The Dreaded V-Tail and my part in its downfall.

[Doc J]

Hi Guys - I was recently told that in California I have apparently garnered a really bad rep for my V-Tail design, and, I'm sitting here in too-hot Taiwan trying to figure it out.

This is really a bit mystifying because I have ever only designed TWO V-Tail models that have actually flown. So I thought I'd go through the history of the planes and share it with you guys to see if you can catch the reason - because I really can't. Maybe I'm too close to the forest to see the wood?

OK lets ake an honest look: Two models are involved: My first V-tail was way back when I designed the RCRCM Strega, and the second when I did the Redshift.

Strega:
Background:
In fact, the Strega - as I have reported for years - had the basic design, and the rigging angles quite extensively modified by someone associated with RCRCM (possibly from Germany? - I never did find out) before it was actually produced. At the time I was parting ways with those guys due to construction issues, and I never did get a test fly model - but that's another story.
When I found out that the Strega design had been modified was quite a long time later, when a local guy brought me a production model to take a look at - still incidentally with construction problems. I measured everything and I was pretty shocked at what I saw: There were so many modifications to the rigging angles that only the outline of the model really remained the same as my orginal design. After that I asked RCRCM to remove my name as the designer, but they never did.

Oddly, there never were any complaints about the Strega V-Tail at all that I ever heard of - Construction = Yes, V-Tail = No.
Hmm...so why did I get a bad rep there? Or did I?

Redshift:
Background:
Here I admit was so mad keen to get my new wing design going that I really did not spend the amount of time I should have to design the back end, and maybe I was a bit arrogant there because I thought as long as its in the ball park, then it should be OK.
Yep - I did design the tail area on the small side of the envelope, thinking that I'd keep the wetted area down, but within the normal parameters for a model of this size and configuration.
Yep - I designed the V-Tail angle a little on the obtuse side at 104 degrees - thinking that as long as there was enough vertical area in the breeze, then elevator response on a racing model would be more important than rudder. In flight testing in the UK, the model was found to be really quick, but a bit hard to head in very turbulent conditions - otherwise it was OK.

Anyway, since the anomaly was described as "Nothing a competent pilot couldn't easily handle", and also the model did win a few podiums and fastest time slots in Europe, I didnt worry too much about high turblence flying. The 'problems' even if left alone, were as the UK pilots had pointed out, not dire or game-changing for the plane's performance, it still flew fast, turned fast, and landed nicely. But since no designer wants anything to be questionable or mysterious on his design, I resolved to revisit the design theory before I set out to draw my next V-tail model. Also - and this is really no disclaimer! - in my own test flying I was pretty happy as I couldn't find any problems at all - but then I'm no longer a racing pilot! Hmm.

It was only when the few models that went to USA started to fly in California F3f that rough air heading problems were highlighted, again by Konrad, that I really gave it any attention at all. Konrad (happily for me) was crashing quite a lot and so had the chance to chop and change the back end in different angles to test the flying properties of the model as designed, and as modified by him. He was very helpful indeed in a isolating the causes of rough air heading problems, which, when boiled down indicated that I needed a bit more tailplane area and a slightly more acute V-angle. I was happy indeed with those conclusions but anyway I did another, much more thorough examination of the old and the new Spada design just to make sure. I was then able to confirm that those were the only mods to the basic design that were needed.

But actually, since only a very few Redshifts actually flew in California that I know of, I'm still wondering:

Where the heck did the bad rep come from??? Or is this all just a storm in a tea cup?

Cheers,

Doc.

 

[thenated0g]

Haven't heard anybody talking about it.

 

[Red]

Doc,

I wouldn't put much faith in hearsay. I've learned that the vocal minority never seem to never seem to shy away from telling anyone who will listen how smart they are. Fact is, most of the time it is the exact opposite. Dunning/Kruger effect and all that. I never stop trying to do better, but that's for me, not because somebody on the internet said so.

Cheers
Red

 

[Doc J]

Haven't heard anybody talking about it.

Thanks, Nate.

Doc.

 

[Doc J]

Doc,

I wouldn't put much faith in hearsay. I've learned that the vocal minority never seem to never seem to shy away from telling anyone who will listen how smart they are. Fact is, most of the time it is the exact opposite. Dunning/Kruger effect and all that. I never stop trying to do better, but that's for me, not because somebody on the internet said so.

Cheers
Red

Red, you are a man exactly after my own heart - only more so!

