HOW CAN A NOVICE ACCURATELY JUDGE
WHICH KIT HELICOPTER PROVIDES THE BEST VALUE?
In our experience, there are many methods that prospective
customers have used in the past. A few include:
- Reading a magazine article on a particular machine
- Sending for a brochure or video
- Talking to a salesman
- Talking to the builder of a particular machine
These are all good ideas, however we believe there is
an even better way. It is not a quick and easy method, but it will unquestionably
yield good results. It's still based on the question and answer method,
but with a computational twist. It's performed in two parts. (a) We
will provide a list of the right questions to ask and comment on the
answers you might receive, & (B) we will then provide you with a very
novel comparison formula. If you knew nothing about kit helicopters
before you read this, by the time you're finished you should be able
to evaluate relative quality right along with the experts. We'll begin
by listing the areas we are concerned about.
I. The history and track record of the design and flight-test
team. (This might be only one person, in the kit business)
II. The evolution of the prototype.
III. The performance and longevity parameters of the machine.
IV. What is supplied in the kit, what's the quality level, what
kind of Instructions?
V. What is the cost of the kit and how do you pay for it.
VI. How and by whom is this kit manufactured and what is the level
of in-process quality control?
VII. What final check out service is performed or available? Next
is a list of the correct type of questions to ask for each area. We
will also comment on the type of answer you might receive and how
to evaluate it. Ok, we told you this was not going to be quick or
easy, but just hang in there. You may want to copy these questions,
because they can be asked word for word. If you're an engineer, you
might re-phrase some of the technical ones, however if you're not,
you will probably want to ask them verbatim.
Group I Questions:
- Who did the original design and when?
- How long was the designer involved in helicopters before this
design? How many helicopter designs is he responsible for and what
are the gross weights?
- Was the designer also the test pilot or not?
- If the flight test program was not performed by the designer
was the test pilot truly a "Test Pilot".
- Any capable helicopter designer has paid his dues and has a long
history of involvement.
- It takes a while to explain why, but in the kit helicopter business,
the designer needs to also be the test pilot.
- A wide spectrum of gross weights signifies a designer with broader
experience, i.e. from say 600 lbs. to 3000 lbs.
- If a test pilot was employed, he needs to be a true "Experimental
Test Pilot", not just a helicopter pilot with 5000 or more hours.
This is a lengthy subject but if the designer is the test pilot,
he does not need a great deal of flight experience. It's just the
extreme opposite for the hired "Test Pilot". (Maybe we should make
the reason for this the subject of a future question.)
Group II Questions:
- What kind of rotor hub system is used? What type of blade retention
Is utilized? How are the centrifugal force loads dealt with?
- What is the safety factor in the blade retention area?
- What materials are used in the rotor blades?
- Is a geared main transmission utilized? If so, are the gears
designed and produced specifically for this application or not?
- What type of crashworthiness testing has been performed?
- How much component longevity testing has been done? How are component
lifetimes going to be finally determined and how will that information
be made available?
- What power plant modifications have been made to get the engine
working properly in this design?
- How much routine maintenance is necessary and how does the designer
or company know this for sure.
- A design utilizing surplus or timed out parts from other helicopters
is not a good idea, but it takes a very experienced designer to
come up with a new high quality rotor hub system.
- Ball bearings are not the best solution for dealing with high
blade centrifugal force loads.
- Rotor cross section areas near the root should provide an 8 to
1 safety factor, not 4 to 1.
- Blade materials should not be mixed. Aluminum spars with wrap
around composite skins are questionable. 6061-T6 aluminum alloy
belongs in window frames, not on helicopter blades. Helicopter blades,
if aluminum must be 2024-T351 or 7075-T6. Blades formed of a one
piece metal extrusion must be carefully avoided on powered shaft
- Automotive gears are not suited for helicopter spiral bevel geared
main transmissions. Single spur gears are not used in commercial
helicopter transmissions. If spur gears are used, they are in planetary
form where 3 or more small spur gears engage the drive gear.
- Drop testing is required to meet FAA type certification requirements.
Can the designer or company provide you with photo proof of this
type of testing?
- It takes five times or more as long to log hours on a new rotorcraft
than it does on a fixed wing. It's a big job to fly, tear down,
inspect and reassemble the hub & gearboxes every 5-10 hours for
the first 100-150 hours of flight on a brand new rotorcraft. If
a salesman flippantly gives you some impressively large number,
be very cautious.
- Long term high component lifetimes must be determined by the
factory and possibly a few other customers who may desire to participate
in the extended hours program. The data from this operational testing
must be shared with all operators regularly. No operator is allowed
to exceed the current hourly limit, which was previously established
by the test group. This information is easily disseminated these
days through a web site.
