1/7 Harvard Conversion

1/7 Harvard Conversion

Postby Dale » Tue Apr 16, 2013 11:05 am

(Is it wrong to have 2 build threads on the go?)

Anyway, let me tell you guys a story.

A few years ago, i decided it was time to move up to bigger models. (Bigger flies better right?) Life up to that point had consisted of 40-60 2 stroke glow, and a bunch of smaller electrics.
As a lot of us do, i have a soft spot for the old Harvard, having been watching them since being a lad, and so some money was exchanged for the 1/7 scale World Models Texan ARF at Top RC.
I acquired an RCV.91, and had much fun tinkering with this, and eventually flew it, and had great delight in flying it too, this model flew really well, can't complain about her flying characteristics.
However, her time came too early, with a deadstick on takeoff, the resulting forced landing pretty much destroying the nose, cowl and wing center section.
This setback made me ever more keen, being left with a feeling of "unfinished business".
#1 Pre-flight
IMG_3086.JPG (128.08 KiB) Viewed 10395 times

#1 In Flight
IMG_3704.jpg (98.81 KiB) Viewed 10395 times

Sometime more recently, I won a TM auction for the same kit NIB, from a kindly gentleman in Chch. - this is a story in itself:
The auction closed like a day before the big earthquake, and naturally he had more pressing issues to deal with than send out trademe packages. However after a couple of weeks, he emailed me to say that the plane was fine, and at his first opportunity, he would get it sent up. Almost as an aside, he mentioned that his house was heavily damaged (up on the port hills i recall), wasn't allowed in it, but the garage (where the box was) was ok.
Eventually it arrived at my place, and all good there.
So, my good man (sorry i have forgotten your name), i hope you have been treated well during the rebuild and life has returned to normal for you. (If you read this, drop me a line on here).

So this second airframe went together, including the use of some parts from the original.
By this time the RCV had disappeared, and on the nose went a pumped OS .91 4st,, with onboard glow driver.
We had a couple of good flights on it, then early on the third, she went in, victim of radio failure. (Since identified and resolved).
The amazing thing is she went in vertically into one of the large drains that surround our field, so the mud and long grasses absorbed the impact forces. Other than an good soaking, there was only little damage, and nothing structural.
The engine was removed and cleaned up, and now has a home in the nose of a P-40.

This unfortunately (second time!) left me very determined to get her flying again, so her time has come. (I think i also owe it to the TM seller after all his efforts!)
The bits to put back together (or make a biplane from?)
DSC01258.JPG (187.69 KiB) Viewed 10395 times

This time we're going different:
Colour scheme will be different, i think i've done my dash with the classic 078.
Every last piece of stupid iron-on plastic covering will be finding a new home in the bin, replaced with something a bit more "genuine"
It will NOT be glow powered.
Along the way, we'll be making a few improvements and adjustments, hopefully to come out the other side with a reliable, good looking, and good to fly model.
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Re: 1/7 Harvard Conversion

Postby Dale » Sun Apr 21, 2013 3:12 pm

Well i have stripped the fuse, and started the repairs.
One day soon i'll meet up with a mate with a laser cutter and whack out a couple of new bits to reinforce some damaged areas in the framing in the front fuse. (Wing seat mounting, doublers, and will put a new skin on firewall)
Managed to get the factory-glued rudder and elevators off, and have pulled off all the iron-on off with some assistance from the Missus' hair dryer.
Build quality looks pretty good on this model, certainly no less than the Top Flite kit i've been working on for years. Wood of apparently suitable quality, with glue in the right places. Pretty happy, and much better than some of the rubbish ARF's i've played with over the years.
Once the wooden repairs are done, this fuse assy will be getting fibreglassed.
Weight of this assy as pictured is 666 g.

