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Author Topic: Weight of Hyper Viper and Cox Chipmunk  (Read 2677 times)

Offline goozgog

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Weight of Hyper Viper and Cox Chipmunk
« on: December 25, 2018, 09:50:34 AM »
   Building the Cox Spitfire replica and
the Form-Flite P-47 , I have discovered
that wet molded balsa makes for stiff
and light components and is easy to do.

  I'm thinking that a Focke Wulf Long
Nose Dora is a natural subject for molding.
Now I need a target weight to aim for.

  Please!  Could someone tell me the weight
of the Hyper Viper and/or The Cox Chipmunk?

  The Spitfire is 7.2 oz and the P-47 is 4.7 oz.
( both ready to fly but dry. )
They both have adequate power with  simple
reedies.   I have lots of good choices in my
Cox collection but knowing a maximum weight
will help me choose.

Thanks in advance for any help!  - K.

 
Keith Morgan

Offline Chancey Chorney

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #1 on: December 25, 2018, 11:43:30 AM »
Hi there Keith. If this is the plane in question, the weight on my kitchen scale is 12.4 oz. This is with the handle, lines, tape holing the handle to the wing. Hope this helps.


Offline kenneth cook

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #2 on: December 25, 2018, 12:49:31 PM »
           Keith, my Chipmunk with solid foam weight 11.70 oz's. I have the Me-109, essentially the same plane but with the hollow fold wings which weighs 10.89. The Viper weighs 10.2 oz's. The Viper needs more power. The Chipmunk flies like a brick and the ME-109 isn't far behind it. Your creations from balsa would do all of them justice.

Offline goozgog

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #3 on: December 25, 2018, 03:15:14 PM »
Thank you Chauncey!

Thank you Kenneth!

And thank you for the quick replies. y1

OK..I am surprised that they are that light.
I was imagining them at about 14 oz.

  My "thought experiments " made me think
that my target weight would be about 10 oz.
Obviously I need to do better.

  The plot thickens - k.
Keith Morgan

Offline goozgog

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #4 on: December 26, 2018, 08:02:19 AM »
 I'm continuing to crunch the numbers for
my FW190-D  stunter and it's becoming obvious
that keeping it under 10 oz is going to be
a challenge.
 Respect to Larry Renger for designing the
Cox stunters  at less than 12 oz. using
foam and polystyrene .

  I have a few things I won't surrender to
save weight.

- Minimum 200 sq/inch wing & flap area

- Swept leading edge

- 23% elevator/stab to wing ratio

- Full fuselage

  I'm using my Beaufighter which has a
30 inch span and weighs 13 oz as a
base line for weight calculations.
  It uses two OK Cubs with Larry Renger's
modifications and it's fast and maneuverable.

   The picture shows my engine choices.
If you look closely you can see that I have
some interesting options.
  All of these engines are in good condition,
but I would love to use the Killer Bee since
there are so many of them available.

Decisions...  Decisions.......
Keith Morgan

Offline Dave Hull

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #5 on: December 26, 2018, 12:39:51 PM »
Where is your Killer Bee?

Dave

Offline Chancey Chorney

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #6 on: December 26, 2018, 01:53:04 PM »
The design looks very good so far.

Offline goozgog

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #7 on: December 26, 2018, 02:32:23 PM »
Hey Dave,

 I think you'll find that the centre engine
with the black plastic back plate is a Killer Bee.
  I know it doesn't have a gold crankcase,
but it's factory fresh and came with a
two bypass cylinder and a high compression head.

Please educate us if I'm incorrect.

Cheers! - K.
Keith Morgan

Offline Dave Hull

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #8 on: December 26, 2018, 06:25:10 PM »
Keith,

The reason I ask is because from the outside, that engine does not have the features of a KB. Different drive plate for a contacting spring starter, different needle valve, etc. So the question is whether it has a KB crank? If so, then along with your dual bypass cylinder and high compression head you are close enough powerwise.

