Below is a typical letter I get concerning the Windrose. I have taken the time to answer as best I can .

Without knowing the author I would suspect that he is an amateur builder with few planes to his credit and very little time actually flying gliders and even less time working in composites. I doubt if his windrose will ever get built with this current attitude.

An well educated person in aircraft building who felt that the windrose was his plane of choice to build would take everything written about it and upgrade the plans using accepted practices, go and visit a flying example , fly it and do a lot of testing. He should also compare the aerodynamics of his favorite glider to that of the windrose as well as recalculate the structural values used and compare them to JAR 22..

Date sent: Tue, 7 Aug 2001 17:49:11 -0500
To: mat@continuo.com
From: "Doug B. Hoffman" <dhoffman@oakland-info.com>
Subject: You Asked for Comments

Mat,

<I hesitatingly write this because I wonder if it will do any good. Some
issues we have discussed before, but to no avail apparently. Sigh. Here
goes again, one more time:>

I have less and less time to deal with the Windrose, it is about 5 planes ago now and I am building ,test flying and aiding in design constantly, but I do appreciate you writing. I do feel I will never ever change my opinion of the windrose, especially more so as I learn more in the field of aerodynamics and composites.

I believe you are building a Windrose and you are not going to change your mind either. Best to build the glider and see for yourself if it flies as you think it should.

<In discussing the Windrose I believe we need to separate the tangible from
the intangible.

The tangible is anything that can be directly measured or quantified.
These are easier to deal with. For example, either a wing spar has failed
or it hasn't. Simple, straightforward, no subjective judgement.>

I agree!

I think it better to take a standard such as JAR 22. You need to design it to a standard and then prove it. The spar building on the windrose is simply an inferior construction especially in the light of carbon rods. The hand layup carbon tow is at about 40,000 psi in tension and probably only about 25,000 in compression. We know we did the testing! The carbon rods will do 225,000psi and we have thoroughly tested it with documentation, film etc. Have you done your homework on the calculations... if not I can supply you with the formulas. See the site Jim Marske has authored on the use of carbon rods and how to attach those to the bolts etc. Again, a accepted proven method!

<The intangibles are the difficult issues. In this case we are talking
about the handling characteristics of the Windrose in flight. There is not
a meter that we can attach that will measure the tendency, or lack thereof,
for stalling or spinning or whatever under the wide range of conditions
possible. This is a subjective assessment and the problem we have is that
your subjective assessments are quite different from subjective assessments
made by others. We need to understand why this is.>

The difference probably is that I put my Windrose under more realistic thermal conditions than other pilots, and even Dan armstrong concurredc that the windrose ( in the 13 meter version) was more likely to stall a wing tip in the SHA article.... have you forgotten his opinion too.

In order to assess the flight characteristics you must have something to compare it to and in my case it did not measure up even close to a ask 21, grob 102, grob 103, schwiezer 1-34... etc. A professional test pilot with a proper test program can easily tell you what is not correct and suggest changes. Dave Wells said he was worried about the turning characteristics. He felt that in a turn , a stall progressed down the wing and that this should be investigated. I started that study by adding turbulators on the tips.

<Mat, a big problem that *you* have, in my opinion, is that you have almost
completely destroyed your credibility by making outlandish and
unsupportable statements concerning *tangible* issues with the Windrose.
Therefore people do not believe what you are saying about the intangibles,
be they true or not.>

I may have lost credibility with you, but you have never come here, visited or flown some of the aircraft I have built. I am so busy with building and flying I haven't noticed the lack of interest in what I do. What other people think of me is not important, I will always tell the truth despite being unpopular. Again I will gladly discuss any item you bring up. But you must also do your homework, show me your figures and references then do a test sample. What are your examples of the outlandish remarks?