- Power plant installation in a helicopter is several times as
difficult as in a fixed wing. The power take off and clutching system
requires extensive testing. Vibration analysis to determine that
no harmful effects are being transferred to the power plant crankshaft
is vital. Engine cooling capability in a hover at gross weight in
hot weather is always a tough problem to solve. A fixed wing at
high power is moving fast, so it's easy to shed BTU's. It's just
the opposite in a whirly bird.
- If you build a kit helicopter and find out when you start to
operate it that you have to work on it 3 or 4 hours for every hour
of flight, don't be surprised. The first generation of kit helicopters,
including my original Scorpion and EXEC designs were no better.
The second generation of kit designs including the HELICYCLEŠ strive
to model the ultra-low maintenance of the R-22.
Group III Questions:
- What's the power to weight ratio?
- What altitude can the ship hover IGE (in ground effect) at or
near gross weight?
- What seat load specification was the ship designed for?
- What is the overall vibration level at maximum cruise speed?
- What is the percentage of increase from normal cruise speed to
maximum speed in level flight at gross weight?
- A 10 to 1 power to weight ratio will allow in ground effect operation
at relatively low altitudes i.e.: 4000/6000 ft. a 7.5 / 1 ratio
like the Hughes 500 will provide great performance at high altitudes
like 9000/11000 ft. A recent kit helicopter, which enjoyed brief
popularity, had a ratio of 12 / 1. If customers had only asked this
question up front
- Performance specifications on type-certificated machines have
to be verifiable. The list of specifications you read for most kit
helicopters could be what ever the sales team decides will sell.
Use some common sense here. High cruise speeds and high altitude
performance are not generated by low power to weight ratios.
- The FAA considers a 175-lb. pilot to be the norm. If a helicopter
is designed around this number and a 220-lb. pilot flies it, the
fatigue life on highly loaded components would be dramatically effected.
- Vibration isolation in any helicopter is a very complex task.
When the source is determined, it's not always easy to attenuate
or get rid of it. It usually takes extensive redesign. It's the
designer's responsibility to take care of this issue during the
design and testing phase. If the designer is not the test pilot,
needed refinements might not have been attended to. Please understand
we are not talking about rotor static or dynamic vibrations here.
These are easily adjusted during and after the construction phase.
A kit helicopter builder should not deceive himself into thinking
that he will solve a vibration problem, which is caused by some
inherent design deficiency in the rotor or drive train system.
- A wide spread (over 7 - 10%) between normal cruise and flat out
maximum level flight should raise eyebrows. Some manufacturers quote
a VNE speed, which is a maximum dive speed. It will be necessary
to be very specific here to get the correct answer.
Group IV Questions:
- All kits are not equal. You must ask specific questions to find
out just what it is you will be doing to complete a kit. Do you
need to do any welding, machining, hand forming or moldless composite
work? Will you be doing enough fabrication work to qualify you to
receive an airworthiness certificate?
- To judge quality you will need to talk to a customer, be knowledgeable
enough to quiz the designer or salesman or make a trip to the factory.
- How are the kit components packaged?
- Kit instructions are given in two formats. Picture and caption
with some drawing & prints or a video presentation. Manufacturers
commonly start out with paper instructions and then later include
video. The best method is a combination of the two, however the
level of detail in either method is what is important. Ask to see
some portion of the instruction package, so you can determine whether
it meets your expectations.
- To be legal to fly, an amateur built aircraft must be issued an
airworthiness certificate. FAA advisory circular 20-27D covers this
in detail with straightforward step by step instructions. The key
to receiving a certificate lies in compliance with the rules. Individuals
who believe they will purchase a kit and get someone else to completely
build it for them will probably not be successful in obtaining an
airworthiness certificate. Beware of 50-100 hour construction times
published by any kit builder. The phrase "Fast Build Kit" is now
common, however this is primarily a marketing technique. A kit that
does not comply with the FAA Amateur Built 51% rule will not be
- It's hard to see inside somebody's main transmission to find out
about the quality of the gears and bearings. Ask if any technical
video's are available which would help to enlighten you. Look at
the fit and finish of the assemblies supplied in the kit. If you
have an engineering background, ask questions about the materials
used in construction.
- A manufacturers part numbering system is a great indicator of
his ability to produce quality. Ask for a copy of this system and
see how organized it looks. All kit components or assemblies should
come with part numbers denoted. Parts may be shrink wrapped or packaged
in a separate plastic bag with a label. Whichever way it's done,
the last thing you want to receive is a box full of unlabeled bits
Group V Questions:
- Price cannot be judged until the quality level is known. That's
the whole purpose of this article. Good marks are given for high
quality and reasonable prices. High marks are given for high quality
and low prices.
- Beware of anyone who requests full payment up front for a new
- Ask about the business history of the designer, manager or C.E.O.
of the company. A bonifide operation will be happy to provide this
This group of questions is self-explanatory.
Group VI Questions:
- Is the machining done in-house?
