Little-known American Helicopter Prototypes & Projects

From Popular Mechanics 1966/5,Mr. Pop Wilson and his autogyro bike.
 

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On the back cover of this issue was an ad for Firestone Helicopters that has artwork for the GA-50.

Enjoy the Day! Mark

From these report and site,Firestone XR-14 mock-up.

 

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From these report and site,Firestone XR-14 mock-up.

Dear Hesham, I hope you don't mind if I leave here a bigger resolution pictures?
 

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Hi,

Mr. Horace T. Pentecost founded Hoppi-Copter Inc company,he designed the HX-1 or
Model-100,a one man copter with two contra-rotating rotors,followed by Model-101 &
Model-102,evolved into the 1950 experimental Firefly with an 18' rotor powered by
tip ramjets.

He also designed a very cheap single seat Helicopter,also there was a Model-103 and
Model-104.


Hi,

Hoppi-copter (1945) - The first helicopter designed by Horace T. Pentecost of Seattle was a "back-strap" model intended for military use. Later the American Hoppi-Copters Inc. built other models which had two coaxial rotors and a small engine of variable power depending on the version.

Hoppicopter “Firefly” (1950) - Single place model equipped with a two blades tip powered rotor. It seems that this model did some hovering flights in 1950.

 
May be of interest:

I came across also model 103 - I identify it with having an engine moved below main frame (clearly visible). Model 104 (if I recall correctly) was to be made in England in some cooperation, but I was never able to find any picture which will clearly indicate it as a separate thing)
 

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I came across also model 103 - I identify it with having an engine moved below main frame (clearly visible). Model 104 (if I recall correctly) was to be made in England in some cooperation, but I was never able to find any picture which will clearly indicate it as a separate thing)
Thanks a lot for this!
 
It's amazing what a random search after years can yield:
A pulse-jet Hoppi-copter made by the Capital Helicopters Corp.

In the post here:
you can find picture of this machine (probably named C1 Firefly, picture also attached)

I tried to fix the perspective of the pictures from ebay and came out with that:
1_crop_fixed.jpg
The seller of this item is not very open about where it came from, but after some time I was able to trace down this article. It comes from magazine called Air Trails Hobbies For Young Men, issue from July 1954 (vol 42, No. 4). The article describing "Hoppi-Copter" (this is how it is called there) is on page 16.
air-trails-july-1954-cover.jpg
Finally, my summary so far:
 

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May be of interest:

I came across also model 103 - I identify it with having an engine moved below main frame (clearly visible). Model 104 (if I recall correctly) was to be made in England in some cooperation, but I was never able to find any picture which will clearly indicate it as a separate thing)
This is not straight forward. I Just came on the couple of articles in Aviation Week archives and one said that Model 102 "will" be the production version of currently-being-tested tripod version of Hoppicopter. Like year later an article depicts model 103 (which in my mind was model 102 - with just a battery hanging below pilot) and on the right on the bottom picture is shown flying model 104 - but this is hard to identify - I seems not to have an engine below the pilot like in the version I used to call 103
 

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I gather the only major difference about Model 104 was the more spaced-out rotors.
This may also be true, but I still have some other doubts on models 102 -103 - 104.

I am diving a bit deeper right now, and shortly I will post my recent findings and doubts. This thread however is getting occupied by Hoppi-copters too much so I will create a new one dedicated to Mr Pentecost helicopter endeavours
 
This is the first time I remember seeing this compound helicopter from Grumman. Anyone have any other information?

I suspect the model coaxial lurking behind it is an early Sikorsky LHX.
Grumman never created an attack helicopter that I ever heard of.
 

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