Yes, you are entirely correct. I have been the victim of Dunning-Kruger effect more than once.

"He who knows not, and knows not, that he knows not..."

I appreciate this input as frankly, I stand in awe of your abilities and achievements and the confidence and courage you use to persue them.

Cheers,

Doc.

 

[Red]

Red, you are a man exactly after my own heart - only more so!

Yes, you are entirely correct. I have been the victim of Dunning-Kruger effect more than once.

"He who knows not, and knows not, that he knows not..."

I appreciate this input as frankly, I stand in awe of your abilities and achievements and the confidence and courage you use to persue them.

Cheers,

Doc.

Don't be in too much awe. I'm just too stupid to know when to quit haha

Red

 

[Hawaii Sloper]

Doc,

I wouldn't put much faith in hearsay. I've learned that the vocal minority never seem to never seem to shy away from telling anyone who will listen how smart they are. Fact is, most of the time it is the exact opposite. Dunning/Kruger effect and all that. I never stop trying to do better, but that's for me, not because somebody on the internet said so.

Cheers
Red

 

[Doc J]

Don't be in too much awe. I'm just too stupid to know when to quit haha

Red

Thats a familiar feeling! (Still in awe though )

Dooohhhh!

Doc.

 

[Wayne]

I've only heard one person say anything about your v-tails. LOL

I'm not a fan of v-tails, thought they do look good to me at times. I have fallen in love with Y and inverted Y tails in recent years after flying a few. But these are not race planes.

As I have stated, I love your Forza and am looking forward to getting the shipment of new ones in a week or so. If that plane had a V-tail, I do not think it would have the same fun factor.. Or maybe I prefer the looks of a cross tail. Got me..

 

[Doc J]

I've only heard one person say anything about your v-tails. LOL

I'm not a fan of v-tails, thought they do look good to me at times. I have fallen in love with Y and inverted Y tails in recent years after flying a few. But these are not race planes.

As I have stated, I love your Forza and am looking forward to getting the shipment of new ones in a week or so. If that plane had a V-tail, I do not think it would have the same fun factor.. Or maybe I prefer the looks of a cross tail. Got me..

"I've only heard one person say anything about your v-tails. LOL"

Hmm...Yes, me too.

But I'm sure I'm right in saying that in a model of the size we normally fly, there really is no advantage at all in a V-tail other than a bit of increased ground clearance. But there is a whole lot of disadvantages.

Its all fashion.

To back that up, the record has been consistently broken by conventional X-tail models, and unofficial, but still electronically timed flights have been even faster.

I actually like the way the V-tails look on the smaller models, but for the 3m Racing planes its getting a bit boring now.

Cheers,

Doc.

 

[Konrad]

The properly designed V-tail is going strong. Did you mean to say that the V-tail and how it contributed to your demise.

As my name is mentioned this will be a bit of a rebuttal.

The Strega is very dated and like most V-Tails of the time, most F3F V-tails handled much the same when it came to directional stability. That is they were horrible compared to a properly designed cruciform tail.
To my way of thinking the decalage angle change from RCRCM is a trim drag issue. Having changed it to try to meet the designed criteria I can say I saw little or no change in the directional control of the Strega. The Strega would still make moon shots or yaw madly coming out of a pylon turn at speed. This could very well be as a result of pilot input of set up values. But as this is seen in a lot of Stregas flow by many competent pilots I suspect something in the airframe has a lot to do with directional instability. Again the Strega is dated and flew no worse than many other F3F racers of the time.

Now an aircraft is so much more than the sum of its parts. The fatal flaw, if it has one, in the REDshift is not the V-tail. Rather it is the excessive side area ahead of the center of pressure. The reason for this nose is discussed here. This is known as the Jimmy Durante on this side of the pond or Cyrano de Bergerac nose elsewhere. Unfortunately forward side area has a destabilizing effect on aircraft control and stability. It is one of the function of the rear vertical area to counter the destabilizing effect of the the nose. Now when anybody asks me about the finer points of the REDshift and its stability. It is the problem with the nose that I mention that contributes to the control issue I’ve and others have reported, not the V-tail. Now, I do like the downward droop of the nose to meet the upward flow of air.

