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Old Apr 25, 2013, 09:58 AM
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Build Log
Building Fahim's 1/8 scale Hawker Typhoon

Background/Disclaimer
I was one of the instigators who persuaded Fahim to kit the Tiffie back in ’09. Original design/build thread is here: http://www.rcgroups.com/forums/showt...owplan+typhoon
I have always had a fondness for the Typhoon, despite not particularly liking the Hurri or the Tempest, I don’t find them aesthetically as pleasing. I bought one of the original kits back in ‘10, but for various reasons, including being a little intimidated by the magnitude of the build, I have let it languish until now. Over the years I picked up various motors, esc’s, batteries, pneumatic retracts and such that I thought I might use for the build, most of which I have since discarded as unusable. As usual for me, this is likely to be a pretty slow build, but with the semester winding down, I hope to have a little more free time.
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Old Apr 25, 2013, 10:00 AM
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Beginnings

Fahim always says his models are builder’s kits and I plan to modify this one rather heavily. One issue with the Tiffie is that with that massive Napier Sabre in the nose, it is even more short coupled than most WWII fighters. I think Fahim needed about 12 oz of ballast in his and most of the folks who built the Tony Nijhuis balsa Typhoon (same size) needed even more to get the c/g right. I prefer to carry my ballast as “live” weight, so I figured using an oversized motor and hanging the lipos vertically on the back of the firewall. This will mean altering the nose and the wing attachment, which I don’t think will be a real problem. I am planning to cover at least the flight surfaces with Fliteskin as an alternative to regular fiberglass, and despite the weight concerns, have a retracting tailwheel. Flaps too, of course. Fahim used 3” main wheels, but scale is 4.5”. The problem here is that bigger wheels are thicker and Fahim used a finer airfoil section than scale for the wing, so I don’t think I have clearance for anything bigger than a Dubro thin 4” wheel. I also want them to retract in the scale position, which means getting the retract angles close. Playing with my 3-views I think 17 degrees for the forward rake, backwards retract angle and axle offset should about do it. Electric retracts are really the only way to go these days. Full lighting and probably a half cockpit.
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Old Apr 25, 2013, 10:04 AM
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Motivation

I really love the (sadly discontinued) ERC Monster Power motors, but HobbyPartz has started carrying the Tacon Bigfoot line, which appear to be identical in all respects except color. I was looking at a Power 60 and realized that I could get a Power 110 for the same price and that it was a much better shape (shorter and fatter) for the cowl. The reviews were uniformly excellent and someone was running a 16/10/3 on 8S for 2800W in. Yikes! A scale prop would be 20” diameter and while they are available they are pretty pricey. The 16” is the largest 3-blade MAS make and I have one on the shelf, bought years ago for the Stein Tiffie, so although 2800W is 4 times the power I need, this appeared to be the right motor. In digging through the parts bin I realized that almost all my older esc’s are LV, good only for 4S, so I picked up an 80A HV esc as well. Well, the motor was great but the esc is huge, much too large to fit under the cowl ahead of the firewall as planned. I found I had a 60A HV, which was a much better size, so I wondered if I could make that work.

Plugging my values into P-Calc, I discovered that I had lucked into a perfect power combo. With the 16/10/3 on 6S I get 920W in/ 830W out at 45A with over 90% theoretical efficiency. Tons of power, little heat build-up, well within the ESC specs. I am looking at a pitch speed of 53 mph – no speed demon, but plenty fast enough for scale and 10 lbs static thrust and 6.5 min at WOT. Fahim used a data logger on his plane and most of his flying was done with 4-500W in, which means I am looking at an easy 12-15 min flying time on 2 x 3S 5000.
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Old Apr 25, 2013, 10:17 AM
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The nose