<Also, it could be argued that you have a conflict of interest in reporting
anything about the Windrose given that it is a competitor for the products
in which you are invested (the Marske line of homebuilt sailplanes). So
you need to be extra careful when criticizing the competition if you want
anyone to seriously consider what you have to say. Yes, I know the
Windrose is a motorglider and is offered as plans-only whereas the Marske
products are not motorgliders and are also offered as kits. But, the WR
can be built as a pure glider and you are still competing for the same
sailplane homebuilders' dollars.>

Even if there is direct competition, if I know there is a definite problem with any aircraft I am going to speak up loudly. But there is no comparison between us and the Maupins..... we offer you the chance to fly the glider before you build. We have thoroughly knowledgeable people here who know their aerodynamics and construction practices and you can see gliders being built and tested. Our gliders are thoroughly tested and we have builders manuals and people who will help with every question. Recently I have decided to go more into building finished gliders.... so the gap will even widen.

Let me detail what I see as the major problems with your reporting on the
*tangible* issues with the Windrose. They are listed as follows as items
roman numeral I. through V.

<I. "Remember, it has killed nearly everyone who has built one."
Wow! That is a blockbuster statement! You had better be able to back that
one up! Did you really mean to say "were killed while flying a WR"? Did
you really mean to say "two people have been killed while flying a WR"?
Let's say that we define "nearly everyone" as at least 75%. A conservative
definition. I am aware of the following people having built a WR:>

That was a error on my part which I corrected immediately and more an emotional response to make one aware that the ratio of pilots that have flown the windrose to those killed flying is just too high! I have since changed that on my web site to reflect a more accurate account, but still stressing the amount of deaths is still highly unproportional to the flight time and number of pilots for a safe airplane.

1. Maupin/Culver - source Bob Said, Soaring Dec. 1984 p24
2. John Walkling - source John Walkling
3. B.A.Logan - died, NHTSA report conclusion, INADVERTENT STALL AND THE
PILOT'S IMPROPER EMERGENCY RECOVERY PROCEDURES. A FACTOR WAS THE POWER LOSS
FOR UNDETERMINED REASONS.
4. HICKEY - died, NHTSA report conclusion, THE PILOT-IN-COMMAND'S FAILURE TO
MAINTAIN AIRSPEED RESULTING IN AN INADVERTENT STALL
5. Bob Otis - source Kitplanes, Sept. 1998 p77
6. Mush Hide - source, Internet, Mush Hide
7. Mat Redsell - source, Internet, Mat Redsell; glider destroyed, NHTSA
report conclusion, The pilot's failure to maintain control of the glider.
8. Hans Lohr - source - Redsell website
9. Paul (last name?) - source - Redsell website

I doubt that the above list is complete. But it is all I am aware of. We
need to have at least 7 of the 9 killed to even come close to your
statement. But we only have 2. The reasons for those 2 fatalities were
determined to be pilot error. Mat, where are the other 5 or more deaths
and what were the causes for those deaths? If this list is in error please
tell me where it needs correction. I suspect that the ratio of those
killed while flying a WR to those not is much smaller than 2/9.

Two out of nine is too many people killed, especially when you consider I nearly was number 3.... and the people listed above have very little time in flying the windrose. Note that I should have been the 3rd pilot killed... more like 3 in 9........This is major!

<Mat, stating that "it has killed nearly everyone who has built one" is not
a small error in wording. This is a big time serious allegation. You need
to be much more careful when making a statement like that and you need to
have the proof to back it up when you do. Besides, the two persons killed
while flying a WR were not killed *by* the WR as you state. They were
killed by their own pilot error as determined by NHTSA. I submit that the
WR has killed *no one*.>

The NTSB did not do a thorough investigation of the windrose..... so they presume that it was pilot error. No one interviewed me nor anyone else, or did they research the windrose. Just a beaurocratic way of closing the file without getting too deep.

<II. "The ailerons are held on with pop rivets to the fiberglass wings.
Certainly not a very positive bond to the wing."

