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Tony Nijhuis 63" Spit

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Brent Hudson12/09/2007 02:04:00
7 forum posts

has anyone converted to electric as I'm starting to build (first timer) and require a park flyer.

I've been told that it can't be done because the plans are for petrol motor.

what I need to know is the motor to motor ratio and prop size.

any ideas ," as I've already started on the wings(thinking about retracts)"

regard

Brent

Martin McIntosh12/09/2007 21:16:00
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3144 forum posts
1133 photos
Brent, don`t build it without retracts. They are a real pain but a Spit without them looks like a toy. You can always build them in line with each other if you do not feel that you can cope with the Spit geometry but you must still angle the units forward to get the wheels as near to the wing LE as possible. This gives problems when they are retracted though. If you want to know how to do it properly without tearing out your hair, see RCME article April 2001. If you must go for the 180 deg set up, keep them as far forward as possble. I am no expert regarding electric set ups, but I believe that you need about 100W per lb., so for 7 to 7 1/2 lb. this would require quite a powerful combination. My i/c installation is somewhat more powerful than that, but it would fly well with much less. If this is your first attempt at a model - forget it. These are for very experienced model builders and fliers only!
Graham Eccles12/09/2007 22:02:00
18 forum posts

Brent, this thread for the 63" wingspan Spitfire, I suspect from what you say you are probably building the smaller 46" wingspan model. I suggest you check your plan before people start quoting all sorts of motor and battery combinations.

Martin McIntosh12/09/2007 22:10:00
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3144 forum posts
1133 photos
Graham, you could be right there. That would be much easier for leccy, but I suspect that like all of us were, everyone wants a Spit! MM.
Shaun K13/09/2007 13:43:00
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192 forum posts
38 photos

Hi folks, I've just had the 63" spit plans delivered this week and just starting to put together a materials list to get moving. The plans show wing spars being made of obechi.

I'm in Australia and I've never actually heard of obechi before - it's not in any hobby shops around my area and not in any hardware stores.

Can anyone suggest a decent alternative to obechi for the wing spars on the spit? Is obechi anything like spruce?

Martin McIntosh13/09/2007 19:30:00
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3144 forum posts
1133 photos
Shaun, obechi is something like spruce,which I would have thought would be the normal choice; depends probably on what your local shop has in stock at the time. Having said that, I just used medium hard balsa which has proven to be very adequate despite my attempts to test the structure to the extreme. When you consider that the whole wing is sheeted with 3 3/2 balsa, the spars are really just a constructional aide and something to hang the u/c on. The liteply ribs take care of the stress here. MM.
wlfk13/09/2007 23:06:00
97 forum posts

I was thinking of doing an electric conversion too. I was wondering about an Axi 4120 - shame as I have an Axi 2826/10 knocking around. According to the specs this won't be quite powerful enough...

K

Shaun K13/09/2007 23:25:00
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192 forum posts
38 photos

Thanks Martin, much appreciated. It may seem strange to you folks in the UK, but while spruce is common in the hobby shops here in Oz our choices of balsa are usually limited to a choice of three grades - soft, soft or  wait for it....    soft.

 I'll go with spruce.

Martin, it would be great to see some photos posted of your finished spit, if you haven't done so already.

Martin McIntosh14/09/2007 19:02:00
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3144 forum posts
1133 photos
Go with the spruce, Bruce! Will get some photos including out in the field when I can remember to take my camera and then work out how to get them onto this forum. MM.
Shaun K24/09/2007 13:44:00
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192 forum posts
38 photos

To washout or not washout, that is the question...

As a relative newcomer to RC flying I've been warned by the local hobby shop guys that Spitifres are known to bite at landing and that adding some washout would be a must.

For perspective on my abilites, this will be my second plan build and also second low wing model. For those of you who have already built this 63" spit, did you add washout? Tony Nijhuis mentions in the RCM&E build articles that it wasn't required, but is that because he's a master of design or a master of flying?

Finally, if I was to add washout, how far along the wing does washout typically begin? Is washout a gradual twist along the length of the wing or is it just the last xx% of the wingtip that has washout? 

I'm starting to think this should have been posted in the beginners forum...

Tony Nijhuis24/09/2007 15:53:00
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609 forum posts
233 photos

Shuan,

Good question...From a designers perspective, Tip stall at slow speed is generally over come by adding washout at the tips and that means twisting the wing, usually along its span so the tip profile 'angle of attack' is say 2deg less than the Root profile 'angle of attack' What this means is the lift from the wing is concentrated closer to the root of the wing and not the tips. As you slow the model down in flight the tendancy to 'tip stall' is therefore reduces which means the model can be landed at a slower speed.

Now this is all very well but adding washout and reducing the lift at the tips does mean reduce lift of the wing overall. If your model has washout, you will require more power to fly it and more power may result in more weight, more weight will result in a faster landing speed and so you end up needing flaps to slow the model down ...yet more weight! So what you end up with is very little benefit between a light model without washout and the heavier model with washout

The 63" Spit is designed with lightness in mind (7lbs) which results in slow flying/good lift characteristics.

During testing, the model was flown round very slowly (definitely not scale) with no hint of stall so it seem pointless to consider washout unless it really did bite.....and believe me I did push it!!!