- If machining is done outside, ask to see a copy of the first 3
or 4 pages of the quality control manual. (This is the manual used
by the kit company to check out parts made outside.)
- Are company assembly manuals written for use in assembling the
main and tail rotor gear boxes and the rotor hub and blades. Are
sign-offs required during the assembly process?
- If metal blades are supplied are blade bonding coupons catalogued
on each production group? If composite blades are supplied what
type of permanent records are kept.
- What parts are serialized and traced? How is the parts tracibility
system set up?
- What is the company policy in regard to a part that wears out
or fails prematurely, even if no formal warranty is offered?
- If machining is done in-house, you can be pretty confident that
machining tolerances are being held to specifications. The most
probable reason for machining being done outside is that management
is just not too familiar with the machinist trade. It is vital to
have a world class quality control system set up in-house to check
the tolerances on parts made outside. A co-ordinate measuring machine
is a vital piece of quality control equipment in this case. These
machines cost five figures, so if the shop has one, you can be pretty
sure they know what they're doing. To find out, you must of course
ask. If they don't have this piece of equipment and parts are made
- If the company doesn't use in-house produced assembly manuals,
with the need for quality control sign offs at critical assembly
points, you need to look for a different kit supplier. Assembling
a main transmission for an R-22 or an Apache or a HELICYCLEŠ is
at least a 100-step process. Once this process is worked out, it
is impossible to remember each detail from memory. You must have
a manual to refer to.
- Some permanent record must be kept in regard to rotor blade bonding
procedures on each batch of blades that is constructed. This goes
for metal or composite blades. Ask what method the kit company utilizes.
- Serialization of critical parts is more important to the company
than it is to the customer. How can the company possibly stay in
business if they find out a part has failed in the field and they
have no record of what production batch it was in. They simply can't
afford to ground every ship and replace every part! Be aware that
in the amateur built category there is no requirement for the company
to keep these kinds of records. If the kit manufacturer you're looking
at doesn't keep these records, you need to find someone who does.
- Most amateur built kits don't have a warranty, but a quality company
will make every effort to solve field problems in the most equitable
manner. See what kind of an answer is given to the warranty question.
Group VII Questions:
- Is a final construction checklist supplied?
- Is the customer (even if they are helicopter rated) going to
be the first person to fly this machine?
- What type of checks and balances are in place to insure the customers
safety and success as he begins to operate his newly finished machine?
- A final construction checklist for double checking the adjustment
of each system or component is a vital must for any helicopter.
You can't afford to miss one item. You would want to comply with
this checklist for two reasons. First, you wouldn't be ready to
have your ship inspected for airworthiness without it and second,
when the factory test pilot comes to fly it, if it's not ready,
you'd be running up a higher bill than necessary.
- Every commercial helicopter, when it comes off the production
line, is handed off to two people. A production test pilot and a
flight-test engineer. These folks test fly the helicopter side by
side for many hours in order to check out and adjust all the systems
and calibrate them to meet the operational type specifications.
This is a critical task, performed by specially trained, very experienced
personnel. If the kit manufacturing company does not provide this
kind of personal check out service either at your place or at the
factory, beware. Be sure to ask this critical question.
- It comes down to this. It takes years of experience before a
kit helicopter manufacturer gets his arms around the whole banana.
Learning the kind of mistakes kit builders make, and designing a
construction and flight program which will keep the customer out
of trouble, is no small task. It requires lots & lots of experience.
Go with the company or the designer who has paid their dues & been
through the fire.
THE COMPOUND EQUATION RATING THE
We have provided a list of 33 questions. Pick out 15 or so of those
you feel most appropriate. You may wish to add a couple more of your
own. Use this exact list to evaluate each prospective design in order
to achieve apples to apples comparison.
Answers are to be weighted according to the following
Now it's time to use the "Compound Equation" to achieve
a bottom line number for each design.
I cannot take credit for this elegantly simple, foolproof
method of assessing relative quality. The "Compound Equation" was promulgated
by my friend Tom Stuelpnagel, who was for many years the C.E.O. of Hughes
Helicopters, Summa Corporation.
This formula was used to provide a comparison of value
for their equipment. It helped confirm the value of the Apache during
the period of time when Mr. Stuelpnagel was selling this major helicopter
program to the U.S. Army.
Here's how it works, and its sooo simple. Multiply the
rating weight number of each question together to calculate the total
value of each design.
A design, which answers .9 to each of 10 questions for
example, has a final rating of .348. a design, which answers 1.1 to
each of 10 questions, has a final rating of 2.59. This is a 7.4 times
improvement! Of course, every design has its strengths and weaknesses
so the spread will be much closer than 7 to 1.
Utilizing this simple rating system in conjunction
with the compound equation not only is an eye opener; it's a qualitative
method of determining what designs it would be prudent to avoid.
Eagle RnD 2512 Caldwell Blvd. Nampa, Idaho USA 208-461-2567 Fax 208-454-3752