SEN 1906

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Table of Contents SEN 1906

  1. Robert Lesko Process
  2. Looking for F1C
  3. W&O Results

Robert Leško Raketa Nera building process

Everyone had admired both the looks and performance of Robert Lesko’s “Raketa Nera” World and Euro Champs winning F1A. Over recent months Robert has been generous in sharing information and drawings about his airplanes. He just wrote up his personal process of how be builds the aramid core, carbon covered wings. This appeared on the F1A Flappers group on FaceBook.

In the words of Robert…

Material used: Textreme IMS 76g/m2 (Torayca® M 30 SC 18k fiber) for wing skins. Aramid honecomb 29kg/m is used as sandwich material. Epoxy resin LF386 (pot time is long enough for using in this application). For spars Tenax UM46 carbon roving. For leading edge and wing joiner I used Tenax IMS65 carbon roving. Moulds-negatives, upper profile and bottom profile side.

Carbon skins are made first (vacuum bag) use 40% resin compared to carbon weight (on 100g carbon 40g of epoxy). Do that carefully and make some pretest to get all carbon wet evenly not to exceed 40% resin. When carbon skins are cured take spar (carbon balsa carbon) and trailing edge (carbon cape strip 1.5 x 02 mm) and glued it on bottom carbon skins (still in mould) again with epoxy in vacuum bag.

When this is done next I put few roving’s of carbon on front for leading edge, and glue 5mm balsa end ribs. Next in process is Aramid honeycomb gluing to bottom skins. Best way I have found to do that to get reasonable weight is little complicated but it works fine for me. First I cut honeycombs to fit in. Take bottom mold and carefully sand a carbon skin (just a bit to get better surface for gluing honeycomb). Take some flat table and cower it with large sheet of nylon. Take resin on piece of cloth and make thin film of epoxy evenly on nylon. Take Honeycomb and weight it. Put honeycomb sheet on nylon and make small circle moves while pressing it to soak resin from nylon. Weight honeycomb sheet to get info how much epoxy did soak in. Repeat the process until you get desired amount of epoxy on honeycombs.

Maybe it would be the best to do some tests with honeycomb to get value of minimum resin needed to achieve adequate bond to carbon skins. When you get good sample just take amount of resin used and dive it with area to get formula for the wings. The amount of epoxy I used was 0.3g/dm2. When you get enough resin on honeycomb sheet press it to bottom mold on carbon skin, and put it in vacuum bag. When epoxy cures it is time to sand honeycombs top side to desired profile. Put profile templates on ends and sand it. Use large piece of wood board with sand paper grain 120 or similar.

When you sanded to profile templates take fine sand paper grain 1500 on your fingers and sand honeycombs to get out all Aramid hairs from previous sanding process. Be gentil not to over sand, use forceps if needed to remove larger parts that bend in to honeycomb holes. After that next is boring process of drilling over 20000 holes (0.3 mm diameter) on aramid honeycomb walls to achieve open air flow all across thru aramid honeycomb. Every comb has to connected with hole to breathe freely, if not you will end with bubbles and caves on your wing after first sunny flights or heat treatment. Air has to circulate freely inside of wings.

After drilling your wing is ready for closing process. Take out your wing from bottom mould and weigh it. Process is the same as it was for gluing honeycomb to bottom carbon sheet. Take some flat table and cower it with large sheet of nylon. Take resin on piece of cloth and make thin film of epoxy evenly on nylon. Put your wing top side (open honeycomb side) on nylon and make small circle moves while pressing it to soak resin from nylon. Weight honeycomb sheet to get info how much epoxy did soak in.

Repeat the process until you get desired amount of epoxy on honeycombs, for safety reason I used 0.5g/dm2 that is more than on bottom side but I do not want to ruin all the work I done with possibly unboned area at the final step. If there are some dry area take resin on brush and gently wet honeycombs. When you are sure that every part is covered with epoxy press your wings on top carbon skin in top profile mould. Try to be precise in first attempt and not to move unnecessary so epoxy will stay on skin-honeycomb contact not to be smeared on area where it is not needed (inside honeycomb holes). Put some tape to secure wings from movement in mould, and put all in vacuum bag. Vacuum will press your wing to top profile mould and bonded it perfectly. Do not use too much pressure, I did it on -0.4 to -0.6 Bar. If there are some small imperfections in wings profile from sanding process it doesn’t matter and your wings will be bonded to top carbon skin perfectly.

