REFLECTOR: Velocity twin

Tue Nov 8 12:34:57 CST 2011

The center vertical stab and rudder was inverted. They said they tried the traditional vertical stab but the prop shock wave reverberated against it and made it way too noisy in the cabin.
[cid:image001.jpg at 01CC9E1B.34829360]

Best regards,

Nick and Connie Jones
Velocity XL-RG
N10CN
99% done 90% to go

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Scott Derrick
Sent: Tuesday, November 08, 2011 10:56 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Velocity twin

Here is a picture of a most famous Twin canard, notice the (total) absence of a centerline empennange.

attached

This snippet is from a Starship RAQ

b)  Reduced yaw during engine out.

The Starship's aft mounted pusher props are about 8 feet apart, providing almost centerline thrust from each engine. In the event of an engine failure there is almost imperceptible yaw moment.

Scott

-------- Original Message --------
Subject: Re: REFLECTOR: Velocity twin
From: Scott Baker <scottb33333 at gmail.com><mailto:scottb33333 at gmail.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org><mailto:reflector at tvbf.org>
Date: 11/08/2011 05:50 AM

While I do not pretend to be an aeronautical engineer, factors in favor of a central vertical stabilizer and rudder on the prototype Twin Velocity take into consideration:
A.     The main wings are extended to gain additional wing surface area.  The main wing spar(s) however, are the original XL length.  This means that winglets, if they were used, would not be tied directly to the main wing spar.
B.     In non-centerline twin engine aircraft, an engine out results in a great deal of yaw towards the dead engine.  The shape and area of the central upper and lower fins, vertical stabilizer, and rudder allow the pilot to offset the yaw of the dead engine.  A key design element in the Twin Velocity is that these surfaces are large enough to offset the yaw caused by an engine out situation - and be able to do so at an airspeed (read, available energy) that is below the canard stall speed.  Getting to Scott D's point about the strong rudder effectiveness of single engine Velocity aircraft - while the rudders are effective at stall speed, winglet rudder input at slow speeds causes the aircraft to _roll_ more than it affects yaw.  In the Twin Velocity, strong yaw control is important in an engine out situation - and for this reason I think the central vertical stabilizer "wins out" over winglet stabilizers/rudders.  Maybe this is "conventional thinking" on my part.  It might be interesting to put both models into a computer simulator.
C.     In the case of the prototype Twin Velocity, using a central vertical stabilizer/rudder allows more direct routing of the rudder cables and the use of larger cables - giving stronger authority to rudder control.

Should winglet stabilizers and rudders be used in future Twin Velocity models, aspects of the Velocity design can easily be changed to overcome the issues mentioned in (A) and (C).

Just my thoughts.
Scott B

----- Original Message -----
From: Scott Derrick<mailto:scott at tnstaafl.net>
To: velocityoner at yahoo.com<mailto:velocityoner at yahoo.com> ; Velocity Aircraft Owners and Builders list<mailto:reflector at tvbf.org>
Sent: Monday, November 07, 2011 4:40 PM
Subject: Re: REFLECTOR: Velocity twin

This sounds like Apples and Oranges to me?
I had a good talk with Duane one day regarding a twin velocity long before any cloth was cut for it. Duane wanted to design a twin that would not have a VMC issue. The deal with the big fin and rudder is that the canard will stall before VMC is reached, which will lower the nose and increase speed. This will prohibit the aircraft from loosing directional control even if they were nose high and as slow as they could go.

The Rudders be they one or out on the winglets has nothing to do with the speed of the canard stalling?

With any of the singles, you can slow to canard stall speed, hold it there and have plenty of rudder to yaw the airplane. You never run out of rudder control like you do in a conventional single with a single tail and stall speed. Partly because the fuselage blocks a lot of the airflow to a single conventional tail when in a stall attitude.  Our speed brake/rudders out on the winglets don't have this problem. Also it takes just a little larger rudder out on the winglet to greatly increase the rudder force because of the leverage you get out at the end of the wing. Seems like this single tail is duplicating a bad thing and removing a good thing?

I probably don't understand or am misinterpreting it?

Scott

-------- Original Message --------
Subject: REFLECTOR: Velocity twin
From: velocityoner at yahoo.com<mailto:velocityoner at yahoo.com>
To: 'Velocity Owners and Builders list' <reflector at tvbf.org><mailto:reflector at tvbf.org>
Date: 11/07/2011 02:05 PM

Velocitites,

I had a good talk with Duane one day regarding a twin velocity long before any cloth was cut for it. Duane wanted to design a twin that would not have a VMC issue. The deal with the big fin and rudder is that the canard will stall before VMC is reached, which will lower the nose and increase speed. This will prohibit the aircraft from loosing directional control even if they were nose high and as slow as they could go.
The other objective that Duane wanted was for the airplane to be able to climb on one engine at gross weight. That probably meant that it needed slightly more wing. With a longer wing if you put large winglets on it that would require more structure in the wing.
Bottom line is that Duane thought about this for a long time before mixing glass. I would bet that this airplane will do everything it was intended to do and in the end it will be a great looking airplane. How many million dollar Provost coaches would look good without great paint schemes on them? It's a square box you know. Ken Brock believed that every design could always be improved. The space shuttle could have been improved but who would argue that it was a great machine?
I know one thing, if Velocity builds it, I have no reservation in flying it. I believe that this airplane is going to change the way that others look at homebuilts.

Victor Taylor
Velocity N93DV
Flying for 19 years.

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