X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mail-iw0-f180.google.com ([209.85.214.180] verified) by logan.com (CommuniGate Pro SMTP 5.3.10) with ESMTP id 4551120 for flyrotary@lancaironline.net; Mon, 01 Nov 2010 18:15:07 -0400 Received-SPF: pass receiver=logan.com; client-ip=209.85.214.180; envelope-from=wdleonard@gmail.com Received: by iwn37 with SMTP id 37so9515157iwn.25 for ; Mon, 01 Nov 2010 15:14:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:in-reply-to :references:date:message-id:subject:from:to:content-type; bh=0tLlmyJFnShTCxp//nXU7Su2fDFZe19cDcZ4w8mMvGc=; b=JiYV2JAmqzgDSZfrTtYdBySIADwSIRE2hPkMF96HyW1uTZ+8Eyf9zJGIzt6ooMNcNf I3TPdyacuqmdb2bftcZnPCbFoDPp321PdqZR6gobHE3KCvUlWf5jKNdvXXZgLydLeI6d DeybtUAHroR6tJQZBNZdteHnd1O1snd3NlXQU= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=WaVjSvAIlqdxASgEIpGc1XsYY50EnVeX5UilRpMjDYcwhAjGDp+ClevVaGmBSMGQQb JZOP6eUos9LDCuaWQxxT/WjvhEaSK8qWz0XnCDEy88TeEbdPw4CwbFs3My07JS3oPl1z lirrjrEL2UXJ4Cpa+Xmtgbe/73iql9SPub5BA= MIME-Version: 1.0 Received: by 10.42.15.67 with SMTP id k3mr11860482ica.490.1288649670571; Mon, 01 Nov 2010 15:14:30 -0700 (PDT) Received: by 10.231.31.195 with HTTP; Mon, 1 Nov 2010 15:14:30 -0700 (PDT) In-Reply-To: References: Date: Mon, 1 Nov 2010 15:14:30 -0700 Message-ID: Subject: Re: [FlyRotary] Re: Vne is the question was Re: How fast is it safe to turn a Prop. Opinion Poll From: David Leonard To: Rotary motors in aircraft Content-Type: multipart/alternative; boundary=20cf304275aadabcfe0494052101 --20cf304275aadabcfe0494052101 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Hi Ed, Now that you bring it up, I have always taken exception to that article. A= t the start it basicly makes 2 assumptions without giving any sutable support= : 1) that Vans published Vne speed is due to flutter. 2) Flutter is based on TAS not IAS. The rest of the article basicly explains the difference between TAS and IAS and gives examples of aircraft that might be exceeding Vne unknowingly. Where is the reference to the data that shows flutter is purely a function of TAS? Where is Vans Flutter analysis data? At one point it says that flutter is not resonance, but a function of "energy input to the system" - but then wouldn't dynamic pressures (read IAS) be primarily responsible for adding energy to the system. He then goes on to use the Tacoma narrows bridge as an example of flutter, but that is the pent-ultimate example of resonance. It also just makes sense to me that dynamic pressures must play some role i= n flutter. Some examples: suppose you had an aircraft that was susceptible to flutter, you could make it less-so by beefing up critical areas (supposedly resisting the forces of flutter). Suppose you look at the extreme case, and aircraft going very fast in a very very thin atmosphere. If you make the atmosphere thin enough, you will not be able to generate enough force to destroy a plane (from flutter) no matter how fast the molecules are traveling. Now I am definitely no AE, and I am not saying that TAS does not play a rol= e in flutter, if not possibly the predominate role in normal atmospheric conditions. I am just saying that Ken's article is far from the final word on the subject and has never really convinced me of anything. It does however have one excellent piece of advise: that if you want to go raging around at those higher airspeeds you are better off buying an aircraft built for the purpose. For me, it is not about raging around at those airspeeds on every trip, but about positing some big numbers to fulfill some underlying need to legitimatize my choice of a rotary engine. Like Tracy did in the SUN 100. And to do that, I have to outrun, in a public forum, the guys who are using lycs and paid 3x the price. And to do that, I have to fly nearly 250mph. (and then fly home at 150kts). But I don't want to wreck my engine, plane, prop, or myself in the process. --=20 David Leonard Turbo Rotary RV-6 N4VY http://N4VY.RotaryRoster.net http://RotaryRoster.net On Mon, Nov 1, 2010 at 2:15 PM, Ed Anderson wrot= e: > Hi Dave, > > From what you said, I'm not certain whether we should take issue with the > article or Van's limit for Vne. We all know that Van is pretty damn > conservative on his limits. So I for one am not surprised that his Rv's = can > push past his published Vne without ill effect. But, I'm just not certai= n > that invalidates the substance of the article - but, then I'm not a > aerodynamic