Go Back  RCU Forums > RC Airplanes > Seaplanes
Reload this Page >

what happens if the floats are too short?

Notices
Seaplanes Aircraft that typically take off and land on water...radio control seaplane discussions are in here.

what happens if the floats are too short?

Old 06-14-2002, 08:25 AM
  #1  
FHHuber
Banned
Thread Starter
 
Join Date: Jan 2003
Location: gone,
Posts: 4,923
Likes: 0
Received 0 Likes on 0 Posts
Default what happens if the floats are too short?

Part of the reason for the floats needing to be long is to give good pitch stability. If the plane is too long (or tall) compared to float length, theres a good chance that you won't have adequate elevator control to overcome even small waves, and then the plane can dig in the nose of the floats and flip over.

With a light enough plane, with the CG kept close enough to the floats (or with smooth enough water) you can get away with short floats. It just makes stability issues more difficult.
Old 06-14-2002, 03:00 PM
  #2  
JimCasey
Senior Member
My Feedback: (1)
 
JimCasey's Avatar
 
Join Date: Mar 2002
Location: Lutz, FL
Posts: 1,957
Likes: 0
Received 1 Like on 1 Post
Default what happens if the floats are too short?

ARE the floats too short?

Rule of thumb is for the floats to be 75-80% of the length from the prop washer to the rudder hinge line.

Also, and probably as important, about 5% of the float should be in front of the prop.

Lastly, the step of the float should be about under the balance point of the airplane.

Generally, this all works out so that the step is at 53% of the length of the float, according to Chuck Cunningham.

NOBODY's float installation is perfect.

If you have the nose of the float too short, it's more possible for the plane to nose over. This makes for an awkward and embarassing takeoff run. (WAAAA..bloop) Or, it exposes the prop to the bank (seawall) if you successfully land and taxi in. That would challenge your propellor budget.
Old 06-14-2002, 09:15 PM
  #3  
FHHuber
Banned
Thread Starter
 
Join Date: Jan 2003
Location: gone,
Posts: 4,923
Likes: 0
Received 0 Likes on 0 Posts
Default what happens if the floats are too short?

Just 5% ahead of the prop? I've seen up to 15% of the float ahead of the prop. Depends on CG and distance from CG to prop arc as a percentage of float length.

Now, since we're get into mounting considerations:

Bathtub test the floats to determine where the CG of the plane should fall in relation to the float length:
(Purchased floats should list where the aircraft's CG should be... you can go aft a bit... not forward.)
Wire the floats in position relative to each other, (as they will be when mounted) and set a weight on the floats (centered between... use a X of music wire to support the weight), roughly equal to the aircraft weight. Move the weight forward and aft to where it doesn't change the angle the floats ride in the water. CG of the plane goes from that point to very slightly aft of that point. (Full fuel tank CG shouldn't be forward of there.)

Its crude... but it works. If the plane's CG is too far forward (relative to the floats...) Yep, the plane's going to dig in every time, and you can't stop it. Too far aft, and you'll have problems getting "on plane," and thus take-offs will be difficult, but landings would be a bit easier, as it would be harder to accidentally nose-over. (up to a point... where things are just bad all around...)
Old 11-09-2002, 04:11 PM
  #4  
alasdair
 
alasdair's Avatar
 
Join Date: Nov 2002
Location: Scotland, UNITED KINGDOM
Posts: 746
Received 14 Likes on 11 Posts
Default what happens if the floats are too short?

If the floats are too short you will get away with it on smooth water and not notice a problem. When the water is choppy however you get problems with the prop clipping the waves, slowing the engine and kicking up spray.

You want a bit of float, minimum 10% to 12% or even up to 15% of the length, ahead of the prop so that they help to lift the prop clear of the waves. Jim Casey's rule of thumb probably works with most models, but mine works on any conventional model (i.e. engine at front, tail at back).
Make the float length at least two and a half times the Prop to CG distance.
Place the centre of the float at the aircraft CG.
Place the step on the float about 2 to 3% of float length aft of the CG.
Make the step depth at least 1% of float length.

Another tip is to make sure the floats are held parallel by tie bars front and rear.
Happy splashing
Alasdair
Old 12-03-2002, 09:28 AM
  #5  
Mariner
Junior Member
 
Join Date: Dec 2001
Location: MO
Posts: 22
Likes: 0
Received 0 Likes on 0 Posts
Default what happens if the floats are too short?

My first attempt to fly off of water was not very successful I have a Sig Kadet LT40 that just would not take off the palne has a Super Tigre 51 with 11x6 prop the floats are 36" with the step located 3/4 in in front of the CG on the first attempt the plane just plowed water the second attempt the plane flipped onto it's nose are there any suggestions thanks
Old 12-03-2002, 01:47 PM
  #6  
alasdair
 
alasdair's Avatar
 
Join Date: Nov 2002
Location: Scotland, UNITED KINGDOM
Posts: 746
Received 14 Likes on 11 Posts
Default what happens if the floats are too short?

mariner,
Your ST 51 with an 11x6 should be loads of power and the floats sound long enough.
You said in your post that you have
"the step located 3/4 in front of the CG "
The step should be be behind the CG, about 3/4" is fine. About 4" of the floats should be ahead of the prop.
If the floats are are sensible shape and are rigged with their top flat surface (and planing bottom) parallel to the aircraft's datum line, which is usually parallel to the tailplane (H stab) then it should plane well and take off no trouble. The only other common problem is that the floats throw up so much spray into the prop that the engine gets drowned and either stops or is way down on power.
It is important to fit spray strips to the lower inside edges of the floats from the front back to the step such that they will deflect the water out and down - away from the prop.
I have made them from three layers of 1/16 x 1/4 balsa stuck on at the edge, overlapping slightly. Each layer overlaps the previous one a little, i.e. it sticks out. When the glue dries you carve them into pointed triangles and then glass them. I apply them on both sides of each float back to the step and they deflect the water out and down, keeping the spray away from the prop and helping to lift the float.
Don't hold on full up elevator during the take off run!
Keeping the tails of the floats down in the water causes drag, so when it starts to plane let the aircraft ride level to pick up speed, just skimming on the centre of the floats just ahead of the step. Then after speed has built up rotate to take off.
Alasdair

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.