Interesting, note the root fairings and taiplane fairing are fibreglass, as are several other bits on the wing.
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Re: 1/7 Harvard Conversion

Postby Dale » Tue Apr 23, 2013 8:27 pm

I spent a couple of hours reminding myself how to draw with cad, and came up with this:
Harvard Parts.jpg

This was followed by spending last night bugging me mate learning about laser cutting and related taskings.
The end result is we have these:
DSC01310.JPG (133.07 KiB) Viewed 10366 times

New fuse doublers and firewall (The large ply circle) is the short explanation. The firewall had a few too many holes in it to be comfortable moving forward, as i am not replacing the original engine with the same. - The evidence points to this airframe had the RCV bolted to it at one point, so slightly confusing the story presented in the opening post, and adding at least 4 more holes to the "swiss cheese" that called itself a firewall.
A small fettle with the sandpaper and file, and we have this:
DSC01313.JPG (151.41 KiB) Viewed 10366 times

This is one of me new doublers in approx position, prior to gluing.
It goes all the way from the rear of the firewall (you can make out the blind nuts still in the firewall to the left), past the wing "dowel" slotted former, doubling the wing seat, all the way to the back wing saddle, and note the slot for the wing bolt plate to the right. (this had broken out on both sides). (ok i lied when i said "nothing structural" was broken).
You'll note the bottom of this new doubler is not "wing shaped", this will be manually trimmed to exact shaped once glued in postion.
You may also note that the fuse is in process of getting spackled, wood repairs are completed. Will be glassing fuse once have finished adding the new wood parts.
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Re: 1/7 Harvard Conversion

Postby Dale » Tue Apr 23, 2013 8:30 pm

Re laser cutting, it's only fair i give a plug:
Milestones Trophies and Engraving, details at http://www.milestonesengraving.co.nz/
Check 'em out if you need any trophies, engraving, awards etc etc.
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Re: 1/7 Harvard Conversion

Postby Dale » Sun Apr 28, 2013 9:20 pm

Slight tangent:
It will NOT be glow powered.

Conveniently, this arrived in the post the other day from Mike's Chainsaws & Outdoor Power (http://www.mikeschainsawshop.co.nz)
DSC01448.JPG (193.68 KiB) Viewed 10315 times

DSC01451.JPG (173.89 KiB) Viewed 10315 times

So my first foray into petrol (gas) begins with the GT17 from NGH. (17cc)
-Separate cylinder head and piston liner
-Genuine Walbro WT carburetor
-Remote REXEL CDI ignition system
-Max Power: 1.8 HP @ 12,000 r.p.m.
-Recom. Prop Size: 13 x 8 - 15 x 8
-Net Weight: 730 gram

Appears to be a sweet little engine, certainly looks good. Brian Winch gave it a glowing review. http://www.justengines.co.uk/acatalog/GT17reveiw.pdf (note is 15Mb). Is designed from the outset to be a replacement/alternative for the .91 4st glow motor.

I spent the day giving this about an hour of bench running as per the instructions, which took a surprising amount of getting organised for.
As i haven't had gas before, i needed a field tank, oil, pump, tubing, filters etc etc.
Also needed to organise the test stand, as well as the hardware required to get it running, like a battery for the ignition system, switch, prop etc.
Late in the afternoon i finally got it sorted, and she roared into life without issue.
Put a couple of tanks through it (about an hour and a half of runtime) at 16:1, the first hour without muffler, on a 13x8 prop. Normal fuel is 20:1 which it will go on hence forth, and probably fly on a 14x7.
All well with this, real happy with the operation. Have been doing a lot of reading on RCGroups about gas engines. Next time it runs it'll be bolted to a firewall.
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Re: 1/7 Harvard Conversion

Postby Dale » Wed May 01, 2013 5:37 pm

Fuse repairs and additions are complete.
New wood items are in, the new firewall skin i had no choice but to epoxy on, as the firewall was of course already epoxy coated for fuel proofing.
The firewall backing and fuse doublers were PVA'd in.
Weight of fuse now is 861g, so added 195g with the new bits and repairs. Quite a bit i agree, but this is getting a larger and heavier motor than it was perhaps designed for, so i feel increasing the rigidity and strength is a worthwhile exercise.
New bits in
DSC01454.JPG (167.71 KiB) Viewed 10294 times