Now the only aerodynamic issue I’m aware with the REDshift's V-tail, is the angle. One normally uses some function of the wing's aspect ratio to find the most suitable angle. This is based lot on the of writings from men far more versed than I on the subject. I’ve used the writing of Dr. Drela and Don Stackhouse to great effect on our racers. I’ve been in discussion with the designer on this point. It is my experience that the 100° to 104° angle is best used with 15:1 aspect ratio wings. Aircraft with higher aspect ratio wing respond better the the sub 100° angle. Not only do I respect the writing of the afford mentioned men but I put my money where my mouth is and have upgraded 2 of my REDshifts to sub 100° V-tails. Leaving all other variables a lone this one change to the REDshift had a very positive effect on directional stability of the REDshift. I hope that designer thinks is acceptable handling isn’t what I noticed in the prototype I purchased.

I want to be clear on this point. The issue I’ve seen with the Redshift is not with the V-tail but rather the nose! I worked on the V-tail angle to adders the destabilizing nature of the front side area. This is an engineering solution.
The designer is coming out with a new 3 meter V-tail ship. With what little information he has shared with us, it looks like he has addressed the large nose side area. He has also made some adjustments to the V-tail angle to address the interaction with the high aspect ratio wing. I also see some changes to the moment arms. These are all things I’ve reported to the designer in my findings with the REDshift.

I’m looking forward to the release of this new model to see what more can be done with the wing in the 3 meter size glider. The Redshift as released was found lacking both by me (directional stability) and by the market place (poor sales, mainly as a result of quality and mechanical issues). Now there is a lot of potential in the REDshift. That is why I own 3! And I can unequivocally state the the 96° V-tail has harnessed much of this potential.

As to the Dunning-Kruger effect that is why I give references to the subject I’m trying to discuss. I don’t expect anyone to take what I say at face value.

Actually it was a dealer of molded gliders that mentioned to me the market’s perception of the Hammond V-tail. Now I’ve heard this reinforced on the slope. But I try to point to the real issue with the stability is NOT the V-tail.

Yes, I think the V-tail is a tempest in a tea pot, acting as a RED hearing. The issue is stability not the V-tail. The Strega and REDshift both exhibited stability issues.

All the best,
Konrad

 

[Doc J]

The properly designed V-tail is going strong. Did you mean to say that the V-tail and how it contributed to your demise.

Apparently, yes.

As my name is mentioned this will be a bit of a rebuttal.
The Strega is very dated and like most V-Tails of the time, most F3F V-tails handled much the same when it came to directional stability. That is they were horrible compared to a properly designed cruciform tail

To my way of thinking the decalage angle change from RCRCM is a trim drag issue. Having changed it to try to meet the designed criteria I can say I saw little or no change in the directional control of the Strega.

The Strega would still make moon shots or yaw madly coming out of a pylon turn at speed. This could very well be as a result of pilot input of set up values. But as this is seen in a lot of Stregas flow by many competent pilots I suspect something in the airframe has a lot to do with directional instability. Again the Strega is dated and flew no worse than many other F3F racers of the time.

Now an aircraft is so much more than the sum of its parts. The fatal flaw, if it has one, in the REDshift is not the V-tail. Rather it is the excessive side area ahead of the center of pressure. The reason for this nose is discussed here. This is known as the Jimmy Durante on this side of the pond or Cyrano de Bergerac nose elsewhere. Unfortunately forward side area has a destabilizing effect on aircraft control and stability. It is one of the function of the rear vertical area to counter the destabilizing effect of the the nose. Now when anybody asks me about the finer points of the REDshift and its stability. It is the problem with the nose that I mention that contributes to the control issue I’ve and others have reported, not the V-tail. Now, I do like the downward droop of the nose to meet the upward flow of air.

Now the only aerodynamic issue I’m aware with the REDshift's V-tail, is the angle.

One normally uses some function of the wing's aspect ratio to find the most suitable angle. This is based lot on the of writings from men far more versed than I on the subject. I’ve used the writing of Dr. Drela and Don Stackhouse to great effect on our racers. I’ve been in discussion with the designer on this point. It is my experience that the 100° to 104° angle is best used with 15:1 aspect ratio wings. Aircraft with higher aspect ratio wing respond better the the sub 100° angle. Not only do I respect the writing of the afford mentioned men but I put my money where my mouth is and have upgraded 2 of my REDshifts to sub 100° V-tails. Leaving all other variables a lone this one change to the REDshift had a very positive effect on directional stability of the REDshift. I hope that designer thinks is acceptable handling isn’t what I noticed in the prototype I purchased.

