Fisher P-75 versus Davis Manta

[KJ_Lesnick]

So the Davis corrected was the actual foil?

[jcf]

Yep, based on mathematical analysis.

[KJ_Lesnick]

Everybody

I'm curious about some basic details about the design, being that it started in 1935 before dying out in 1941-42: If I recall, it was pitched as a long-ranged fighter from the outset.  I am uncertain as to what the original concepts looked like

• I know the initial concept was based around a non-specified 1200 hp inline engine: I don't have any clue as to estimates for length and span
  
• I know as it evolved, the V-1710 was specified for the aircraft: I don't know when the twin-boomer appeared
  

While I'm on this subject: I'm curious if the original reason little interest was shown because of the fact that the USAAC didn't want to develop an escort fighter (they figured escort fighters would be more expensive than regular fighters, even if they could achieve the goal, and were trying to build a bomber-force) more than anything else?


Flyer

Adding even a small tilt of nose up to clear the prop adds degrees of AoA to the wing, if they had tried it and it worked out then cool, but some designs can be unstable in ground handling with a higher nose attitude

Do you mean it might rotate off too early?

can have trouble with bouncing or wheelbarrowing on touch down.

So you mean it could bounce or pitch up and flip backwards?

[KJ_Lesnick]

joncarrfarrelly

Yep, based on mathematical analysis.

I read the earlier post and from what it says

Sometime ago I got ahold of the famous Davis airfoil equations, that
produce the airfoil used on the B-24.  With some help from George
Schairer, I found what constants to use and over the weekend, finally
succeded in producing the B-24 basic wing airfoil.  If you want the
equations, I can pass them on - they appear to be based upon pseudo-
science.  This airfoil should replace the one labeled "Davis" in the
collection.

David Lednicer
May 28, 1996

Did Davis just pull this all out of his rectum, and Consolidated simply morph the hell out of them in order to get the B-24 design?  Or were the figures used for the B-24 simply conceived by Davis and simply listed differently?

Davis wanted money to develop his ideas, so he exaggerated. Nothing new, nothing unique.

I'm curious if he even realized NACA had the new 6-series foils that were being used on the P-51 (Considering this was dated 1941, and the NACA foils were used as early as 1940).

[KJ_Lesnick]

Flyer

Yes, and refusing to settle on landing if it didn't have spoilers or similar to destroy lift until slowed.

So if it worked, there'd be no problem; if it didn't the wing would need a redesign?

Not flip backwards, simply repeatedly bouncing back into the air until it is too slow and stalls or runs out of runway, and wheelbarrowing is the aircraft running along solely on it's nosewheel when the pilot tries to pin it to the runway by pushing the stick forward.

Sounds troublesome or dangerous...

[KJ_Lesnick]

Flyer

Is troublesome and can be dangerous, no idea about any fixes for hypothetical problems.

Okay, so for the time being we could, for WHIF purposes, assume it'd work if need be

That being said, I was thinking the most obvious modifications that would be practical would be

• Swap the V-1710 for a V-3420
  

.
The switch from the V-3420 from the V-1710 is obvious as it provides twice the power it would profit off this substantially: Since propeller-thrust is tied to several variables

• Propeller-blade geometry & pitch
  
• Propeller-disc diameter
  
• Rotational velocity of the propeller
  
• Air pressure, density, and the speed of sound
  

.
The original propeller was a contra-prop 6'2" in diameter: This seems even small for the V-1710 and far too little for the V-3420; a 12'7" diameter propeller used on the Fischer Eagle seems more practical, though I'm not sure if it'd provide adequate clearance with a nose-gear



The basic length seems to conform to scale and the clearance from the spinner to the floor is 5'7".  This would make the tail-dragger highly practical

Because the V-3420 is wider and the cylinder heads would need a little bit of room



One could add a blister to make room for them like the Griffon Spitfires right?

[wuzak]

The original propeller was a contra-prop 6'2" in diameter: This seems even small for the V-1710 and far too little for the V-3420; a 12'7" diameter propeller used on the Fischer Eagle seems more practical, though I'm not sure if it'd provide adequate clearance with a nose-gear



The basic length seems to conform to scale and the clearance from the spinner to the floor is 5'7".  This would make the tail-dragger highly practical

If you change to a tail-dragger, what happens when you lift the tail during the take-off run?

https://www.youtube.com/watch?v=gv01Yk4iijs
https://www.youtube.com/watch?v=_iEpnl5g-s8
https://www.youtube.com/watch?v=znxM3QJ6l74
https://www.youtube.com/watch?v=qhV1f1g-HLA

You would also have to always make 3 point landings.

[KJ_Lesnick]

Wuzak

If you change to a tail-dragger, what happens when you lift the tail during the take-off run?

Good catch!  Looking at the videos the plane usually was slightly nose up in the pictures, whereas in the drawing it was nearly level so I suppose you'd have a little clearance though I'm not sure if it'd be acceptable by most standards.

I've made a slight estimate of the propeller diameter in this particular drawing and I've gotten a propeller diameter of around 8'2.5" to 8'3" in the drawing as an interesting note...

You would also have to always make 3 point landings.

True enough...

[KJ_Lesnick]

wuzak

I've done some calculations based on the image and based on the doubling of the propeller-area

• Baseline Propeller Diameter and Radius: 74" and 37" respectively
  
• Baseline Propeller Area: 4300.84 square inches (approx)
  
• Doubled Propeller Area: 8601.681 square inches (approx)
  
• Baseline Propeller Diameter and Radius: 104.652" approximate
  

Ground clearance is 14.674": Is that too little?

[KJ_Lesnick]

wuzak

What was generally the minimum acceptable propeller clearance thouse days

[wuzak]

wuzak

What was generally the minimum acceptable propeller clearance thouse days

I have no idea.

[KJ_Lesnick]

wuzak

Would the P-47D with paddleprop have been acceptable prior to WWII with a tail-dragger?

[wuzak]

wuzak

Would the P-47D with paddleprop have been acceptable prior to WWII with a tail-dragger?

It wouldn't have worked on a Spitfire.

[KJ_Lesnick]

wuzak

It wouldn't have worked on a Spitfire.

Just to be clear, we're talking about prop to ground clearance right?

[wuzak]

wuzak

It wouldn't have worked on a Spitfire.

Just to be clear, we're talking about prop to ground clearance right?

Yes, and the Spitfire's engine (pre WWII) wasn't powerful enough to swing such a large prop.