Dave

Offline goozgog

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #9 on: December 27, 2018, 03:48:21 AM »
Hello again Dave,

   After checking Killer Bees on the
Cox Forum, I'm almost certain that
you are correct. Possibly this is an
Este's cobbled together engine.

  This engine is just one of many
that came in "The Big Box of Cox"
that was given to me at Brodak's.
  Just looking at it made me wonder
what it is, so I compared it to an ad
for Killer Bees on the back cover of
July 1995 Flying Models. ( Cox Products, Corona CA )
Everything matches except the drive
plate.

  I didn't know that Killer Bees are
rare since I have many that look
like one.
Dave, thank you for the information.

  BTW..  The Big Box of Cox was an
amazing gift. Now I wish I had asked
who's stuff it was. They were a VERY
serious 1/2A competitor.
  The box was stuffed full of engines
and parts including a few TD's , Black Widows,
22 piston and cylinder sets, cranks,
tanks and all kinds of Cox fittings.

Gratitude is the mother of happiness - K.
« Last Edit: December 27, 2018, 11:15:49 AM by goozgog »
Keith Morgan

Offline Larry Renger

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #10 on: December 27, 2018, 07:10:20 AM »
The real Killer Bee had a special crankshaft with a hole drilled in the crankpin and cutouts from the crank web for balance.

The cylinder had two main bypass flutes and one booster flute per side. The exhaust had dual slits, but the bottom slit was larger to allow sub piston induction. The pistons and cylinders had Tee Dee style taper ground in.

 The backplate had an enlarged venturi and no screen. As shown in Dave’s photo, the drive washer was old style and an old style spring starter was used. It also had a steel washer between the drive plate and crankcase to allow use of electric starters.

Finally, the needle valve was shortened and extended with a bit of plastic tube. This was to reduce weight because the full length needles would vibrate loose due to the rpm.

ESTES put out fake Killer Bees and Venoms at the end.
Think S.M.A.L.L. y'all and, it's all good, CL, FF and RC!

DesignMan
 BTW, Dracula Sucks!  A closed mouth gathers no feet!

Offline paw080

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #11 on: December 27, 2018, 05:07:06 PM »


   The picture shows my engine choices.
If you look closely you can see that I have
some interesting options.
  All of these engines are in good condition,
but I would love to use the Killer Bee since
there are so many of them available.

Decisions...  Decisions.......

Hi goozgog,  NONE of those engines are any good for a stunt platform.

Either use a Medallion or a PAW .049 sbr. These engines have a perfect

power/torque delivery; the PAW .049 sbr uses considerably less fuel

than the glow engines.  My PAW powered Ringmaster Jr can fly the entire

Stunt pattern plus I don't recall how many extra laps on 44' X .008" lines.

It uses a  Perfect 1/2 ounce fuel tank.  My kit bashed Ring Jr weighs 7.2 oz's.

Tony G  D>K

Offline kenneth cook

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #12 on: December 27, 2018, 08:37:04 PM »
             The only difference between a Estes Killer Bee and a Cox are just a few things. The Estes didn't provide a lightened crank. High performance cranks are available today. Davis Diesel offers also offers a crank which the crankweb is cutout, however the shaft is entirely the same diameter which can rob some rpm's. It's not going to break.  I don't believe they have the drilled conrod pin, the cylinder was correct which in my opinion is the heartbeat. I have a Estes Killer Bee and it's not using a Sure Start cylinder. It has the wider lower slit.


 The needle valve isn't correct but the original was nothing special as this is easily replicated. To go one step further, one could press out the needle and put in the 128TPI which I don't believe either Cox or Estes used on the Killer Bee. I purchased a Killer Bee backplate which was black from Cox. I might be incorrect on this but I'm pretty positive.

  The Estes version did provide the proper backplate as well. I can't comment on the original case that Cox used as the Estes doesn't use the anodized case. They use a Sure Start and I found them to wear rapidly in which I had a few bushed.