I have deleted all my replies to the points above. Some of your comnents are correct, some, in my opinion are not. But we have been through this, ad infinitum. The obtuse V-Tail problem is like that "lovin feelin", its gone, gone, gone.

In any case this post was to try to find out how much my reputation had been damaged by the "V-tail" derogatory comments and not just another reiteration of the already much-discussed aerodynamic points.

I want to be clear on this point. The issue I’ve seen with the Redshift is not with the V-tail but rather the nose! I worked on the V-tail angle to adders the destabilizing nature of the front side area. This is an engineering solution.
The designer is coming out with a new 3 meter V-tail ship. With what little information he has shared with us, it looks like he has addressed the large nose side area. He has also made some adjustments to the V-tail angle to address the interaction with the high aspect ratio wing. I also see some changes to the moment arms. These are all things I’ve reported to the designer in my findings with the REDshift

Wonderful, so we dont need to go into all that again, do we.

I’m looking forward to the release of this new model to see what more can be done with the wing in the 3 meter size glider. The Redshift as released was found lacking both by me (directional stability) and by the market place (poor sales, mainly as a result of quality and mechanical issues). Now there is a lot of potential in the REDshift. That is why I own 3! And I can unequivocally state the the 96° V-tail has harnessed much of this potential.

As to the Dunning-Kruger effect that is why I give references to the subject I’m trying to discuss. I don’t expect anyone to take what I say at face value.

Hmmm.

Actually it was a dealer of molded gliders that mentioned to me the market’s perception of the Hammond V-tail. Now I’ve heard this reinforced on the slope. But I try to point to the real issue with the stability is NOT the V-tail.

Well, that certainly clears things up a bit. If the derogation was coming from someone who is effectively a competitor, or potential competitor in the future, then this all becomes much clearer.

Yes, I think the V-tail is a tempest in a tea pot, acting as a RED hearing. The issue is stability not the V-tail. The Strega and REDshift both exhibited stability issues.

Well, I guess we can all be thankful for that red Herring, as the "Duranti" nose instability effect has now magically disappeared, and in any case was not the subject of the original post, while the V-Tail bad rep either never was, or was to be expected from a competitor.

Case closed.

All the best,
Konrad

View attachment 12463
View attachment 12464

 

[ORRich]

View attachment 12441

Dang - this explains a lot - I wish someone would have told me about this years ago!

 

[Hawaii Sloper]

Dang - this explains a lot - I wish someone would have told me about this years ago!

Lol yeah! If I knew what it was when I was younger I would have kept my mouth shut a lot more

 

[gp49]

V-Tail problem? What V-tail problem? Just look below

 

[Konrad]

Apparently, yes.
...

Well, that certainly clears things up a bit. If the derogation was coming from someone who is effectively a competitor, or potential competitor in the future, then this all becomes much clearer.

Well, I guess we can all be thankful for that red Herring, as the "Duranti" nose instability effect has now magically disappeared, and in any case was not the subject of the original post, while the V-Tail bad rep either never was, or was to be expected from a competitor.

Case closed.

I don’t believe I mentioned who or that they were even a competitor. But yes, one needs to be leery of what a salesman tells you. He isn’t unbiased, after all he is trying to get your money.

Now what should be a concern for future sales is the talk on the slope. Rightly or wrongly the scuttle butt on the slope about your V-tail designs is how they appear to have issues with stability and control power. To that end the Jimmy Durante nose is very much at the heart of the stability issue with the REDshift. Not the V-tail.

Where did you come up with the idea that it majical disapeared? Nothing magical has happened. The added stability to the REDShift was as a result of my hard work, combing through theory, on the bench and on the slope. I worked rather hard to develop a “fix" to the Jimmy Durante nose found on the REDshift. While the 96° V-tail is a nudge in the right direction to add the needed vertical area to the rear of the fuselage, it is far from the cure. The Redshift in test still shows directional instability making it difficult to place the ship where needed. It also still take active command inputs to pull the Redshift out of a spin at the same time it takes an inordinate amount of altitude to recover. The ailerons lack power, again as a result of inefficient vertical area to work with.


I’m livid that you might think that my work coming up with 96° V-tail exonerates the design flaws, as to control and stability, found in the Redshifts! In this post I recently learned of the reason for the Jimmy Durante nose. It shows a fundamental misunderstanding of control and stability. At first glance it might make since, much like the equal transit theory of lift. But when examined and tested in the real world of full size or as with our models such as with the REDshift it is totally without merit!

