From: dfr@usna.navy.mil (PROF D. Rogers (EAS FAC))
Newsgroups: rec.aviation.piloting
Subject: Re: Frost accumulation
Date: 18 Dec 92 23:20:41 GMT
Organization: U. S. Naval Academy

In article <BzGpt2.9Mv@tss.com> burke@tss.com (Jim Burke) writes:
!In article <2549@usna.NAVY.MIL!, dfr@usna.navy.mil (PROF D. Rogers (EAS FAC)) writes:
!
!|! You are going to get so much mail and flames on this one that you
!|! had better get out the fire hose and asbestos suit.
!
!Actually, I have not received a single flame.  I have received approximately
!five responses by e-mail.  Two of them were from people who indicated that
!they have done pretty much the same thing after taking precautions, and
!three who made thoughtful comments on why they wouldn't feel comfortable
!taking off with any frost at all on the wings.  Actually, unlike past
!experiences I've had on the net, I was quite pleased to find that there
!don't seem to be as many hot-heads flaring off at the mouth on this one.
!Perhaps my request that people make thoughtful comments that I and others
!might benefit from was actually taken to heart.  I appreciate it, from those
!who have mailed to me.  This has certainly been a lot more helpful to me
!than flamage.

It's great that the heat has been moderated.

!|! Briefly, taking-off with ANY frost, snow, ice on the aircraft
!|! ANYWHERE is foolish. Basically the frost, snow, ice destroys the
!|! aerodynmaic efficiency (characteristics) of the wing and adds weight
!|! etc. So far you have gotten away with this but if you continue
!|! you WILL have problems that could lead to loss of control and
!|! a crash.

!Well, that's a fairly strong statement, and I don't necessarily disagree
!with the fundamental wisdom in what you are saying (despite the rather
!strongly worded way of stating it).  The reason I asked the question was
!because when I have done this (alone, way below max gross, thin layer of
!smooth frost) I have not experienced _any_ noticable difference in the
!way the airplane flew.  Granted, I did not test for changes in stall speed.
!In fact, I carried a little extra speed before rotating and climbing to
!compensate for such a change.  I certainly was not recommending that anyone
!take off with frost on their wings.  It is not a practice anyone should
!make a habit of.  Mainly, I was trying to find out just unsafe it truly
!is, given the precautions and so forth.
!
!|! 
!|! Recommendation: Don't do it again. Get ALL the frost, snow, ice
!|!                 off the aircraft before flying. Be picky.
!|! Dave Rogers
!|! Professor of Aerospace Engineering

The recommendation was strongly worded because as an aerodynamist
you scared the h... out of me doing this.

Let's take a sort of worst case situation:

Suppose you `polish' the thin coat of ice nice and smooth, hold
extra airspeed etc. All the things you have done before and
gotten away with.

Now while accelerating down the runway for take-off the
vibration, increased airflow, etc causes part of the
ice coating on the leading edge of ONE wing to break away.
You now have extreme roughness right at the leading edge.
Upon rotation for lift-off there is a very good possibility
that the airfoil and hence a good part of the wing will
stall. The result will be a roll towards that wing, your aileron
input to lift the wing will make the problem worst, your will also
have a yaw towards than wing due to the additional drag etc.

The result is very possibly an uncontrolled crash. It might
ruin your whole day.

Again I recommend deicing the entire aircraft before flight.

Dave Rogers

BTW, if you deice in a heated hangar make sure the control
linkages are free of water since it might freeze upon
reaching altitude. One way to help this is to use and air
hose on the hinges and still wait a bit for that last of
the water to evaporate.
Newsgroups: rec.aviation.piloting