Given some of the mods I am making, I started in the middle of the manual. Cut the cowl out (that clear cowl is the cat’s pyjamas, btw), used that as a template for a ¼” ply firewall. I used 6 blocks and mounting screws, rather than 4, based on my experiences with the Stein Typhoon. 8-32 cap screws and T-nuts to mount the motor, cooling holes drilled as per instructions. I added a 5th hole where the oil cooler will be mounted to let more air into the lipo compartment. With that done, I made a pair of 6cm wide side battery box sides of 1/16” ply. I spaced them the same distance apart as the existing kit battery box. They are 18cm tall, more than enough to handle any 3S 5000 mAh lipo. Bottom of the box is 1/8” ply and the half-height back is 1/16”. I also reinforced the sides with 10mm balsa angle. I have burned myself enough in the past to make the lipo compartment a little oversize. That way slightly swollen lipos will still fit, and I am covered if the manufacturer changes dimensions slightly. I could also go to 3S 6000's if I need the weight, although I would prefer to use the 5000's I have on hand. With 2 large lipos and that motor, I am hanging nearly 3 lbs on the firewall, which should help c/g a great deal.

Since the nose foam piece is held together only by the top bridge, I cut through that so that I had two halves. This made cutting and fitting the foam to the ply firewall/battery box much easier. When I was satisfied with the fit, I used PU (white gorilla) glue, and taped and weighted everything in place. I like the GG for a job like this b/c it expands and fills in any voids.
While the front fuse/firewall unit was drying, I started on the mid-fuse. Taking off the tape and disassembling all the bits is like working on a 3D puzzle. I continue to be impressed with Fahim’s skill as a designer, working all these things through and reassembling them so carefully. I did the rear fuse as per the manual with the 1/8” ply wing mounting plate and foam reinforcement, plus gluing the centre seam, all done with epoxy. When everything had cured, I roughly cleaned up the front piece and then glued the front and centre pieces together, making sure the wing saddles were aligned. I am doing the hatch as per the manual. It will give me access to load batteries and I can use the rest of the compartment for electronics. Plus I figure the balsa-lined compartment adds significantly to the structural integrity of the main fuse. Currently I am doing the fiddly bits, sheeting the compartment and all the hatch edges.
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Old Apr 25, 2013, 05:57 PM
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Hi Jeff! I'm signing up for this one

This will be an interesting build and I like your idea about getting the batteries right up front.

I have had one of Fahim's 80 inch Marauder kits sitting in my garage for years too.
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Old Apr 25, 2013, 07:10 PM
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Jeff,

Wow, now that's what I call a big model! I doubt I'll ever build something this big or powerful, so I'm along for a vicarious ride!

PS. I'm a fan of the Typhoon too.

Steve
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Old Apr 26, 2013, 01:10 AM
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Hey Jeff, looking forward to seeing this one shape up. Count me subscribed

D-Rock
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Old Apr 26, 2013, 06:40 AM
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Looking great Jeff! Watching too.

J
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Old Apr 26, 2013, 08:57 AM
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Oh Jeez, now I have the best scale builders on rcgroups looking over my shoulder. No pressure there. Another caveat: this one will not be up to y'alls standards, but I thought the Typhoon was a little out of the ordinary. Kind of nice to know you guys are watching.

I also seem to be digging myself into a hole fairly early, so any input/advice/suggestions would be most appreciated.

Regards,
Jeff
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Old Apr 26, 2013, 09:16 AM
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&*()&*# Retracts

Okay, since I am chopping up the fuse some right at the wing saddle and planning to mess with the retract system, it seemed prudent to assemble the wing centre section and start blocking out the retracts, The wing comes in 5 pieces and the retracts will mount out by the dihedral break, so I started just with the 3 centre pieces.

I notched the wing LE to clear the new battery box. When the wing saddle is finished and sheeted I will trim the notch and line it with 1/32" ply. This should stablize the wing side-to-side. Instead of a dowel at the front, I will use a couple of bolts, a la FMS. Fahim used a single ply spar in the middle of the wing, which won't work with the gear in scale position, so I will fill that slot and put two spars in the scale locations.

I have put retracts in several of my foamies, so I wasn't too worried initially. Laid out the well position using a cardboard template made from blown-up 3-views. Measured the rearward retract angle (20 degrees, which seems like a lot), and made a balsa template to trace the angle for the 1/8" ply mounting plate. Quickly realized I had to make the plate smaller to keep it within the depth of the wing, then started excavating foam.
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Old Apr 26, 2013, 09:57 AM
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Problems

Okay, as with the B24, Fahim has used a much finer aerofoil section than scale, presumably to improve flight characteristics. Trouble is, that thin wing is only 32mm or so thick at the root and leaves no room for wheels. Fahim got around it by using 3" wheels on the prototype, but the 1/1 had massive 36" wheels, which works out to 4.5" at 1/8 scale, and the 3" look too tiny. Unfortunately, in the model world, the aspect ratio of wheels gets disproportionately lower as diameter increases. I knew I couldn't manage 4.5", but thought I could get away with 4". This has turned out to be wildly optimistic.