Maybe that Dunning-Kruger effect statement wasn’t aimed at me?

Now I know that you know about the stability issue with a large nose. That is why I showed the Schwing fuselage. It has the minimum front side area to get the job done. It has a rather large vertical fin to counter this area and give the ailerons something to work against. It is by far the best flying Aeroic design I own and fly. Not because of the cruciform tail but because it has adequate vertical area.

Doc, you made a gross error when you designed the Redshift when it comes to stability. Please Doc swallow your pride, and just own up to it. It will save us a lot of time and words. It might even help with the sales of the REDshift replacement, if you can show that the lesson from the REDshift have been learned. This time around what little I’ve seen of the replacement, it does look like most of the destabilizing effects have been minimized.

 

[Konrad]

V-Tail problem? What V-tail problem? Just look below

LOL.

They really messed up on that design. When they added the larger wing to the make the Destiny. The TE drooped over the rear of the mount adding a lot of decalage also they didn't increasse the V-tail area to adress the added forces from the larger wing.

I don't think it was a Hammond design!

 

[Doc J]

LOL.

They really messed up on that design. When they added the larger wing to the make the Destiny. The TE drooped over the rear of the mount adding a lot of decalage also they didn't increasse the V-tail area to adress the added forces from the larger wing.

I don't think it was a Hammond design!

I want to see a Konrad Design!

C'mon Konrad -Money? Mouth?

Show everyone that you have been right all along, dude!

Put down the lines and justify.

No excuses, not "its not my job", no "I'm not a designer" etc etc

Doc.

 

[gp49]

I don’t believe I mentioned who or that they were even a competitor. But yes, one needs to be leery of what a salesman tells you. He isn’t unbiased, after all he is trying to get your money.

Now what should be a concern for future sales is the talk on the slope. Rightly or wrongly the scuttle butt on the slope about your V-tail designs is how they appear to have issues with stability and control power. To that end the Jimmy Durante nose is very much at the heart of the stability issue with the REDshift. Not the V-tail.

Where did you come up with the idea that it majical disapeared? Nothing magical has happened. The added stability to the REDShift was as a result of my hard work, combing through theory, on the bench and on the slope. I worked rather hard to develop a “fix" to the Jimmy Durante nose found on the REDshift. While the 96° V-tail is a nudge in the right direction to add the needed vertical area to the rear of the fuselage, it is far from the cure. The Redshift in test still shows directional instability making it difficult to place the ship where needed. It also still take active command inputs to pull the Redshift out of a spin at the same time it takes an inordinate amount of altitude to recover. The ailerons lack power, again as a result of inefficient vertical area to work with.


I’m livid that you might think that my work coming up with 96° V-tail exonerates the design flaws, as to control and stability, found in the Redshifts! In this post I recently learned of the reason for the Jimmy Durante nose. It shows a fundamental misunderstanding of control and stability. At first glance it might make since, much like the equal transit theory of lift. But when examined and tested in the real world of full size or as with our models such as with the REDshift it is totally without merit!

Maybe that Dunning-Kruger effect statement wasn’t aimed at me?

Now I know that you know about the stability issue with a large nose. That is why I showed the Schwing fuselage. It has the minimum front side area to get the job done. It has a rather large vertical fin to counter this area and give the ailerons something to work against. It is by far the best flying Aeroic design I own and fly. Not because of the cruciform tail but because it has adequate vertical area.

Doc, you made a gross error when you designed the Redshift when it comes to stability. Please Doc swallow your pride, and just own up to it. It will save us a lot of time and words. It might even help with the sales of the REDshift replacement, if you can show that the lesson from the REDshift have been learned. This time around what little I’ve seen of the replacement, it does look like most of the destabilizing effects have been minimized.

They did go the easy way out and not made tail at least bigger, but that Destiny is still a hoot to fly ( as long as you remember it's quirks) The micro Floh is a very nice flyer too. Even with the known problems the Destiny speed record is just below 290mph (!?)

 

[Doc J]

They did go the easy way out and not made tail at least bigger, but that Destiny is still a hoot to fly ( as long as you remember it's quirks) The micro Floh is a very nice flyer too. Even with the known problems the Destiny speed record is just below 290mph (!?)

Holy Moly GP - I didn't knw that.

The only time we tried to get the Destiny going was along a slope but in really light winds, and it didnt really like it.

Doc.