"Lippsing" a Q-tip propeller

Thought I'd ask for comments before doing something stupid and irreparable
to our propeller.

We have a Hartzell Q-tip prop on our Glasair. That's the fancy bent over tip
that gets all the jokes about the FAA Inspector who grounded a Cheyenne when
the propellor first came out. (Looks like the prop had a ground strike.)
When we got it, the Q-tip was a hot thing, and we were coming off a Prince
P-tip, which also had a turned under "winglet."

Then Paul Lipps came along and wrote that putting a big hunk of metal out
there on the prop tip is about the stupidest thing one could do, since the
prop tip is where velocity - and therefore, drag - is highest. He wrote
about cutting the tips off a Prince wood prop and getting a phenomenal
improvement in propeller efficiency.

I'm not going to cut off the Q-tip entirely. But I thought I would try a
compromise solution, and cut part of it off. I should link a photo to show
you my markups on the tip, but the plan is to cut the front of the winglet
to put a 60 degree shear on the front, like you see on the Katana wingtips
and on Paul Lipps' Lancair. I will be careful, will sand out the stress
risers, etc. I have a good gram scale to weigh the cutoffs to match, and a
dynamic prop balancer to rebalance after the operation.

It's a homebuilt, so I'm deep into "experimental" mode on this one. Anyone
want to warn me about how I might kill myself doing this? Has anyone done
this before?

Thanks,

Mike Palmer

To clarify, I'm not shortening the blade. Here's the plan in pictures.

This photo shows the Q-tip as it is now.

http://img13.imageshack.us/img13/6228/qtipbefore.jpg

This photo shows what I'd like to do.

http://img17.imageshack.us/img17/9960/qtipafter.jpg

Naturally, I'd radius the tip better... this was just a quick "photo-shop"

Again, the idea is to "shear" the blade tip much like a sheared wing tip.

Anyone seeing anything horribly wrong with trying this?

Thanks,

Mike Palmer

"MP" wrote in message
...
To clarify, I'm not shortening the blade. Here's the plan in pictures.

This photo shows the Q-tip as it is now.

http://img13.imageshack.us/img13/6228/qtipbefore.jpg

This photo shows what I'd like to do.

http://img17.imageshack.us/img17/9960/qtipafter.jpg

Naturally, I'd radius the tip better... this was just a quick
"photo-shop"

Again, the idea is to "shear" the blade tip much like a sheared wing tip.

Anyone seeing anything horribly wrong with trying this?


Removing weight from the tip will change the blades natural resonant
frequencies.

The less metal you remove, the less you are going to change them, but do
you know how much room you have between the engine firing order frequencies
and the current resonant frequencies of the prop?

I see a fair amount of risk for not much (if any) gain.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

"Capt. Geoffrey Thorpe" The Sea Hawk @See My Sig.com wrote in message
...
"MP" wrote in message
...
To clarify, I'm not shortening the blade. Here's the plan in pictures.

This photo shows the Q-tip as it is now.

http://img13.imageshack.us/img13/6228/qtipbefore.jpg

This photo shows what I'd like to do.

http://img17.imageshack.us/img17/9960/qtipafter.jpg

Naturally, I'd radius the tip better... this was just a quick
"photo-shop"

Again, the idea is to "shear" the blade tip much like a sheared wing
tip.

Anyone seeing anything horribly wrong with trying this?


Removing weight from the tip will change the blades natural resonant
frequencies.

The less metal you remove, the less you are going to change them, but do
you know how much room you have between the engine firing order
frequencies and the current resonant frequencies of the prop?

I see a fair amount of risk for not much (if any) gain.


Oh - forgot to mention - if you do decide to hack at the prop, it would be
a good idea to install a "chicken strap" between the engine and airframe
just in case things do go wrong and you break the motor mount. Eh?

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

On Apr 17, 2:59 pm, "Capt. Geoffrey Thorpe" The Sea Hawk @See My
Sig.com wrote:

Removing weight from the tip will change the blades natural resonant
frequencies.

The less metal you remove, the less you are going to change them, but do
you know how much room you have between the engine firing order frequencies
and the current resonant frequencies of the prop?

I see a fair amount of risk for not much (if any) gain.

Every certified prop has a Type Certificate Data Sheet, and that sheet
will specify maximum and minimum diameters for particular engines. The
info is there so it's not necessary to go kill oneself learning it all
over again. Here's the TCDS, for example, for the McCauley 1C160 prop
used on many 172s:
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library%5CrgMakeModel.nsf/0/A2153BC309BE73C0862571A800643E15/$FILE/P-910.pdf

For instance, it says that for a Lyc O-320, 150 hp @ 2700 RPM, the max
is 75" and the min is 74".

So you would go he http://www.airweb.faa.gov/Regulatory...e?OpenFrameSet

and look up your Hartzell model and see for yourself.

Dan