engineer either. > > Just wanted to bring it to the list's attention, because I was surprised = at > what I read and really had not the knowledge to accurately assess it - it > appeared to make sense. > > Ed > > *From:* David Leonard > *Sent:* Monday, November 01, 2010 4:51 PM > *To:* Rotary motors in aircraft > *Subject:* [FlyRotary] Re: Vne is the question was Re: How fast is it > safe to turn a Prop. Opinion Poll > > Well yes, that is the the jist of the article, but one article does not = a > 100% fact make. Here is a link for those interested: > http://www.vansaircraft.com/pdf/hp_limts.pdf > > The limiting factor for Vne can be any of number of factors which may o= r > may not be fluttler, dynamic pressures, tran-mach waves etc. Vans Vne > number represents the upper limit of factory testing and imply an > untested zone above that number. There is little reason to suspect that > some flutter boundry lies 'not too far' beyond Vne. True, there are a > couple of isolated reports of something that may have been flutter (but > likely not true destructive flutter). OTOH, there are a lot more reports= of > RV's being tested well beyond Vne without incident. This includes Dave > Anders RV-6 and many of the other cross country race planes, a number of > super-6 and super-8 RVs, and my own RV-6 that I tested to 205 KIAS (about > 235KTAS - but I did not do elevator and aileron slaps at that speed). (f= or > those of you without RV's, Vans suggests 210mph (187kts) as Vne. In ligh= t > civil aviation, Vne is usually expressed in terms of indicated air speed) > > Not that I want to encourage anyone to exceed Van's Vne limit, go there a= t > your own extreem peril. > > So, Vne issues asside, what say you about the prop speed issue? > -- > David Leonard > > Turbo Rotary RV-6 N4VY > http://N4VY.RotaryRoster.net > http://RotaryRoster.net > > On Mon, Nov 1, 2010 at 12:24 PM, Bryan Winberry < > bryanwinberry@bellsouth.net> wrote: > >> Ed, >> >> That=92s the way I recall the article. >> >> Bryan >> >> >> ------------------------------ >> >> *From:* Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] *= On >> Behalf Of *Ed Anderson >> *Sent:* Monday, November 01, 2010 3:19 PM >> >> *To:* Rotary motors in aircraft >> *Subject:* [FlyRotary] Vne is the question was Re: How fast is it safe t= o >> turn a Prop. Opinion Poll >> >> >> >> Interesting article back a couple years ago in Van's RVator about Vne. >> If I understood it properly, unlike every other airspeed of interest whi= ch >> is based on Indicated air speed or Q factor or dynamic pressure, Vne is = not >> based on IAS but TAS. >> >> >> >> According to the article (as best I recall) when flying high (where IAS >> is low) and fast - it is True Air Speed that is the limit factor on flut= ter >> and other dastardly happenings. Apparently the excitation of the airfra= me >> components is due to the true air speed at which the molecules of air ar= e >> moving across said component and not the dynamic pressure which is a >> combination of air density and true airspeed. >> >> >> >> The message was you could find yourself in trouble particularly at high >> altitude with low IAS (and thinking you are safe because its below state= d >> Vne) and high TAS. >> >> >> >> So unlike just about all other airspeed limitations which are based on I= AS >> (dynamic pressure, Q factor, etc) , apparently the Vne is True air speed >> based - always assuming I understood the article. >> >> >> >> Ed >> >> >> >> >> >> *From:* Mark Steitle >> >> *Sent:* Monday, November 01, 2010 3:07 PM >> >> *To:* Rotary motors in aircraft >> >> *Subject:* [FlyRotary] Re: How fast is it safe to turn a Prop. Opinion >> Poll >> >> >> >> Dave, >> >> >> >> What is Vne for the 6A? Van's site only shows "Top Speed" as 208 mph wi= th >> the 180hp engine. Is this considered Vne? >> >> >> >> Mark >> >> On Mon, Nov 1, 2010 at 1:49 PM, David Leonard >> wrote: >> >> So I am getting a little more bold with my new turbo. On the way home >> today I decided to open it up a little bit. At 8500' and MAP around 34"= , I >> was at 6700 RPM and 201 KTAS (about 3060 RPM at the prop with the tips d= oing >> 860fps). Temps still less than 160, plenty of throttle left. I just >> couldn't accept turning the prop any faster, not knowing what the limit >> really is. >> >> My prop is a 64" diameter (pretty short) Catto (wood/composite) with a >> number of nicks in the leading edge and has not been