The thinnest 4" wheels I could find online were Dubro inflatables, 30 mm thick, but they are really heavy. I also picked up a set of Sullivan Skylites, which are 1/3 the weight, but 35 mm thick. Initially, I figured if the wheel was a little proud of the wing upper surface, I could maybe glue a sheet of 3 mm depron on the inner section and blend it it, but I am starting to do the math, and even with the Dubros, by the time I add the width of the oleo strut, I am looking at 40+ mm, which leaves 8 or 10 mm of wheel sticking out the top. No way to fudge that one, I will never get the wing root/fuse to mate properly.

I began to realize the magnitude of the problem as I mounted the electric retracts. I shortened the ply plate some to fit better towards the LE. I backed the plate with a couple of pieces of 3/8" x 1/2" basswood to give the mounting screws something to bite into. Got the plate to fit, just, and then as I started to fit the retract, realized that I would have 5 mm or so of it sticking out the top of the wing. Eyeballing it, I figured I could shim the retract body downwards, so I put a pair of 1/8" ply spacers in front of the mounting plate, which should let the edge of the retract plate be close to flush with the wing lower surface. Even so, the outer edge of the retract body pushed through the wing upper surface. Only a mm or so, I can hide that okay before sheeting.

What need is a high aspect ratio wheel. I have a spare set of wheels for my FMS Fw 190, which have the right aspect ratio, but are only 3.5" diameter. I have searched all over the net and as it stands, the only thing I haven't tried are the Robart scale wheels. They don't list the wheel thickness, but claim that they are exact scale duplicates of the Goodyear 32 x 8, in which case a 4" wheel (102 mm) should be only 25.4 mm thick. Guess I can order a set and see. Aside from that I am fresh out of bright ideas. Suggestions?

Regards,
Jeff
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Old Apr 26, 2013, 01:48 PM
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Current Wheel Options

So, looking at everything side-by-side, this is what I currently have available. The least scale and most practical option is clearly the FMS wheel. I have a set or Robart 4" scale wheels on order from Tower. I guess I will wait til I have them in had to make my final decision. If I can make them, I would prefer to use the larger wheel. It's at least Tempest scale, if not Typhoon.

Decisions, decisions. Jeff
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Old Apr 26, 2013, 04:54 PM
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Yikes, I'm getting flashbacks of trying to do something similar with a Hurricane a couple years back. Funny how thick some of the real airfoils were on early WWII warbirds, the Typhoon included.

Can you find any solid foam wheels of the right (or close to the right) diameter? For my Hurri I had to slice the outer few mm off of each wheel sidewall, and then cut a similar amount out of the hub before re-assembling the newly-thin wheel. Works okay with solid wheels, but obviously not with inflatables...

Steve
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Old Apr 26, 2013, 05:48 PM
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Hi Jeff, here are some wheels to check out. Hobbyking has a good range...

102 x 26mm - 4 inch and good looking (and $6!)
http://hobbyking.com/hobbyking/store...2pcs_Set_.html

These have exactly the same look as scale robarts...
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Old Apr 27, 2013, 06:58 AM
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Steve, I remember seeing you slice and dice those wheels and thinking what a tricky job that had to be. Option of last resort, I think.

Gree, 26 mm is the magic number, I will order a pair, many thanks. I hadn't looked on the HK site for wheels as my last couple of orders from them have taken upwards of 4 weeks to arrive.. In fact I am waiting on one, supposedly coming from the US warehouse, everything listed as "im stock" and as far as I know nothing has shipped yet. In this case, I have the gear plates and struts mounted, lots of other stuff to keep me busy while the wheels drift across the Pacific on the equatorial current.

Again, thanks gentlemen.
Jeff.

Arrgh, darn things are on backorder. I have an email alert for them.
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Last edited by jhspring; Apr 27, 2013 at 07:04 AM.
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