That is all, your work with moulds is done. When you completely finish your wings last thing is to do heat treatment according to epoxy resin technical datasheet. In my case for LF386 it was 80 degrees Celsius for 15 hours. Since we did all that drilling on honeycomb walls there will be free air flow inside the wings there will be no bubbles or caves on wing surface that will reduce flight performance.

I believe this is in short words all that you need to take care when building your wings using Aramid honeycombs. Or let’s say after many planning, samples testing and problem solving this was the way I get the best overall results at the end. Finished wings weight was 220 g. Time I spent to build last wings was over 400 working hours, for first one it was more than double time, but at the end you have stiff and long lasting beautiful wings.

Robert Lesko

Looking for F1C Model

Hello free flight community,
I am making a transition from F1P to F1C and would like to know if anyone has F1C models that they are willing to sell to me. It can also be damaged just as long as it can be repairable. You can contact me through my email at gtsjet
– Junior Team Member Taron Malkhasyan


Wilbur & Orville Sep 6-7, Wawaywanda NY

It was expected to rain on Saturday. The day started off being windy, then it
calmed down and later it begun to rain. Maxes for F1Q were set at 2 minutes
and the motor runs were reduced to 2/3rd. Dave Lacey CDed the Saturday
events.

It continued raining overnight but was over by dawn. On Sunday the drift was
expected from the north. This time of year he field has very high corn and beans
on its south western side and we were also constrained by segments with fresh
sod planting. So in the third round when the drift started coming from the north
west, across the narrowest portion of the field, the maxes were cut to 2-minutes.
Next round the drift shifted and came from the north allowing flying 2:30 minute
maxes. John Clapp’s F1B model landed on a tree along the eastern part of the field,
required the services of a tree climber. The tree climber came with his two young
kids and his daughter enjoyed flying a small Cat glider.

In E36 we experimented with 10 second motor runs in the first three rounds. This
was sufficient to determine the winner. The contest was attended by 15 adults and
two juniors – Joel Yuri and Rebbecca Avla.

Aram

 Saturday Sep 6 
 F1Q
120 120 120 120 120 600 Dick Ivers
120 120 87 120 120 567 Joel Yuri J
101 91 120 79 110 501 David Lacey
120 120 Yuda Avla 
 F1H

65 92 117 120 120 514 Bob Sifleet

120 59 59 63 86 387 Andrew Barron 
 F1G
120 83 95 120 120 538 Carrol Allen
66 120 120 84 390 John Clapp
96 80 120 60 356 Don Rousseau
120 67 187 Bill Buss
120 120 Larry Pelatowski 
 HLG (both days)
129 Larry Pelatowski
116 Bob Morris 
 Sunday Sep 7
 Dawn Unlimited
120 Rich Wagener 
 F1A 
 160 180 120 150 150 150 150 150 1210 Bob Sifleet
210 180 66 150 150 150 150 150 1206 Andrew Barron
146 71 217 Tzvetan Tzvetkov 
 F1B
240 150 120 150 150 150 150 150 1260 Tom Vaccaro
240 124 120 150 150 150 150 150 1234 Carrol Allen
240 98 59 55 150 150 150 150 1052 Aram Schlosberg
177 150 327 John Clapp 
 E36
120 120 120 360 Dick Ivers
120 120 98 338 Drake Hook
87 120 120 327 Rebbecca Avla J
92 92 Dave Lacey 
 Electric B
120 120 120 360 Rich Wagener
120 119 120 359 Drake Hooke
109 120 120 349 Dick Ivers
120 76 196 Yuda Avla 
 Open Rubber
120 120 64 304 Rich Wegener

1/2 Classic
120 93 67 280 Ronald Monkres

........
Roger Morrell