Mat, please list for me the incidences of failures of this attachment on
the WR.
Again Mat, implying that the flaperons are likely to come off in flight is
a big time serious allegation. Do you have proof?>

Again go to your JAR 22 (JAR 22.395 - Control System Loads) and see what is necessary there for the ailerons/flaperson. Pop rivets in fiberglass are not acceptable! Again get out your math and do the calculations for the stresses. Then put a pop rivet in fiberglass and pull on it... then give it a number of cycles then test again. It will not pass!

<III. "The main bolts should not go through the carbon (roving) due to
galvanic action..."
Mat, you and I have already discussed this. I still have my AN bolt with
some carbon roving wrapped tightly around it. It's been that way for many
months now. Still no signs of corrosion. Could you direct me to a
reference that addresses this issue? Can you list for me the incidences of
corrosion that have been found on a Windrose or Carbon Dragon main bolt?

Again Mat, stating that major structural assemblies like the main spar and
attachment hardware are subject to corrosion is a big time serious
allegation. Where is your proof?>

Galvanic Corrosion (Electrochemical). All metals have specific relative electrical potential. When metals of different electrical potenial such as steel and copper are in contact in the presence of moisture, a low energy electric current flows from the metal having the higher position in the galvanic series. This is called "galvanic action." Note that Graphite is at the bottom of the list (negative charged) and Steel is near the top just under aluminum. I think you had better do some homework!

Look at the article of Dan Armstrong in the SHA.... he also concurs. No-one will accept this practice. It is common engineering knowledge. The complete carbon Monarch I have just built has phenolic bushings between the carbon and the stainless steel or 4130.

<IV. "... and the carbon fibers should not be cut which renders them
useless, only those strands of carbon not cut by the bolts are able to
carry any load."
<Mat, you and I have already discussed this. This statement is simply
wrong. The engineering truth is that strands cut by the bolt holes are
still solidly bonded to adjacent strands that are *not* cut. The tensile
and compressive loads are transmitted through the bonds to the adjacent
rovings. With a bolt epoxied in the hole the compressive strength will be
almost unaffected. Most spar failures happen to the upper spar with it
failing in compression. Materials are generally weaker in compression than
tension.>

The windrose bolts actually go though the upper and lower caps.... the
ones on the upper cap are in compression, and the lower ones are in tension and there should be no holes in either area. It should instead be epoxied to fiberglass blocks using multi layers of cloth ( properly calculated) with the correct strength requirements. Then the bolts go through the fieberlass. See the article on our site by Jim Marske who has extensively researched and tested this accepted construction method.

<Consider a 3 inch wide roving layup. Then consider a 4 inch wide roving
layup. Now drill a 1" hole in the middle of the 4 inch layup and epoxy a
1" bolt in the hole. You are saying that the 3" layup and 4" layup would
have the same tensile and compressive strengths, all other things being
equal. That is wrong and a simple test would prove it. The 4" layup will
have significantly greater compressive and tensile strengths.>

This is very simple to prove. We have extensive data and testing done on spar building. The first point is never use carbon rovings in a hand layup, you cannot certify the strength. Jim had a professional group do a sample layup and it tested about 40, 000 psi in tension and much less in compression..... Carbon rods are a certifiable item... yes 225,000 psi in tension and very close to that in compression.

Again show me your math. And what are you going to use for the values of a hand layup carbon roving. Irv Culver used 65,000 psi I believe... but that's not what we found with test samples laid up by professionals!

In the calculations for a carbon spar cap you do not count the area where the bolts go through.