Have been going over it with the filler and final sanding
Next step will be to seal the wood, to prevent it soaking up too much epoxy during the glassing stage. This was something i didn't do on the Typhoon, and thus added a not inconsiderable amount of weight in terms of excess epoxy. Followed by glassing proper.
ready to begin the glassing process
DSC01452.JPG (167.81 KiB) Viewed 10294 times
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Re: 1/7 Harvard Conversion

Postby DH100 » Wed May 01, 2013 9:30 pm

You are certainly on the right track with sealing the balsa before glassing. I'll interested in the results you get with your petrol engine.

Good stuff.

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Re: 1/7 Harvard Conversion

Postby Dale » Sun May 05, 2013 3:25 pm

Cheers Brian.

Re sealing, I was recommended to look into Wattyl's Estapol Hi-Build sanding sealer, so i did.
Bought a small tin, and gave the entire fuse a coat.
Interestingly, the wet coat apparently weighed some 20 odd grams, which then when dried weighed only 14g. After a quick sand, it was down to 11g. (so my $20 trademe scales tell me - probably has all the accuracy of a wooden ruler)
(Pic stolen from Wattyl's website)

So next stage is glassing, and rubbish weather this weekend has given me the incentive to get on with that.

I got some resin and cloth and some other bits and pieces from NZ Fibreglass Ltd (via trademe), and set to work.
The front fuse i've done with 48gm/m2, from the firewall back to the front of the cockpit opening at top and rear of wing seat area, to hold the repairs and bits and pieces together, including wrapping the cloth around onto the firewall and over the wing seat and onto me new doublers.
The mid and rear fuse, and the find and tailplane are all being done in 25gm/m2.
I thin the resin with around 1/3 straight methanol (cause i have plenty of this lying around), makes it go on real easy, and then the methanol evaporates out in minutes. Followed up by the tissue paper excess absorber trick.
Hoping to do a bit a day as the previous part dries off.

Once it's all done i'll mix up another batch, with some microballoons mixed in, to fill the weave and strengthen it up a bit more.
Glassing in progress in what was once the spare room in the house. Now resembles a modelling shed!
DSC01467.JPG (192.34 KiB) Viewed 10274 times
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Re: 1/7 Harvard Conversion

Postby Dale » Sun May 12, 2013 11:26 am

Glassing of the fuse continues, which pretty much means spend 10 min getting organised, 10 min putting the piece of glass on, 10 min cleaning up, and then 23 hours and 30 min waiting for it it dry to do the next bit.

In the mean time, i thought i'd start playing with the next bit, which is the wing centre section.
Wing centre top

Wing centre underside

This has had a repair previously but this time is pretty much good to go, after stripping the covering and a tickle up, will be glassing.
The wheel bay area (painted yellow) is factory fibreglass.

The only major mod i have planned here is to hinge the flaps in a different manner than factory, to enable scale flap deployment of flaps at something like 60°, rather than the typical arf value of way-not-enough.
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Re: 1/7 Harvard Conversion

Postby Dale » Tue May 14, 2013 8:30 pm

Colour Scheme:
Last time i was in Chch, i dropped around the Air Force Museum, as was pleasantly surprised to see the Havard on the the pole had been repainted and looked real shiny, and i quite liked the scheme, and knew straight away that this was the scheme my bird would go in when she got back on the building bench.

Inside said museum, i picked up a great paper model of her, which gives me more detail - in short, if it is printed on here, it will be represented on mine. means i get the main detail, without going "overboard", i can't bring myself to put on rivets and stitching etc...


In short, painted silver, with the bits of orange (dayglo) around the place, with markings etc will likely be vinyl cut.
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