dynamical balanced = to >> date. >> >> >> >> I talked to Craig Catto about the issue and what he told me completely >> makes sense, but is utterly unhelpful in setting my racing redline. He = said >> that I could turn it as fast as I want, but the risk of separating the p= rop. >> increases as I go faster. I just depends on too many factors. >> >> >> >> I realize the the final number is going to depend on my risk tolerance a= nd >> how much I really want to post some big numbers in a race. But it is ha= rd >> for me to balance that without better understand or the factors on the p= rop, >> hence, the opinion poll, on various factors.. >> >> >> >> I have heard that it is important to keep the prop tips under 900 fps, >> while others say it is not a factor. Is there some important number for= the >> max tip speed? Is it a safety issue or an efficiency issue? >> >> >> >> Most of my nicks in the paint and composite layer are in the outer 1/3 o= f >> the prop. Are these a big deal for safety? Efficiency? >> >> >> >> If I were to run the engine at 7000 RPM that would give me 3225 at the >> prop, tips doing 900 FPS an an aircraft speed of around 209 kts (240mph)= . >> This seems pretty reasonable to me as an upper limit, but it is scary a >> little. >> >> >> >> But what about 8000RPM at the engine (if I have the power to get there)? >> With a cleaned up and balanced prop, that would be almost 3700 RPM at th= e >> prop, tips doing 1020fps, aircraft going something less than 240kts (275 >> mph). Stupid though? Or give it a try and see how close to those number= s I >> can get? >> >> >> >> Any issues with the gear-box going that fast, other factors I am not >> considering? >> >> >> >> Anyway, it feels really cool to have broken 200kts in level flight. >> >> -- >> David Leonard >> >> Turbo Rotary RV-6 N4VY >> http://N4VY.RotaryRoster.net >> http://RotaryRoster.net >> >> >> > > > > --20cf304275aadabcfe0494052101 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable
Hi Ed,
Now that you bring it up, I have always taken exception to that articl= e.=A0 At the start it basicly makes 2 assumptions without giving any sutabl= e support:
1) that Vans published Vne speed is due to flutter.
2) Flutter is based on TAS not IAS.
=A0
The rest of the article basicly explains the difference between TAS an= d IAS and gives examples of aircraft that might be exceeding Vne unknowingl= y.
=A0
Where is the reference to the data that shows flutter is purely a func= tion of TAS?=A0 Where is Vans Flutter analysis data?=A0 At one point it say= s that flutter is not resonance, but a function of "energy input to th= e system" - but then wouldn't dynamic pressures (read IAS) be prim= arily=A0responsible for adding energy to the system.=A0 He then goes on to = use the Tacoma narrows bridge as an example of flutter, but that is the pen= t-ultimate example of resonance.
=A0
It also just makes sense to me that dynamic pressures must play some r= ole in flutter.=A0 Some examples:=A0 suppose you had an aircraft that was s= usceptible to flutter, you could make it less-so by beefing up critical are= as (supposedly resisting the forces of flutter).=A0 Suppose you look at the= extreme case, and aircraft going very fast in a very very thin atmosphere.= =A0 If you make the atmosphere thin enough, you will not be able to generat= e enough force to destroy a plane (from flutter) no matter how fast the mol= ecules are traveling.
=A0
Now I am=A0definitely no AE, and I am not saying that TAS does not pla= y a role in flutter, if not possibly=A0the predominate role in normal atmos= pheric conditions.=A0 I am just saying that Ken's article is far from t= he final word on the subject and has never really convinced me of anything.=
=A0
It does however have one excellent piece of advise:=A0 that if you wan= t to go raging around at=A0those higher airspeeds you are better off buying= an aircraft built for the purpose.=A0 For me, it is not about raging aroun= d at those airspeeds on every trip, but about positing some big numbers to = fulfill some underlying need to legitimatize my choice of a rotary engine.= =A0 Like Tracy=A0did in the SUN 100.=A0 And to do that, I have to outrun, i= n a public forum, the guys who are using lycs and paid 3x the price.=A0 And= to do that, I have to fly nearly 250mph. (and then fly home at 150kts).
=A0
But I don't want to wreck my engine, plane, prop, or myself in the= process.
=A0
--
David Leonard

Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net

=A0
On Mon, Nov 1, 2010 at 2:15 PM, Ed Anderson <eanderson@ca= rolina.rr.com> wrote:
Hi Dave,
=A0
From what you said, I'm not certain whether w= e should take issue with the article or Van's limit for Vne.=A0 We all = know that Van is pretty damn conservative on his limits.=A0 So I for one am= not surprised that his Rv's can push past his published Vne without il= l effect.=A0 But, I'm just not certain that invalidates the substance o= f the article - but, then I'm not a aerodynamic engineer either.=
=A0
Just wanted to bring it to the list's attenti= on, because I was surprised=A0at what I=A0read and really had not the knowl= edge to accurately assess it - it appeared to make sense.
=A0
Ed

Sent: Monday, November 01, 2010 4:51 PM
Subject: [FlyRotary] Re: Vne is the question was Re: How fast i= s it safe to turn a Prop. Opinion Poll

Well yes, that is the the jist of the article, but one article does no= t a 100% fact make.=A0 Here is a link for those interested:
=A0
=A0The limiting factor for Vne can be any of number of factors which m= ay or may not be fluttler, dynamic pressures, tran-mach waves etc.=A0 Vans = Vne number represents the upper limit of factory=A0testing and imply an unt= ested=A0zone above that number.=A0 There is little reason to suspect that s= ome flutter boundry lies=A0'not too far'=A0beyond Vne.=A0 True, the= re are a couple of isolated reports of something that may have been flutter= (but likely not true destructive flutter).=A0 OTOH, there are=A0a lot more= reports of RV's being tested well=A0beyond Vne without incident.=A0 Th= is includes Dave Anders RV-6 and many of the other cross country race plane= s, a number of super-6 and super-8 RVs, and my own RV-6 that I tested to 20= 5 KIAS (about 235KTAS - but I did not do elevator and aileron slaps at that= speed).=A0 (for those of you without RV's, Vans suggests 210mph (187kt= s) as Vne.=A0 In light civil aviation, Vne is usually expressed in terms of= indicated air speed)
=A0
Not that I want to encourage anyone to exceed Van's Vne limit, go = there at your own extreem peril.
=A0
So, Vne issues asside, what say you about the prop speed issue?
--
David Leonard

Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRo= ster.net

On Mon, Nov 1, 2010 at 12:24 PM, Bryan Winberry <bryanwinberry@bellsouth.net> wrote:

Ed,

That=92s the wa= y I recall the article.