<Mat, the carbon rovings or fiberglass rovings when laid up with epoxy can
be thought of as a structure similar to wood. Think of wood as strands of
"cellulose rovings" that are bound together with an adhesive. As I believe
even you will agree, it is ok to drill holes in wood, if done properly. I
presume the Pioneer II and the non-carbon Monarch have wood spars in which
bolt holes are drilled? Are you saying that the wood inboard of the bolt
holes is doing no good whatsoever? Are you saying that one should not
drill bolt holes in the wood spars for the Pioneer and (non-carbon) Monarch?>

The wood is very different, as you require a much greater mass due to the Modulus of Rupture to achieve the strength needed. The wood structure has to be designed to handle those bolts correctly and the calculations for the pioneer in wood we regularly do in our workshops... but we have accepted, realistic and tested values to work with. Even in wood we are becoming aware that you cannot have iron , wood and fiberglass together. They delaminate and the bolts rust over time. So even now the Wood spar is not an accepted practice with us anymore. Designs should evolve and imporve as more research is done. The windrose has not evolved.

<Mat, I have *never* suggested drilling holes in the Graphlite carbon rods.
That is a completely different situation and of course any sane builder
will know we should not drill holes in the rods. But I get the impression
that you are confusing the two issues. When I say you *can* safely drill
holes in carbon roving layup it seems you always respond with "Jim Marske
says one should never drill holes in carbon rods". Am I talking to the
wall?>

No, I'm talking about drilling holes in any spar cap..... wood whatever! There are much superior ways of designing spars and Jim has taken the time to design and test all of these. For your method do some test samples and see the results. Of the formulas I know of none will accept the bolts through the spar cap. Again show your math for the windrose spar using realistic values for the hand laid up roving by amateurs.

<V. Related to IV. Mat, you are directly implying that anyone with a
Windrose built to plans has a spar system that will fail under normal
flight loads. Mat, please list for me the WR spars that have failed. Can
you? Do you realize that you are directly implying that Maupin and Culver
either did not do a proof load or they did it incorrectly? Mat, this is a
very serious allegation. Again I ask, where is your proof that the WR spar
design is inadequate? Which Windrose spars have failed and what were the
modes of failure?>

With the modulus of rupture in great question, the strength of the hand laid up carbon rovings in question and not knowing any formulas that take into consideration of putting holes in the carbon tow, I would not spend time building the wings the way they are designed on the windrose. Why use inferior methods when a vastly superior system has been proven? Instead I would redesign them with the knowledge of someone like Jim Marske who has a proven method with very predicable results.

If you are going to design an airplane you should have a well tested craft not only aerodynamically but structurally designed to some standard such as JAR 22. The design should be well thought out and have a thoroughly documented test flight. Note that with the aircraft I work with, there have been many upgrades and new processes and ideas developed over the 30 years of the design. The windrose has never gone through any upgrades.

<Mat, another problem I have with your criticisms of the WR is that you
nonchalantly mix relatively small issues that could be considered
nitpicking with extremely serious life-threatening allegations. I wonder
if you realize how all of your comments appear to the outside observer?
The good, correct, and constructive criticisms that you do make about the
WR (such as the need for the gas strut on the large delta spoiler) get
totally lost because of your outlandish and obviously unsupportable
statements of mortal danger due to likely spar failure and so forth that
floor the reader.

I don't know what else to tell you, Mat. I've discussed some of this
before with you and it apparently has done no good. I've long ago simply
tuned you out because of the outlandish statements you seem prone to make.
Perhaps you should consider having a non-involved (with either the WR or
Marske product) third party review your words before you post them to the
world.

Doug Hoffman>

Well those that are not current with modern building and design practices and safety may tune me out but right now. I have hundreds of people a day visiting the Marske site, I have a long line of building projects ahead of me, I am test flying constantly and have a lineup of people who come here to study with me in the shop....... Maybe you should come for a visit and fly the gliders. In fact I will offer you a free workshop coming up this Oct 4-6th where you can study some accepted methods of building and designing.

I have posted my finding on the windrose, you can post yours and we can disagree.... that is healthy. But those that value their life should research the windrose very carefully: those with excellent building skills and test pilot qualifications can construct the windrose and fly it and develop the craft but I would really suggest doing some basic redesign and aerodynamic study first..

