I have just bought a Ripmax Spitfire EP ARTF which I plan to power with an interesting (Chinese!) brushless motor. Test show I can spin an APC-E 11 x 7 at 8500 rpm on 10 CP1700 cells which should give about 55+ oz of thrust (according to motocalc) and a reasonable pitch speed.

But...

This aeroplane has no undercarriage so here's the question. If I use the APC 11 x 7 am I bound to break it (or the motor mount) sooner or later or can I get away with it if I'm careful?

I have considered using a Graupner or Aeronaut folder but they seem to be less efficient (according to data on www.flyingmodels.org) and/or have a lower pitch speed at the same size. I might be able to use one more cell to get over the pitch speed problem but duration may be reduced. This adds extra weight too which I am trying to keep down to maitain at least 1:1 t/w ratio.

Another alternative would be to fit retracts and go with the APC. I have never used retracts before so can anyone suggest what I could use for a 3 1/2 lb aeroplane and how much weight would it add?

Thanks in advance,

Giz

Retracts will add 250-500g of weight depending on what system you use. Air will be a little lighter & more expensive , mechanical - a bit fidly to setup & will need a strong preferably 'retract' servo.

IMHO A spitty doesn't look great 'strafing' with it wheels down.

The APC E props are quite thin so are a bit prone to breaking if you come down hard with the prop is the wrong position. The Aero-naut folders work well as do the graupner ones.

A 1:1 thrust ratio is great if you can get it but I don't know if a spit will prop hang that well. I'd rather go for longer flight times with a thrust ratio of around 0.6/0.8 to 1. I feel that if an electric plane can't fly for at least 10 minutes with today's technology then I'm doing something wrong.

I had a 130cm span Spitfire with scale retracts that ran on a S600 Race and graupner 2.5:1 'box & 10 cells once, 1.5x9.2 prop, 1.9kg AUW with around 1.1kg static thrust and it flew really well as long as it was flying fast, it tip stalled (as spitfire's do) on an approach one day and was written off.
Just mount the retracts (if you do put them on) well, they are prone to pulling out.

Some photo's of it can be seen here:

http://myweb.absa.co.za/pardus/eco.html

cheers
Graham

I like the Aero-Naut folders, especially with direct drive applications. The "Turbo Aluminum Spinner" collet type prop adapter is my favorite.

http://www.hobby-lobby.com/propadap.htm

If you want to pick up some pitch the following can add either 2.5 or 5 degrees to the pitch.

http://www.hobby-lobby.com/freudaccy.htm

The collet type is more reliable than the set screw type in my experience.

Len

Wow, I didn't realise retracts would be so heavy . I guess that rules them out.

It sounds like I may be OK with the APC prop but I should expect to break one now and again. The main thing is that I don't want to break the motor mount.

I'm not interested in prop hanging. I just want good climbs and big loops with a decent turn of speed so perhaps I should exchange some thrust for some pitch speed and drop down to a 10 x 7? Throttle back to a cruise above 50mph, this should give me around 10 minutes flight time.

Thanks for your help. Any more experiences anyone?

Giz

A clubmate maidened his this weekend. It flies really well - unfortunately, I dont know what setup he has (I think it is a modelmotors brushless, on 8 cells with about a 9" folding prop folding) it really goes nicely! We did discuss adding undercarriage and the conclusion was, no!!

What you really want is for it to look good in the air and fly well !

The retracts add a wonderful realism to the spitfire, mine operated in the scale way - pulling up from inside to out. A take off, then pull the wheels in - looked fantastic. It also obviously allowed taxi-ing - I fly off a tarmac runway. I could never have hand launched it, way too heavy.

Pardus

Your avitar is giving people the wrong idea. They will think there are lions in the streets of Joburg!! I used to live in Fourways, Sandton. Do you fly at JOMAC?

The retracts are nice but it would mean modifying a ARTF to take them, adds weight on an electric and, we have a grass strip with all the problems that it creates for retracts!!

Giz

On my second landing I broke my 12*8 APC E prop so I am going to a folder as it so happens I have a Graupner 13.5*7 on my zagi so I am going to try this as soon as the weather gets better. The amp draw was 32 amps on 8 cells using AXI 2820/10. Tested it by holding the Spitfire upright giving full throttle and it pulled up so more thrust then weight AUW 50 oz.I just hope the pitch speed is enough.

Paul

I've just finished my spit today. I decided to forget about retracts.

AUW is 52oz
10 x CP1700SCR
Feigao 5408425L direct drive
APC-E 11 x 7
T/W > 1:1 @ 8500 rpm

I had been thinking about hand launching or using a dolly. When I finally picked up the completed model today I just could not imagine hand launching it! It ssems so heavy and so fragile. It feels like the slightest dodgy launch would lead to disaster.

I don't think the model is heavy for its size really. The wing loading is 17.5 oz per sq ft. Seems reasonably. I have just never hand launched something of this size before.

I'm thinking about designing a dolly with a castoring tail wheel and using the rudder for steering once it gets going. Has anyone ever tried this. I plan to sit the plane level on the dolly with a small post in front of each wing and heave it off at about 20 mph.
Should be interesting!

Thanks for your advice.

Giz

I think a model of this size should have wheels. I'd hate to see the underside after a few landings.

BTW- Do retracts really weigh between 9-18 ounces?

Giz

I had no problem hand launching there was no sink it just climbed straight away although the launch holes are to far back when full power is used it tilts forward so I used slight up trim but when launched it climbed with out a problem.

Paul

Paul

When you hand launch is the plane very twitchy? I have a highly aerobatic 30" foam Tucano and whilst it climbs away well, it is easy to get into trouble trying to correct unexpected attitudes at low level. Sort of lurching from left to right and back again.

The Tucano is OK because it is EPP and easily repairable but I worry about the Spitfire, especially for the first launch. I think I'm just chicken!

By the way, did you launch it yourself or get someone else to do it? Right handed chuck? Did you have plenty of time to get to the right hand stick?


Giz

Originally posted by Giz

I had been thinking about hand launching or using a dolly. When I finally picked up the completed model today I just could not imagine hand launching it!

Giz

If you hold it upside down it is a lot easier to hold! Just a touch of down elevator and away you go!

I have seen a few guys who really launch like that but, don't really recommend it !!

Giz

The Spitfire is very stable just flew straight and climbed with out a problem.
I hand launched with my right and it didn't need much of a throw to get it under way the only thing is it tipped forward when full power was applied to launch so I gave it a little up trim before launching as said before the launch holes are to far back.
It sounds that we both have about the same amount of power and weigh about the same so I think you will find it will climb the same just give a little up trim and if possible get some one to throw it for the maiden flight.

Paul

Try and do a couple of test glides over long grass first, to find out what speed it needs.

My guess is aroun 15mph, which is a fairly hard throw,

Ive landed fioxed props on teh belly, and its mostly OK unless the motor is still running. They just windmill in, and if you stall and flop - basically hold the model off at an inch otr two until it slows down and flops in, you don' OFTEN break the prop - it just gets knocked out o the way.

I have had worse breakages from simply tipping over on the nose on a UC model frankly.