Bryan

= =A0

From:= Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Monday, November 01, = 2010 3:19 PM=20


To: Rotary motors = in aircraft
Subject: = [FlyRotary] Vne is the question was Re: How fast is it safe to turn a Prop.= Opinion Poll

=A0

Interesting article back a couple years ago= =A0in Van's RVator=A0about Vne.=A0 If I understood it properly, unlike= every other airspeed of interest which is based on Indicated air speed or = Q factor or dynamic pressure, Vne is not based on IAS but TAS.

=A0

According to the article (as best I recall)= =A0when flying high (where IAS is low) and fast - it is True Air Speed tha= t is the limit factor on flutter and other dastardly happenings.=A0 Apparen= tly the excitation of the airframe components is due to the true air speed = at which the molecules of air are moving across said component and not the = dynamic pressure which is a combination of air density and true airspeed.

=A0

The message was you could find yourself in = trouble particularly at high altitude with low IAS (and thinking you are sa= fe because its below stated Vne) and high TAS.

=A0

So unlike just about all other airspeed lim= itations which=A0are based on IAS (dynamic pressure, Q factor, etc) , appar= ently the Vne is True air speed based - always assuming I understood the ar= ticle.

=A0

Ed

=A0

=A0

From: Mark Steitle=

Sent: Monday, November 01, 2010 = 3:07 PM

Subject: [FlyRotary] Re: How fas= t is it safe to turn a Prop. Opinion Poll

=A0

Dave,

=A0

What is Vne for the 6A?=A0 Van's site only shows = "Top Speed" as 208 mph with the 180hp engine.=A0 Is this consider= ed Vne?

=A0

Mark

<= /div>

On Mon, Nov 1, 2010 at 1:49 PM, David Leonard <wdleonard@gmail.com> wrote:

So I am getting a little more bold with my new=A0turb= o.=A0 On the way home today I decided to open it up a little bit.=A0 At 850= 0' and MAP around 34", I was at 6700 RPM and 201 KTAS (about 3060 = RPM at the prop with the tips doing 860fps).=A0 Temps still less than 160, = plenty of throttle left.=A0 I just couldn't accept turning the prop any= faster, not knowing what the limit really is.

My prop is a 64" diameter (pretty short) Catto (wood/composite) wi= th a number of nicks in the leading edge and has not been dynamical balance= d to date.

=A0

I talked to Craig Catto about the issue and=A0what he= told me completely makes sense, but is utterly unhelpful in setting my rac= ing redline.=A0 He said that I could turn it as fast as I want, but the ris= k of separating the prop. increases as I go faster.=A0 I just depends on to= o many factors.

=A0

I realize the the final number is going to depend on = my risk tolerance and how much I really want to post some big numbers in a = race.=A0 But it is hard for me to balance that without better understand or= the factors on the prop, hence, the opinion poll, on various factors..

=A0

I have heard that it is important to keep the prop ti= ps under 900 fps, while others say it is not a factor.=A0 Is there some imp= ortant number for the max tip speed?=A0 Is it a safety issue or an efficien= cy issue?

=A0

Most of my nicks in the paint and composite layer are= in the outer 1/3 of the prop.=A0 Are these a big deal for safety?=A0 Effic= iency?

=A0

If I were to run the engine at 7000 RPM that would gi= ve me 3225 at the prop, tips doing 900 FPS an an aircraft speed of around 2= 09 kts (240mph).=A0 This seems pretty reasonable to me as an upper limit, b= ut it is scary a little.

=A0

But what about 8000RPM at the engine (if I have the p= ower to get there)?=A0 With a cleaned up and balanced prop, that would be a= lmost 3700 RPM at the prop, tips doing 1020fps, aircraft going=A0something = less than 240kts=A0(275 mph).=A0 Stupid though? Or give it a try and see ho= w close to those numbers I can get?

=A0

Any issues with the gear-box going that fast, other f= actors I am not considering?

=A0

=A0






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