr Falcon. Both would work out fine as a first plane.
Bipe Flyer's LST trainer,
http://www.rcuniverse.com/forum/m_2301186/tm.htm
Jr Falcon kit,
http://www.selecthobbies.com/
plans,
http://my.pclink.com/~dfritzke/

So you see what size plane your gear will fly!
windy city

TFF

I am partial to the Jr Falcon as it was my first plane but I think the Papillon would be easier to build and fly from scratch and cheap to make.

planebuilder66

My Feedback: (8)

Speaking of LST, did dave bronk ever fly his? or is he gone from the 1/2A fourm for ever?

hogflyer

Just checked Dave Bronks profile and he last logged in here 02/21/2008. His last posts appear to have been in the boat forum. I guess he's deserted the 1/2A forum - maybe too much Kraft & dogs or what ever he mixed in?

Hogflyer

planebuilder66

My Feedback: (8)

Ha Ha! I disappeared for sometime too, but my kryptonite is offroad trail jeeps/rigs. I try to limit my dosage so I can still remain sane and not broke.