Tony

Tim Mackey24/09/2007 16:45:00
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20920 forum posts
304 photos
15 articles
Nice simple to understand expanation of washout Tony - nice one, I'm sure many will have learned a bit from that.
Martin McIntosh24/09/2007 19:09:00
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3144 forum posts
1133 photos
I have built the 46 and 63 versions. I was unsure with the 46 so I made tapered TE packing to keep the centre line of the tip section in line with the root. The result was a model which just mushes on application of low throttle and gradual full up elevator. The landing can be very slow indeed, just what you want despite an AUW of 3lbs 10oz. I built the 63 in the same way, but this will drop the left wing when pushed, certainly due to a minor warp (oops!) The weight is 7 1/2 lbs. I have not attempted to calculate the relative wing loadings, but the 63 refuses to slow down on landing. Currently using a 12x7 prop and very slow idle. I think that the answer will be to use a larger diameter/ lower pitch because the model otherwise now flies very well. May replace the motor (YS63) with a YS 53 which is happier with a lower pitch and will provide more than adequate power. Hope that this is of some help.
Shaun K25/09/2007 03:12:00
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192 forum posts
38 photos

Geez, so much info!    Thanks so much Tony and Martin.

Martin's comment raises one more question I have re prop size.

I have the same ASP .61 4 stroke that Tony used. I'm currently flying my original trainer with it on a 12 x 6 as there's no huge performance requirement for the trainer. I've been thinking that a 13 x 6 may suit the spitfire.

Tony - did you do any testing with various props? What did you settle on in the end?

Tony Nijhuis25/09/2007 11:57:00
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609 forum posts
233 photos

Shaun, The prop i used was a 13x5 I think...bigger, slower turning with a finer pitch gives a good scale model speed.

Martin, Warps can be a real problem especially on elliptical wings such as the Spitfire. What happens is you ailerons (as you may note) have to correct for the warp by addiing oposite deflection to hold up the wing tip which is giving less lift (and pushing the opposite tip down as well) . But ailerons are ultimately creating drag which at differ speeds alters dis-proportionately to wing lift. So at slow speed the model might wander left slightly and at fast speeds wander to the right. The result is aileron deflection only deals with the symptoms and doesn't cure the problem of warp. So on landing when tip stall is at its most dangerous and ailerons become almost unusable, the wing tip that has a greater angle of attack will stall first (i.e. the one without washout). You may have noticed this that when a model is about to tip stall, the wing tip which is about to stall will lift more than the other for a split second seemingly turnning the model one way and then violently flicking the other...at that point you either need 50' height or just inches from the ground to survive.

Having said all this minor warps are less of a problem..The 11-foot electric lanc I am currently flying has a very nasty warp in the Left wing and consequently 12mm of aileron deflection is needed......and before you ask, I didn't build the model......never the less she still flys well...Cheers

Tony  

Martin McIntosh26/09/2007 01:07:00
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3144 forum posts
1133 photos
Tony, I have put one aileron up, as opposed to one up/one down to give washout. Does not excuse the unforgivable error in the build although I once flew an aerobatic model at the Nats with a huge warp. Only one flight under its belt before the comp. but it still managed 2nd place. The warp did not seem to bother it too much. Have not tried to work out the comparative wing loadings for the two sizes, but would suspect that the 63 should be more lightly loaded. About 4 pics on the gallery but hopefully lots more to follow.
Shaun K27/11/2007 11:50:00
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192 forum posts
38 photos

Hi guys, been a while since this thread has been used, so I'll hopefully spark some interest here again. I've started building the 63" Spit and got myself the first half of a great looking wing structure. I'm now at the point where Tony's instructions from the June 07 mag tell me to sheet the top of the wing with balsa.

I've only ever done open frame wings covered in Solarfilm before. Any tips on the best way(s) to sheet a wing would be greatly appreciated. My key questions are:

  • Do you join all the 4" balsa sheets together first or lay down one 4" sheet at a time?
  • What's the best way to secure the sheets down onto the framework while the glue is still setting? Weights, pins, voodoo?
  • I read elsewhere on the web that spraying the top of balsa sheeting with 50/50 ammonia/water will make the sheeting sag and magically fall into the right shape. Fact or fiction?

Thanks, Shaun K.

Martin McIntosh27/11/2007 20:58:00
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3144 forum posts
1133 photos
Shaun, I flew the model on Sunday last with the smaller 53 motor using a 13x5 Zinger wood prop. I think that the landing speed was quite a bit slower but it was rather windy. The power reduction was quite noticeable but very adequate because I do not wish it to tear around like a pylon racer. Re your building queries. You must join the sheeting prior to applying to the wing surface. I do this as follows: I lay the cellophane backing from transparent Profilm onto the building board; you could use greaseproof paper or just rub the board with a candle. Take each sheet of balsa, pin down to the board and using a straight edge trim both edges carefully so that they are perfectly straight. you only need to remove a small ammout of material. (continued).
Martin McIntosh27/11/2007 21:24:00
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3144 forum posts
1133 photos
Shaun. You now need to join them. Pin one edge of a sheet to the board. You can either coat the adjoining sheet with medium or slow Zap and offer it to the pinned sheet smoothing the cyano with your finger, or pin both sheets closely together and run thin Zap down the joint. Either works. Repeat for the other sheets. Remove from the board. The flattest surface will be the underside. Sand each face as level as possible-I use an electric sander. You would find it hard to level the joins after applying to the wing. Coat all surfaces on the pinned down wing with `slow` or `sheeting` Zap and apply the (trimmed to slightly oversize) sheet, pressing down the length of the spars first, then gradually onto the LE and TE. Keep up the pressure until you think that it has stuck to the ribs, but do not try to force down a low area or you will end up with a dip. (continued).
Martin McIntosh27/11/2007 21:35:00
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3144 forum posts
1133 photos
Shaun. You can now remove the wing half from the plan, trim the LE and TE and add aliphatic, PVA, cyano or whatever you prefer from the underside of the top surface to strengthen the joints. The fun really begins when you come to fit the retracts, servos, and sort out the ailerons! Never heard of the amonia trick, so don`t try it. Best of luck.

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