Mat

Date sent: Thu, 9 Aug 2001 20:48:07 -0500
To: mat@continuo.com
From: "Doug B. Hoffman" <dhoffman@oakland-info.com>
Subject: C of G Answer

Mat,

If someone were to ask me what the center of gravity was on my own personal
glider, my answer would be a quick and simple "37% MAC". I know this
because it is a critical parameter which must never be exceeded. I
directly measured it with *me* in the cockpit with chute etcetera.

Your response to Mike Burns was a whole page of text that said next to
nothing. You never answered his question.

Your words:

>Dave Wells a professional test pilot also flew it on the first
>flights and felt the CG was correct.

Good to hear that he *thought* the CG was ok, but why would there be any
question? Didn't you *measure* it?

>Once I started flying the windrose and became more familiar with the
>flying characteristics I started to bring back the CG with good results.

Yes, bringing the CG aft, within limits, can improve performance. But how
far back did you go? Maupin told you the limit. Did you exceed it? A
little too far and your otherwise docile glider can turn into a tiger.
Hmmmm....

>I work as a test pilot myself and am very familiar with flying the
>ranges of CG and can certainly feel it in the flying.

Bullroar! You must NOT trust your life to "feeling" the center of gravity!
You must measure!

I suddenly have many questions and suspicions related to the root cause of
the fate of your WR.

-Doug Hoffman

Hi Mat,

I assume you are aware of Mush Hide's 15 meter Windrose. We seem to have
a significant difference in flying experience between his WR and yours.
The only significant deviation from plans that Mush made was in the
elevator trim tab and spring arrangement. He also made changes to the
propellor and eventually added a two-wheeled landing gear but those
changes are not flight characteristic related.

So. What are your thoughts about this? Mush reports no bad habits. No
tendency to steepen the bank while thermalling. Overall he reports
excellent handling and is quite pleased with the glider. Any ideas?

-Doug B. Hoffman" <dhoffman@oakland-info.com>

One difference with mine compared to the motorized version was also the weight which means that with the motor it has a higher stall speed which made higher reynolds numbers of the tips. But read Dan Armstrongs analysis in the SHA magazine... .. he also agreed that the tips do stall easily even on the 13 meter. It would be good to analyze the speed differences with varying weights and resulting reynolds numbers... and the airfoils used.

Much of my criticism has to do with the construction which is detailed on my site which no one has addressed. Have you reviewed that?

Note too that Janet Maupin has said that I made changes to the windrose but neglects to list them.... implying that there were major changes that affected the flying qualities....there were no aerodynamic changes: read my web site for more details.

The SHA neglected to publish the report of Jim Marske who was in complete agreement with my assessment.

Remember too that in calm weather and light thermals I was very pleased with the windrose but the moment you have strong thermals and you enter the era of the wing tip stalls you will get into trouble. That the glider will not recover from a steep dive with about 40 percent flaps is serious. I did stalls.... everything but the spin... which bit me more than once! Its an awful feeling not being able to recover.

I do know my flying well... I have hundreds of flights a year and act as test pilot for most of those flights. I build planes constantly with about one or two a year: I know my building practices, aerodynamics and flying well.

Do your homework on the building practices and aerodynamics.... the airfoil and the pitching moment, the all flying tail, the reynolds numbers and then see if they all agree with your concept of a safe glider.

This glider is a design that needs careful study, and yes it has potential but as it is it lacks careful study. Remember it has killed two people so far ( correction as per Pauls email)... so it is something to be careful about.

Another thing you can do if you are really serious is to build a 1/4 scale model of the windrose and fly it... put it in very difficult situations and see if it recovers. If you want to build it... redesign it with modern materials sand carefully analyze the airfoils.

If your object is just to criticize me it is easily done, but if you want the truth you must do some original research on your own. Do the aerodynamic study... do the materials and construction study... publish it and then you can make your decision.

-mat