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Author Topic: I am thinking of building  (Read 1168 times)

Offline john vlna

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I am thinking of building
« on: March 04, 2011, 07:23:40 PM »
This, a Vickers 125 Vero for scale carrier. At a 42" span it has about 360 sq in. Sort of a British low wing MO-1. It is legal since it underwent deck trials on the HMS Furious although it was never put into production. Currently working on a plan.
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Offline bill bischoff

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Re: I am thinking of building
« Reply #1 on: March 04, 2011, 09:12:17 PM »
That's homely enough that Ted Kraver should like it! Except for maybe a little bit too much fuselage side area, the proportions look pretty good. Go for it!
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Offline john vlna

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Re: I am thinking of building
« Reply #2 on: March 05, 2011, 06:15:27 PM »
Bill,
I am sure Ted will love it. I can use the 5% to slim the fuse a bit, but it won't make a big difference.
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Offline john vlna

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Re: I am thinking of building
« Reply #3 on: March 06, 2011, 01:06:28 PM »
Ty
I don't have a 4 stroke radial nor the $'s to but one, but I do have a 4 stroke. It is a Magnum 52 which would make the plane a class I. But I am not sure the 60% rule applies to scale, maybe only profile
John
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Offline bill bischoff

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Re: I am thinking of building
« Reply #4 on: March 06, 2011, 01:27:37 PM »
The 60% rule comes from CL General, and applies to all 3 classes. I vote 4 stroke!
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Offline Bob Reeves

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Re: I am thinking of building
« Reply #5 on: March 08, 2011, 01:04:53 AM »
As some of you may know I love 4 strokes, run them on my stunt ships and have a little experience with the silly things. I wanted so bad to put a Saito 56 on the big FJ-4 but decided in favor of the TT36 for a couple reasons. First you can only push a 4 stroke to about 10 grand without it self destructing. I found a prop pitch/speed calculator on the internet and came to the conclusion I couldn't put enough pitch in a prop to make up the difference between a 10 grand Saito and a 15 grand TT36. Second don't remember the exact figure but the Saito weighed 4 or 5 ounces more than the TT. This wouldn't have necessarily been a deal killer but the RPM limit was. As much as I like 4 strokes don't think they would be a good choice for carrier.

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Offline john vlna

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Re: I am thinking of building
« Reply #6 on: March 08, 2011, 11:09:53 AM »
Bob,
What you cite is probably why 4 strokes aren't seen in carrier. Still looking at options but maybe I'll build 3
1. 4 stroke for scale.
2. 2 stroke carrier.
3. electric carrier.
Now I would have to remember what contest I was at and what I was flying,  and that could be a problem.

John
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Offline Douglas Ames

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Re: I am thinking of building
« Reply #7 on: July 04, 2011, 09:38:15 PM »
Quote from: Bob Reeves on March 08, 2011, 01:04:53 AM
As some of you may know I love 4 strokes, run them on my stunt ships and have a little experience with the silly things. I wanted so bad to put a Saito 56 on the big FJ-4 but decided in favor of the TT36 for a couple reasons. First you can only push a 4 stroke to about 10 grand without it self destructing. I found a prop pitch/speed calculator on the internet and came to the conclusion I couldn't put enough pitch in a prop to make up the difference between a 10 grand Saito and a 15 grand TT36. Second don't remember the exact figure but the Saito weighed 4 or 5 ounces more than the TT. This wouldn't have necessarily been a deal killer but the RPM limit was. As much as I like 4 strokes don't think they would be a good choice for carrier.



What about multi-blade props? (are they legal?) Powerplant Engineers in WWII ran into the same problem- dia. was limited by tip speed and RPM. Their solution was add more blades and/or increase the chord of the blades. Surely a Saito .56 under full song will swing a 3 or 4 blade prop and generate ample thrust?
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Offline bill bischoff

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Re: I am thinking of building
« Reply #8 on: July 04, 2011, 09:54:25 PM »
There are no prop restrictions in the rules. The problem is that to get the same theoretical top speed with only 2/3 the rpm, you would need 3/2 or 1 1/2 times the pitch. Not a problem once you get up to speed, but before takeoff when forward speed is zero, the prop is stalled because the angle of attack (pitch) is so high. This gives very poor acceleration. This is why real airplanes have props that can change their pitch. For takeoff and climb they use lower pitch, and for cruise they use higher pitch. With a high revving two stroke, you can use less pitch for good acceleration, but due to the high rpm, the pitch x rpm still gives a high theoretical top speed.

(Sorry to all the engineering types for the gross simplification.)
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