Offline 944_Jim

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #13 on: December 28, 2018, 04:45:51 PM »
  I'm using my Beaufighter which has a
30 inch span and weighs 13 oz as a
base line for weight calculations.

Two engines? Is this a twin? Where can I find plans? Who designed it?

Thanks in advance,

Offline goozgog

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #14 on: December 29, 2018, 05:46:26 AM »
Hey Jim,
             I designed and built the Beaufighter
back in 2008 for 1/2A scale. It was a very rush
build of just five days. I would have won but
I had an engine quit so I didn't get twin engine
points.

  It's powered by two OK Cubs with the Larry
Renger mods and has plenty of power.
The Cubs run like proper stunt engines.
Not super powerful, but consistent and
they needle well.

  Some things worth saying.....

    The wing is flat bottomed and uses
"Spread Fingers" construction, which is a
fast way to build a scale wing. See my
Replica Cox Spitfire Replica Build post .
The pictures explain it.

  The engine nacelles are full bodied on this
Profile eligible plane . I had to get advanced
permission to use them.
   Both engines are mounted with outboard
thrust. When the inboard engine quits, the
outboard engine still keeps the lines tight.
Not a good set up for stunt, but OK for
"Scale".

  The butterfly tail has two control horns,
one for each elevator. It is larger than
the scale size but no problem getting the
Beaufighter through  loops and eights.

  If I was going to build a twin for Stunt,
I would definitely build a better Beaufighter. 

Pictures by Paul Smith

 


   
 
« Last Edit: December 29, 2018, 08:55:22 AM by goozgog »
Keith Morgan

Offline Chancey Chorney

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #15 on: December 29, 2018, 09:40:51 AM »
Wow Keith. That is a great looking build. And to think in only 5 days! Amazing.

Offline MikeyPratt

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #16 on: December 29, 2018, 06:54:28 PM »
Hi Keith,
The Hyper Viper was designed for under 11 ounces, so at 10.2 to 10.8 your good.  It was powered by a Cox production Sure Start .049.  I wanted to have it powered by a Keller Bee but they said no way on the KB.  It flew OK on the production engine, but it flew way way better on the KB engine.  Also at that time I was working on Sure Start .09 that showed lots of promise and I wanted to put that engine in the HV (sometimes a really good idea gets shot down because of the people at the top, I protested and was fired).

Later,
Mikey

Offline Dave Hull

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #17 on: December 29, 2018, 07:24:43 PM »
Mikey,

After I saw my first HyperViper and helped a buddy tune and run it, it was pretty obvious that it was underpowered. But I liked the shapes and really, really liked the graphics. I offered to build up a Mouse-Stunt motor, but that never happened.

So one day, I call up Cox while they are still in production and had a long conversation with someone about the HV. I kept telling them that the plane had lots of potential, but needed a Medallion .049 up front.

After hearing about your employment exit, I hope my call came the very next day.....

Dave

Offline 944_Jim

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #18 on: December 30, 2018, 07:34:25 AM »
Thanks for the details, Keith. Beautiful model. Loops and eights, eh? I think I'd be too chicken!

Offline goozgog

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Re: Weight of Hyper Viper and Cox Chipmunk
« Reply #19 on: January 01, 2019, 05:02:30 AM »
Happy New Year Everyone !

   Hello Mike.  I apologize if I accredited Larry with
all of the responsibility for these clever products.
  I worked most of my life as an industrial designer
and I have been in similar situations as yours with the
Hyper Viper / .09.  It's excruciating when the
customer just can't see the potential of an idea.
   It sounds like the marketing department should have
considered releasing the .09 version as the
" Super Hyper Viper" parallel to the Sure Start version.
C'est la vie.

  Strangely, I had to choose what to build this winter
and the options were another molded 1/2A or one
of my Sig Magnum kits.  Thanks for that fine design!   y1

  Cheers guys for the compliments on the Beaufighter.
It's a good plane that makes me feel confident about loops.
The lazy eights are no problem but both engines have
to keep running. They haven't quit on me yet .... but......    ~^
Keith Morgan


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